CA1191839A - Branched amides of l-aspartyl-d-amino acid dipeptides - Google Patents

Abstract

Abstract of the Disclosure L-Aspartyl-D-amino acid dipeptides of the formula ---(I) and the physiologically acceptable cationic and acid addition salts thereof, wherein Ra is CH2OH or CH2OCH3;
and R is an alkyl, cycloalkyl or heterocycloalkyl group which is branched at the alpha carbon atom and branched again at one or both of beta and beta' carbon atoms; their use as sweetening agents for food, food compositions containing them and intermediates for their production.

Description

33~
, . ~ ~

The invention relates to novel amides of L-aspartyl-D-serine and L-aspartyl-D-O-methylserine which are especially useful in view of their potent sweetening properties, novel methods for their use in foods and edible composition containing them.
In United States 3,492,131 certain alkyl esters of L-aspartyl-L-phenylalanine were found to be up to 200 times as sweet as sucrose and to be substantially free of bitter flavor notes which detracted from earlier artificial sweeteners such as saccharin. These compounds were subsequently found to have only limited stability in a~ueous systems due to diketopiperazine formation especially at the neutral-acidic p~ conditions prevalent in most food systems.
Mazur et al., J. Med. Chem., 16, 1284 (1973) has disclosed that lower alkyl esters of L-aspartyl-D-alamine and certain homologs thereof, especially L-aspartyl-D-alanine isopropyl ester, have sweetness potencies of up to 125 times sucrose.
Sukehiro et al., Seikatsu Ka~aku, 11, 9-16 (1977); Chem.
Abstr., 87, 168407h (1977) has disclosed certain amides of L-aspartyl-D-alanine of the formula ,~3 - 1-

2 n ~1~ /NH~/ C\NHRl where Rl is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary butyl, cyclohexyl or the carbon residue of the methyl esters of glycine/ d alanine or I-alanine. The most potent compounds were those wherein R1 is one of the above butyl groups or cyclohexyl, having respectively, 100-125 and 100 times the sweetness of sucrose. Since the n-butylamide was found to have 125 times the sweetness of sucrose and the isobutyl and secondary butyl amides are 100 x sucrose, it was concluded that the potency of these amides is affected mainly by the number of carbon atoms in the alkyl group, Rl, and that structural isomerism in the alkyl group has little effect on the sweetness potency.
Esters of L-aspartyl-D-serine and L-aspartyl-D-threonine have been found by Ariyoshi et al., Bull.
C_ . Soc. Japan, 47, 326 (1974) to be sweeter than the corresponding esters of L-aspartyl-D-alanine and L-aspartyl-D-2-aminobutyric acid, respectively. The most potent of these esters, L-aspartyl~D-serine n-. propyl ester, was 320 times as sweet as a 5~ sucrosestandard.

United States 3,971,822 discloses esters o-f L~aspartyl-D-alaninol with carboxylic acids, including 2-methyl-butyric, cyclopropanecarboxylic, cyclobutanecarboxylic and 2-methylcyclo-butanecarboxylic acids. The esters with cyclo-propane- and cyclobutanecarboxylic acids were 200 x and 220 x sucrose, respectively~ The ester with 2-methylcyclobutanecarboxylic acid was only 160 x sucrose. Corresponding L-aspartyl-D-serinol esters are also disclosed, the sweetest of which, the ester with propionic acid, is 160 x sucrose.
United States 3,959,245 and United States 3,907,766 dis-close, respectively, L-aspartylaminomalonic acid methyl 2-methylcyclohexyl diester, and the corresponding alkyl fenchyl diester. The former is reported to be 6600 x sucrose, the latter 4200-33,000 x sucrose. In a related publication by the inventors, Chem. Pharm. Bull., 24, 2112 (1976), a series of L-aspartylamino-malonic acid diesters is disclosed. one of the ester groups being methyl or ethyl and the other being one of a variety of branched alkyl and cycloalkyl groups.
In our related United States Patent No. 4,411,925 issued October 25, 1983, it was found -that it is not merely the size of the amide substituent that is critical for a high degree of sweetness in L-aspartyl-D-alanine amides, but, to the contrary, it is the precise spatial arrangement of the amide substituent, R, that is critical. Certain L-aspartyl-D-alanine amides which are branched at the alpha carbon atom (the carbon atom bearing the amide nitrogen atom) and also branched again at one or bo-th of beta and beta' carbon atoms were -found to have significant advantages.

- 3 -a~l~
~ ~ v ~ ~

The present invention provides certain novel branched amides of L-aspartyl-D-serine and L-aspartyl-D-O-methylserine dipeptides which have unexpectedly , high sweetness potency and are free from undesirable flavor qualities at conventional use levels. They have also been found to have surprisingly high stability both in solid form and in aqueous systems over the pH
range found in most food systems even at the elevated temperatures used in baking and conventional food processing.
The novel compounds of the invention are the L-aspartyl-D-amino acid dipeptide amides of the formula ~ C~NH ~ ~ HR
COOH Ra and the physiologically acceptable cationic and acid addition salts thereof, wherein Ra is CH2OH or CH2OCH3, and R is a branched member selected from the group consisting of fenchyl, diisopropylcarbinyl, d-methyl-t-butylcarbinyl, d-ethyl-t-butylcarbinyl, di-t-butylcarbinyl, 2-methylthio-2,4-dimethylpentan-3-yl, R3 ~ R3 R
, ~( CH2 ) m R6~ C~2 ) n~X

where at least one of R3, R4, R5, R6 is alkyl having from one to four carbon atoms and the remainder are hydrogen or alkyl having from one to four carbon atoms; X is O, S, SO, SO2, C=O or CHOH; m is zero, l, 3~3 ~

2, 3 or 4; n and p are each zero; 1, 2 or 3 and the sum of n ~ p is not greater than 3; the sum of the carbon atoms in R3, R , R5 and R6 is not greater than six and when both of R3 and R4 or R5 and R6 are alkyl they are methyl or ethyl;

(CH2)m where m is as defined above, one of R7, R8, R9 is alkyl having from one to four carbon atoms and the remainder are hydrogen or alkyl having from one to four carbon atoms and the sum of the carbon atoms in R7, R~ and R9 is not greater than six;
n ~1_(CH2) ( CH2 ) q where m and q are the same or different and each have the values previously defined for m;

R R

~ (C72)t O~Z

where each of R12 and R13 are methyl or ethyl, or R12 is hydrogen and R13 is alkyl having from one to four carbon atoms, Z is O or NH and t is 1 or 2;

3~

_<~CH2)2 R16~

where w i5 Or 1, 2, 3 or 4, R14 and R16 are each alkyl having from one to four carbon atoms, R15 i~
hydrogen, OH or alkyl having from one to two carbon atoms, where the sum of the carbon atcms in R14, R15 and R16 is not greater than six and when both of R14 and R15 are alkyl they are methyl or ethyl; and Rl~

whe:re R17 and Rl9 are alkyl having from one to four carbon atoms, R18 and R20 are hydrogen or alkyl ha~ing from one to two carbon atoms, taken separately, A is OH and s is hydrogen, OH or methyl and when taken together A and B are -CH20C-, -CH2NHC-, -OCCH2~, O O O
-NHCCH2-, OC-, -NHC- or -OCO-, where the sum of the ~ 1l n n O O O O
carbon atoms in R17, R18, Rl9 and R20 is not greater than six and when both of R17 and R18 or Rl9 and R20 are alkyl they are methyl or ethyl.

33~

While the preferred sweeteners of the invention are those dipeptide amides of formula ~I) wherein the aspartylamino acid dipeptide moiety is derived from L-aspartic acid and a D-amino acid, RaCH(NH2)COOH, also included within the scope of the invention are mixtures containing the most preferred L-aspartyl-D-arnino acid amides of formula (I) wherein one or both of the aspartyl or the other amino acid (i.e., serine or O-methylserine) moieties is racemic such as e.g., DL-aspartyl-D-serine amides, DL-aspartyl-DL-serine amides, L-aspartyl-DL-serine amides, L-aspartyl-DL-O-methylserine amides, DL-aspartyl-DL-O-methylserine, and DL-aspartyl-D-O-methylserine amides.
Those compounds of formula (I) wherein the aspartyl moiety is entirely of the D configuration or the other amino acid moiety is entirely of the L-configuration have little or no sweetness.
An especially preferred group of L-aspartyl-D-amino acid amides of formula (I) are those wherein R
is an acyclic member selected from the group consisting of diisopropylcarbinyl, d-methyl-t-butylcarbinyl and di-t-butylcarbinyl.
Another especially preferred group of L-aspartyl-D-amino acid amides of formula (I) are those wherein R is a member selected from the group consisting of R3 ~ ~3 R4 (CH2)m 1 ~~(CH2)n~X
R6 ~ R6 ~ 2)p 33~3 R7 R8 ~ CH2~m ~ R ~ , `n (CH2)q (CH2)m R12 R13 R14 ~15 ~ C72)t ' ~ (CE~2)W

o// Rl OH

and ~1 ~
B

R2~

wherein R3-R9, R12 R20, A, B, X, Z, m, n, p, q, t and w are as defined above; and more particularly preferred are those compounds of formula (I) wherein R has one of the first four values of the group immediately above.
Particularly preferred amides of formula (I) are the L-aspartyl-D-serine amides, i.e., those wherein Ra is CH20H.
Examples of the more valuable L-aspartyl-D-amino acid dipeptide amides of the inventio.n include those of for~ula (I) wherein R is-(~)fenchyl, diisopropylcarbinyl, d-methyl-t-butylcarbinyl, di-t-butylcarbinyl, 2,6-diethylcyclohexyl, 2-methylcyclopentyl, 2-ethyl-6-methylcyclohexyl, 2-ethylcyclohexyl, 2-methylcyclohexyl, 2,2-dimethylcyclohexyl, 2-ethylcyclopentyl, 2-methyl-6-isopropylcyclohexyl 2,2,6,6-tetramethylcyclohexyl, 2,2,4,4-tetramethyltetrahydrofuran-3-yl, lS 2,2,6-trimethylcyclohexyl, 2-isopropylcyclohexyl, 2,5-dimethylcyclopentyl, 2,6-dimethylcyclohexyl f 2 isopropylcyclopentyl, 2,2,5,5-tetramethylcyclopentyl, t-butylcyclopropylcarbinyl, 2,2,4,4-tetramethylthietan-3-yl, 2,2,4,4-tetramethyl~ dioxothietan-3-yl, 2,2,4,4-tetramethyltetrahydrothiophene-3-yl, 3,5-dimethyltetrahydrothiapyran-4-yl, 2-t-butylcyclohexyl or dicyclopropylcarbinyl;
Especially valuable sweeteners include the above compounds wherein R is:
di-t-butylcarbinyl, 2,2,6-trimethylcyclohexyl, 2-t-butylcyclohexyl, 2-isopropylcyclohexyl, 3~

2,6-dimethylcyclohexyl, 2,5-dimethylcyclopentyl, 2 isopropylcyclopentyl, 2,2,5,5-tetramethylcyclopentyl, 2,2,4,4-tetramethyltetrahydrothiophene-3-yl, t-butylcyclopropylcarbinyl, dicyclopropylcarbinyl, 2,2,4,4-tetramPthylthietane-3-yl or 2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl.
More especially preferred are those compounds of formula (I) wherein R is.
2,2,5,5-tetramethylcyclopentyl, 2,2,4,4-tetramethyltetrahydrothiophene-3-yl, t-butylcyclopropylcarbinyl, dicyclopropylcarbinyl, 2,2,4,4-tetramethylthietan-3-yl, and 2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl.
Most particularly preferred compounds of formula (I) are those wherein:
R is C~2OH and R is dicyclopropylcarbinyl, 2,2,4,4-tetramethylthietan-3-yl, 2,2,4,4~tetramethyl-1,1-dioxothietan-3-yl, and those wherein Ra is CH2OCH3 and R is 2,2,4,4-tetramethylthietan-3-yl and 2,2,4,4~tetramethyl-l,lrdioxothietan-3-yl, which have sweetness potencies of from 200-1200 times that of sucrose.
The invention further provides compositions for sweetening edible materials which comprises a sweeten-ing amount of a compound of formula (I) and a non-toxic carrier. Most particularly preferred compositions are those containing L-aspartyl~D-serine N-(dicyclo-propylcar~inyl)amide, L-aspartyl-D-serine N-(2,~,4,4-tetramethylthietane-3-yl)amide, the l,l-dioxo deriva~
tive of the latter.
Additionally, sweetened edible compositions comprising an edible material and a sweetening amount of a compound of the invention, are provided.
Also provided is a method for sweetening edible compositions which comprises adding thereto a sweeten-ing amount of a compound of the invention.
The invention further provides compositions for sweetening edible materials which comprises a sweet-ening amount of a mixture of a compound of formula (I) and saccharin or a physiologically acceptable salt thereof.
Especially preferred such mixtures are those wherein in said compound of formula (I), Ra is CH2OH
and R is dicyclopropylcarbinyl, 2,~4,4-tetramethyl-thietan-3-yl or 2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl. Most particularly preferred are mixtures of L-aspartyl-D-serine N-(2,2,~,~-tetramethylthietan-3-yl)amide and said saccharin, especially those wherein said compound and said saccharin are present in a weight ratio of from 1:1 to 1:8.
By physiologically acceptable salts of saccharin is meant the salts of saccharin with physiologically acceptable cations such as e.g., the sodium, potassium, calcium or ammonium salts.
By physiologically acceptable cationic salts of the compounds of the invention is meant the salts formed by neutralization of the free carboxylic acid group of the compounds of formula (I) by bases of physiologically acceptable metals, ammonia and amines. Examples of such metals are sodium, potassium, calcium and magnesium. Examples of such amines are N-methylgluc~mine and ethanolamine.
By the term physiologically acceptable acid addit:ion salts is meant those salts formed between the fxee amino group of the compound of formula (I) and a physiologically acceptable acid. Examples of ~uch acids are acetic, benzoic, hydrobromic, hydro-chloric, citric, fumaric, gluconic, lactic, maleic, malic, nitricr phosphoricr saccharic, succinic and tartaric acids.
The invention still further provides valuable novel intermediates, useful in preparation of the invention compounds of formula (I). Said inter-mediates are the D-amino acid amides of the formula RaCHCONHR
NH~

where Ra is as previously defined and Rc is a member selected from the group consisting of fenchyl, diiso-propylcarbinyl, d-methyl-t-butylcarbinyl, d-ethyl-t butylcarbinyl, di-t-butylcarbinyl, cyclopropyl-t-butylcarbinyl, cyclopentyl-t butylcarbinyl, dicyclo-propylcarbinyl, R3 ~ 40 C 2)m where ml is 1, 2 or 3 and when ml is l: R30, R40, R50 and R60 are each methyl, when ml is 2: R30 is methyl, ethyl or isopropyl and R40, R50 and R60 are each hydrogen or R30 and R50 are each methyl and R40 and R60 are each hydrogen, and when m is 3:
(a) R is :isopropyl or t-butyl, R , R and R60 are each hydrogen, (b) R is ethyl, R is methyl, R40 and R
are each hydrogen, or (c) R30 and R40 are each methyl and R50 and R60 are each hydroyen or methyl, and CH __~R
~ (CH2)n ~ C 2 ) P2 where when n2 and P2 are each zero: R41 and R61 are each mPthyl and X2 is S, SO2, C=O or CHOH, when n2 is zero and P2 is 1: R41 and R61 are each methyl and X2 is O, S, or SO , and when n2 is 1 and p~ is 1: R~l and R51 are each hydrogen and X2 is S or SO2.
The suffix n car~inyl" as used herein denotes the moiety -CH-. Thus, for example, diisopropylcarbinyl is the group (i-C3H7)2-CH- and dicyclopropylcarbinyl-amine is ( ~ )2CHNH2.

The instant dipeptide amides are convenientlymanufactured by methods suitable for coupling of amino acids. A preferred method for preparing the dipeptide amides of formula (I) is outlined below.

3~

NHQ Ra (l) condense L- ~ + D-~IH2CHCOORll (2j H2O
COOR COOH
or carboxyl activated derivative NHQ Ra N~Q Ra COO ~ ~ RNH2 ~ OHN ~ ONHR

(II) / (III) /deprotect (I) In the above L-aspartic acid derivatives Q is one of the well known amino-protecting groups which can be selec~ively removed such as those described by Boissonnas, Advances in _r~anic Chem., 3, 159-190 -(1963). Particularly preferred amino-protecting groups are benzyloxycarbonyl and tert-butyloxycarbonyl.
R10 is preferably an alkyl group having from one to four carbon atoms or benzyl. The D-serine or D-O-methylserine employed may be in the form of the free amino acid wherein Rll is hydrogen, but is preferably a carboxyl-protected derivative wherein Rll may be the residue of an ester group such as methyl or ethyl, but is preferably a silyl group such as trialkylsilyl, having from three to twelve carbon atoms. An especially preferred such group is trimethyl-silyl for reasons of economy and efficiency.
In the first step of the above reaction sequence the diprotected ~-aspartic acid is condensed with the appropriate D-amino acid or a carboxy-protected 3~

derivative to provide the diprotected dipeptide of formula ~II). While this step may be carried out with the diprotected aspartic acid in the presence of condensing agents such as, for example, dicyclohexyl-carbodiimide, it is preferred to employ an alpha-carboxyl activated derivative of the diprotected aspartic acid. Preferred such carboxyl activated derivatives are the chloride, bromide, anhydride or mixed anhydride. Especially preferred for reasons of efficiency are the mixed anhydrides of the above diprotected-L-aspartic acids with esters of chloro-carbonic acid, particularly the alkyl esters wherein said alkyl has from one to four carbon atoms. Most preEerred mixed anhydrides are those prepared from the methyl and ethyl esters of chlorocarbonic acid for reasons of economy.
In one preferred method for preparing the compounds of formula (I), beta benzyl-N-benzyloxy-carbonyl-L-aspartic acid is reacted with ethyl chlorocarbonate to form the corresponding mixed anhydride by methods known in the art. In a separate vessel the D-amino acid, RaCH(NH2)COOH, which is obtained from commercial sources or by resolution of the racemic amino acid by known methods [see e.g.
Yamada ~,al., J. Or~. Chem., 38, 4408 (1973)], is converted to the trimethylsilyl ester by contacting the amino acid with an equimolar amount of trimethyl-silyl chloride in the presence of a reaction inert organic solvent; for the case when R is CH2OH, two molar equivalents of silylating agent is ordinarily employed. Suitable solvents for this purpose are, for example, pyridine, dimethylformamide or dimethyl-acetamide; especially preferred i5 dimethylformamide.

~3~Lr~

In a typical reaction according to this method, the D-amino acid e.g., D-O-methylserine, dissolved in dlmethylformamide and an equimolar amount of tri-methylchlorosilane is added at room temperature. In a separate flask beta-benzyl N-benzyloxycarbonyl-L-aspartic acid and a molar excess of an acid binding agent, preferably triethylamine are dissolved a mixture of dimethylformamide and tetrahydrofuran and an equimolar amount of ethylchlorocarbonate is added at room temperature or below, preferably at about -25 to 25C. and especially at about -10 to 0C. to form the mixed anhydride. To this is added the solution of e.g./ D-O-methylserine trimethylsilyl ester, preferably at a temperature within the sarne range.
Reaction is ordinarly complete within one to two hours arter which the reaction mixture is poured into water or agueous acid, for example hydrochloric acid, and the product of formula (II) extracted with a water immiscible solvent, typically chloroform, methylene chloride or ethyl ether and isolated by standard methods. The diblocked dipeptide (II) is ordinarily of suf~icient purity for use in the next step, but may be further purified if desired, for example by columrl chromatography.
In the second step of this method the diblocked dipeptide (II) is reacted with an equimolar arnount of primary amine of formula RNH2 to provide the corres~
ponding di~locked dipeptide amide intermediate of ~ormula (III) wherein Ra, R, R10 and Q are as previously defined. As in the first step, the carboxylic acid forrn of the reactant (II) can be successfully employed by use of condensing agents, for example dicyclohexyl- -carbodiimide to provide the intermediates of formula (III).

However, it is preferred to convert the compound of formula (II) to a carboxyl activated derivative, for example the chloride, bromide or mixed anhydride, the latter being preferred. Thus, employing the particular-ly preferred compound of formula (II) wherein R10 isbenzyl and Q is benzyloxycarbonyl, the mixed anhydride is prepared. As above, the preferred anhydrides are those obtained from esters of chlorocarbonic acid and the methyl or ethyl esters thereof are particularly preferred. The mixed anhydrides of compound (II) are prepared employing reactants and conditions described above for the first step of this sequence. In a typical reaction the compound of formula (II) and triethylamine in approximately equimolar amounts are combined in a reaction inert organic solvent, for example tetrahydrofuran, the mixture cooled to about -10C. and ethylchlorocarbonate added to obtain the mixed anhydride. To this is then added an equimolar amount of the amine of formula R~H2 or a solution ~0 thereof, for example in the same reaction inert solvent and at a temperature in the range of from about -50 to 25C. and preferably at from -35 to -5~. After the addition of the amine is complete, the reaction mixture is allowed to warm to about ~oom temperature and maintained at this temperature until reaction is substantially complete, ordinarily from about 1 to ~0 hours. The desired intermediate of formula ~II) is then isolated and purified, if desired, by the same methods described above for compound (II).
In the final step of this method the carboxyl protecting group, R10 and amino protecting group, Q, are removed to provide the desired s~eeteners of formula (I)G

The method selected for removal of protecting groups from the dipeptide amide of formula (III) will vary depending on a number of factors which will be apparent to those of skill in the art. Two important factors for such selection are the nature of the protecting groups ~10 and Q, and the nature of the amide substituent, R. For example, when R10 and Q
are, respectively, the especially preferred groups benzyl and ~enzyloxycarbonyl and R does not contain sulfur, a preferred method for removing said protect-ing groups is, ordinarily, by hydrogenolysis.
However, when R10 is benzyl or alkyl as defined above and Q is tert-butyloxycarbonyl and R has any of the ~alues above, it is ordinarly preferred to remove the protecting groups by hydrolysis. A combination of hydrolysis and hydrogenolysis is preferred in those cases wherein R10 is alkyl, Q is benzylo~ycarbonyl and R does not contain sulfur.
When hydrogenolysis is selected for removal of protecting groups from the intermediate of formula (III) it is preferred to carry out the reaction in the presence of a catalytic amount of a noble metal catalyst, palladium being especially preferred, and in the presence of a reaction inert solvent. Examples of such solvents include the lower alkanols, such as methanol, ethanol, isopropanol and n-butanol; ethers, such as tetrahydrofuran, ethyl ether, 1,2-dimethoxy-ethane and diethyleneglycol dimethylether; esters such as ethyl acetate, methyl propionate and dimethyl-succinate; and dimethylformamide. Particularlypreferred such solvents are methanol and ethanol for reasons of economy and efficiency. While the hydro-genolysis may be carried out successfully at higher pressures and temperatures, use of pressures of from about 1-10 atmospheres and room temperature are preferred for reasons of economy and convenience. ~t the preferred temperature and pressure the reaction is ordlnarily complete in from about 30 minutes to about six hours, after which the catalyst is removed, 5 typically by filtration, the solvent evaporated and the resulting product purified, if desired, by standard methods, ~or example by recrystallization or column chromatography.
When hydrolysis is selected for removal of one or both of protecting groups R10 and Q any of the well ~nown methods for alkaline hydrolysis or acid hydrolysis of esters and the like may be employed with some success. However, when blocking groups R10 are to be removed by hydrolysis, alkaline hydrolysis is preferred, and especially preferred conditions are use of at least an equivalent amount of a strong base, for example, sodium hydroxide or potassium hydroxide in the presence of water and a lower alkanol, particularly methanol or ethanol, at or about room tempera~ure. Under these preferred conditions hydrolytic removal of the R10 group is ordinarily complete in a few hours or less.
When the amino protecting group Q is tert-butyloxycarbonyl it is preferred to use acid hydro-lysis for its removal. Especially preferred is dilute aqueous hydrochloric acid in the presence of methanol or ethanol and heating the mixture at reflux.
Under these conditions hydrolysis is ordinarily complete in a few hours or less.
Isolation of the products of formula (I) after removal of protecting groups by an~ of the above hydrolysis methods employs standard procedures known in the art. For example, after acid hydrolysis the reaction mixture is evaporated to remove solvent, the 3~

aqueous residue washed with a water immiscible non-polar solvent, for example, ethyl ether or chloroform after which the aqueous layer is made alkaline and the product extracted with a water-immiscible solvent such as, for example, ethyl acetate and the product obtained by evaporation of solvent. If desired, the product can be further purified, for example, by recrystallization or column chromatography. ~en alkaline hydrolysis to remove a protecting group RlO is followed by hydrogenolysis to remove the amino protecting group Q, the reaction mixture from the alkaline hydrolysis is preferably neutralized by addition of acid, for example, hydrochloric acid, and the neutralized reaction mix~ure subjected to hydro-genolysis as described above.
A second preferred method for manufacture of the instant compounds of formula (I) is shown below.

