WO2006063706A1

WO2006063706A1 - Novel process for the manufacture of 3-pyrrolidin-2-yl-propionic acid derivatives

Info

Publication number: WO2006063706A1
Application number: PCT/EP2005/012991
Authority: WO
Inventors: Fritz Bliss; Michel Lalonde; Rudolf Schmid; Rene Trussardi
Original assignee: F. Hoffmann-La Roche Ag
Priority date: 2004-12-13
Filing date: 2005-12-05
Publication date: 2006-06-22
Also published as: CA2589042A1; IL183591A0; MX2007006746A; US20060128970A1; KR20070086128A; EP1828117A1; JP2008523001A; TW200633977A; CN101076515A

Abstract

The present invention relates to the manufacture of the compounds of formula (I) said compounds of formula (I) being valuable intermediates in the manufacture of Dolastatin 10 analogues, which are useful in the treatment of cancer.

Description

NOVEL PROCESS FORTHE MANUFACTURE OP 3-PYRROLIDIN-2-YL-PROPIONIC

ACID DERIVATIVES

The present invention relates to a new process for the manufacture of derivatives of 3-pyrrolidin-2-yl-propionic acid. According to the present invention, said derivatives are obtainable using two different reaction sequences A) and B) which require the same starting material.

The compounds obtainable by the process according to the present invention are valuable intermediates in the manufacture of Dolastatin 10 analogues. Dolastatin 10 is known to be a potent antimitotic peptide, isolated from the marine mollusk Dolabella auricularia, which inhibits tubulin polymerization and is a different chemical class from taxanes and vincas (Curr. Pharm. Des. 1999, 5: 139-162). Preclinical studies of Dolastatin 10 have demonstrated activities against a variety of murine and human tumors in cell cultures and animal models. Dolastatin 10 and two synthetic dolastatin derivatives, Cemadotin and TZT-1027 are described in Drugs of the future 1999, 24(4): 404-409.

Subsequently it had been found that certain Dolastatin 10 derivatives having various thio-groups at the dolaproine part show significantly improved anti-tumor activity and therapeutic index in human cancer xenograft models ( WO 03/008378 ). However the synthesis disclosed in WO 03/008378 suffers from low yields, mainly due to laborious separation of the diastere'oisomer mixtures, obtained in the β-addition reaction ( s. scheme 1, below ), by chromatography. Therefore it remains a need to provide new and improved processes.

The present invention addresses this problem by providing a new, improved process for the manufacture of compounds of the general formula (I), which are key fragments in the synthesis of the above-mentioned Dolastatin 10 derivatives. More precisely, it has now surprisingly been found that the process of the present invention provides an improved diastereoisomer ratio and an improved yield of the compounds of formula (I), which is subsequently retained in the synthesis of said Dolastatin 10 derivatives. Furthermore the process according