Ra Ra D-QNHCHCOOH + RNH2 QNHCHCONHR
or carboxyl activated ~ (IV) derivative NHQ

deprotect Ra COO ~ COOH
- - ~ NH2CHCONHR ~ (III)----~(I) (V) Ra, R, R and Q are as defined above.
The amino protected D-amino acid or its carboxyl activated derivative is reacted with an equimolar amount of amine RNH2 employing methods and conditions dPscribed above for the preparation of intermediates (II) and (III) to obtain an amino protected D-amino acid amide of formula (IV). The protecting group Q

3~3~

is removed by hydrogenolysis or hydrolysis as described above and the resulting free amino amide (V) is condensed with a diblocked L-aspartic acid derlvative or a carhoxyl activated derivative thereof, as described above for the preparation of intermediates of formula (II), to provide the diblocked dipeptide amide of formula (III) from which the desired sweetener of formula (I) is obtained as previously described.
In a modification of this method an intermediate of fo~nula (IV) wherein R contains a cyclic or acyclic sulfide moiety ~-S-) may be oxidized to the corresponding sulfoxide or sulfone prior to its conversion to intermediate (V) and subsequent reactions as described above, to provide compounds of formula (I) wherein R is a sulfoxide or sulfone.
In a third preferred method for preparing the compounds of the invention the D-amino acid amide of formula (V), described above, is reacted with L-aspartic acid N-thiocarboxyanhydride to provide directly the compounds of formula (I). In carrying out this method the intermediate (V) in a suitable solvent is contacted with an equimolar amount of L-aspartic acid N-thiocarboxyanhydride at a mildly alkaline pH at a temperature of from about -25 to 10C. to provide the compound of formula (I). The alkaline p~ for this reaction is provided by means of a strong base, for example, sodium hydroxide or potassium carbonate. Suitable solvents for this reaction are those that dissolve at least a portion of the reactants under the reaction conditions employed without reacting with either xeactant to an appreciable extent and allow the products formed in the reaction to be isolated with relative ease.
Examples of such solvents for this reaction are -2~

water, tetrahydrofuran, 1,2-dimethoxyethane, diethyl-eneglycol dimethylether, dimethylsulfoxide, dimethyl-formamide and combinations thereof; preferred solvents are water, and its mixtures with te-trahydrofuran. A
preferred alkaline pH range for this reaction is from about 8 to 10 and a pH of about 9 is especially preferred. An especially prefexred temperature is in the range of about -10 to 0C.
Vnder the preferred conditions mentioned above the reaction is ordinarily complete in one to two hours. The product of formula (I) then isolated by standard methods, for example, the pH of the reaction mixture is a~justed to the isoelectric pH of the product, ordinarily about pH 5.0-5.6, to precipitate the product of formula (I), the bulk of the solvent removed by evaporation or filtration and the crude material slurried with an organic solvent, for example, methanol, ethanol, ethyl ether, ethyl acetate or mixtures thereof. ~he product of formula (I) is then isolated, by filtration for example. It may be further purified, if desired, by, e.g., recrystal-lization or column chromatography.
The sweetness potency of the instant compounds was determined by comparison of their gustatory sweetnesses with sucrose. Aqueous solutions o~ the compound of formula (I~ diluted to a suitable range of concentrations were compared with a sucrose standard by an expert taste p2nel. Comparisons were generally made with aqueous sucrose solutions of 7-9%, i.e., 7-9 g. per 100 ml. Higher sucrose concentrations have a distinctive mouthfeel which may influence results and lower sucrose concentration are no~ -indicative of normal use situations. If, for example a 0.014% solution of the compound of formula (I) is judged to be equally as sweet as a 7% sucrose solution, then the sweetness potency of that compound is 7/0.014 = 500 x sucrose. All of the sweetness potency values stated herein for the compounds of the invention were determined by this method. At threshold concentrations (i.e., the lowest concentration at whlch sweetness is first noticed, whlch for sucrose is ordinarily at concentrations in the range of 2-3%), the potency of a sweetener, such as the compounds of the invention, is generally twice that observed by comparison of its gustatory sweetness with 7-9% solutions of sucrose.
The requisite amines of formula RNH2 wherein R
is as previously defined are either commercially available or can be obtained from readily available precursors. For example, the 2-alkylcyclohexylamines and 2,6-dialkylcyclohexylamines can be obtained by catalytic hydrogenation of the corresponding alkyl substituted anilines. Many of the amines are obtained by reductive amination of the corresponding ketone using a variety of conditions known in the art. For example, reductive amination by the well known Leuckhart reaction employing formic acid and formamide as reducing agents, see for example, the review in Or~anic Reactions, Wilev and Sons, New York, Vol. 5, p. 301, 1949, may be employed. Alternatively, the appropriate ketone can be reductively aminated employing sodium cyanoborohydride and ammonium acetate see for example, J. AmerO Chem. Soc., 93, 2897 (1971), or by means of ethanolic ammonia in the presence of a hydrogenation catalyst such as Raney nickel, platinum or palladium, see, for example, Or ~nic Reactions, 4, 174 (1948). Many of the amines of formula RNH2 are obtained from the corresponding ketones by formation of an intermediate oxime formed by reacting the ketone with hydroxylamine or its salts under conditions well known in the art. The oxime intermediate is then reduced by catalytic hydrogenation or by means of sodium in the presence of a lower alkanol at elevated temperatureO
particularly preferred method, especially useful for reducing oximes of sulfur-containing ketones, employs reduction of the oxime in ethanol and a molar excess of sodium at the reflux temperature of the mixture.
The reguisite ketone precursors of the amines RNH2 are ei~her commercially available, known in the axt or prepared by known methods. For example, the ketones of formula (VI) and (VII) ~ CH2)m ~ 2)p /

(VI) tVII) where R , R , R5, R , X, m, n and p are as defined above, except those of formula (VII) wherein X is C=O, may be obtained by alkylation of the correspond-ing compounds wherein R , R4, R5 and R6 are each hydrogen to provide compounds of the above formula wherein from one to all of R3, R4, R5, ~6 are alkyl as defined above. The alkylation is carried out, for ~ example, employing alkylating agents such as the appropriate alkyl hal:Lde or alkyl sulfate under neutral or alkaline conditions provided by strong bases, for example, sodium hydride or sodium amide.
~sing the same method compounds of the formula (VI) and (VII) wherein only 1, 2 or 3 of the substituents alpha to the keto group are alkyl can be converted to compounds of the same formula wherein from two to 3~

rour of R3, R4, R5, R6 are alkyl. Gem-dialkyl compounds of formula (VI) and (VII) wherein either R3 and R4 or R5 and R6 are said alkyl can be obtained from the appropriate monoalkyl compound hy blocking the unsubstituted alpha-position prior to alkylation and subsequent removal of the blocking group. For example, 2,2-dimethylcyclohexanone may be obtained by condensation of 2-methylcyclohexanone with ethyl-formate in the presence of sodium methoxide and the resulting intermediate alkyiated as outlined below.

O O
- ~ ONa I J .L HCO2C~H5 ~ C~ I
NaOCH3 \~

Na H2O, OH- ~

Ketones of formula (VI) or (VII) wherein one or both of R3 and R5 are propyl or butyl may be obtained by condensation of the corresponding alpha-unsubstitut-ed compound with the appropriate aldehyde or ketone under alkaline conditions to an intermediate alpha-or alpha,alpha'-alkylidene ketone which can then be hydrogenated to provide the-desired ketone.
The requisite cyclobutanones are obtained by methods described by Conia et al., Bull. Soc. chim~
France, 726 (1963) and Conia, Ind. chim. Belge, 31, 981 (1966).
An alternative method for preparing the ketones of formula (VI) and (VII) involves a cyclization of an acyclic precursor. For example, by means of the well known Dieckmann cyclization of dicarboxylate YL i~ ~ ~

esters and subsequent hydrolysis and decarboxylation;
see e.~., Moaern Synthetic Reactions, ~. A. Benjamin, ~enlo Park, Cal., 1972, p. 740. The alpha-keto esters produced, especially those with no other alpha-substituent, can also be alkylated prior to hydrolysis and decarboxylation, if desired. This reaction can also be used to provide ketones (VI) and tVII) which are unsubstituted at the carbons adjacent to the carbonyl group which can be alkylated as described above~
For preparation of diketones of formula (VII) wherein X is C=O the keto group of acyclic keto-dicarboxylate ester precursor is converted to a ketal or thioketal, e.g., dimethyl ketal, diethylthio ketal, ethylenedioxy ketal or ethylenedithio ketal, prior to Dieckmann cyclization. Ester group hydrolysis and decarhoxylation affords a keto-ketal which may be converted to the corresponding amino ketal, by methods described above, followed by hydrolysis of the ketal group by methods well known in the art. The resulting amino ketone can be hydrogenated, if desired, to the corresponding hydroxyamine tX = C~OH) by known methods, e.g. by reduction with sodium borohydride.
2,2,4,4-Tetraalkyl-3-hydroxycyclobutylamines are prepared from the corresponding 1,3-diones by the method of ~.S. 3,125,569.
The amines of formula R ~
NH2--~--( C~2 ) n\
6,~t C~I2 ) /
R R
where X is CEIOH and R3-R6, n and p are as defined above, or N~protected derivatives thereof e.g., N-benzyloxycarbonyl derivatives, may be oxidized, e.g.

3~

by chromium trioxide, to the corresponding cornpounds wherein X is C=O. Alternatively, the hydroxyamine may be reacted first with e.g., a carbo~yl activated derivative of an ~-protected D-O-methylserine and the resulting intermediate of formula (IV) wherein R is sald hydroxy-containing group, oxidized, e.g., with chromium trioxide, to provide the corresponding ketone. The resulting ketone of formula (IV) is then converted to the desired product of formula (I) where R is a ke-to-containing group as desired above.
Certain of the ketones of formula (VII) are also obtained from acyclic precursors derived from ketones of the formula (VIII) wherein R , R , R and R are R6 ~ R3 ---(VIII) R R

as previously define~. For example four-membered ketones of formula (VII) where X is O or S are obtained by bromination of (VIII) with two moles of bromine and the resulting alpha,alpha'-dibromo compound cyclized with, e.g., sodium hydroxide to provide an oxetanone or hydrogen sulflde to provide a thietanone. The corresponding five-membered ring ketones (VII) are obtained when (VIII) is firs~
reacted with formaldehyde to provide an intermediate alpha-hydroxymethyl compound which is then brominated at the alpha'-position and cyclized with sodium hydroxide or hydrogen sulfide to provide the corresponding compounds of formula (VII) wherein X is O or S, respectively.
~ertain of the tetrahydropyran-~ ones and tetra-hydrothiapyran-4-ones of formula (VII) are obtained by adding the elements of water or hydro~en sulfide to the appropriately substituted divinylXetone.

-~8-Ketone intermediates of Eormula (IX) which ~ay be converted to amines via the oxime are obtained by methods outlined below where R17, ~18, Rl9 and R are as defined above~

Rl9 ~ 1 8 CH2O 1 ~ R18 PR1 ~ R17 (X) (XI) (IX) The appropriately substituted acetoacetic ester (X) is condensed with formaldehyde, e.g. under alkaline conditions, and the resulting hydroxmethylated inter-mediate (XI) is then cyclized, for example by heating in the presence of a mild acid or base with removal of ethanol as it forms.
Bromination of acetoacetic esters of formula (X) and subsequent treatment of the product with, e.g.
sodium hydroxide, provides ketones of formula (XII) which are converted to the corresponding amine as described above.

X ~ R ~ R13 R20 ~ 17 (XII) Alternatively, the ketolactones (XII) can be prepared by the method described in Zeit. Chemie, 13, 11 (1973~; Chem. Abstr., 78, 135596e (1973), by reaction of the appropriate cyclobutan-1,3-dione with hydrogen peroxide.

~29-The dibromo derivative of (VIII), described above, can also be treated with alkali hydroxides, e.g. sodium hydroxide under mild conditions, to form the corresponding 1,3-dihydroxyketone which is converted to the corresponding 1,3-dioxane-2,5-dione of formula ~XIII) by reaction with phosgene.

VIII~ R20 ~ 17 - 20 ~ COCl2 R ~ R17 Rl B BrR OH O~ O~_,O
o (XIII) The 5-oximino intermediate of (XIII) upon treatment with sodium in ethanol as described above, provides the corresponding 5-amino compound.
Treatment of a monobromo derivative of ketones of formula (VIII) with, e~g. ethyl malonate, and subsequent hydrolysis, decarboxylation and esterification of resulting product affords intermediates of fo~mula (XIV) which serve as precursors of the ketones (XV) as shown below, for example.

R2 ~ ~R ~ R18 ~ R

(XIV) (XV) The ketolactones (XV) are then converted to the corresponding 4-amino compound, e.g. by reduction of the oxime, as described above.

~r~

The 1,3-dibromoketone derivatives of (VIII), aescribed abo~e, also can be converted to the corres-ponding 1,3-dimercaptoke-tone by reaction with at least two moles of sodium hydrosulfide. Treating the dimercaptoketone with reagents such as iodine, hydrogen peroxide or hypochlorous acid under disulfide forming conditions, well ~nown in the art provides the ketones of forrnula XVI which are converted to amines by reduction of the oxime employing, e.g., sodium in ethanol.
o R6 L~R3 R5~\ ~R
S - S
(XVI) ~ nines of formula tXVII) are provided directly, for example, by the method of Nagase et al., Chem.
Pharm. Bull. 17, 398 (1969) as shown below.
_ R ~ CHO CH20 ~ CHO NH4Cl R13 ~ CN

/ H20, K

~J~ 2 Rl 2 ~//
~ ~ 13 (XVII) Use of ethylene oxide in place of formaldehyde in the first step of the above reaction seguence affords the corresponding 3-amino-2-pyrones, -~Rl O ~ R

3~

Lactarns corresponding to the above lactone inter-mediates or those of formula (IX), (XII), (XV~ or (XVII), are obtained by reaction of the appropriate lactone with ammonia; for example, the above lactone is contacted with an excess of anhydrous ammonia in ethanol and the mixture allowed to stir overnight at ambient temperature to provide compounds of the forrnula ~ 2 R12 ` ~ ~
HN

Alternatively, certain lactam intermediates are provided by the following reaction sequence.
O
X ) CH 2 Rl ~RRl 7 H 2 (C6H5CH2)~NH C02C2H5 Pd/C
N(CH2C6H5)2 ~ ~ R20~R173 The resulting ketones are then converted to the requisite amines by methods described above.
The isomeric ketolactams are obtained by the following reaction sequence:

o o o R2 ~ l71.Br2 ~R ~ l ~Rl ~ ~ Rl7 Rl ~ R 8 (C6H5~H2)2NH R19 ~ IR18 R 9 ¦ ¦ R18 \ 3.H2, Pd/C NH ~ H
C02C2HS C02C2~5 o The corresponding 5-membered lactams are also obtalned by the method of U.S. 3,125,569:

R20 NOH PCl~ ~ O
Rl~/ ~ R18 poidyphosphoric Rl9~ ~ R18 Cyclic or open chain alpha-hydroxyketones or alpha,alpha'--dihydroxyketones of the formula Rl4 ~ 5 Rl ~ A
~ (CH2)m or O ~ B
R16X~ R20~

where R -R , m, A and B are as previously defined are prepared by bromination with one or two moles of bromine and treatment of the bromo or dibromo inter-mediate with an hydroxylic base, e.g., sodium hydroxide or potassium hydroxide as described above. The reaction sequence is exemplified as follows:

O O
C~3~ ~ 3 _ 2 ~3 ~ OHH3 2. NaOH, ethanol P ~
2. NaOH, HO ¦ OH
ethanol ~

~ icycloalkylketones (XVIII) and alkylcycloalkyl-ketones (XIX) are prepared by the reaction of the appropriate acid halide and Grignard reagent employing conditions and reagents well known in the art, e.g., as shown below.

COCl MgCl~ (CH2)m + ~ - ~ ~
~(CH2)q ~ (CH2)mL(CH2)q t XVI I I ) R_ ~

(CH2)m (XIX) lQ A~ines of formula RNH2 where R is as pre~lously defined are also obtained by the well known Hofmann reaction by convexsion of t~e appropriate carboxamide with alkali metal hypohalite. This procedure is especially useful for the preparation of cyclopropyl-amines. The corresponding cyclopropyl amides are obtained and converted to amlnes, e.g. as shown below.

RS ~ R ~ N2CHCO2C2H5 ~ R ~ R4 1. NH R5 \ / R4 \ /
2. NaOBr y N~2 The first step of the above sequence to form the cyclopropylcarboxylic acid ester is known in the art, see for example, Mescheryakov et al., Chem. Abstr., 54, 2~436 (1960).
The compounds of formula (I) or intermediate amides therefore, wherein R is 2 ) n R6 ~ (C 2)p where X is SO or SO2 are obtained from the correspond-ing compounds wherein X is S by oxidation employing reagents and conditions known to form sulfoxides and sulfones from sulfides. Alternatively, the appro-priate ketone of formula (VII) where X is S or theamine derived from said ketone, as described above, can be oxidized to the sulfoxide or sulfone prior to coupling to form the dipeptide amide of formula (I).
Preferred reagents and conditions for such oxidation of sulfides include use of hydrogen peroxide in a solvent, for example, ace-tic acid or acetone. ~en equimolar amounts of reactants are employed the product is the sulfoxide, which is readily converted to the 3 i~

corresponding sulfone by an additional moie of peroxide.
O-ther ?referred oxidants are potassium permangante, sodium metaperiodate or chromic acid, for pre?aration of the sulfones, and m-chloroperbenzoic acid. The latter reagent being especially use~ul for conversion of the above thioketones (VII) to the corresponding sulfoxide employing one mole of this reagent, or the sulfone when two moles of the peracid are employed.
The compounds of formula (I) and the physio-logically acceptable salts thereof provide advantages as sweetening agents in view of their high potenc~, their physical form and stability. They are, ordinarily, crystalline, non-hygroscopic, water soluble solids.
They are uniquely characterized by possessing a sweet taste, devoid of undesirable harsh or bitter flavor qualities at ordinary use levels. They can be usefully employed to impart sweetness to edible materials. The term "edible materials" as used herein signifies all non-toxic substances consumable by humans or other animals, in solid or liquid form. Illustrative of such substances are: foods, including foodstuffs, prepared food items, chewing gum and beverages; food additives, including flavoring and coloring agents as well as flavor enhancers; and pharmaceutical preparations.
The compounds of the invention can be prepared in a variety of forms suitable for utili2ation of sweeten-ing agents. Typical forms which can be employed are solid forms such as powders, tablets, granules and dragees; and liquid forms such as solutions, suspensions, syrups, emulsions as well as other commonly employed forms par1icularly suited for combination with edible materialsO These forms can consist of the compounds of formula (I) or their physiologically acceptable salts either apart or in association with non-toxic sweetening agent carriers, i.e. non-toxic substances ~36-commonlv ernployed in association with sweetening agen-ts. Such suitable carriers include liquids such as water, ethanol, sor~itol, glycerol, citric acid, corn oil, peanut oil, soybean oil, sesame oil, propylene glycol, co:rn syrup, maple syrup and liquid paraffin, and solids such as lactose, cellulose, starch, dextrin, modified s~arches, polysaccharides such as polydextrose (see, e.g. ~.S. 3,76~,165 and U.S. 3,876,794), calcium phosphate (mono-, di- or tri-basic) and calcium sulfate.
Likewise ~seful and compatible are compositions containing a compound of the invention combined with a known sweetening agent such as, for example, sucrose, saccharin, cyclamate, L-aspartyl L-phenylalanine me-thyl ester and the like, useful for sweetening edible materials. Especially useful are the mi~tures of compounds of formula (I) and saccharin or a physio-logically acceptable salt thereof, e.g., the sodium, potassium, calcium or ammonium salt of saccharin. In said mixtures with saccharin the compounds of formula (I) reduce or completely mask the well known, undesirable bitter aftertaste of the saccharin.
Particularly useful such sweetener compositions are those containing saccharin in admixture with compounds o-E formula (I) which are at least 400 times as sweet as sucrose, especially those wherein Ra is CH20H and R is dicyclopropylcarbinyl, 2,2,4,4-tetra-methylthietan-3-yl or 2,2,4,4-tetramethyl-1,1-dioxo-thietan-3-yl. Most particularly preferred are such mixtures of saccharin and L-aspartyl-D-serine ~-(2,2,4,4-tetramethylthietan-3-yl)amide, especially such mixtures which contain the latter compound of formula (I) and saccharin in a weight ratio in the range of from 1:1 to 1:8. These mixtures are not only pleasantly sweet tasting and appreciably devoid of bitter aftertaste, they a e, unexpectedly, significantly sweeter than calculated by summation of sweetness of the indlvidual components of the mixture. That is, they exhibit a synergist effect, being up to 50~
sweeter than calculated. In mixtures of saccharin or its salts and l,-aspartyl-D-serine N-(2,2,4,4-te-tramethyl-thietan-3-yl)amide in ratios outside the above range the synergist effect is consideraly reduced.
The invention also provides sweetened edible compositions comprising an edible material and a sweetening amount of a compound of formula (I), a physiologically acceptable salt thereof alone or in combination with a non-toxic carrier or known sweeten-ing agent. Examples of specific edible materials which provide such sweetened edible compositions include: fruits, vegetables, juices, meat products such as ham, bacon and sausage; egg products, fruit concentrates, gelatins and gelatin-like products such as jams, jellies, preserves, etc.; milk products such as ice cream, sour cream and sherbet; icings, syrups including molasses; corn, wheat, rye, soybean, oat, rice and barley products such as bread, cereals, pasta~ cake and cake mixes, fish, cheese and cheese products, nut meats and nut products, beverages such as coffee, tea, carbonated and non-carbonated soft drinks, beers, wines and other liquors; confections such as candy and fruit flavored drops, condiments such as herbs, spices and seasonings, flavor enhancers such as monosodium glutamate and chewing gum. The instant sweeteners are also of use in prepared packaged products such as dietetic sweeteners, liquid sweeteners, granulated flavor mixes which upon reconstitution with water provides non-carbonated drinks, instant pudding mixes, instant coffee and tea, coffee whiteners, malted milk mixes, pet foods, livestock feed, tobacco and consumable toiletries such as mouth washes and toothpaste as well as proprietary and non-proprietary pharmaceutical preparations and o-ther products of -the food, pharmaceutical and sundry industries.
Fspecially preferred sweetened edible composi-tions are carbona-ted beverages con-taining one or more of the instant sweeteners.
The L-asparatyl-D-amino acid dipeptide amides of the instan-t lnven-tion and -the corresponding dipeptide amides of our rela-ted Uni-ted States Patent No. 4,411,925 issued October 25, 1983, of the formula NH2 Rai where R is as defined herein and Ra is methyl, e-thyl, n-propyl or isopropyl, are also useful in the applications disclosed in the art for L-aspartyl-L-phenylalanine methyl es-ter and analogs thereof. For example, they are useful in -the same functions disclosed in the following patents and paten-t appli-cations for L-aspartyl-L-phenylalanine methyl. es-ter. In these uses they have the advantages disclosed for the dipeptide ester as well as their previously mentioned advantages in stability and potency:

.æ~

U.S. Patent Nos.:
______ 3,64 ,491 3,971,857 3,865,957 3,761,288 3,982,023 3,800,046 A,001,456 3,818,077 4,004,039 3,829,5~8 4,007,288 3,875,311 4,031,258 3,875,312 4,036,~92 3,886,295 4,051,268 3,922,369 4,059,706 3,934,048 4 r 122,195 3,947,600 4,139,636 3,955,000 4,143,170 3,956,507 4,153,737 5 Canadian Patent Nos.:
1,026,g87 1,027,113 1,028,197 1,043,~58 1,046,840 Netherlands Patent A~plicatlon Nos.
73-04,314 73-11,307 75-14,921 76-05,390 76-08,963 West German Offenle~ sschrift Nos.:
2,438,317 2,456,926 2,509,257 ~,518,302 2,609,999 2,646,224 2,713,951 ~40-Bel lan Patent Nos -830,020 838,938 863,138 882,672 Great Britian Patent No 1 454 571-Ja~an Kokai No. 77-04,176;
French Patent No. 2,338,651 and Swiss Patent No. 590 615 The invention is further illustrated by the following examples.

-41~

L-Aspartyl-D-serine N-(dicyclopropylcarbinyl)amide I, Ra = CH2OH, R =

A. D-HOCH2CHCOOH
NHC'.bz 5' A solution of 4.41 g. (0.042 mole) D-serine in 21 ml. of 2N sodium hydroxide was cooled to 5 to 10C., adjusted to pH 10.0-11.5 wi-th concentrated hydrochloric acid and 6.9 ml. (0.048 mole) benzyl chloroformate was added in increments over 1.5 hours with simultaneous addition of 2N sodium hydroxide to maintain the mixture within the above range of pH.
The mixture was stirred overnight at room temperature, washed with ethyl ether and the aqueous phase acidified (pH 2.5-3.0) with 6N hydroehloric acid. Extraetion with ethyl acetate, washing the extracts with brine and drying (MgSO4), afforded 3.14 g. of product as a eolorless solid whieh was reerystallized from 20 ml.
ethyl acetate to yield 2.64 g. of product, Rf 0.93 [thin layer ehromatography (TLC), ethyl acetate/
hexane/acetie acid, 9:9:2, by volume~.

-~2-B. D-~OCH2CHCONH
N~ICbz ~
To a slurry of 2.~ g. (0.01 mole) of N-Cbz-D-serine, obtained in Part A, in 75 ml. chloroform was added 1.1 ml. (0.01 mole) N-meth~lmorpholine. A
solution was obtained which was cooled to -12C. To this was added 0.96 ml. (0.01 mole) ethyl chloro-formate, the mixture stirred at -10C. ror five minutes, a solution of 1.11 ~. (0.01 mole) dicyclo-propylamine in 5 ml. chloroform was added and stirring continued for five minutes at -15C. The reaction mixture was allowed to warm to room temperature, washed successively with 0.5N hydrochloric acid, 5%
sodium bicarbonate solution, water and the chloroform evaporated ln vacuo. The aqueous washes were combined and extracted with ethyl acetate. The ethyl acetate extracts were combined with the residue obtained by evaporation o~ chloroform and the ethyl acetate was dried (MgSO4~ and evaporated ln vacuo to afford a white solid which was dried in the vacuum oven overnight to give 3.2 g. of the desired product, Rf 0.54 which was used ln the next step.

3~:~

-~3-C. D-HOCH~CHCONH
2 ~
The 3.2 g. (9.6 mmole) N-Cbz-amide, obtained in Part B, was dissolved in 70 ml. methanol, 1.0 9. 5~
Pd/C catalyst added and the mixture hydrogenated at 60 psi (4.2 kg./cm.2) for 30 minutesO The catalyst was removed by filtration and the filtrate evaporated in vacuo to yield 1.93 g. of product as a soap-like solid.
D. C6H5cH2ococ~2cHcoNHcH(c~2oH)coNHcH( ~ )2 NHCbz A mixture of 3.4 g. (9.5 mmole) beta-benzyl N-benzyloxycarbonyl-L-aspartate, loO ml. (9.5 mmole) N
methylmorpholine and 0.9 ml. (9.5 mmole) ethyl chloroformate was stirred at -15 to -10C. for five minutes and a solution of l.9 g. (9.5 mmole) D-serine N-dicyclopropylcarbinylamide, obtained in Part C, in 10 ml. chloroform was added at -15C. The resulting mixture was stirred at -10C. for five minutes, allowed to warm to ambient temperature and stirred for one hour. The reaction mixture was evaporated ln vacuo to remove solvent, the residue taken up in ethyl acetate (250 ml.), washed in turn with lN
hydrochloric acid, 5% sodium bicarbonate solution, brine and dried over anhydrous magnesium sulfate.
The solvent was evaporated in vacuo to obtain a gelatinous solid. This was taken up in 75 ml~ hot ethyl acetate. Upon cooling a crystalline solid was obtained which was dried in vacuo at 40C. to yield 2.75 g. of the desired diprotected dipeptide amide as a fine white solid, Rf 0.30.

E. A mixl_ure of 2.75 g. of the diprotected di-pep-tide amide, obtained in Part D, 200 ml. methanol and 1.0 g. 5~ Pd/C catlayst was hydrogenated at 60 psi (4.2 kg./cm.2) for one hour during which product precipitated. The catalyst/product mixture was filtered, the filter cake slurried in 100 ml. hot water and filtered again. The combined filtrates were e~aporated to dryness, triturated with water, filtered and dried ln vacuo to arford 260 mg. of product as a fine white, fluffy solid, M.P. 252-254C., Rf 0.58 (TLC, n-butanol/water/acetic acid 4:1:1, ninhydrin spray).
The filter cake from the hydrogenation was slurried in 50 ml. of O.lN hydrochloric acid, the mixture filtered through diatomaceous earth (Supercel), the filtrate ~pH 1.6) was adjusted to pH 5.9 with sodium hydroxide solution, and the precipitated product collected by filtration and dried in vacuo to yield an additional 800 mg. of product. Total step yield, 68~.
Mass spectrum (m/e) 313 (M )~
Sweetness potency: 700 x sucrose.

~r~

L-Aspar-tyl-D-serine N-(2,4-dimethyl-3-pentyl)amide I, Ra = C~2OH, R =

A. D-HOCH2CHCONH
NHCbz A mixed anhydride was prepared as follows:
l.0 g. (4.3 mole) N-benzyloxycarbonyl-D~serine was dissolved in 50 ml. tetrahydrofuran, cooled to -10C.
under a nitrogen atmosphere and 0.47 ml. (4.3 mmole) N-methylmorpholine and 0.41 ml. (4~3 mmole) ethyl chloroformate were added. The mi~ture was stirred at -10C. for 30 minutes.
To the solution of mixed anhydride was added 495 mg. (4.3 mmole) 2,4-dimethyl-3-aminopentane dissolved in a small amount of chloroform, the mixture stirred at -10C. for 15 minutes and allowed to warm to room temperature. Ethyl acetate (40 ml.) was added and -the mixture was washed with lN hydro-chloric acid, sodium bicarbonate solutionr brine and the organic layer was dried over anhydrous magnesium sulfate. Evaporation of solvent in vacuo gave 1.27 g. colorless solid which was triturated with ethyl ether, filtered and air dried to afford l.0 g.
of colorless product, Rf 0.77 (TLC, ethyl acetate/
hexane, 7:3 by volume, vanillin spray).

B. D~HOCH2CHCONH
__ 2 The above 1.0 g. of product was dissolved in 50 ml. methanol, 0.5 g. 5% Pd/C catalyst added and the mixture hydrogenated at 50 psi (3.52 kg./cm.2) until hydrogen uptake ceased. Filtration and evapora-tion of filtrate gave 700 mg. of the desired product.

C. C6H5CH2OCOCH2CHCONHCH(CH2OH)CONH
NHCbz A solution of 1~36 g. (3.8 mmole) beta-benzyl N-benzyloxycarbonyl-L-aspartate in 10 ml. tetrahydrofuran was cooled to -10C. and 0.42 ml. (3.8 mmole) N-methylmorpholine was added. To this was added dropwise 0.36 ml. (3.8 mmole) ethyl chloroformate and the resulting mixture stirred at -10C. for S minutes.
Then 566 mg. (2.8 mmole) D-serine N-(2,4-dimethyl-3-pentyl)amide (from Paxt B, above) in a few milliliters of tetrahydroEuran was added dropwise and stirring continued for 15 minutes. The reaction mixture was allowed to warm to room temperature and evaporated in vacuo to afford a solid residue. This was mixed with ethyl acetate, washed with lN hydrochloric acid and the organic phase washed with 5% aqueous sodium bicarbonate, brine, dried (MgSO4) and the solvent evaporated to afford 1.6 g. of product as an amorphous solid which was used in the next step.

3~ 3~

D. To a solution of 2.7 g. of the diblocked di-peptide amide (preparation as described in Part C, above) in methanol was added 1.5 g. 5% Pd/C catalyst and the mixture was hydrogenated at 50 psi (3.52 kg./cm. ) until hydrogen uptake ceased. The catalyst was removed by filtration and the filtrate evaporated in vacuo to a small volume and allowed to stand at room temperature. The precipitated product was collected by filtration and dried in vacuo to afford 342 mg. of ____ colorless solid.
Sweetness, 180 x sucrose.

L-Aspartyl-D-serine N-(2,2,4,4-tetramethylthietan-3-yl)amide C~3 CH3 I, Ra = CH2OH, R = ~ S
CH/ CH
A. D-HOCH2CHCOOH
NH_-Bo The method is that described by Moroder et al., Z. Physiol. Chem. 357, 1651 (1976), for preparing t-Boc-amino acids. To 10 ml. each of dioxane and water was added 2.18 g. (10 mmole) di-t-butyl dicarbonate 1.6 ml. (11.5 mmole) triethylamine and 1.05 g.
(10 mmole) D-serine. The mixture was stirred for 30 minutes at room temperature and the dioxane evaporated _ vacuo. The aqueous residue was cooled in ice, ethyl acetate was added and the mixture stirred while adding dilute potassium bisulfate solution to pH 2-3. The aqueous layer was separated, extracted twice with ethyl acetate and the combined extracts washed with water, dried (Na2SO~) and the solvent evaporated ln ~acuo to yield 1.7 g. of product as a viscous paste.

_~9_ ~<
B. D-HOCH2CHCONH ~ S
NH2 CH'`CH
A mixed anhydride was prepared from 2.85 g.
(14 mmole) of N-t-butoxycarbonyl-D-serine, 1.55 ml.
N-methylmorpholine, 1.34 ml. ethyl chloroformate ln 75 ml. methylene chloride at -12 to -10C. by the method of Example l r Part B. To this mixture was added 2.01 g. (14 mmole) of 3~amino-2,2,4,4-tetra-methylthietane and stirring continued for five minutes at -12C. The product was isolated as described in Example l, Part B to afford 4 g. of a viscous liquid residue. The residue was dissolved in 40 ml. methylene chloride, 12 ml. trifluoroacetic acid (d = 1.480) was added and the mixture was stirred at room temperature for three hours. The reaction mixture was made alkaline with 40% sodium hydroxide solution, the organic layer separated, the aqueous layer was saturated with sodium chloride and extracted with methylene chloride. The combined extracts were dried (MgSO4) and concentrated to dryness in vacuo to yield 2.21 g. amorphous off-white solid. Crystallization from ethyl ether/hexane gave 1.92 g. of product as a fine r white solid.

(CH3)2 C~ t-ButylOC(:)CH2CIHCONH(~HCONH ~ S
NH-t-soc ( 3)2 A mixture of 2.3 g. (8.0 mmole) beta-t-butyl N~
t-butoxycarbonyl-L-asparate, 0.88 ml. (8.0 mmole) N-methylmorpholine and 0.77 ml. (3.0 mmole) ethyl chloroformate in 40 ml. methylene chloride was stirred at -12C. for five minutes. ~ solution of 1.85 g. (8.0 mmole) D-serine N (2,2,4,4~tetramethyl-thietan-3-yl)amlde in 5 ml. of the same solvent was added and stirring continued at -12 to -10C. for ten minutes. The mixture was allowed to warm to room temperature, stirred for one hour at this temperature and the solvent evaporated. The residue was taken up in ethyl acetate, washed with dilute hydrochloric acid, sodium bicarbonate solution, brine, dried (MgSO4) and the ethyl acetate evaporated to afford 3.34 g. of amorphous solid. Crystalliæation from ethyl ether/hexane gave 2.91 g. of colorless solid product, Rf 0.70 (ethyl acetate/he~ane, 7:3).

D. A solution of 2.4 g. (4.78 mmole) of the product obtained in Part C, above, in 60 ml. chloroform was fitted with a gas inlet tube and anhydrous hydrogen chloride bubbled through the solution. After f,ive minutes, precipitation of solid was observed. The hydrogen chloride addition was continued for ten minutes, then the mixture was stirred at ambient temperature for one hour and evaporated to dryness ln vacuo. The residue was taken up in water, washed with chloroform, the pH adjusted to 5.6, washed again with chloroform, and the aqueous phase evaporated ln vacuo. Ethanol was added to the residue and the mixture evaporated to dryness in vacuo. The residue was dissolved in 25 ml. hot water and allowed to cool. The precipitated product was collected by filtration and dried in vacuo to yield 1.12 g. (67~) of product, M.P. 193-196C. Rf 0.32 (n-butanol/water/
acetic acid, 4:1:1).
Analysis Calculated for C14H25N3O5S:
C, 48.39; H, 7.25; N, 12.09; S, 9.23.
Found: C, 46.77; H, 7.48; N, 11.91; S, 8.82 Sweetness potency, 1200 x sucrose.

3'~

L-Aspartyl-D-serine N-(2,2,4,~-tetramethyl~l,l-dioxothietan-3-yl)amide I, R = CH2H' R = ~ SO2 __ A.3-~mino~2,2,4,4-tetramethylthietan-1,1-dioxide A solution of 14.53 g. (0.1 mole) 3-amino-2,2,4,4-tetramethylthietane and 64.17 g. (0.3 mole) sodium m-periodate in 500 ml. water was stirred overnight at room temperature. The reaction mixture was adjusted to p~ 13 with sodium hydroxide solution and the precipitated sodium iodate removed by filtra-tion. The filtrate was washed with 100 ml. ethyl ether, the aqueous phase extracted continuously with methylene chloride over 18 hours, the extract dried (MgSO4) and solvent evaporated ln vacuo. The residual solid was recrystallized from ethyl acetate to provide 8.5 9. of product, M.P. 104-106.5C. A
second crop of crystals was obtained, 2.7 g., MoP~
103-106C. Total yield, 63%.

B. D-Serine N- ( 2,2,4,4-tetramethyl-1,1-dioxo-thietan-3-yl)amide _ ~ ~ ~
By the method of Example 1, Part B, 1.33 g.
(6.5 mmole) N-benzyloxycarbonyl-D-serine, 0.715 ml.
N-methylmorpholine, 0.62 ml. ethyl chloroformate and 1.15 g. (6.5 mmole) 3-amino-2,2,4,4-tetramethyl-thietane-l,l-dioxide gave 2.3 g. of N-benzyloxy-carbonyl~D-serine N-(2,2,4,4-tetramethyl-1,1-dioxo-thietan-3 yl)amide as a viscous li~uid, Rf 0.37 (ethyl acetate/hexane, 7:3). This liquid was dis-solved in methanol, 750 mg. of 5% Pd/C catalyst added and the mixture hydrogenated by the method of Example 1, Part C. After filtering to remove the catalyst, the methanol was evaporated in vacuo, the residue taken up in lN hydrochloric acid and extracted with chloro-form. The aqueous layer was made alkaline with sodium hydroxide saturated with sodium chloride and extracted continuously wlth chloroform overnight.
Evaporation of solvent gave 1.54 g. of product as a viscous liquid which solidified upon standing~ Rf 0.32 (m-butanol/water/acetic acid, 4:1:1).

-5a_ 6 5 2 2,E ' ~ H32 _ _____Cbz CH2OH CH3 CH
The diblocked dipeptide amide of the above formula was prepared on a 4.7 millimolar scale employing the method of Example 1, Part D, with 1.7 g. beta-benzyl N-benzyloxycarbonyl-L-aspartate, 0.51 ml. N-methylmorpholine, 0.45 ml. ethyl chloro-formate and 1.24 g. D-serine N-(2,2,4,4~tetramethyl-1,1-dloxothietan-3-yl)amide. The product, 2.45 g., was obtained as a colorl~ss amorphous solid. Two grams of this material was purified by chromatography on 60 g. of silica gel, eluting wlth ethyl acetate to afford 1.2 g. of amorphous solid product, Rf 0.30 (ethyl acetate/hexane, 7:3).
D. A mi~ture of 1.2 g. of purified product from Part C, above, 75 ml. methanol and 0.6 g. of 5% Pd/C
was hydrogenated at 80 psi (5.6 kg./cm.2). When hydrogen uptake ceased, the catalyst was removed by filtration, and the filtrate evaporated to afford a colorless solid residue. The residue was taken up in water, washed with chloroform and the aqueous layer evaporated 1n vacuo. The residual solid was crystal-lized from ethanol to afford 255 mg. of the desired dipeptide amide as a fine white solid, M.P. 170-173, Rf 0.20. An additional 180 mg. of product was obtained by reworking the filter cake from the hydrogenation.
Sweeetness potency: 850 x sucrose.

D-O-Methylser~ne A. N-Chloroacetyl-dl-O-methylserine .. ~. ... ~
To 125 ml. water was added 59.55 g. (0.5 mole) dl-O-methylserine, the mixture was stirred and 20 g.
(0.5 mole) sodium hydroxide was added. The resulting solution was cooled in ice and simultaneously, from two dropping funnels was added over one hour, a solution of 20 g. of sodium hydroxide in 125 ml.
water and 47.8 ml. 10.6 mole) chloroace-tyl chloride.
The addition rates were adjusted to maintain the reaction mixture at pH 9.0-9.5. After the addition was completed, the resulting mixture was stirred for one hour at pH 9.0-9.5. The mixture was washed twice with methylene chloride, the aqueous phase acidified to pH 1.5 with concentrated hydrochloric acid while cooling in ice, saturated with sodium chloride and extracted several times with chloroform. The combined extracts were dried (MgSO4) and the solvent evaporated in vacuo. The residue was stirred with ethyl ether .
to precipitate a yellow solid product which was collected by filtration and dried, 69.38 g. (71%).
M.P. 104-]07C., Rf O.Z3 (ethyl acetate/hexane/acetic acid, 9:9:2, phosphomolybdate spray). A second crop was obtained from the aqueous phase by adding more sodium chloride and extracting with chloroform.
Evaporation of chloroform gave 3.65 g. of product.
Total yield 75%.

3~

B. N-Chloroacetyl-~-O-methylserine To 3000 ml. of water at 35-37C. was added 73.03 g. (0.37 mole) N-chloroacetyl dl-O-methylserine and the mixture adjusted to pH 7.1g by addition of concentrated ammonium hydroxide. Water was added to make a total volume of 3700 ml. To this was added 17 mg. of commercial porcine kidney aminoacylase, N-acylamino acid amidohydrolase; EC 3.5.1.14 (Acylase I) having 1845 units/mg. (1 unit is defined as the amount required ~o hydrolyze 1 micromole of N-acetyl-L-methionine per hour at pH 7.0 and 25C.). The amount of enzyme added was that calculated to hydro-lyze the susceptible isomer in six hours. The xesulting solution was maintained at 37-38C. for 28 hours with intermittent addition of ammonium hydroxide to maintain the pH at 7.1 to 7.2. An adclitional 5 mg. of enzyme was added after 24 hours.
The hydrolysis mixture was acidified to pH ~.5 with glacial acetic acid, filtered through a 0.6 ~
millipore filter (type BD) and the filtrate evaporated in vacuo below 35C. to reduce the total volume to __ 100-150 ml. The residual mixture was acidified to pH 2.00 with hydrochloric acid and extracted several times with ethyl acetate and further extracted with chloroform.- The separate organic extracts were each washed with water, dried ~MgSO4) and solvent evaporated ln vacuo to afford a yellow liquid residue. Addition of hexane and evaporation ln vacuo induced crystalli-zation. The ethyl acetate extracts afforded 16.67 g.
(~6%) of N-chloroacetyl-D-O methylserine, M.P.
95-96C., [alpha]D - 15.5 (C = 1, lN NaOH). The chloroform extracts gave 4.61 g. (13%) of the same product, M.P. 90-34C. (odor of chloroacetic acid).
Both crops of product showed a single spot upon thin-layer chromatography on silica gel plates, R~ 0.35;9:9:2 eth~l acetate/hexane/acetic acid, phospho-molybdate spray.

33~

C. To 16.67 g. (0.085 mole) N-chloroacetyl-D-0-methylserine was added 25 ml. of 2N hydrochloric acid and the m:ixture heated a-t reflux for three hours.
The mixt~re was concentrated in vacuo, chasing any residual chloroacetic acid with additional water.
The solid residue was washed with ethyl ether and collected by filtration to afford 12.31 g. (93O) D-0-methylserine hydrochloride, M.P. 188-190C.; [alpha]D -16~7 (C = 0.7, CH30H).

3~

L-Aspartyl-3-O-methylserine N-(dicyclopropylcarbinyl)amide I, Ra CH2OCH3, R =

A. D-CH3OCH2C~ICOOH
NHCbz -A solution of 12.31 g. (0.079 mole) 3-O-methyl-serine in 40 ml. water containing 6.32 g. (0.158 mole) sodium hyciroxide was cooled to 5-10C. and 11.74 ml. (0.0806 mole) benzyl chloroformate and 4M
sodium hydroxide were added simultaneously at pH
8-9. The resulting mixture was stirred until the pH
remained at 8 without further addition of base.
After washing with methylene chloride, the aqueous phase was acidified with concentrated-hydrochloric acid, extracted four times with methylene chloride~
the extracts dried (MgSO4) and solvent evaporated in va_uo. The viscous liquid residue was stirred with hexane and the precipitated solid collected by filtration to yield 18.6 g. oE product (93%), [alpha]D ~
2.7 (C = 1, lN NaOH), Rf 0.43.

B. D-CH3OCH2CHCONH
NHCbz To a solution of 3.80 g. (0.015 mole) N-benzyl-oxycarbonyl-D-O-methylserine in 75 ml. m~thylene chloride was added 1.68 ml. (0.015 mole) N--methyl~
morpholine and the mixture cooled to -15C. To this was added 1.43 ml. (0.015 mole) ethyl chloroformate, the mixture stirred at -20 to -15C. for ten minutes and 1.68 g. (0.015 mole) dicyclopropylcarbinyl amine was added. The mixture was allowed to warm to room temperatu:re and stirred for -two hours. The resulting mixture was washed twice with lN sodium hydroxide, twlce with lN hydrochloric acid and dried over magnesium sulfate. Evaporation of solvent in vacuo gave 5.1 g. (98~) of the desired product, Rf 0.59 upon silica gel TLC in 1:1 ethyl acetate/hexane, phosphomolybdate spray.
The structure of the product was confirmed by ~-NMR spectroscopy.

3~

C . D-CH3OCH2CH ( NH2 ) CON~

. . . _ The 5.1 9. of N-benzyloxycarbonyl-D-O~methylserine N-(dicyclopropylcarbinyl)amide, obtained in Part B, above, was hydrogenated by the procedure of Example 1, Part C, to afford 2O96 g. (95%) D-O-methylserine N-(dicyclopropylcarbinyl)amide as a liquid, Rf 0.39;
[alpha]D ~ 23.2 (C = 0.7, lN HCl). The structure was confirmed by lH-NMR spectroscopy.
D. C6H5CH2OCOCH2CH(NHCbz)CONHCH(CH2OCH3)CONHCH( ~ )2 . . . _ _ .
A mixture of 4.97 g. (13.9 mmole) beta-benzyl N-benzyloxycarbonyl-L-aspartate, 1.55 ml. (13.9 mmole) N-methylmorpholine and 1.33 ml. (13.9 mmole) ethyl chloroformate were reacted as described in Example 1, Part Dl to provide 7.43 g. (97~) of the diblocked dipeptide amlde which was recrystallized twice from e-thyl acetate to g:ive 4.25 g. of colorless product, Rf 0.45 (7:3 ethyl acetate/hexane). The structure was verified by 1~-NMR.
E. Hydrogenation of the 4.25 g. of purified di~
blocked dipeptide amide obtained in Part D, above, by the procedure of Example 1, Part E, gave 2.4 g. (95%) of the desired dipeptide amide, M.P. 215~217C.
(dec.); [alpha]D + 37.6 (C = 0.8, 1.2N HCl); Rf 0.41.
Sweetness potency, 85 x sucrose.

3~

_ L~Aspar-tyl-D-O-methylserine N-2,2,4,4-tetramethylthietan-3-yl)amide 3~/ 3 I, Ra = CH2OCH3, R = ~ s A. D-CH3OCH2CHCOOH
NHt-Boc . =
To a solution of 2.89 g. (18.6 mmole) D-O~
methylserine hydrochloride in 11 ml. water was added 6.48 mlO (46.5 mmole) triethylamine, 5.10 g. (20.7 mmole) 2-(t~butoxycarbonyloxyimino)-2-phenylaceto-nitrile ("BOC-ON"~ and 11 mi. tetrahydrofuran. The mixture was stirred at room temperature overnight, diluted with 25 ml. water and washed with ethyl acetate. The aqueous layer was acidified to pH 1.8 with lM hydrochloric acid, extracted with ethyl acetate (3 x 75 ml.), dried (MgSO4) and evaporated in vacuo to afford 4.2 g. of product as a viscous liquid, Rf 0.65 ~9:9:2 ethyl acetate/hexane/acetic acid, phosphomolybdate spray).

B. N-t-Boc-D-0-Methylserine N-(2,2,4,4-tetramethyl-thietan-3-yl)amide ~o a solution of 4.2 g. (18.6 mmole) N-t-Boc-D-0-methylserine in 90 ml. me-thylene chloride was added 2.08 ml. N-methylmorpholine, the rnixture cooled to -15C. and 1.78 ml. ethyl chloroformate added.
After stirring for 8 minutes at -20 to -15C., 2.70 g. (18.6 mole) 3-amino-2,2,4,4-tetramethyl-thietane dissolved in 10 ml. methylene chloride was added at the same temperature and the mixture allowed to warm to room temperature. After stirring for two hours the mixture was washed with dilute sodium hydroxide, dilute hydrochloric acid, dried over anhydrous magnesium sulfate and the solvent evaporated _ vacuo to yield 6.04 g. (94%) of colorless solid, Rf 0.35 (3:7 ethyl acetate/hexane, phosphomolybdate spray~. The structure was verified by H-NMR.

C. D-O-~ethylserine N-(2,2,4,4-tetramethylthietan-3-y~_amide To a solution of 6.04 g. (17.4 mmole) of N-t~
Boc-D~O-methylserine N-(2,2,4,~-tetramethylthietan-3-yl)amide in 13.4 ml. methylene chloride was added 6.7 ml. (87 mmole) trifluoroacetic acid (sp. gr.
1.480) and the mixture was stirred at room tempera-ture for three hours. An additional 1.0 ml. in ? ml.
methylene chloride was added and stirring continued for one hour. The reaction mixture was made alkaline with 40% (w/w) sodium hydroxide solution, the organic layer separated and the aqueous layer extracted several times with fresh methylene chloride. The combined extracts were dried (MgSO~) and solvent evaporated _ vacuo to give 4.29 gO of crude liquid product. This was taken up in 20 ml. lN hydrochloric acid, washed with ethyl ether, the aqueous layer made alkaline with sodium hydroxide (40% w/w), saturated with sodium chloride and extracted with methylene chloride. Evaporation of the extracts afforded 3.21 9. (75~) of the desired product, Rf 0.41;
[alpha~D - lg.8 (C = 0.8, lN HCl). The structure of this product was verified by its H-NMR spectrum.

D. t-Butyl OCOCH2CH CONH CH CONH ~ S
NH-t-BccH20cH3 CH3CH3 By employing 3.76 g. of product obtained by the procedure of Part C, above, the procedure of Example 3, Part C, was repeated on a 13 millimolar scale using 50 ml. methylene chloride as solvent to afford 5~0 g~
(74%) of the desired diblocked dipeptide amide as a brittle foam, Rf 0.40 (ethyl acetate/hexane, 1:1;
phosphomolybdate spray). The structure was verified by the 1H-NMR spectrum of the product.
E. Anhydrous hydrogen bromide was bubbled through a solution of 5.0 g. (9.7 mmole) of the diblocked dipeptide amide provided in Part D, above, while stirring at room tempexature for one hour. The resulting mixture was evaporated to dryness in vacuo 15 and the resulting yellow solid residue dissolved in water. The solution was washed twice with ethyl ether, once with methylene chloride, the aqueous phase adjusted to pH 5.8 with sodium hydroxide solution and evaporated to dryness 1n vacuo. The 20 residual solid was dissolved in 10 ml. 95% ethanol and ethyl ether added to precipitate the title compound in two crops:
1.66 g., [alpha]D + 13.4 (C = 0.9, 1~2N HCl), M.P. 85-90C.;
1~20 9~ r [alpha]D + 13.9 (C = 0~8r 1 o2N HCl) ~
TLC of each crop showed product spot at Rf 0.51 with small amount of material of Rf 0.44.

-6~-F. Purification via p~toluenesulfonate salt To 10 ml. water was added 1.39 g. (3.85 mmole) of the combined crops of product obtained above and 0.66 g. ~3.83 mmole) p-toluenesulfonic acid. The resul~ing solution was stirred at room temperature for two hours. The precipitated solid was collected by filtration and washed with a small amount of water to afford 0.94 g. of p-.oluenesulfonate salt. The salt was combined with 3 ml. of liquicl anion exchange resin (Amberlite LA-l~), 6 ml. hexane, 2 ml. water and the mixture stirred for two hours. The aqueous phase was separated, washed with hexane and evaporated to dryness in vacuo to give 0.72 g. of off-white solid, [alpha]D ~ 22.43 (C = 0.8, 1.2N HCl); Rf 0.48.
Sweetness potency: 320 x sucrose. The sweet taste was judged to be unusually clean, free of off flavor notes and to have a quick sweetness impact.

~ A registered trademark of Roh~ and Haas Co.

E~AMPLE 8 L Aspartyl-D-O-methylserine N-(2,2,4,4-tetramethyl-l,l-dioxothietan-3-yl)amide __ A. D CH3OC~2CHCONH ~ S
NHCbz CH3 H3 I~ 75 ml. methylene chloride was dissolved 3.8 g. (15 mmole) ~-benzyloxycarbonyl-D-O-methyl serine. N-methylmorpholine (1.68 ml.) was added, the solution cooled to -15C. and 1.43 ml. ethyl chloro-forrnate added. The resulting mixture was stirred ior 8 minutes at -15C., then 2.18 g. (15 mmole) 3-amino-2,2,4,4~tetramethylthietane was added and the mixture allowed to warm to room temperature. Stirring was continued for two hours at room temperature, the reactlon mixture was~ed with dilute sodium hydroxide, dilute hydrochloric acid, dried (MgSO4) and the solvent evaporated ln vacuo to give 6.11 g. of liquid product, Rf 0.58 (ethyl acetate/hexane 1:1; phosphomolybdate spray).

3~

B. Oxidatlon to l,l-dioxide The product from Part A, above, 6.11 g., was dissolved in 75 ml. chloroform and cooled in ice while adding 7.12 g. m-chloroperbenzoic acid in portions. The reaction mixture was allowed to warm to room temperature and stirred for three hours.
Additional chloroform (75 ml.) was added and the solution washed twice each with 5~ (w/v) sodium carbonate solution, 0.5N sodium thiosulfate and lN
hydrochloric acid. After drying the organic phase (MgSO4) and evaporation of solvent, 6.24 g. of product was obtained as a viscous liguid, Rf 0.22 (ethyl acetate/hexane, 1:1; phosphomolybdate spray) with traces of starting material and sulfoxide. The H-NMR spectrum was in agreeement with the structure for the desired sulfone with a small amount of chloroform.

C . D-CH30CH2CHCONH~ S2 N~2 ~ 3 A mixture of 6.11 g. of N-benzyloxycarbonyl-D-O-methylserine N-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide, 250 ml. methanol and 3.0 g. 5% palladium-on-carbon catalyst was hydrogenated at 50 psi (3.52 km./cm.~) for two hours. The catalyst was removed by filtration, the filtrate was evaporated 1n vacuo and the residue taken up in 35 mlO lN hydrochloric acid.
The acidic solution was washed three times with chloroform, made alkaline with solid sodium hydroxide, saturated with sodium chloride and extracted with 3 x 50 ml. chloroform. The eombined extracts were dried (MgSO~) and solvent evaporated in vacuo to give 3.37 g. (80%) of the alpha-amino amide product as a colorless liquid, Rf 0.29; [alpha]D - 15i7 (C = 0.8, lN HCl). The structure was verified by ~-NMR
spectroscopy.

CH~H3 D . C 6H 5CH 20COCH2Cfl ( NHCbz ) CONHCH ( CH 20CH3 ) CONH S<50 2 Employing 3.37 g. (12 mmole) of the product obtained in Part C, above, as starting material, in the procedure of ~xample 1, Part D, the desired diblocked dipeptide amide was obtained as a clear glass, 6073 g. (91%), Rf 0.28 (ethyl acetate/hexane, 70:30). The lH-NMR spectrum was in agreement with the structure for this compound.
E. A mixture of 6.73 g. beta-benzyl N-Cbz-L-aspartyl-D-O-methylserine N-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide, 250 ml. methanol and 2.0 g. 5% Pd/C
catalyst was hydrogenated by the procedure of Part C, above. The residue remaining after evaporation of solvent was stirred overnight in ethyl ether and the solid product collected by filtration and dried in the vacuum oven to yield 3.3 g. (77~) of the desired dipeptide amide, Rf 0.23; M.P. 140-150C. (dec.);
[alpha]D + 20.3 (C = 1, 1.2N HCl).
Sweetness potency: 200 x sucrose.

3~

L-Aspartyl-D-serine N-(dl-cls,trans-2,6-dimethylcyclohexyl)amide I, Ra = C~I2OH, R -A. dl-cis,trans-2,6-Dimethylcyclohexylamine A solution of 2.1 g. trans-2,6-dimethylcyclo-hexanone oxi~e in 30 ml. dry ethanol was heated at reflux. TG this was added in portions 3.1 g. of metallic sodium. When the addition was complete, the mixture was maintained at reflux fox 30 minutes and allowed to cool to room temperature. The resulting gel was dissolved in water, adjusted to pH 2.0 with hydrochloric acid and washed with ethyl ether. The aqueous phase was made alkaline with sodium hydroxide, extracted wlth ether, the extracts dried (MgSO4) and evaporated to provide the desired amine as a colorless liquid.
B. D-Serine N-(dl-cls,trans-2,6-dimethylcyclohexyl)amide Employing 1.47 g. (6.15 mmole3 N-Cbz-D serlne, 775 mg. (6.15 mmole) _ -cis,trans-2,6-dimethylcyclo-hexylamine and equimolar amounts of N-methylmorpholine and ethyl chloroformate and subsequent removal of amino-protecting group by catalytic hydrogenation by the procedures of Examples 1, Parts B and C, afforded 0.70 g. of the desired D-serine amide as a white solid, Rf 0.64 (ethyl acetate/hexane, 7:3).

C. ~ t~ tide Amide By employirlg 600 mg. (2.8 mmole) of D-serine-N-(dl-cis,trans-2,6~dimethylcvclohexyl)amide in the procedure of Example 1, Part D, the corresponding beta-benzyl N-benzyloxycarbonyl-L-aspartyl-D-serine amlde, 1.2 g., was obtained as a colorless solid.
Recrystallization from isopropyl ether gave 1.0 g., Rf 0.35 (ethyl acetate/hexane, 7:3).
D. Catalytic hydrogenation of the diprotected dipeptide amide provided in Part C, above, (1.0 g.) in methanol in the presence of 0.6 g. 5% palladium/
carbon catalyst by the procedure of Example 1, Part E, yielded 435 mg. of the title compound as an off-white crystalline solid.
Sweetness potency: 200 x sucrose.

Beta-Benzyl N-benzyloxycarbonyl-L-AspartyI-D-O-methylserine C~H5cH2occH2cHcoNHcHcooH

Cbz D~O-Methylserine (~.65 g., 56.1 mmole) ls dis-solved in 100 ml. of ~,N-dimethylformamide (DMF) and to the solution is added dropwise at room temperature 6.7~ g. (62.4 mmole) OL trimethylchlorosilane. In a separate flask is placed beta-benzyl N-benzyloxycar-bonyl-L-aspartate (18.0 g., 50.~ mmole), triethylamine (12.35 g., 122 mmole) and 110 ml. each of ~MF and tetrahydrofuran and the resulting solution cooled to -15C. ~o the solution is added ethyl chloro-formate (5.95 g., 55.1 mmole) and the resultin~
mixture stirred for ten minutes at -10C. To this is then added dropwise the DMF solution of silylated D-O-methylserine prepared above while maintaining the mixture at -5 to -10C. The mixture is stirred at -5C. for one hour, 0.2 N hydrochloric acid added until the mixture is acidic and the resulting mixture extracted with chloroform. The chloroform extracts are combined and washed several times with dilute hydrochloric acid to remove remaining DMF. The solvent is evaporated in vacuo to provide the title compound.
When the procedure is repeated, but employing D-serine in place of D-O-methylserine and twice the above amount of trimethylchlorosilane, beta-benzyl N-Cbz-L-aspartyl-D-serine is obtained in like manner.

'3~

Beta-Methyl-N-benzylo~ycarbonyl-L-aspartyl-D-ser ne A suspension of 80.7 g. ~0.78 mole) D~serine in 200 ml. of DMF is cooled to lO~C., 184 g. (1.70 mole) of trimethylchlorosilane is added in portions and the resulting mixture s-tirred at 25C. for one hour.
In a separate flask is placed a solution of 158 g. 10.86 mole) of beta-methyl L-aspartic acid hydrochloride in one liter of water. To this is added 34.5 g. ~0086 mole) of sodium hydroxide followed by 80 g. of sodium bicarbonate and the resulting mixture stirred vigorously. After cooling to 5-10C. 161 g.
(0.94 mole) of benzyloxycarbonyl chloride is added in portions and stirring continued for two hours at this temperature. The reaction mixture is washed with 100 ml. of ethyl acetate, acidified by addition of 80 ml. of concentrated hydrochloric acid and extracted with ethyl acetate (2 x 450 ml.). The extract (900 ml.) is found to contain 218 g. (0.78 mole, 90~ yield~ of beta-methyl-N-benzyloxycarbonyl-L-aspartate. It is used in the next step without further purification.
The ethyl acetate extract is cooled to -20C., 165 g. (1.63 mole) of triethylamine and 84 g. (0.78 mole) ethyl chloroformate are added. The solution is stirred at -15 to -20C. for 30 minutes then treated quickly with the DMF solution of silylated D-serine prepared above and the resulting mixture is allowed to warm to ambient temperature over one hour with stirring.
The reaction mixture is washed with water (3 x 500 ml.), the organic layer dried over sodium sulfate and evaporated _ vacuo to afford the title compound.

When the procedure is repeated, but employing D-O-methylserine in place of D-serine and only half the above amount of trimethylchlorosilane, beta-methyl N-Cbz-L-aspartyl-D~O-methylserine is obtained.
By use of DL-serine or DL-O-methylserine in the procedures of Examples 10 and 11 the corresponding diblocked L-aspartyl-DL--amino acid dipeptides of the formula below are obtained.

RlOOOCCH2CHCONHCHCOOH
NHCbz CH20Rb where Cbz is CcH2c6H5~ R is H or CH3 and R is CH3 ~_ 1 3 ~L ~

L-Aspzrtyl-D-serine N-(trans-2-methylcyclohexyl)amide _ A. To a solution of 228 g. (0.62 mole) of beta-methyl-N-benzyloxycarbonyl-L-aspartyl-D-serine in one liter of ethyl acetate is added 69 g. (0~68 mole) triethylamine, the mixture is cooled to -20C. and 67 g. (0.62 mole) of ethyl chloroformate is added.
The resulting solution is stirred for 30 minutes at -15 to -20C~, then treated with 76.5 g. (0.68 mole~
of trans-2-methylcyclohexylamine and stirring continued for 30 minutes. After allowing to warm to room temperature the mixture is washed twice with 500 ml.
portions of water containing 15 ml. of concentrated hydrochloric acid, twice with 500 ml. of 5~ aqueous sodium bicarbonate, then water. The organic layer is dried (Na2SO~), concentrated in vacuo to about 200 ml.
and 400 ml. of hexane was added whereupon beta-methyl-N-benzyloxycarbonyl-L-aspartyl-D-serine N-(trans-2-- 20 methylcyclohexyl)amide precipitated.

. . _ ~3~J

B. ~o 230 g. (0.50 mole) of the product obtained in Part A, above, dissolved in S00 ml. of methanol is added a solution of 24 g. (0.60 mole) of sodium hydro~ide in 500 ml. of water. The mixture is stirred at 30C. for o~e hour, neutralized to about pH 7 with dilute hydrochloric acid and charged into an autoclave.
Two grams of 5% palladium/carbon catalyst is added and the mixture hydrogenated at 25C., 3.5 kg./cm.2 ~50 psi) for one hour. The catalyst is removed by filtration, the filtrate evaporated ln vacuo to 200 ml., the concentrate acidified to pH 5.2 with concentrated hydrochloric acid, then granulated at 5C. for one hour. The resulting precipitate is collected by filtration, the wet cake ~issolved in a mixture of water and concentrated hydrochloric acid, carbon treated, filtered and the filtrate adjusted to pH 5.2 with 50% (w/w) sodium hydroxide solution.
After granulation at 5C., filtering, washing with cold water and drying, the desired product is obtained.
By employing the appropriate beta-methyl~N-Cbz-L-aspartyl-D (or DLj-amino acid dipeptide in the above procedures the corresponding dipeptide amides of the formula below, where R is CH2OH or CH2OCH3, are obtained in like manner.

/ CH2--CH CONHCHCONH~
COOH NH R

L-Aspartyl-D-O-methylserine N-(dl-t-butylcyclopropylcarbinyl)amide:
, ( 3)3~ 2 3 .. ~ . . . .
A. t-Butylcyclopropylcarbinylamine To 0.5 mole each of cyclopropanecarbonyl chloride and cuprous chloride in 500 ml. of dry ethyl ether was added dropwise under a nitrogen atmosphere 238 ml.
(0.5 mole) of 2.1 M t-butylmagnesium ehloride in the same solvent at -10C. The reactlon mixture was poured into a mixture of 250 ml. of 3 M hydroehloric aeid and 700 g. of iee, the organic layer separated, washed with water, sodium biearbonate solution, brine and dried over anhydrous magnesium sulfate. The ether was eYaporated at reduced pressure and the residue distilled at atmospherie pressure to provide 45 g.
(72%) of t-butyleyelopropylketone, B.P. 145-153C.
The 45 9. (0.36 mole) of ketone was reacted with hydroxylamine hydroehloride and sodium aeetate in 1:1 ethanol/water by the method of Preparation Q. After heating at reflux overnight the reaetion mixture was eooled and the preeipitated oxime colleeted and washed with cold ethanol to obtain 23.5 g. of t-butylcyclopropylketoxime. An additional 7.7 g. was obtained from the mother liquors. The eombined crops were reerystallized from 1~1 ethanol/water to provide 25.2 g. (50%) of oxime, M.P. 113.5-114C.

To a solution of 5.0 g. (0.035 mole) of oxime in 80 ml. of ethanol was added 8.0~ g. (0.35 mole) of sodium and the reaction carried out and product isolated as described in Preparation Q, to afford 3.31 g. of crude dl-t-butylcyc]opropylcarbinylamine.
This was distilled at atmospheric pressure to yield 2.01 g. (45~) of product boiling at 153-155C.
/C(CH3)3 B. C6H5CH2OCOCH2CHCONHCHCONHCH ~
NE~Cbz C~I20CH3 V
. . .
To a 250 ml. three-necked flask fitted with a stopper, thermometer, drying tube and magnetic stirring bar was added 2.82 g. (6.6 mmole) of beta-benzyl-N-benzyloxycarbonyl-L-aspartyl-D-O-me-thylserine, 50 ml.
tetrahydrofuran and 1.0 ml. (7.0 mmole) triethylamine.
The mixture was cooled to -10C., 0.69 ml. (7.0 mmole) ethyl chloroformate was added, stirred for 20 minutes, cooled to -35C. and 0.76 g. (0.66 mmole) of dl-t-butylcyclopropylcarbinylamine added. The reaction mixture was allowed to warm slowly to room temperature and stirred overnight. The mixture was poured into 100 ml. water, extracted with 170 ml. of ethyl acetate and the organic phase washed with 5% aqueous sodium bicarbonate (2 x 50 ml.), 3M hydrochloric acid (2 x 50 ml.), brine (1 x 70 ml.) and dried over anhydrous magnesium sulfate. The dried extract was evaporated to dryness ln vacuo to provide the crude diblocked dipeptide amide which was purified by column chromato-graphy on silica gel.

3~

C. The purified product from Part ~, 2.33 g., was hydrogenated over a palladium-on-carbon catalyst as described in Example 1, Part E, to afford the desired dipeptide amide.
T'ne compound of formula ~I) wherein R ls /(CH3)3 CH ~ ~ and R is CH20H is similarly obtained from the appropriate diblocked dipeptide.

By employing the appropriate amine or formula RNH2 i.n the procedure of the preceding Examples the following L-aspartyl-D-amino acid amides are provided in lik.e manner.
~CH2-CHCONHCHCONHR

where R~ is CH2OH: R -_ _ 2,5-dimethylcyclopentyl, 2,6-diisopropylcyclohexyl, 2,5-diethylcyclopentyl, 2,2-dimethylcyclohexyl, 2,5-dilsopropylcyclopentyl, 2,2,6 trimethylcyclohexyl, 2-methyl-5-1sopropylcyclo- 2,2,6,6 tetramethylcyclo-pentyl, hexyl, 2,2,5-trimethylcyclopentyl, l-fenchyl, 15 trans-2-ethylcyclohexyl, dl-~enchyl, trans,t.rans-2-methyl-5- 2-methylcyclopentyl, ethylcyclohexyl, 2-ethylcyclopentyl, 2,2,5,5-tetramethylcyclo- 2-isopropylcyclop~ntyl, pentyl 2-t-butylcyclopentyl t 2,2,4,4-tetramethyltetra- t-butylcyclopentylcarbinyl, hydrofuran-3-yl, diiscpropylcarbinyl, 2-methy:1-6 ethylcyclohexyl, d-methyl-t-butylcarbinyl, 2,6-diethylcyclohexyl, dl-methyl-t-butylcarbinyl, 2 isopropylcyclohexyl, di-t-butylcarbinyl, 2-t-~utylcyclohexyl, isopropyl-t-butylcarbinyl, 2-met~yl~6-t-butylcyclohexyl, methyl-isobutylcarbinyl, dicyclobutylcarbinyl, 2,2,3,3-tetramethylcyclo-dicyclopentylcarbinyl, propyl, dicyclohexylcarblnyl, 2,2,4,4-tetramethylcycl butyl, .

where R. is CH2OH:
_ R _ __ R _ __ dieyclc,heptylcarbinyl, 2-methyloxetan-3~yl, cyclobutylcyclopropyl- 2,2-dimethyloxetan-3-yl 5earbi.nyl 2-t-butyl~4-methyloxetan-3-eyclobutylcycloheptyl- yl, earbi.nyl 2,4-diethyl-2,4-dimethyl-cyelopentyleyclopropyl- oxetan-3-yl, earbi.nyl 2,4-dimethyloxetan-3-yl, 2,2,4,4-tetramethyl-3-oxo- 2,2-diethyl-4,4-dimethyl-eyelobu-tyl oxetan-3-yl, 2,2,4,4-tetramethyl-3- 2-see-butyleyelopentyl, hydroxyeyelobutyl, 2,2-di-n-propyleyelopentyl, 2-methyleyelobutyl, 2,4-dimethyltetrahydrofuran-15 2,4-dimethyleyelobutyl, 3-yl, 2,2-dimethyl-4-ethylcyelo- 2-methyltetrahydrofuran-3-yl, butyl, 2-t-butyltetrahydrofuran-3-2,2,4,~l-tetramethyleyelo- yl, buty:L 2-ethyl-4-n-butyltetrahydro-2,2-diethyl-4~4-dimethyl- furan-3-yl, eyelobutyl, 2-n-butyl-4-ethyltetrahydro-2,4 di:isopropyleyelobutyl, Euran-3-yl, 2-t-bul:yleyelobutyl, 3,5-dimethyltetrahydropyran-2-methyleyeloheptyl, 4-yl, 25 2-isopropyleycloheptyl, 3,5-diisopropyltetrahydro-2-t-bu~:yleyeloheptyl, pyra-n-4-yl, 2,7-dirnethyleyeloheptyl, 3,3,5,5-tetramethyltetra-2,7-diisopropyleyeloheptyl, hydropyran-4-yl 3-t-butyl-5-rnethyltetrahydro- 2,2,4,4-tetrahydropyran-3-yl, pyran-4-yl 4,4-dimethyltetrahydropyran-2-methyltetrahydropyran-3-yl, 3-yl, _ _ where Ra is CH20H: ¦ ~

4-methyltetrahydropyran-3-yl, 2,2,5,5-tetramethyl-3-cyclo-4-sec-bu1:ylte~rahydropyran- pentenyl, 3-yl, 2,5-dimethyl-3-cyclopentenyl, 2-isopropyltetrahydropyran- 2-methyl-3-cyclopentenyl, 3-yl, 2,5-diisopropyl-3-cyclo-2,4-diisopropyltetrahydro- pentenyl, pyran-3-yl, 4-methyloxepane-3-yl, 2-methyloxepane 3-yl, 2,2,4,4-tetramethyloxepane-2,4-dimethyloxepane-3-yl, 3-yl, 2,4-diisopropyloxepane-3-yl, 2,2-dimethyloxepane-3-yl, 3-methyloxepane-4-yl, 5,5-dimethyloxepane-4-yl, 3,3-dimeth.yloxepane-4-yl, 3-isopropyloxepane-4-yl, 3,5-diisopropyloxepane-4-yl, 2,4-dimethyltetrahydropyran-

5-isopropyloxepane-4-yl, 3-yl, 2-isopropylcyclopropyl, 2-t-butylcyclopropyl, 2,2-dimethylcyclopropyl, ethylcyclopropylcarbinyl, lsopropylcyclopropylcarbinyl where Ra is CH OCH :
_ 2 - 3-R
2,2-dimethyl-5-t-butylcyclopentyl, 2-isobutylcyclohexyl, 2-n-butyl-6-ethylcyclohexyl, 2,2-diethylcyclohexyl, 2-t-buty~-6-methylcyclohexyl, 2,4-diethyl-2,4-dimethyltetxahydrofuran-3-yl, 2,4-dimethyltetrahydrofuran-3-yl, 2,2,4,4-tetramethyltetrahydrofuran~3-yl, 3,5-dimethyltetrahydropyran-4-yl, 3,3,5,5-tetramethyltetrahydropyran-4-yl, 2,2,4,4-tetramethyltetrahydropyran 3-yl, 4,4-dimethyltetrahydropyran-3-yl, 2,2-dimethyltetrahydropyran-3-yl, 3,3,5,5~tetramethyloxepane~4-yl, 2,3-diisopropylcyclopropyl, - 2-t-butylcyclopropyl, isopropylcyclopropylcarbinyl, d-methyl-t-butylcarbinyl, diisopropylcarbinyl, di-t-butylcarbinyl, l-fenchyl, 2,2,5-trimethyl-3-cyclopentenyl.

R R R

~ CH2)2 ~ CH3 ~ C2H5)3 CH3 ,CH3 (COH ) ~ ~C (CH2)3cH3 3 C~3 ~CH~CH(CH3)2]2~CH~C(C~3)3/CH(CH3)2 'b b ~

(C~3)2 f -C(CH3)3 ~ ( 2 3)3~ C 2 3 b \a ~CH2,3 ( 2C 3)2 /C 2CH3 C(CH3)3 b ~CH2,3 ~ (CH3)3~ CH(CH3)2 ~ C (C 2CH3)2 b ~ 2)3 CH2CH2CH3 Fl <~ 12 ( CH2 ) 2CH3 _<~H ( CH3 ) 2 <b 3~

R R

CH ( CH3 ) 2 CH2CH3 ,a b _<~CH2)3CH3b CH3 o ~CH(CH2)3CH3 ~C(CH3)3 b `O b _~CH ( CH2CH2CH3 ) 2 </( CE~2 ) 4C 3 ~ CH2 ) 3 `O b 5 ~ ~0 c~o3,2 -~b ~3)2 CH(CH3)2 ~0 C~ C~33 _ ~3 ) 3 C~3 C:2 35 -86~

L Aspartyl-D-O-methylserine N-(3~5-dimethyltetrahydrothiopyran-4 yl)amide:
C~
I, R = ~ , Ra = CH2OCH3 C~3 mixture of cis/trans and trans/trans isomers _ A. 3,5-Dimethyltetrahydrothiopyran-4-one A mixture of 2 g. of sodium acetate and 25 ml. of ethanol was saturated with hydrogen sulfide gas. To this was added 7.0 g. (0.063 mole) diisopropenylketone while cooling in an ice bath until the reaction was no longer exothermic. The mixture was stirred at room temperature while passing hydrogen sulfide through the mixture for four hours then allowed to stand overnight.
The ethanol and excess H2S were evaporated in vacuo and the residue taken up in ethyl ether, washed in turn with water, potassium carbonate solution, dilute hydrochloric acid, and water again. The ether extracts were dried (Na2SO4) and evaporated to provide 6.8 g.
of oil. This was distilled in vacuo through a 10 cm.
Vigreaux column to provide 1.67 g. of product, B.P.
83-86C./9 mm. which was used in the next step without further purification.

3. 4-Oximino 3!~ dlmet yltetrahydrothiop~ran A mixture o~ 1.67 g. (0.011 mole) of the cyclic kel:one obtained in Part ~, 1.6 g. (0.023 mole) hydroxyl-amine hydrochloride and 1.9 g. ~0.023 mole) sodium acetate in 30 ml. of water and 10 ml. of ethanol were heated at reflux for three hours, cooled and the precipitate recovered by filtration. After recrystal-lization from 1:1 methanol-water 1.5 g. of oxime was obtained as a white solid, M.P. 60-85C. which is a mixture of isomers of suitable purity for use in the next step.
C. trans/trans and cis/trans-4-Amino-3,5-dimethyl-tetrahydrothiopyran To a solution of 1.45 g. (0.009 mole) of the oxime obtained in Part B in 15 ml. of ethanol wasadded in portions 5 g. of sodium shot followed by an add:itional 25 ml. of ethanol and the resulting mixture heated at reflux for about 30 minutes. The reaction mixture was diluted with water, extracted with ethyl ether, and the extracts washed with water. The ether layer was extracted with dilute hydrochloric acid and the aqueous layer washed with fresh ether. The a~ueous layer was made alkaline by addition of sodium hydroxide solution and extracted with ether again.
The organic layer was dried (MgSO4) and the ether evaporated to obtain 1.1 g. of residual colorless oil.
Gas--liquid chromatography (OV-l column with temperature programming from 30 to lOO~C.) showed the product to contain two major components in a 60/40 ratio. lH-NMR
(CDC13) indicated the product to be a mixture of 4-amino-3-trans-5-trans-dimethyltetrahyarothiopyran and . .
the corresponding 3-cis-5-trans-isomer.

--g8--D. N(3~5-Dimetllyltetrahydrothiopyran 4 yl) t-butoxycarbonyl-D-O-methylserine amide C~
t-Boc-NH-CHCONH ~ ~

_ _ _ _ _ _ .
Vnder anhydrous conditions, to a mixture of 1.96 g. (8.9 mmole) of N-t-Boc-D-O-methylserine obtained in Example 7, Part A, 1.98 g. (19 mmole) triethylamine and 40 ml. of tetrahydrofuran, cooled to -10C., is added dropwise 0.96 g. (8.9 mmole) ethyl chloroformate and the resulting mixture stirred at this temperature for 20 minutes. To this is added 1.1 g. (7.5 mmole) of the mix-ture of lsomers of 4-amlno-3,5-dimethyltetrahydrothiopyran obtained in Paet C and the resulting mix-ture stirred at ~lO~C.
for 10 minutes then allowed to warm to room temperature.
The reaction mixture is diluted with water and extracted with ethyl acetate. The organic layer is washed with sodium bicarbonate solution, dilute hydrochloric acid, water, brine then dried (Na2SO4) and the solvent evaporated at reduced pressure to obtain the product.

~

E. N-(3,5-Dimethylketrahydrothiopyran-4-yl)-D-O-methylserine amidec~

NH 2 CHCONH~S

The t-Boc-amide obtained in Part D is dissolved in 15 ml. of ethanol and a mixture of 5 ml. of concen-trated hydrochloric acid and 10 mlO o water are added.
The resulting mixture is heated at reflux for 30 minutes, cooled and the ethanol removed by evaporation in vacuo. The aqueous residue is washed with ethyl ether, made alkaline with sodium hydroxide solution, extracted with ether and the extracts dried (Na2SO4).
Evaporation of solvent provides the desired amino amide.
F. Coupling of D-O-methylserine amide with L-aspartic acld N-thiocarboxyanhydride The D-O-methylserine amide provided in Part E, 1.25 g. (5.1 mmole) is dissolved in 5 ml. of tetra-hydrofuran and 5 ml. of water was added. The clear solution is cooled in ice and 0.89 g. (5.1 mmole) of L-aspartic acid N-thiocarboxyanhydride is added in one portion. To this is added as required, 0.5 M sodium hydroxide to maintain the mixture at pH 9 . After stirring 30 minutes the reaction mixture is washed with ethyl ether then ethyl acetate and the washes discarded. The aqueous phase is acidified with dilute hydrochloric acid to pH 5.6 and evaporated to dryness at reduced pressure. The residue is taken up in hot methanol (100 ml.), filtered and the methanol evaporated.
The residue was taken up a~ain in hot methanol, filtered and the filtrate decolori~ed with activated carbon, 3~3 filtered through diatomaceous earth and the filtrate evaporated to obtain the crude product. The crude product is dissolved in hot water (11 ml.) and filtered, evaporated under a stream of nitrogen to 5 ml. and cooled in ice to precioitate the product which is collected by filtration and dried.
~ se of t-Boc-D-serine, t-Boc-DL-serine or t-Boc-DL-O-methylserine in place of t-Boc-D-O-methyls2rine in the procedure of Part D, above, and reacting the resulting N-t-Boc-D ~or DL)-amino acid in the procedures of Parts D, E and F, provides the corresponding compounds of formula (I) wherein R is 3,5-dimethyltetrahydrothio-pyran-4-yl and Ra is CH20~ or C~20C~3.

L-Aspartyl-D-serine N-(2,2,4,4-tetramethyltetrahydrothiophene-3-yl)a~ide:
3 ~ 3 I, R - ~ ~ , Ra = C~2OH

... . ~
3 ~ 3 A. t Boc-NHCH-CONH ~ ~
3 C~3 To a solution of 2.26 g~ ~11 mmole) of N-t-butoxycarbonyl-D-serine in 75 ml. of tetrahydrofuran is added 1.47 ml. (10 mmole) of triethylamine and the mixture cooled to -10C. At this temperature is added 0.96 ml. (10 mmole) of ethyl chloroformate and stirring continued for 15 minutes. After cooling to ~20C., 1.6 g. (10 mmole) of dl-3-amino-2,2,4,4-tetramethyl-tetrahydrothiophene is added and the resulting mixture is allowed to warm to room temperature. ~thyl acetate lS is added and the mixture is washed twice with 50 ml.
portions of 5% ~by weight) aqueous citric acid, aqueous sodium bicarbonate (1 x 50 ml.) and saturated brine (1 x 50 ml.). The organic layer is dried (Na2SO4) and evaporated to dryness at reduced pressure to afford N(2,2,4,4-tetramethyltetrahydrothiophene-3-yl)-t butoxycarbonyl-D-serine amide. This product is used without further purification in the next step.

~ 3 B. HocH2~H(~H2)cONH ~ 1 >~S

. _ To 3 g. of the product from Part A i5 added 5 ml.
of methanol and 30 ml. of lM hydrochloric acid and the rnixture is heated on the steam-bath for 30 minutes.
S The methanol is removed by evaporation and the xesidue extracted with ether. The ether is discarded and the aqueous phase is adjusted to pH 11~0 with sodium hydroxide solution, extracted with ethyl acetate, the extracts dried (Na2SO4) and evaporated to dryness to 11~ obtain D-serine N(2,2,4,4-tetramethyltetrahydrothio-phene-3-yl)-amide.
C. Coupllng to form dipeptide amide The D-~serine amide obtained in Part B, 1.03 g.
(4.25 mmole) is mixed with 10 ml. of water, cooled in l!; ice and the pH of the mixture adjusted to 9.2 with 0.5 N sodium hydroxide solution. To this is added portionwise with stirring 0.8 g. (4.25 mmole) of L-aspartic acid N-thiocarboxyanhydride while maintaining the mixture at pH 9 with sodium hydroxide solution (0.5 N). When the addition is completed the resulting mixture is stirred at O~C. for 45 minutes, adjusted to pH 5.2 wit:h hydrochloric acid and evaporated to dryness ln vacuo. The residue is slurried with methanol, filtered to remove precipitated solids and 2S methanol :removed from the filtrate by evaporation at reduced pressure. The resulting crude product is purified by column chromatography on silica gel.

Employing the procedures of Examples 3, 7, 8, 15 and 16, corresponding L-aspartyl-D-amino acid amides (I) wherein Ra is CH20H or CH20CH3 and R is as defined below are prepared from the appropriate starting rnaterials via D-RaCH(NH2)CONHR intermediates.
The corresponding L-aspartyl-DL-amino acid amides are similarly provided when a t-Boc-DL-amino acid is employed in place of the D-enantiomer. Likewise, use of DL-aspartic N-thiocarboxyanhydride in the coupling step affords the DL-D or DL-DL compounds of formula (I).
HOOCCH CHCONHCHCONHR -~
2NH2 Ra where R = CH20H or R R R
- ~3 ~ CH3)3 ~ ~O

C~13 CH2CH3 CH3 C(CH3)3 C2H ~ CH3 ~ S ~ S ~ 2 C(CH3)3 C2 5 C 3 CH3 ~CH2;3C3; ~ S

(CH3)2 3~ C 3 C ~ 3 CH ( CH3 ) 2 ~5CH3 ) 2 ~S

CH(CH3)2 CH(CH3)2 -~94--R R

CH~I C ~ CH3 ) 3 -~52 C~ ~ 3 ,~
_~ ~S ~ ,SO
`r ( CH2 ) 2 ,>~( CH2 ) 2 CH~ l H3 S (CH2)2 S

_~CH3 --~ 2 CH~H3 H2)2 ~
CE~2C~H3 CH3 CH2CH3 CH(t H3)2 CH3 CH3 C 3 ~ CH2 ) 3 >~
CH ( CH3 ) 2 3 3 t~H~103 ~SCH2 ) 3CH~

C;~CH3 ~5 ~

-95~
R R R

C ~ CH2 ~ CH3)2 ~ 2 3 3 3 CH2)3 CH(CH3)2 3)2 C ~ CK3 CH ~ H3 ~ ~ oCH3 CH(CH3)2 CH ~ CH3 ~ CH(CH3)2 C ~ CH3 CH ~ I3 C ~ CH3 ~ 3)3 3 3 C(~H3)3 CH(CH3)2/C~CH3)3 CH(CH3)2 ~0 ~ ~0 ~7 1 V CH(CH3~2 3)2 CH3C ~ H2CH3 ~ 2 ~S02' 35~

L~Aspartyl-D-serine N-(2-methylthio-_ 2,4-dimethylpentan-3-yI)amide A. 2-Methylt_io-2,4-dlmethylpentan-3-one A solution of 200 ml. of methanol containing 9.2 g. (0.40 mole) sodium metal was cooled in an ice-bath and saturated with gaseous methyl mercaptan. To this was added 77.2 g. (0.40 mole) of 2-bromo-2,4-dimethyl-pentan-:3-one at room temperature and the resulting mixture stirred for two hours. The reaction mixture was diluted with water, extracted with ethyl ether, the extracts washed with water, brine and dried over anhydrous sodium sulfate. The ether was evaporated and the residue distilled i vacuo to afford 50.4 g.
of prodllct, B.P. 76 (20 mm.).
B. 2-Methy~thio~2,4-dimethyl-3-aminopentane A e;olution of 6.0 g. (0.038 mole) 2-methylthio 2,4-dime!thylpentan-3-one, 9.9 g. formamide and 2.1 g.
of 100% formic acid was heated at reflux while removing water formed in the reaction by means of a fraction-ating heacl. After 12 hours an additional 2.5 g. of formic acid was added and reflux continued for another 24 hours in the same manner, by which time the reaction mixture reached a temperature of 190C. The mixture was cooled, diluted with water and extracted with ethyl acetate. The extracts were washed with water and evaporated to dryness at reduced pressure to provide - 5.3 g. of residual oil. The oil was refluxed with 40 ml. o 6N hydrochloric acid for six hours, diluted with water, washed with ether and the aqueous phase 3~

made strongly alkaline with sodium hydroxide. After extracting with ethyl ether and evaporation of the extract, 3.3 g. (56%) of colorless amine was obtained which gave a single peak by gas-liquid chromatography on a six foot OV-l column at 110C.; retention time 412 seconds.
C. 3-Serine N-(2 methylthio-2,4-dimethylpentan-3-yl)amide To a solution of 3.47 g. (0.017 mole) N-t-butoxycarbon~yl~D-serine and 2.5 g. (0.017 mole) triethylamine in 100 ml. of tetrahydrofuran at -15C.
is added 1.63 ml. of ethyl chloroformate. After stirring fox 15 minutes, 2.49 g. (0.017 mole) 2-methylthio-2,,4-dimethyl-3-aminopentane is added and the mixture stirred for one hour. The reaction mixture is diluted with ethyl acetate, washed with water, 5%
aqueous citric acid (w/v), sodium bicarbonate solution and brine. The organic phase is evaporated to dxyness.
The residue is taken up in 100 ml. methanol~ 60 ml. of concentrated hydrochloric acid added and the mixture refluxed for one hour. After evaporation of methanol, the residue is taken up in water, washed with ether, the aqueous phase adjusted to pH 12 with sodium hydroxide and extracted with ethyl ether. Evaporation of the extracts affords the desired D-serine amide.

~98-D. A solution of 3.3 g. (0.013 mole) of the D-serine amlde, obt.ained in Part C, in 30 ml. acetone and 17 ml. water is adjusted to pH 9.9 with sodium hydroxide solution a.nd cooled to -2C. To this is added 2.78 g.
(0.013 mole) L-aspartic N-thiocarboxyanhydride in small portions over 20 minutes while maintaining the p~I at 9.9 with lN sodium hydroxide. When the addition is compl~ted, the resulting mixture is stirred for 30 minutes at -2C., washed with ethyl acetate acidified to pH 2 with hydrochloric acid and washed again with ethyl acet.ate. The aqueous phase is then adjusted to pH 5.2 and. evaporated to dryness. The crude dipeptide amide is obtainea by slurrying the residue in methanol, filtering, treatment of the filtrate with ether and filtering to obtain a second crop.
The c:rude product is purified by preparative layer chromatography on silica gel plates (20 x 20 x 2 mm.) eluting with butanol/water/acetic acid, 4:1:1 by volume. The product zone was cut out and eluted with methanol l:o give the purified L-aspartyl-D-serine amide.
When N-t-butoxycarbonyl-D-O-methylserine is employed :in the procedure of Part C, above, in place of the N~t-Boc-D~serine used therein, and the resulting product traated by the procedure of Part D, above, the corresponding L-aspartyl-D-O-methylserine amide is obtained.

-EXAMPLE_19 L-Aspartyl-D-serine N-(2-hydroxy-2,4-dlmethyl-3-pentyl)amide, /CH(CH3)2 I, Ra = CH2OH, R = ~
\C(CH3)2 OH
A. ~ oxy~2,4-dim ~ r~ o~
To a s1:irred solution of 28.3 ml. (0.2 mole) 2,4-dimethyl-3-pentanone in 100 ml. chloroform was added dropwise 10 3 ml. (0.2 mole) bromine in 30 ml. of the same solvent. The resulting mixture was stirred for a few minutes, the sol~ent evaporated in acuo, the residue taken up in 100 ml. ethanol. Water, 50 ml., and 10 M sodium hydroxide, 50 ml., added. The resulting mixture was stirred at reflux for one hour, diluted with 200 ml. water and extracted with 3 x 50 ml. ethyl ether. The extracts were dried (MgSO4) evaporated to dryness and the residue distilled to obtain 15.95 g.
(61%) of the hydroxy-ketone, b.p. 60-62C.jl8 mm.
B. 3-Amino-2~hydroxy-2,4-dimethylpentane The hydroxy ketone from Part A, 15 g. (0.115 mole~
was reduced in refluxing mixture of formamide and formic acid by the method of Example 13, Part D, to obtain 4.5 g. (30~) of the hydroxy amine, b.p. 80-81C./
17 mm.

C. _blocked dipeptide amide To a solution of 2.22 g. (5.0 mmole) beta-benzyl-N-benzyloxycarbonyl-L-aspartyl-D-serine in 35 ml. tetrahydrofuran cooled to -15C. is added 5 0.55 ml. (5.0 mmole) N-methylmorpholine and 0.48 ml.
(5.0 mmole) ethyl chloroformate. The mixture is stirred at -15 to -10C. for two minutes and 0.66 g.
(5.Q mmole) 3-amino-2-hydroxy-2,4-dimethylpentane is added. The mixture is allowed to warm to room tempera-lO ture, stirred overnight and worked-up as described in Example 13, Part B, to obtain the diprotected dipeptide amide which is used directly in the next step.
D. The product from Part C, above, in 250 ml.
methanol is hydrogenated over l.0 y. 5% Pd/C at 15 60 psi (17 kg./cm.2) for two hours. The catalyst is removed by filtration and the solvent evaporated ln vacuo. The residue is dissolved in methanol and ethyl ether is slowly added with stirring to precipitate the title compound which is collected by filtration, and dried in vacuo.
._ ~ ~ \
3~

L-Aspar1:yl-D-O-methylserine N-(DL-2-amino-3,3-dlmethy:L-4-hydroxybutanoic acid lactone)amide, I, Ra = CH2OCH3, R =

A. DL-2-Amino-3,3-dimethyl-4-hydrogybutyric acid lactone hydrochloride Prepared by the method of Wieland, Chem. Ber., 8l, 323 (1948)-2-Keto-3 r 3-dimethyl-4-hydroxybutyric acid lactone, 3.5 g. was neutralized with dilute sodium hydroxide and the aqueous solution evaporated ~o dryness in vacuo. The residue was taken up in lO0 ml. warm ethanol, filtered hot and a solution of 700 mg. sodium metal in lO ml~ ethanol containing 2 g. hydroxylamine hydrochloride was added. The sodium salt of 3,3-dimethyl-4-hydroxy-2-oximinobutyric acid lactone, 5 g.
precipitated and ~as recrystallized from methanol.
The oxime wa; formed by decomposition of the sodium salt in 2 N 'hydrochloric acid, from which it slowly crystallized. After recrystallization from benzene-hexane, M.P. l60C.
A solut:ion of 25 g. of the oxime in lO0 ml.
ethanol was added in portions to 5 g. platinum oxide suspended in 150 ml. 2 N hydrochloric acid and the mix~ure hydrogenated at atmospheric pressure for 2 days. Th.e catalyst was filtered off, the filtrate evaporated and the residue taken up in 150 ml. ethanol.

3~

Treatment with 500 ml. ethyl ether precipitated DL-2-amino-3,3-~imethyl-4-hydroxybutyric acid lactone hydrochloride, 22 g., which was recrystallized from ethanol/ether, M..P. 208-212C.
B. Dibloccked dipeptide amide The aminolactone hydrochloride from Part A, 1.65 g. (0.010 mole) in 10 ml. methylene chloride and an equimola.r amount of triethylamine is employed in the procedure of Example 13, Part B, to provide C6H5cH2ococE[2cH-coNHcH(cH2ocH3)coNH

NHC02CH2C6H5 C E~3 C. The product from Part B, above, (2.5 g.) is dissolved in 200 ml, methanol, 0.2 g. of 5~ Pd/C
catalyst added, the mixture hydrogenated and the product isolated as described in Example 13, Part C, to afford the! desired dipeptide amide.

L-Aspartyl-D-serine N- ( 2, 2, 4, 4-tetr~methyl -3 -hydroxycyclobutyl)amide, ~CE~3)2 I, Ra = CH2OH, R = ~OH
... . ... .,,, ,,, ,, ~CH3)2 ..... .... .. . .. . .. . .
(~CH3 ) 2 A. D-HOCH2CHCONH~OH
-NHCbz (CH8~2 -N-Benzyloxycarbonyl-D-serine (0.1 mole), is reacted with cis/trans 2,2,4,4~tetramethyl-3-hydroxy-cyclobutylamine by the method of Example 8, Part A, to provide the N-Cbz-serine amide.
B. Hydrogenation of N-Cbz-serine amide by the method of æxample 8, Part C provides the corresponding 2-amino compo~md, D-serine N (2,2,4,4-tetramethyl-3-hydroxycyclobutyl)amide. The latter compound is converted to the title compound by the procedures of Example 8, Parts D and E.
The corresponding L-aspartyl-D-O-methylserine amide is obtained in like manner.

L-Aspartyl-D-serine N-(2,2,4,4-tetramethyl-3-oxocyclobutyl~amide ~CH3)2 `I, Ra = CH2OH, R = ~
~ CH3 ) 2 ~H3)2 Ao D-HOCH2CHCONH ~
N~IC~z (CH3)2 N-Benzyloxycarbonyl-D-serine N-(2,2,4,4-tetra-methyl-3-hydroxycyclobu~yl)amide prepared in Example 21, Part A, 36.4 g., ~0.10 mole) dissolved in 1500 ml.
acetone is cooled to -10C. under a dry nitrogen atmosphere and 42 ml. (0.11 mole) 2.67 M chromic anhydride in di.lu~ed sulfuric acid is added. After stirring for 15 mi.nutes at 10C.I the solvent is evaporated in v.acuo, the residue poured into an ice-_, water mixture, neutralized with sodium hydroxide solution and ext:racted with ethyl ether. The ether extracts are dri.ed IMgSO~) and evaporated to dryness to obtain the crude product which may be purified, if desired, by colu;mn chromatography on silica gel.
B. Hydrogenation of the product of Part A, above, by the method of Example 8, Par~ C provides D-serine N-(2,2,4,4~tetramet:hyl~3-oxocyclobutyl)amide. This is, in turn, converted to the title compound by the methods described in Example 8, Parts D and E~

~6~ ~ 3 Employing the appropriate amine of formula RNH2 in the above procedures the compounds of formula ~I) below, where R ic. CH2OH or CH2OCH3, are similarly prepared 2 ~
HOOC CONHCHCONHR ( I ) R R

(CH3)2 ~OH ~OH
3)2 (CH3)2 ~3)2 ~ 3 ~0 ~ (CX2)4 ~ CEI3 ) 2 CEI~HH3 _f~CH5 ) 2 >~H H H

CH3~ OH ~ ) ~ ~ ~ I
>~/ HO~C2H5 H>~:~C2H5 n C3~7 ~JH ~
H 2 5 HO n-C3E~7 ~.

3~

R R
E.10 n-C~Hg (~C2H5 ) 2 C~>CE $~C52 ) 4 HO~E13 ~H3 ~ ~0 n-C3H7 ~E.13 ~3 _C_OH rl ~0 ~OH C~H5 ~0~ ~) C2~5 2 5 _$rOH ~2 2H5 CH3)2 (CH3)2 ~

~OH n~C3H7 ( H3)2 3~t R

~-C3H7 3 ~-C3037 ~

_~OH n C4 9 \CrH3cH2 ) 2 ~CH2 ) 2 n-C4Hg c4 9 ~COH2 ) 2 -~CH2 ) 2 n-C4Hg HO CH3 ~(CH2~2 ~
~30H n-C4Hg ~3 ) 2 HO~CH3 ~t) ~
2H5 ) 2 (J~3 ) 2 HO C2H5 ~:NH ` C2H5 ~5 ) 2 H~)H3 3~

--10~--R R

HO~ E~ 5 O n-C4H9 n~C3H7 ~ 3 ~H ~CH2)4 Hg n C3H7 OH

_~) 2 f~H~I3 ) 2 H3 ) 2 (~5 ) 2 ~H3 ~OH
0/ C~13 ~OH2 ~ ~OH
o~ (CH3)2 ~Hg foHH2)3cH3 ~;IH ~OH

3~

R R

HO C:H3 CH3 ~CH3 HO l-C,~lHg C2H5 2~> _~LOH
/\ ~n-C H

HH g HO `n-C3H7 HO~,CH3 _~n-C4Hg S ~ ~OH
HO `CH C2H5 --3~X2 ) ~ CH~3H33 HO~C 3 _~3 7 ~10 CH3 3x7 ro3 ) 2 HOki-C3H7 C 3 3~

R R

$~ ~OH
HO~C4H9 ~3CH3 i-C4Hg n C3H7 r OH _~OH
\rOH ~ 3 ) 3 ( CH3 ) 2 ~~ ~ OH

5)2 (C 3)3 C~H 5 _~ ) 2 2H5 ( CH3 ) C2~5 _~H ~O
CH3)3 CH3)2 n-C4~9 ~ ) 2 ~)H ~O
CH3)2 (C2H5)2 ~L9~ 3~

R R

C2H5 ~Ho3 ) 2 _~LOH ~C=O
~CH3 (CH3)2 c2~s _¢~co ~C3P

C~C 2 H 5 _~
H

CH3 C21~I5 CH3 ~3 2 5 C~

~2 5 ( CEI3 ) 2 _~3 7 ~Lo3 ) 2 ~3H7 C~3 c~3 C3 7 -~FO
i-C3EI7 3 7 --1 12~
R R

~0 4 9 ~ ~
CH~C H C 2 H 5 ~LH~H) 2 ~o4 9 o 3)2 ~CH3)2 3)2 (C 3)2 <LN~O ~
~H ( C2H5 ) 2 C2~5 ( C2H5 ) 2 ~0 ~0 ~C2H5)2 CH3)2 n-C4Hg CH3 C2~I5 ~H3 n C3 7 _~H ~0 ~3 n-C3H7 3ffl R R

3)2 (CH3)2 ~-0 {~
( CE3 ) 2 c~3 (CH3) 2 (CE~3) 2 ~2 ~(C(~=5)2 C~5 _~) 2 CH3 C2H5 ~ CH3 ) 2 ~ ~9 I CH3 ) 2 n~4H9 $~ ~H
2 S (C 3)2 3~

R R

( CH3 ) 2 CH3 C2H5 ~ ~0 ~ ,k ( CH3 ) 2 CH C H

i-C4Hg . .
~H
F2~

3~

Carbonated CoIa Beverage A carbonated cola beverage was prepared according to the composition given below. The resulting beverage 5 was judged to have sweetness intensity comparable to a control beverage containing 11% sucrose.
In~redient ~, weiqht Caffeine (1% aqueous solution) 0.700 L-Aspartyl-D-serine N-(cis,t _ -2,6-dimethylcyclohexyl)amide (10~ aqueous) 0.540 Cola flavor concentrate 0.080 Phosphoric acid (50% aqueous) 0~040 Citric acid (50% aqueous) 0.066 Sodium citrate (25% aqueous) 0.210 Caramel color (25% aqueous) 0.370 Lemon oil extract 0.012 Lime oil extract 0.021 Carbonated water (3.5 volumes carbon dioxide) 9 ~ _ 100.000 Replacement of the L-aspartyl-D-serine N-(cis, trans-2,6-dimethylcyclohexyl)amide in the above formulation with 0.090% of 10% aqueous L-a~partyl-D-sexine acid N-(dicyclopropylcarbinyl)amide or 1.35% of 10% aqueous L-aspartyl-D-O-methylserine N-(dicyclo-propylcarbinyl)amide affords carbonated cola beverages of like qualityO

Dietetic Hard Cand~
A hard candy is prepared according to the rollowing i.ormulation and procedure:
]n~redi nts Grams I,-Aspartyl-D-serine N-(dicyclopropylcarbinyl)-amide 0-59 Water ~.oo FD and C Red ~40 (10~ aqueous) 0.30 Cherry flavor 0.6Q
Citric acid 6.00 Polydextrose* 420.00 Water 180.00 In a small beaker dissolve the sweetener in 15 water, add color, flavor and citric acid and mix well to dissolve. In a separate beaker combine polydextrose cmd water. Stir while heating to 140C. then allow t:o cool to 120-125C. Add other ingredients from small beaker and mix or knead thoroughly. Transfer mass to an oil coated marble slab and allow to cool 1:o 75-80C. Extract the mas~ through an oil coated :Lmpression roller.
Use of 0.49 gO of L-aspartyl-D-serine N-(2,2,4,4-tetramethyl-l,1-dioxothietan-3-yl)amide or 2.33 g. of L-aspartyl-D-serine N~(2,2,4,4-tetramethyl~3-pentyl)amide as sweetening agent in place of L-aspartyl-D-serine N-(dicyclopropylcarbinyl)amide affords similar results.

*U.S. 3,766,165 3 ~"

-117~

A gelatin dessert is prepared according to the following composition and procedure.
Ingredients Grams __ Gelatin 225 Bloom 7.522 Citric acid 1.848 Sodium citrate 1.296 Strawberry flavor 0.298 L~Aspartyl-D-serine N-(2,2,4,4-tetramethyl-thietan-3-yl)amide 0.036 Boiling water 240.000 Cold water 240.000 491.000 Premix the first five ingredients, add to boiling water and stir to dissolve completely. Add cold water and stir briskly. Transfer to serving dishes and refrigerate until set.

.83~

_ Low calorie table sweeteners are prepared according to the following formulations:
A. A powder form of sweetener is prepared by blending the following ingredients.
In~redients ~L_wei~ht L-Aspartyl-D-serine N-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide 0042 Crystalline sorbitol 49.52 10 Dextrin (dextrose equivalent 10) 50.00 Monosodium glutamate 0.02 Glucono-delta-lactone 0.02 Sodium citrate 0.02 100.00 15 One gra~ of the resulting blend is equivalent in sweetness to about three grams of sucrose.
B. A table sweetener in liquid form is prepared as follows.
Ingredients ~, weight 20 L-Aspartyl-D-serine N-(dicyclopropylcarbinyl)-amide 0.17 Water gg.73 Sodium benzoate 0.10 100.00 25 One gram of the resulting solution is equivalent in sweetness to about 1.2 grams of crystalline sucrose.
When the sweetener of formula (I) employed in Part A, above, is 0.83 g~ of a 1:4 mixture of L-aspartyl-D-serine N~2,2,4,4-tetramethylthietan-3-yl)-amide and sodium saccharin comparable results are obtained. Similarly when the L-aspartyl-D-serine N-(dicyclopropylcarbinyl)amide employed in Part B, above, is replaced by 0.34 g. of a 1:6 by weight mixture of the same compound and sodium saccharin a comparable liquid table sweetener is obtained.

33~

EXAMPI.E 28 . ~ _ Frozen Dessert .~ __ . .
A vanilla sugarless fro~en dessert is prepared according to the following formulation by conventional practice.
In~redients %, weight Heavy ,-ream (35% butterfat) 23.00 Nonfat milk solids 10.50 Mono and diglyceride emulsifier0.25 Polydextrose* 11.20 Water 54.49 L-Aspartyl-D-O-methylserine N-~2,2,4,4-tetramethyl-l t l-dioxothietan-3-yl)amide 0.06 Gelatin (225 Bloom) 0.50 100.00 *U.S. 3,766,165 3~

Canned Pears -- .
Fresh pears are washed, peeled, cored, sliced into pieces and immersed in an aqueous solution containi.ng 0.05~ by weight of ascorbic acid. The sliced fruit is packed into screw-cap jars and the jars filled with a syrup containi~g the following ingredients:

Sorbitol 25.000 L-Aspartyl-D~serine N-(2,2,4,4-tetramethyl-thietan-3-yl)amide 0O025 Citric acid 0.125 Water T q- 5 -~00.000 The jars are capped loosely and placed in an autoclave containing hot water and processed at 100C. for 45 minutes. The jars are removed, immediate ly sealed by tightening the caps and allowed to cool.

33~

Powder Beveraqe Concentrate Ingredients ~, Welght Citric acid 31.78 5 Sodium citrate 5.08 Strawberry flavor 57.72 Strawberry FD and C color 0.54 L-Aspartyl-D-O-methylserine N-(2,2,4,4-tetra-methylthietan-3-yl~amide 2.44 10 Carboxymethyl cellulose 2.44 100.00 Combine all ingredients in a blender and blend until homogeneous. For use, 1.73 g. of powder beverage concentrate is dissolved in 4 fluid ounces (118 ml.) of water.

3~

Baked Cake A highly acceptable vanilla cake was prepared employing the following recipe:
Ingr~dients Grams Emulsified shortening 16.09 Water 20.83 Eggs 23.00 Sodium bicarbonate l~lO
Vanilla extract, single fold 0.28 Glucono-delta-lactone 1.75 Polydextrose*, 70% aqueous solution 80.00 Nonfat dry milk 2.50 Cake flour 56u20 ~hole milk powder 0.80 Wheat starch 1.40 L-Aspartyl~D-serine N-(2,2,4,4-tetxamethyl-thietan-3-yl)amide 0.05 204.00 Combine nonfat dry milk, whole milk powder, polydextrose solution and emulsified shortening. ~ix at low speed until creamy and smooth (about 3 minutes), add eggs and beat until a homogeneous creamy mix is obtained. Dissolve sweetener in water, add to creamy homogenate and mix 2-3 minutes. Add remaining ingre-dients and mix until creamy and smooth ~3-5 minutes).
Place 120 g. of batter in small pregreased pan and bake at 350F. (176C.) for 30 minutes.

*~.S. 3~766,165 EXAlqPL~S 3 2 Synergistic Mixtures of L-Aspartyl-D-serine N-(2,2,4,4-tetramethylthietan-3~yl)amide, ~I), R = CH2OH, R = ~ S ] and Saccharin /

CH CH, Blends of L-aspartyl-D-serine N-(2,~,4,4-tetra-methylthietan-3-yl)amide and sodium saccharin were prepared and evaluated for taste acceptability and sweetness intensity by comparison with aqueous sucrose standardsv Sweetness potency factors of sodium saccharin and the invention compound (I, Ra = CH2OHt (C 3)2 R = ~ S ) of 300 and 1200 x sucrose, respectively, ~CH3~,~2 were used t:o calculate the theoretical sweetness of the blends. A series of taste panel evaluations were carried out comparing aqueous solutions of the experi-mental blends with sucrose solutions ranging 6 to 12%
(w/v) and 0,.C33% sodium saccharin solutionO Results are tabulated below.

.

3~

Blend,Parts by Weight [I, R =CH2OH, ~3)2 R= ~ ~ ] Sweetness y~ Sodium PotencY x Sucrose ~ Taste ~ I3)2 Saccharin (T)Theory ~A)Actual Syner~y Qual itY
1 : 1 750 1125 50 clean, sweet, not bitter 1 : 2 600 900 50 same 1 : 4 480 720 50 same 1 : 6 430 580 35 same 1 : 8 400 520 30 sweet,per-ceptible metallic taste 1 : 9 390 sweet, slight ` metallic 21) taste 1 : 10 381 sweet, slight to - moderate metallic taste The ~ synergy was calculated according to the following formula-% Synergy = ATT x 100 where A i5 the actual sweetness determined by averaging the taste panel results and T is the theoretical sweetness determined from the composition of the mixtures by weight e.g., for the 1:4 blend the theoretical sweetness is (1/5 x 12003 + (~/5 ~ 300) = 480.
- From the results it is seen that with mixtures of from l:i to 1:8 there is an unexpected increase in sweetness potency of 30-50~. While there appeared to be synergy at the higher ratios, the metallic taste due to saccharin interfered with an accurate determina-tion. Furthermore there is complete masking of the well known bitter aftertalste of saccharin with blends of from 1:1 to 1:6 and effective masking of bitterness in blends containing up to one part L-aspartyl-D-seri~e N-(2,2,4,4 tetramethylthietan~3-yl)amide and 5 8 parts sodium saccharin.
The 1:8 blend of L-aspartyl-D-serine N~(2,2,4,4-tetramethylthietan-3-yl)amide/sodium saccharin at a concentration of 0.0192% (w/v3 was found to be equi-valent in sweetness to a 10~ (w/v) sucrose solution and to 1:10 saccharin/cyclamate at 0.1177% (w/v).
In further sensory evaluation, a triangle test in which trained taste panel members were presented three samples. consisting of aqueous solutions of the above 1:8 blend of invention compound/sodium saccharin at 0.0192% and 1:10 saccharin/cyclamate at 0.1177%.
Panelists were asked to match the two like samples and to indicate any preference. Seven of ten taste panel members were not able to correctly differentiate the two sweetener blends. Of those that corre.ctly paired the like samples, the degree of difference between the two blends was rated as being "very slight" or "just perceptible".
These resu.lts indicate that there is no signi-ficant difference between the 1:8 blend of invention compound/saccharin and the 1:10 blend of saccharin/
cyclamate.

When the above procedure is repeated ~ut the invention compound employed is of the formula (I) wherein Ra is CH20CH3 and R is ( 3)2 (C 3)2 S or ~ ~S02 ( 3)2 ~CH3)2 or wherein, Ra is CH20H and R is (CH3)2 2 or -CH-( ~ )2 (C~3)2 similar results are obtained.

3~

~ 7--Ssdium 5alt of L-Aspartyl-D-serine N-(dicyclopropylcarbin ~)amide _ To a solution of 3.12 g. (0.01 mole) L-aspartyl-D-serine N~(dicyclopropylcarbinyl)amide in 100 ml. of ethanol is added 2 ml. of 5 N sodium hydroxide. The resulting mixture is stirred for ten minutes at room temperature then evaporated to dryness in vacuo. The residue is triturated with anhydrous ethanol, filtered and air dried.
When the sodium hydroxide employed above is replaced with an equivalent amount of potassium hydroxide, calcium hydroxide, magnesium hydroxide or ammonium hydroxide the corresponding potassium, calcium, magnesium and ammonium salts are formed in like manner.
The remaining L-aspartyl-amino acid dipeptide amides of formula (I) are also converted to carboxylate salts as described above.

Acid Addition Salts The L-aspartyl-D-amino acid dipeptide amide of formula (I) is slurried in a small amount of water and an equivalent amount of an acid such as hydrochloric, phosphoric, sulfuric, acetic, maleic, fumaric, lactic, tartaric, citric, gluconic or saccharic acid is added.
The resulting mixture is stirred for 15-30 minutes then evaporated to dryness or precipitated by addltion of a cosolvent such as methanol or ethanol.

PRE PARAT I ON A
Alkylcycloalkylcarbinylamines and dicycloa_ ~ carbinylamlnes _ i. To a mixture of 118.5 g. (1.0 mole) of cyclobutylcarbonyl chloride and 99 g. (1.0 mole) cuprous chloride in 1000 ml. oE dry ether under a nitrogen atmosphere is added dropwise 478 ml. (1.0 mole) of 2 M t-butylmagnesium chloride in the same solvent. The addition is carried out at -5 to -15C.
The resulting mixture is poured into 500 ml. of 3 M
hydrochloric acid and 700 g. ice, the organic layer is separated and washed successively with water, sodium bicarbonate solution, brine and dried (MgSO4).
The dried ether extract is evaporated at reduced pressure and the residue distilled to provide t-butylcyclobutylketone.
ii. The ketone, 105 g. (0.75 mole), is mixedwith hydroxylamine hydrochloride 38.3 g. ~1.16 mole) and sodium acetate, 123 g. (1.50 mole), in sufficient water to effect solution, heated on the steam-bath for A one hour, cooled and the mixture adjusted to p~
7.5 with sodium hydroxide solution. After extracting the mixture with ether, the extracts are dried (MgSO~) and evaporated to dryness to afford the oxime. The oxime is dissolved in anhydrous ethanol (about two liters per mole of oxime) and the solution heated at reflux. Sodium metal (about 10 moles per mole of oxime) is added in portions at a rate sufficient to maintain reflux temperature. Wh~n all the sodium is added the resulting mixture is cooled and 200 ml.
of ethanol Eollowed by 300 ml. of water is added.

The mixture is acidified with hydrochloric acid, evaporated to remove ethanol and the residue made alkaline IpH 12-13) with 10 M sodium hydroxide. The alkaline mixture is extracted several times with ether and the combined extracts dried (MgS04). Dry hydrogen chlorine is passed through the dried extracts until precipitation is complete. The precipitated hydrochloride salt is collected by filtration, washed with ether and air dried. The salt is converted to the free base by means of aqueous sodium hydroxide, extraction with ethyl ether and evaporation of the extracts. The product, t-butylcyclobutylcarbinylamine is of suitable purity for use in preparing the amides of the invention but may be further purified, if 5 desired, e.g. by distillation or column chromatography.
iii. By employing the appropriate acid halide and Grignard reagent in the above procedure in place of cyclobutylcarbonyl chloride and t-butylmagnesium chloride the following amines are obtained in like manner.

3 ~ 3~

~H2 ~
(CH2)m m R7 R R9 0 C~3 CH3 H

0 CH3 n~C4H7 H
( 3)2 (CH3)2CH H
0 CH3 CH3 C(CH3)3 1 n-C3H7 H H
1 CH3 c~3 H
1 CH3 n~C4H7 H
1 n-C3H7 n~C3H7 H
3 2 ( 3)3 H
2 CH3 CH3 CH3*

3C 2 C 3C 2 CH3CH~

2 n-C3H7 ( 3~2 H
3 2 n~C4H7 H
3 CH3 CH3 C~I3 3 n~C3H7 ~ H
3 CH3 C~I3 H

*B.P. 80-90~C. (21 mm.) 33~

iv., The amines of the following formula are also providecl in like manner.

~ 2)m NH2~
(CH2)q m q The following amines are also prepared by this method:
2,2-dimethyl-3-aminopentane r B.P. 123-126C., atmospheric pressure;
2,2,4-trimethyl-3-aminopentane, B.P. 149-150C., atmospheric pressure.

3~

PREPARATION B
2,2-Dimethyl~clohexylamine i. 2,2- _ clohexanone To a suspension of 13.5 g. (0.25 mole) sodium methoxide in 500 ml. of ethyl ether was added 30.8 g.
(0.28 mole) 2-methylcyclohexanone and 20.3 g. (0.28 mole) ethyl formate. The mixture was stirred at room temperature for 12 hours, fil-tered under a nitrogen atmosphere, the solids washed with ethyl ether and dried in the vacuum oven at 75C. The dried cake was ground in a mortar and pestle to a fine powder to obtain 17.5 g. (43~) of sodium 2-formyl-6-methylcyclo-hexanone which was used in the next step.
The above product, 17.5 g. (0.11 mole) was added to a mixture of 2.88 g. (0.13 mole) sodium shot, 500 ml. anhydrous ammonia and about 0.1 g. ferric chloride.
The resulting gray suspension was cooled to -45C.
and stirred for one hour at the reflux temperature of the system. To this was added 20.86 g. (0.15 mole) methyl iodide, the mixture stirred three hours at reflux and allowed to evaporate while warming to room temperature overnight. The residue was suspended in 300 ml. ethyl ether, refluxed to expell traces of ammonia and water added to dissolve the solids. The ether was extracted with water (3 x 100 ml.), the combined aqueous layers treated with 6 g. of solid sodium hydroxide and heated to steam distill the ketone. The steam distillate was extracted with ethyl ether, the extracts washed with brine, dried and ether e~aporated to provide 2,2-dimethylcyclo-hexanone as a colorless liquid, 2.0 g.

-13~-- ii. The ketone provided above is converted to the oxime and the latter reduced with sodium in ethanol as described in Preparation A, Part ii, to provide 3.1 g. of 2,2-dimethylcyclohexylamine.
The following 2,2-d.isubstituted ketones are pre-pared and converted to amines by the above method in like manner.
2,2-di.methylcyclopentanone 2,2-di.ethylcyclopentanone 2,2-di-n-propylcyclopentanone 2,2-diethylcyclohexylamine 3,3-dimethylthiepane-4-one 3,3-dimethyloxepane-4-one 4,4-dil~ethyloxepane-5-one PREPARATION C
2,2,6,6-Tetramethylcyclohexylamine i. 2,2,6,6-Tetramethylcyclohexanone A 50~ suspension of sodium hydride in mineral oil, 14.3 g. (0.30 mole), was suspended in tetra-hydrofuran, the liquid decanted and the solid resuspended and decanted again to remove the oilO Then 15 g.
(0.12 mole) of 2,6-dimethylcyclohexanone was added followed by dropwise addition of a mixture o 11 g.
t-butanol and 20 ml. of tetrahydrofuran (vigorous hydrogen evolution) and the resulting mixture refluxed until hydrogen evolution was complete. To this was added dropwise 37.8 g. 10.30 mole) methylsulfate and the mixture heated at reflux for 24 hours. After dilution with water, extraction with ethyl ether, washing the extracts with water, drying and evaporation of solvent below 40C., 17 g. of tetramethylketone was obtained. This was distilled to obtain 14.6 g.
of produc~, B.P. 62-64C. ~15 mm.).
ii. The 2,2,6,6-tetramethylcyclohe~anone (8 g.) obtained above was converted to the oxime and the latter compound reduced by the procedure of Preparation A, Part ii, to provide 1.4 g. of the desired amine as a colorless liquid which was of suitable purity for use as intermediate.

,.

- 1 3 ~--PREPARATI ON D
i. 2,2,5,5-Tetrameth ~cyclo~enta one To a slurry of 2.0 moles of sodium hydride (washed to remove oil) in tetrahydrofuran was added l90 ml. (2.0 mole) methyl sulfate at a fast rate.
Simultaneously, 35.7 g. (0.425 mole) cyclopentanone in 50 ml. of the same solvent was added at a slow rate. The reaction mixture warmed spontaneously to a gentle reflux and hydrogen evolution was vigorous.
When the addition was completed, the mixture was allowed to stir overnight at ambient temperature.
After heating to reflux for two more hours a mixture of t-butanol in tetrahydrof~lran was added and reflux continued for three hours. The reaction mixture was diluted with water, extracted with ethyl ether, the extracts washed with water, brine, dried over anhydrous MgSO4 and the solvent evaporated to yield 48.2 g. of crude product. This was distilled to afford 2~.2 g.
of tetramethylketone, B.P. 63-68C., 40 mm.
By employing a lower mole ratio of methyl sulfate to cyclopentanone, the same method affords 2-methylcyclopentanone, 2,5-dimethylcyclopentanone and 2,2,5-trimethylcyclopentanone.
ii. The following ketones are prepared in like manner when the appropriate starting materials are employed in the procedures of Part i, above, and Preparation C. The alpha-propyl and alpha-butyl-ketones are prepared using ~ ~ , the appropriate alkylbromide as alkylating agent.

4 ~ 3g~

2,2,6-trimethylcyclohexanone 2~ethylcyclopentanone 2,2,4,4-tetramethylcyclobutanone 2-methylcyclobutanone 2,2-dimethylcyclobutanone 2,4-diisopropylcyclobutanone 2-t-butylcyclopentanone 2,2-dimethyl-5-t-butylcyclopentanone 2,5-diisopropylcyclopentanone 2-sec-butylcyclopentanone 2-isobutylcyclohexanone 2-methylcycloheptanone 2-t-butylcycloheptanone 2,7 dimethylcycloheptanone 2,7-diisopropylcycloheptanone 3,5-dimethyltetrahydro-4H-pyran-4-one 3,5-diisopropyltetrahydro-4H-pyran-4-one 3,3,5,5-tetram~thyltetrahydro-4H-pyran-4-one 3-mPthyl~5-t-butyltetrahydro-4H-pyran-4-one 3,3,5,5-tetramethyltetrahydro-4H-thiapyran-4-one 3-isopropyltetrahydro-4H~thiapyran-4-one 3,5-diisopropyltetrahydro-4H-thiapyran~4-one 3,-t-butyltetrahydro-4H-thiapyran-4-one 2-methyltetrahydro-4H-thiapyran-3-one 2,4-di~ethyltetrahydro-4H-thiapyran-3-one 2-methylthiepane-3-one 4-methylthiepane-3-one 2,4-diethylthiepane-3-one 2,4-di~sopropylthiepane-3-one 3,5-dimethylthiepane-4-one 3,3,5,5-tetramethylthiepane-4 one 4-methyltetrahydro-4H-pyran-3-one 4- _ -butyltetrahydro-4H-pyran-3-one 33~

2-isopropyltetrahydro-4H-pyran-3-one 2,4-diisopropyltetrahydro-4H-pyran-3-one 2,4-dimethyltetrahydro-4H-pyran-3-one 2-methyloxepane-3~one 4-methyloxepane-3-one 2,4-dimethyloxepane-3-one 2,2,4,4-tetramethyloxepane-3-one 3-methyloxepane-4-one 5-methyloxepane-4-one 3jS-dimethyloxepane-4-one 3,3,S,5-tetramethyloxepane-4-one 3,5-diisopropyloxepane-4-one 3-t-butyloxepane-4-one 5-t-butyloxepane-4-one The ketones provided above are converted to the corresponding amines by conversion to the oxime and reduction with sodium in ethanol as described in Preparation ~, Part ii, or Leuckart reduction o~ the ketone as described in Preparation G, Part ii.

PREPARATION E
2,2,5,5-Tetramethylcyclopentylamine A flask was charged with 35 g n (0.61 mole) of 40% sodium dispersion in mineral oil. The oil was removed by washing with ethyl ether and decantation.
The sodium was then mixed with 400 ml. of ether and a mixture of 32.8 g~ (0.20 mole) 2,2,5,5~tetramethyl~
adiponitrile, prepared by the method of Coffman et alD, J. Am. Chem~ Soc., 80, 2868 ~1957), and 400 ml.
of tetrahydrofuran was added slowly. The resulting mixture was stirred at room temperature for 4 hours, the excess sodium decomposed by dr~pwise addition of saturated aqueous ammonium chloride, the organic layer washed with water, dried (Na2SO4) and evaporated to afford 25 D 1 g ~ of crude 2,2,5,5-tetramethylcyclo~
pentylimine. The imine was dissolved in 75 ml. of ethanol and added dropwise to a flask containing 23.3 9. (l mole) sodium shot. An additional 75 ml.
ethanol was added and the mixture heated at reflux until the remaining sodium metal was consumed. The reaction mixture was diluted with water, acidified to pH 1 with concentrated hydrochloric acid, the aqueous phase washed with ether then made strongly basic by addition of sodium hydroxide. The organic layer was extracted with ether, washed with brine, dried (Na2SO4) and evaporated to dryness. The residue was di~tilled in vacuo to afford 6.6 g. (23%) of the _ desired amine, B.P. 60-61C. (20 mm.).

8~3~

2 kyl- and 2,6-Dialkylcyclohexylamines To a solut:ion of 25 g. of 2,6-diisopropylaniline iII 250 ml. each of ethanol and water was added 10 y.
of dry 5% ruthenium-on-carbon catalyst. The mixture was hydrogenated in an autoclave at 100C., 1000 psi (70.4 kg./cm.2) until hydrogen uptake ceased. The catalyst was removed by filtration and the filtrate evaporated to remove solvent. The residue was distilled ln vacuo to obtain 11.2 g. of 2,6-diiso-propylcyclohexylamine as a mixture of cis,trans and trans,trans-isor~ers, B.P. 122-124C. a~ 22 mm~
____ _ By employing the appropriate 2-alkylaniline or 2,6-dialkylaniline as starting material and hydro-genating by the above method the following cyclo hexylamines are also obtained.
2-methyl-6~ethylcyclohexylamine, B.P. 82-87C.
at 19 mmO (50% ~ield);
2-methyl-6-isopropylcyclohexylamine, B.P. 86 at 14 mm. (45% yield);
2-n-butylcyclohexylamine;
2-ethyl-6-n-butylcyclohexylamine;
2-methyl-6-t-butylcyclohexylamine;
2 t-butylcyclohexylamine;
2,6-dimethylcyclohexylamine;
trans-2-ethylcyclohexylamine, B.P. 77 78 (23 mm.);
2,6-diethylcyclohexylamine, B.P. 96C., (17 mm.);
trans-2,-isopropylcyclohexylamine;
2-isobutylcyclohexylamine;
2 methyl-6-n-butylcyclohexylamine.

33~

PREPARATION G
2-t~Butylcy~lohexylamine i. 2 t-Butylcyclohexanone A solution of 31.25 g. (0.20 mole) t-butylcyclo-hexanol in ~0 ml. of ethyl ether was cooled to 10C.
To this was added dropwise, with stirring, a solution of 21.0 g. (0.07 mole) sodium dichromate dihydxate and 15.75 m]~ (0.30 mole) concentrated sulfuric acid in 100 mlO water whil~ maintaining the reaction mixture below 25~C. The mixture was then warmed to room temperature, stirred for two hours, poured onto ice-water, ether layer sepaxated, the agueous phase eætrac~ed again with ether and the combined extracts washed with water, sodium bicarbonate and dried (MgSO4). Evaporation of the ether afforded 30.6 g.
(99~) of the desired ketone.
iio Leuckart Reductio~`of Xetone , . . . . .. ..
A mixture of 2-t-butylcyclohexanone 30.6 g.
(0.20 mole), formamide 50 ml. (1.2 mole) and formic acid (10 m].) was heated at reflux while removing water as it: formed in the reaction while returning the ketone to the reaction vessel. Formic acid (10 ml.) was added as needed to control deposition of ammonium c~rbonate in the condenser. After four hours the reaction temperature reached 197C. and distillation ceased. The mixture was cooled, diluted with water (50 ml.) and extracted with ethyl acetate (75 ml.). The organic layer was evaporated, concen-trated hydrochloric acid added (50 ml. per 100 ml. of residue), the mixture boiled overnight, cooled and washed with 50 ml. of ethyl ether. The aqueous phase .

3~

was adjusted to pH 11 with sodium hydroxide, cooled, extracted with et:her (2 x 40 ml.) and the extracts dried over sodium hydroxide pellets. The solvent was evaporated and the residue distilled through a 10 crn.
column to obtain 21.93 g. of the title amine (71%), B.P. 86-8BC. (21 mm.) as a mixture of cls and trans-isomers.
iii. dl-Fenchone and l-fenchone are reduced to the corresponding fenchylamines by the Leuckart xeduction method of Part ii, above. (-)Fencylamine is obtained as a water white liquid, B.P. 55-60C.
(6 mm.), [alpha]D -21.9 in 30% yield.

3~

PREPARAT I ON H
2,4-Dimethyl-3-aminopentane In a shaker bottle was placed 0.2 g. platinum dioxide and 10 ml. water. The slurry was hydrogenated at 50 psi (3.5 kg./cm2.) for 15 minutes. To the resulting slurry of platinum black was added 34.26 g.
(0.30 mole) 2,4-dimethyl-3-pentanone, 20.0 g. (0.37 mole) ammonium chloride, 225 ml. ammonia saturated methanol and 25 ml. concentrated ammonium hydroxide.
The reslllting slurry was hydrogenated at 60 psi (~.2 kg./cm.2) and room temperature ~or 20 hours, filtered, refluxed for for 1 hour and cooled. The mixture was adjusted to p~ 2.0 with concentrated hydrochlorlc acid and the volume was reduced by evaporatioll at reduced pressure. After washing with 75 ml. ethyl ether, the aqueous solution was brought to pH 13 with 10 M sodium hydroxide solution and extracted with three 100 ml. portions of ether. The extracts were combined, dried over anhydrous MgSO4 and saturated with gaseous hydrogen chloride. The precipitated amine hydrochloride was collected by filtration, air dried and decomposed with 75 ml. 10 M
sodium hydroxide solutionD The oily amine layer was separated and distilled at atmospheric pressure, B.P.
129-132~C, yielding 17.6 g.

3~

PRE PARATI ON
trans-2-Ethylcy_~lopentylamine i. 2-Ethy~_yclopentanone In a three-necked flask 5.0 g. of sodium metal was dissolved in 250 ml. of dry ethanol and 31.24 g.
(0.20 mole) 2-carboethoxycyclopentanone added. To the resulting yellow solution 18.4 ml. (0.23 mole) ethyl iodide was added dropwise and the mixture heated at reflux for two hours. After cooling, 250 ml. of brine and 50 ml. of water were added and the mix-ture extracted with ethyl ether (2 x 100 ml.).
After drying (MgSO4) and evaporation of solvent 36.5 g. (99%) of 2-ethyl-2-car~oethoxycyclopentanone was obtained.
This was decarboxylated by heating at reflux with a mixture of 200 ml. of concentrated hydrochloric acid and 100 rnl. of water. After four hours at reflux carbon dioxide evolution was complete. The mixture was cooled, saturated with sodium chloride, extracted with ethyl ether, the extracts dried (MgSO4) and ether evaporated. The residue was distilled to obtain 12.62 g. (56%) of 2-ethylcyclopentanone, B.P.
97-98C. 1100 mm.).
ii. The product obtained above was converted to trans-2-ethylcyclopentylamine by the procedure of Preparation ~, Part ii, B.P. 150-151C. in 35% yield.
The identity of the product was verified by its H~NMR spectrum.
By emp3Oying the appxopriate 2-carbethoxycyclo-3~ alkanone or a corresponding hetercyclic ketone (pre-pared by the well known Dieckmann cyclization of the appropriate dicarboxylate ester, see e.g., H. O.
EIouse, "Modern Synthetic Reactions", W. A. Benjamin, Menlo Park, Cal., 1972, p. 740.) and the appropriate alkyl halide in place of ethyl iodide in the above procedure the following amines of formula R N~2 are prepared in like manner.

3~

Where R is ~ ( 21m m 2 t-C4Hg 2 , sec-C4a9 4 t-C4Hg Where R is ~ ~CH2)n- X

X ~ n p R3 O 1 0 . 2-CH3 O 1 0 2-t-C4~9 0 o 2 2-CH
O 0 2 4~CH3 O 0 2 4-sec-C4~Ig O 0 2 2 ' C
O 0 3 2-C~3 O 1 - 2 5-t-C4Hg O 1 2 3-t-C4Hg S2 1 1 ~ C4~9 3~3 PRE PARAT I ON J
trans 2 Isoprop~cycIopentylamine i. 2-Isopropy]c~clopentanone To a solution of 10 g. of sodium metal in 670 ml. of ethanol was added dropwise a mixture of 100 g.
(1.19 mole) cyclopentanone and 60 g. (1.03 mole) acetone and the resulting mixture refluxed for 1.5 hours. The solvent was evaporated ln va o, the residue taken up in ether, the solution washed wit~
3 M hydrochloric acid (5 x 200 ml.), 5% sodium bicarbonate (3 x 200 ml.), brine (1 x 200 ml.) and dried (MgSO4~. The ether was evaporated with mild heating to afford 97 g. of dark liquid which was distilled in vacuo to obtain 55 g. of 2-isopropylidene-cyclopentanone, B.P. 96-100 (2.7 mm.).
To 12.75 g. of the above product in 250 ml. of methanol was added 2.0 g. 5% palladium-on-carbon catalyst and the mixture hydrogenated at 50 psi (3.S kg./cm2.). After one hour the hydrogen uptake was complete. The catalyst was removed and solvent evaporated in vacuo to afford 12.75 g. of colorless liquid. This was distilled to obtain 9.64 g. of 2-isopxopylcyclopentanone, B.P. 74-76C. (20 mm.).
Reducti~n of 2-isopropylcyclopentanone by the method of Preparation A, Part ii afforded the corres-ponding amine, B.P. 167 (atm.) in 31~ yield.

`147-PRE:PARAT I ON K
____ 2,2-DlmethyI _-aminobutane In a 500 ml. flask was placed 10.0 g. (0.10 mole) 2,2-dimethyl-3-butanone, 250 ml. methanol, 76.94 g. (1.,0 mole) ammonium acetate and 4O37 g.
(0.07 mole) sodium cyanoborohydride, and the mixture was allowed to stir at room temperature for 24 houxs.
The pH was adjusted to 2.0 with concentrated hydro~
chloric acid and the methanol removed at reduced pressure. The residual solid was dissolved in 500 ml. water and washed with three 100 ml. portions of ether. The pH of the aqueous solution was adjusted to 13 with 10 M sodium hydroxide and the mixture extracted with three 100 ml. portions of ether. The extracts were combined, dried over anhydrous MgSO4, filtered and distilled. The amine (2.4 g.) distilled at 102-103C at atmospheric pressure.
The racemic amine was resolved by the Polari-metric Control method described by Bruck et al. J J.
Chem. Soc., 921 ~1956) employing the amlne hydrogen tartarates and crystallizing from 70:30 methanol/water ~by volume) to obtain dextrorotatory amine of 93 ~ 4 purity and levorotatory amine of 80 + 4% purity.
When an equivalent amount of 2,2-dimethyl-3-pentanone is employed in place of 2,2-dimethyl 3-butanone in the above procedure 2,2-dimPthyl-3-amino-pentane is obtained and resolved into its enantiomers.

3~

PREPARATION L
L-Aspartic acid N-thiocarboxyanh~
A. L-Aspartic acid (582 g., 4.29 mole) was added gradually with stirring to 350.9 g. (8058 mole) of 50%
S sodium hydroxide solution at 0C. Methyl methyl xanthate t550 g., 4.51 mole) in 405 ml. of methanol was then added as rapidly as possible. The mixture was heated at 45C. for 1.5 hours, cooled to room tempera-ture, and washed with two portions of methylene chloride. The methylene chloride washPs were discarded and the aqueous phase acidified with concentrated hydrochloric acid at 0C. The solution was extracted with three portions of ethyl acetate~ and the combined extracts washed with brine and dried over anhydrous lS magnesium sulfate. The solvent was evaporated ln vacuo to gi~e a yellow oil which crystallized upon addition of ethylene dichloride and n-hexane. The N-methoxy-thiocarbonyl-L-aspartic acid was collected by filtration, washed with fresh n-hexane, and dried (420 g., 47%)-M.P. 128-130C; lH-NMR (DMSO~d6), (delta) 2.73 (d, 2H, J = 6 ~z~, 3.63 (s, 3H), 4.43 (dt, lH, J =

6 Hz, 8 Hz), 6.63 (d, lH, J = 8 Hz); infrared spectrum (KBr) 1715, 1515 cm 1.

3~ `
-B. N-methoxythiocarbonyl-L-aspartic acid (207.0 g., 1.00 mole) was dissolved in 1200 ml. ethyl acetate at 0C. and phosphorous tribromide (47 ml., 0.50 mole) was added in one portion. The cooling bath was removed and the temperature allowed to rlse spontaneously to 35C. The solution was stirred for 10 minutes after which time a granular white precipitate had formed.
The reaction mixture was cooled to 0-5~C.~ the product collected by filtration, washed with a small volume of ether, and dried. The yield of analytically pure L-aspartic acid N-thiocarboxyanhydride was 157.4 g.
(90%) .
M.P. 200-205C. (dec.); [alpha~25 = -109.5 (C =
1, THF); infrared spectrum (KBr) 3225, 1739, 1724, 1653, 1399 cm 1; lH-NMR (DMSO-d6) ppm (delta) 2.83 (d, 2H, J = 5.0 Hz), 4.70 (t, lH, J = 5.0 Hz), 9.23 (bs, 2H, ex); mass spectrum (m/e) 175 (M ), 87, 60.

3~ .

PR~PARATION M
~ =
i. Ethyl 2,2,3,3-Tetramethylcyclo~ropanecarboxy~te The method of Mesheheryakov, Chem. Abstr., 54, 24436d (1960) was employed. To a mixture of 19 g.
(0.226 mole) of 2,3-dime~hyl-2-butene and 2 g. of cupric sulfate is added at reflux a mixture of 51 g.
(0.447 mole) ethyl diazoacetate and 19 g. o~ 2,3-dimethyl-2-butene. The resulting mixture is heated at reflux for 3 hours, cooled, filtered and distilled to afford 19.8 g. (26%) of the desired cyclic ester, B.P.
76-77 (15 mm.~.
ii. To 300 ml. of ethanol containing 40 g. of ammonia is added 17 g. (0.10 mole) of the ester obtained above and the resulting mixture allowed to stand overnight. After heating at reflux for one hour the ethanol was evaporated in vacuo to obtain 2,2,3,3-tetramethylcyclopropanecarhoxamide.
A solution of 2.82 g. (O.02 mole) of the amide in 8 ml. tetrahydrofuran and 4 ml. of water is cooled to 5C. and 10 ml. of 2 M sodium hypochlorite added drop-wise followed by 8 ml. of 20% (w/v) sodium hydroxide.
The two phase mixture is stirred at 5C. for 30 minutes then at ~0C for one hour. The organic layer is extracted with ether, the ether layer e~tracted with 2 M hydrochloric acid (3 x 20 ml.), ~he aqueous acidic layer is made strongly alkaline with sodium hydroxide and extracted with ether. The extracts are dried (Na2SO4) and the ether evaporated at 25 (50 mm.) to give 0.67 g. (25%) 2,2,3,3-tetramethylcyclopropyl-- amine~ NMR (CDC13) ppm tdelta~:
0.95 t6H, singlet); 1.00 (6H, singlet); 1.83 (lH, multiplet); 1.7 (2H, multiplet).

3~

iii. The following substituted cyclopropylamines are prepared in an analogous fashion from the appro-priate olefin.

R ~ R
R6/ \ R

__ i_CH ~ H H H
i_C3H H i_C H H

t-C4H~ H H H
CH3 CH3 t-C4Hg H

Y33~

-152~

PREPARATION N
3-Amino-2,2,4~4-tetramethyloxetane To 13.6 g. (0.12 mole) of diisopropylketonP is added 0.2 ml. of phosphorus tribromide. To this is added dropwise at 10C., 38.4 g. (0.24 mole) bromine and the mixture warmed to 55-60C. and held at this temperature for 1.5 hours. After cooling and partion-ing between chloroform and water, the organic layer is washed with sodium carbonate solution until neutral, dried and the solvent evaporated to obtain 2,4-dibromo-2,4-dimethylpentan-3-one.
To 0;,1 mole of the dibromoketone in 160 ml. of ethanol is added a solution of 8 g. of sodium hydroxide in 80 ml. water and the resulting mixture is stirred at room temperature for 30 minutes. After diluting with water the reaction mixture is extracted with ethyl et7ner, the extracts washed with water, brine and dried (MgS04). The ether is evaporated to provide 2,4-dihydroxy-2,4-dimethyl-3-pentanone. This is dissolved in 50 ml. chloroform and 1.5 ml. concentrated sulfuric acid added dropwise. The resulting mixture is heated at reflux for five hours while removing water clS its azeotropic mixture with chloroform. When no more water is evolved the reaction mixture is washed with water, the organic layer dried (MgS04~ and solvenl_ evaporated to provide 2,2,4,4-tetramethyloxetane~
3-one whiGh is purified by distillation.
The ketone is converted to the oxime and reduced ~ith sodium/ethanol by the procedure of Preparation A, Part ii.

3~

PP~EPARATION O
3-Amino-2,2-dimet Yloxetane 3-~ydroxy-3-methyl-2-butanone, 0.20 mole, is treated dropwise with a equimolar amount of bromine at room temperature and the resulting mixture stirred for three hours. The mixture is taken up in chloroform, washed wit:h sodium carbonate solution until neutral, dried and solvent evaporated to obtain l-bromo~3-hydroxy 3-methyl-2-butanone.
i0 To 0.1 mole of the bromoketone in 160 ml. of ethanol is added a solution of 4 g. of sodium hydroxide in ~ ml. water and the mixture stirred at room temperature for 30 minutes. The mixture is diluted with water, extracted with ether, the extracts washed with water, brine and dried (MgSO4). The solvent is evaporated and the residue taken up in 50 ml. of chloroform. To this is added dropwise 1~5 ml. of concentrated sul furic acid and the resulting mixture heated at reflux while removing water as its azeotrope with chloro~orm. When water evolution is complete the resulting ketone is isolated and converted to the desired amine as described in Preparation N.

3.~ 33~

PREP~RATION P
Employing the procedures of Preparation N and O
but starting with the appropriate ketone or alpha-hydroxykelone in each case the ~ollowing amines are prepared :Ln like manner.

R~ R4 CH3 H t-C H H

C~3 H CH3 H

-C H H H H
-C H H i_C H H

PREPARATION Q
~ .
Dicyclopro~~ c~ i ~n:--In a 500 ml. round bottom flask was placed 41.7 g.(0.60 mole) hydroxylamine hydrochloride and 80 ml.
water. With stirring, 44 ml. of lOM sodium hydroxide solution and 44.4 g. tO.40 mole) dicyclopropyl ketone were added. The mixture was stirred at reflux for three hours. After cooling, 60 ml. methylene chloride was added and the mixture stirred until all oxime had dissolved. The methylene chloride layer was separated and dried over anhydrous magnesium sulfate. The solvent was removed by evaporation at reduced pressure and the residue recrystallized from 55 mlO hexane, yielding 40.3 g. dicyclopropylketoxime, M.P. 69-72C.
In a 500 ml., three-necked round bottom flask was placed 18.8 g. (0.15 mole) dicyclopropylketoxime and 150 ml~ anhydrous ethanol. With efficient stirring 19.2 g. (0.83 mole) sodium spheres was added in portions as rapidly as possib]e, maintaining reflux throughouk the addition. Following dissolution of the sodium, the reaction was cooled to 60C. and 60 ml.
water was added. After cooling, 78 ml. concentrated hydrochloric acid was added dropwise with stirring.
Ethanol was distilled at reduced pressure and 50 ml.
~S water addad to dissolve salts~ The mixture was adjusted to p~ 13 with 10 M sodium hydroxide solution and extracted with three 40 ml. portions of methylene chloride. The extracts were combined, dried over anhydrous magnesium sulfate, filtered and evaporated at reduced pre~;sure. The residual amine was distilled - at 88-90C./95 mm Hg, yielding 11.0 g. of the desired product.

156~

PREPARATION R
2-Amino-3,3-dimethyl~
qamma--butyxoIactone Hydrochloride The melhod is that of Nagase et al., Chem.
Pharm. Bull , 17, 398 (1969).
To a st:irred solution of 2,2-dimethylhydroacryl~
aldehyde [prepared from sec--butyraldehyde and form-aldehyde by the method of Stiller, et al., J. Am.
Chem. Soc., 62, 1785 (1940)] 5.11 g. in methanol (25 ml.), a solution of ammonium chloride, 2.94 g., and sodium cyanide, 2. 9 g., in water ~40 ml.) is added dropwise. After stirring for three hours the mixture is saturatecl with ammonia gas and allowed to stand at room tempera~ture overnight. The resulting mixture is concentrated~ ln vacuo to a small volume and 40 ml. of concentrated~ hydrochloric acid is added. After refluxing for three hours the mixture is evaporated in vacuo and thle residue crystallized from ethanol-ethyl ether and th~en from ethanol to give 2.2 g. of the title compound, M.P~ 214-215C. (dec.).
Use of homologs of 2,2-dimethylhydracrylaldehyde in the above procedure affords the corresponding compounds of the formula ~ 12 where one of R12 and R13 is alkyl having from one to four carbon atoms and the other is hydxogen or alkyl having from one to four carbon atoms.

33~

PREPARAT I ON S
4-Amino-3,3, 5, 5-tetramethyl~tetrahydro-4H-pyran-2-one i. Methyl 5-HYdroxy-2,~,4,4-tetramethyI-3-keto-valerate A mixture of 172 g. (loO mole) methyl 2,2,4-trimethyl-3~ketovalerate, 5.4 g. (0.10 mole) sodium methoxide and 33 g. (0O36 mole) paraformalde in 250 ml. methanol is heated at reflux for eight hours.
The mixture is cluenched by addition of water, neutralized with hydrochloric acid, extracted wi~h ethyl ether, washed with water, brine and solvent evaporated. The residue is purified by vacuum distillation or chromato-graphy on silica gel to provide the purified product.
ii . 2 r 2 r 4,4-tetramet~y~-2,4 dioxotetrahydro-4H-pyran A solution of 101 g. (0.50 mole) of the above product in 200 ml. methanol and 20 ml. concentrated hydrochloric acid is heated at reflux for two hours, cooled, poured into ice~water, extracted with ethyl ether, the extracts washed with sodium bicarbonate solution, water, clried and evaporated to dryness. The residue was heatecl ln vacuo at 80-100C. for two hours to obtain product of suitable purity for use in the next step.
iii. The ketolactone obtained above is converted to the corresponding 4-oximino derivative and this reduced to the tit:le compound by the procedure of Preparation Q.

., 3~

PREPARATI ON T
4-Amino-3,3~5,~-tetra_ethyl 2-~iperidone i. Methyl 5-Dibenzylamino-2,2,4,4-tetramethyl-3--ketovalerate hydrochloride _ _ , To a mixture of 86 g. (0. 5 0 mole) methyl ~,2,4-trimethyl-3-ketovalerate, 117 g. (0.64 mole) dibenzyl-amine hydrochloride and 19O8 g. (0.22 mole) paraform-aldehyde is added a solution of 1 ml. of concentrated hydrochloric acid in 150 ml. 95~ ethanol and the mixture is heated at reflux for four hours. The mixture is filtered, 500 ml. of hot acetone added to the filtrate and the resulting mixture cooled then refrigerated overnight. The precipitated product is collec~ed by filtration, washed with acetone and lS dried.
ii. 3,3,5,5-tetramethylpiperidin-2,4 dione The above hydrochloride salt is parti ioned between 0.1 N sodium hydroxide solution and ethyl ether. The ether extracts are dried (MgSO4) evapor-ated to dryness and the residue taken up in methanol.
To the methanol solution is added 1 g. of 10~ Pd/C and the mixture hydrogenated at 3-4 atmospheres pressure until hydxogen uptake is complete. The catalyst is removed by filtration, the filtrate heated at reflux for two hours, solvent evaporated and the residue heated at 70-80C. in vacuo for two hours. The _ residual product is purified by chromatography on silica gel.
iii. The piperidinedione obtained above is conve~ted to the 4-oximino derivative and this reduced to the title 4-amino analog by the procedure of Preparation Q.

PREPARATION U
3,3,5,5-Tetramethylpyrrolidin-2,4-dione A mixture of 80 g. of 2,2,4,4-tetramethyl-1,3-cyclobutanedione monoxime, prepared by the method of U.S. 3,125,569, and 250 ml. 98~ (w/w) sulfuric acid was warmed at S0-60C. for one hour and allowed to stand overnight at room temperature. The reaction mixture was poured onto 800 g. ice, extracted with methylene chloride, the extracts washed with sodium bicarbonate so]ution, water, dried (MgSO4) and evapor-ated to remove solvent. The resulting mixture of products was purified by column chromatography on silica gel and the fractions containing the title compound combined and evaporated to dryness.
The ketolactam thus obtained is converted to 3-amino-3,3,5,5-t:etramethyl-2-pyrrolidone by methods described above.

3~

PREPARATION V
3-Amino~2,2,4,4-tetramethylthietan and its 1,l-Dioxide A~ 2 _ Dibro~o-2,4-dimet~xIpentan-3-one To 136 g. (1.2 mole) of diisopropylketone was added 2 ml. of phosphorus tribromide and the mixture cooled to 10C. To this was added dropwise 384 g.
t2.4 mole) of bromine, the mixture allowed to warm to room temperature. After two hours at this temperature the mixture was warmed at 55-60Co for one hour then cooled and partioned between chloroform and water.
The water was discarded and the organic layer washed with sodium carbonate solution until neutral. The organic layer was dried (MgSP~) and solvent evaporated to obtain 316 g. (97~) of the desired product.
B. 2,2,4,4-Tetramet~y1-3-oxo h etane Sodi.um metal, 23 g. (1.0 mole), was dissolved in S00 ml. of dry methanol and the resulting mixture cooled to 10C. Hydrogen sulfide gas was passed through t:he mixture until it was saturated. Then 136 g. (t).5 mole) of the dibromoketone obtained in Part A WclS added dropwise while continuing to allow hydrogen sulfide to pass through the reaction mixture.
After the addition was completed the mixture was stirred for two hours at 10C., allowed to warm to room temperature and stirred overnight. After pouring the reaction mixture into water, it was extracted with ethyl ether and the extracts washed with dilute hydrochloric acid and brine. After drying over magnesium sulfate the ether was evaporated, the residue slurried with methanol, cooled and filtered ~o obtain 46 g. 164%) of solid product which was used without purification in the next step.

3~

C. Reducti~le amination of ketone .o 75 m;L. of dry methanol was added 4.5 g.
(0.031 mole) of 2,2,4,4-tetramethyl-3-oxothietane, 2,3.9 g. (0.31 mole) ammonium acetate and 1.36 g.
(0.0217 mole) sodium cyanoborohydride and the resulting mixture heated at reflux for four hours. Additional sodium cyano~orohydride (1.36 g.) was added and reflux-ing continued for three days with a third increment of the same reagent added at the start of the third day.
The resulting mixture was acidified to pH 2 with hydrochloric acid and evaporated to dryness on the rotary evaporator at reduced pressure. The residue was dissolved in water, washed with ethyl ether, the aqueous phase adjusted to pH 11 with sodium hydroxide solution and extracted with ethyl ether. The extracts were washed with brine, dried IMgSO4) and evaporated to dryness to obtain 1.9 g. 142~) of the desired amine as a crystal]ine solid. The structure of the product was verified by its lH-NMR spectrum.

A~

D. 3-Amino-2,2,4,4-tetrameth~hietane-1,1-dioxide The amine obtained in Part C, above, 29 g.
(0.2 mole) was dissolved in 50 ml. acetonitrile and 250 ml. water added. While maintaining the mixture at 5 pH 10 with sodium hydroxide, 35.8 g. (0.21 mole) carbobe!nzoxy chloride was added over 30 minutes, the mixture! stirred for one hour, filtered, the precipitate washed with water and dried in acuo at 50C. to provide the NCbz-amine, Rf 0.7 (hexane/ethyl acetate 4:1 v/v, phosphomolybdic acid spray), 52.1 g. (93.4%).
This was dissolved in 700 ml. methylene chloride, 77 g. (0.372 mole) m-chloroperbenzoic acid was added slowly while maintaining the temperature belo~ 45C.
(20-42C.). The precipltated solid was collected by filtration, the filtrate was washed with lN hydro-chloric acid, aqueous sodium bicarbonate solution, dried (,MgSO4) and the solvent evaporated. The residue was crystallized from acetone-water to obtain 42 g.
(73%) of the Cbz-protected amine l,l~dioxide, Rf 0.7 (hexane/ethyl acetate 1:1 v/v, phosphomolybdic acid spray).
The protecting group was removed by hydrogeno-lysis of 5 g. of Cbz-amine in 250 ml. methanol, 5 ml.
concentrated hydrochloric acid and 2 g. of 5% Pd/C
(50% wet). The product was isolated in the usual manner. Yield: 2.4 g. (85%), Rf 0.6. The retention time upon gas-liquid chromatography on a 1 meter, OV 1 column at 180C. was 1.3 minutes. The overall yield for the three steps starting from 3-amino-2,2,4,4-tetramethylthietane was 65%.
By employing equivalent amounts of amine and m-chloroperbenzoic acid in the above procedure the corresponding sulfoxide is obtained in like manner.

3~

E. Employing the appropriate ketone of formula R3R4cHCoc~R5R6 in place of diisopropylketone in the procedures of Parts A-C affords the corresponding amines of the formula shown below.

R5~ ~ R43 C~H5 H H H
1-C3H7 ~ H H
l-C3H7 H i-C H H
t-C4Hg H H H
t-C~Hg H t-C4Hg H
n-C4Eg H ~-C4H9 The corresponding sulfoxides and sulfones are prepared ~y the procedure of Part D above.

3~

PREPARATIOU W
3-Amino-2,2,4,4-tetramethyltetrahydrothiophene A. 1-~ ~
To sodium methoxide pxepared from 7.5 g. of sodium metal and 250 ml. of methanol was added 72.5 g.
(2.4 moles) paraformaldehyde followed by 250 g. (2.2 moles) diisopropylketone and the resulting mixture heated at re~lux for three hours. The reaction was quenched with water, neutralized with hydrochloric acid, extracted with ethyl ether, washed with water, brine ancl the solvent evaporated. The residual oil (90 g.) was distilled ln vacuo to obtain 28 g. of the desired product boiling at 92-98C. at 16-20 mm. GLC
on OV-l column at 107C., retention time 314 sec., 96%
pure.
When the above procedure was repeated on the same scale but the reaction mixture refluxed for 16 hours, 31 g of product was obtained of 96% purity by GLC.
B. 4-Bromo-l-hydro~y-2,2,4-trimethylpenta_-3-one To a stirred, refluxing solution of 69 g. (0.48 mole) of l--hydroxy-2,2,4-trimethylpentan-3-one in 500 ml. of chloroform wàs added dropwise a solution of 77 g. (0.48 mole) bromine in 100 ml. of chloroform.
When the addition was completed the mixture was stirred at reflux for one hour, allowed to cool and stand overnight at: room temperature. Evaporation of solvent at reduced pressure afforded 127 g. of product which was used in the next step without purification.

" , C. 2,2,4,4-'retramethyltetrahydrothiophen-3-one The product obtained in Part B, 79 g. (0.3 mole) was dissolved in 300 ml. of dry pyridine, cooled to 0C. and 114 g. (0.6 mole) of p-toluenesulfonyl chloride was added in portions at 0C. The resulting mixture was stirred at this temperature for 3 hours, 15 minutes, poured into ice/water and extracted with ethyl ether.
The extracts were washed with dilute hydrochloric acid, water and brine then dried over anhydrous magnesium sulfate. The solvent was evaporated to provide 111 g. (98%) of crystalline tosylate.
The tosylate, 94 g. (0.25 mole) was dissolved in one liter of pyridine, 180 g. (0.75 mole) of sodium sulfide monohydrate added and the mixture heated to 75C. and held at this temperature for one hour and allowed to stand at room temperature overnight. Water was added and the mixture was extracted with ether.
The extracts washed with hydrochloric acid, brine, dried (MgSO4) and the solvent evaporated to obtain 35 g. of the title compound, 89~ yield. The product showed only one spot upon silica gel TLC, eluting with ethyl acetate/hexane (1:4 by volume, R~ 0.5. The H-NMR spectrum was in agreement with the structure for the title compound.

3'~

D. Leuckart reduction of ketone To a 100 ml. round-bottomed three-necked flask fitted with stirrer, thermometer and condenser with fractionating head was added 10.0 g. (0.063 mole) of 2,2,4,4-tetramethyltetrahydrothiophen-3-one r 15.2 ml.
(0.38 mole) formamide and 3.5 ml. (0.092 mole) formic acid and the mixture heated at reflux (163C.) while removing water. The reaction mixture was maintained at 160--180C. for 20 hours with addition of formic acid (10 ml.) at intervals. The pot temperature increased to 200C. over this period. The reaction mixture was cooled, water added and the mixture extracted with ethyl acetate. The extracts were evaporated _ vacuo. The residue was refluxed with 20 ml. of 6N hydrochloric acid for two hours, cooled, the resulting mixture washed with ethyl ether, the aqueous phase adjusted to pH 11 with sodium hydroxide solution and extracted with ethyl ether. The extracts were dried and evaporated to obtain 2 g. of 3-amino-2,2,4,4-tetramethyltetrahydrothiophene which was identifiecl by lH-NMR and appeared homogeneous upon silica gel ~LC.
E. By employing the appropriate ketone as starting material iII place of diisopropylketone in the above procedures and that of Preparation X, the following amines are similarly obtained.

.. i ~` "

N ~

S CH3CE[2~ CH3CH2 H
( 3)2 ~ 3)2CH

O M H (CH3)3C H.
O C~3CH2 H n-C4H H
- 15 CH3 C~3CH2 CH3 CH3CH~

When the t:etrahydrothiophenes of the above formula are contacted with an equimolar amount of hydrogen perox:ide or m-chloroperbenzoic acid the corresponding ,sulfoxide (X = SO) is formed in each case. Treatment of the same starting material or the sulfoxide with a-molar excess of the same reagents or potassium permanganate affords the corresponding sulfone (X = SO2).

3~

--16~--PREPARATI ON_X
3-Amino-2,2,4,4-tetramethyltetrahydrofuran A. 2,2,4,4-Tetramethyltetrahydrofuran-3-one 4-Bromo-1-hydroxy-2,2,4-trimethylpentan-3-one (prepared as described in Preparation W, Parts A and B) 25 g. (0.1 mole) was dissolved in 160 ml. of ethanol and a solution of 3 g. (0.2 mole) sodium hydroxide in 80 ml. of water was added. The resulting mixture was stirred at room temperature for 30 minutes, diluted with water, extracted with ethyl ether, the extracts washed with water, brine and dried over anhydrous magnesium sulfate. ~he solvent was evapor-ated to afford 17.7 g. of 2,2,4-trimethylpentan-1,4-diol as a colorless liguid which was identified by lH-NMR. The diol was dissolved in 50 ml. of chloroform, 1.5 ml. of concentrated sulfuric acid added dropwise.
The mixture was heated at reflux for 3 hours, while distilling water/chloroform azeotrope from the mixture.
After standing overnight at room temperature the reaction mixture was washed with water, the organic layer dried (MgSO4) and solvent evaporated ln vacuo to provide 13.9 g. of colorless liquid. Distillation afforded 8.3 g. of the desired product, B.P. 70-72 (50 mm.), overall yield 58~.
B The k~tone obtained in Part A, 8.0 g. (0O05~
mole), hydroxylamine hydrochloride, 8.0 g. (0.113 mole) and sodium acetate, 2.3 g. (0.113 mole), were combined with 85 ml of ethanol and the mixture heated at reflux for 48 hours. ~he resulting mixture was diluted with water, extracted with ethyl ether, the extracts washed with water, dried and evaporated to yield 9.O g. of a mixture of ~y_- and anti-oximes, identified by its l~-NMR spectrum.

The oxlme obtained above, 1.3 g. (8.28 mmole) was dissolved i31 70 ml~ of dry ethanol, 1.9 g. of sodium metal added and the mixture warmed to reflux and held at this temperature for 15 minutes. Heating was continued for two hours with addition of two more increments (1.9 g. each) of sodium. The reaction mixture was then diluted cautiously with water, extracted with ethyl ether. The ether layer extracted with dilute hydrochloric acid, the aqueous phase made alkaline with sodium hydroxide and re-extracted with ether. The extracts were dried (MgSO4) and evaporated to dryness and the residue distilled to obtain the desired am:ine, B.P. 68-69C. (15 mm). After further purification by precipitation of the hydrochloride salt from ethyl-ether-methanol, basifying the salt and extracting again with ether 0.87 g. of amine of 93%
purity by gas chromatography (OV-1 column) was obtained.

Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for production of L-aspartyl-D-amino acid dipeptide amide of the formula ---(I) and the physiologically acceptable cationic and acid addition salts thereof, wherein Ra is CH2OH or CH2OCH3;
and R is a branched member selected from the group consisting a fenchyl, diisopropylcarbinyl, d-methyl-t-butylcarbinyl, d-ethyl-t-butylcarbinyl, di-t-butylcarbinyl, 2-methylthio-2,4-dimethylpentan-3-yl, where at least one of R3, R4, R5, R6 is alkyl having from one to four carbon atoms and the remainder are hydrogen or alkyl having from one to four carbon atoms, X is O, S, SO, SO2, C=0 or CHOH; m is zero, 1, 2, 3 or 4, n and p are each zero, 1, 2 or 3 where the sum of n + p is not greater than 3 and the sum of the carbon atoms in R3, R4, R5 and R6 is not greater than six, and when both the R3 and R4 or R5 and R6 are alkyl they are methyl or ethyl, where one of R7, R8, R9 is alkyl having from one to four carbon atoms and the remainder are hydrogen of alkyl having from one to four carbon atoms and the sum of the carbon atoms in R7, R8 and R9 is not greater than six, where m and q are the same or different and each have the values previously defined for m, where each of R12 and R13 are methyl or ethyl, or R12 is hydrogen and R13 is alkyl having from one to four carbon atoms, Z is O or NH and t is 1 or 2, where w is 1, 2, 3 or 4, R14 and R16 are each alkyl having from one to four carbon atoms, R15 is hydrogen, OH, or alkyl having from one to two carbon atoms, where the sum of the carbon atoms in R14, R15 and R16 is not greater than six and when both of R14 and R15 are alkyl they are methyl or ethyl, and where R17 and R19 are alkyl having from one to four carbon atoms, R18 and R20 are hydrogen or alkyl having from one to two carbon atoms, taken separately, A is OH and B is hydrogen, OH or methyl and when taken together A and B are where the sum of the carbon atoms in R17, R18, R19 and R20 is not greater than six and when both of R17 and R18 or R19 and R20 are alkyl they are methyl or ethyl.
Characterized by:
(a) reacting a diblocked L-aspartyl-D-amino acid dipeptide of the formula ---(II) or a carboxyl activated derivative thereof with an equimolar amount of a primary amine of formula in the presence of a reaction inert solvent, R10 is a carboxyl protecting group selected from alkyl having from one to four carbon atoms or benzyl and Q is a selectively removable amino protecting group, to provide a diblocked L-aspartyl-D-amino acid dipeptide amide of the formula ---(III) and removal of the carboxyl protecting group, R10, and amino protecting group, Q, by methods known per se;
(b) reacting a D-amino acid amide of formula ---(V) wherein R and Ra are as defined above, with an equi-molar amount of diblocked L-aspartic acid of formula or a carboxyl activated derivative thereof, wherein R10 and Q are as defined above, in the presence of a reaction inert solvent to provide a diblocked L-aspertyl-D-amino acid dipeptide amide of formula (III) as defined above, and removal of protecting groups R10 and Q as defined above;

(c) reacting a D-amino acid amide of formula (V) as defined above, with an equimolar amount of L-aspartic acid N-thiocarboxyanhydride in the pre-sence of a suitable solvent, preferably water or aqueous tetrahydrofuran, at pH
8 to 10 and a temperature of from about -25 to 10°C.

2. A process (a) or (b) according to claim 1 wherein R10 is methyl or benzyl, Q is benzyloxycarbonyl or t-butoxycarbonyl, said compound of formula (II) is in the form of a mixed anhydride prepared from said compound (II) and an alkyl chlorocarbonate ester having from one to four carbon atoms in said alkyl group, said solvent is tetrahydrofuran, N,N-dimethylformamide or mixtures thereof and said reacting is conducted at a temperature in the range of from -50 to 25°C., preferably -35 to 5°C.

3. A process according to claim 1 wherein R10 is benzyl and Q is benzy-loxycarbonyl and said protecting groups R10 and Q are removed by hydrogenolysis, or R10 is methyl and Q is t-butoxycarbonyl and said protecting groups R10 and Q
are removed by hydrolysis.

4. A process according to claim 1 wherein R is diisopropylcarbinyl, d-methyl-t-butylcarbinyl or di-t-butylcarbinyl.

5. A process according to claim 1 wherein R is a member selected from the group consisting of wherein R3-R9, X, m, n, p and q are as defined in claim 1.

6. A process according to claim 5 wherein R is or

7. A process according to claim 5 wherein R is and when m is 2: R3-R6 are each methyl, R3, R4, R5 are each hydrogen and R6 is methyl, ethyl, isopropyl or t-butyl, or R3 and R5 are each hydrogen and R4 and R6 are each methyl, and when m is 3: R3 is hydrogen or methyl and R4, R5, R6 are each methyl, R3, R4, R5 are each hydrogen and R6 is isopropyl or t-butyl, R3 and R5 are each hydrogen, R4 is methyl and R6 is methyl, ethyl or isopropyl, or R3 and R4 are each hydrogen and R5 and R6 are each methyl or ethyl.

8. A process according to claim 5 wherein R is and when n is 1 and p is zero: R3-R6 are each methyl and X is O, S or SO2, when n and p are each zero: R3-R6 are each methyl and X is S, SO2 or C=O, when n and p are each 1: R3 and R5 are each hydrogen and R4 and R6 are each methyl and X is S or SO2.

9. An L-aspartyl-D-amino acid dipeptide amide of the formula and the physiologically acceptable cationic and acid addition salts thereof, wherein Ra is CH2OH or CH2OCH3; and R is a branched member selected from the group consisting of fenchyl, diisopropylcarbinyl, d-methyl-t-butylcarbinyl, d-ethyl-t-butylcarbinyl, di-t--butylcarbinyl, 2-methylthio-2,4-dimethylpentan-3-yl, where at least one of R3, R4, R5, R6 is alkyl having from one to four carbon atoms and the remainder are hydrogen or alkyl having from one to four carbon atoms, X is O, S, SO, SO2, C=0 or CHOH; m is zero, 1, 2, 3 or 4, n and p are each zero, l, 2 or 3 where the sum of n + p is not greater than 3 and the sum of the carbon atoms in R3, R4, R5 and R6 is not greater than six, and when both of R3 and R4 or R5 and R6 are alkyl they are methyl or ethyl, where one of R7, R8, R9 is alkyl having from one to four carbon atoms and the remainder are hydrogen or alkyl having from one to four carbon atoms and the sum of the carbon atoms in R7, R8 and R9 is not greater than six, where m and q are the same or different and each have the values previously defined for m, where each of R12 and R13 are methyl or ethyl, or R12 is hydrogen and R13 is alkyl having from one to four carbon atoms, Z is 0 or NH and t is 1 or 2, where w is 1, 2, 3 or 4, R14 and R16 are each alkyl having from one to four carbon atoms, R15 is hydrogen, OH, or alkyl having from one to two carbon atoms, where the sum of the carbon atoms in R14, R15 and R16 is not greater than six and when both of R14 and R15 are alkyl they are methyl or ethyl, and where R17 and R19 are alkyl having from one to four carbon atoms, R18 and R20 are hydrogen or alkyl having from one to two carbon atoms, taken separately, A is OH and B is hydrogen, OH or methyl and when taken together A and B are where the sum of the carbon atoms in R17, R18, R19 and R20 is not greater than six and when both of R17 and R18 or R19 and R20 are alkyl they are methyl or ethyl.

10. A compound according to claim 9 wherein R is a member selected from the group consisting of and where R3, R4, R5, R6, R7, R8, R9, R12, R13, R14, R15, R16, R17, R18, R19, R20, A, B, X, Z, m, n, p, q, t and w are as previously defined.

11. A compound according to claim 9 wherein R is diisopropylcarbinyl, d-methyl-t-butylcarbinyl or di-t-butylcarbinyl.

12. A compound according to claim 10 wherein R is and R17, R18, R19 and R20 are each methyl, A is HO and B is hydorgen, OH or methyl or A and B taken together form or

13. A compound according to claim 10 wherein R is and R15 is OH, R14 and R16 are each methyl and w is 2 or 3.

. -181-

14. A compound according to claim 10 wherein R is

15. A compound according to claim 10 wherein R is wherein R7, R8, R9 are each methyl.

16. A compound according to claim 10 wherein R is

17. A compound according to claim 10 wherein R is and when m is 2: R3-R6 are each methyl, R3, R4, R5 are each hydrogen and R6 is methyl, ethyl, isopropyl or t-butyl, or R3 and R5 are each hydrogen and R4 and R6 are each methyl, and when m is 3: R3 is hydrogen or methyl and R4, R5, R6 are each methyl, R3, R4, R5 are each hydrogen and R6 is isopropyl or t-butyl, R3 and R5 are each hydrogen, R4 is methyl and R6 is methyl, ethyl or isopropyl, or R3 and R4 are each hydrogen and R5 and R6 are each methyl or ethyl.

18. A compound according to claim 10 wherein R is when n is 1 and p is zero: R3-R6 are each methyl and X is O, S or SO2, when n and p are each zero: R3-R6 are each methyl and X is S, SO2 or C=0, when n and p are each 1: R3 and R5 are each hydrogen and R4 and R6 are each metnyl and X is S or SO2.

19. A compound according to claim 9 wherein said compound is L-aspartyl-D-serine N-(2,2,5,5-tetra-methylcyclopentyl)amide, L-aspartyl-D-serine N-(2,2,4,4-tetramethyltetra-hydrothiophene-3-yl)amide, L-aspartyl-D-serine N-(dicyclopropylcarbinyl)amide, L-aspartyl-D-serine N-(2,2,4,4-tetramethylthietan-3-yl)amide, L-aspartyl-D-serine N-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide, L-aspartyl-D-O-methylserine N-(2,2,5,5-tetra-methylcyclopentyl)amide, L-aspartyl-D-O-methylserine N-(2,2,4,4-tetra-methyltetrahydrothiophene-3-yl)amide, L-aspartyl-D-O-methylserine N-(t-butylcyclopropyl-carbinyl)amide, L-aspartyl-D-O-methylserine N-(dicyclopropyl-carbinyl)amide, L-aspartyl-D-O-methylserine N-(2,2,4,4-tetra-methylthietan-3-yl)amide, or L-aspartyl-D-O-methylserine N-(2,2,4,4-tetra-methyl-1,1-dioxothietan-3 yl)amide,

20. A compound according to claim 9 wherein said compound is L-aspartyl-D-serine N-(dicyclopropylcarbinyl)amide, L-aspartyl-D-serine N-(2,2,4,4-tetramethylthietan-3-yl)amide, L-aspartyl-D-serine N-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide, L-aspartyl-D-O-methylserine N-(2,2,4,4-tetra-methylthietan-3-yl)amide, or L-aspartyl-D-O-methylserine N-(2,2,4,4-tetra-methyl-1,l-dioxothietan-3-yl)amide.

21. A compound according to claim 9 wherein said compound is L-aspartyl-D-serine N-(dicyclopropylcarbinyl)amide, L-aspartyl-D-serine N-(2,2,4,4-tetramethylthietan-3-yl)amide, or L-aspartyl-D-serine N-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide.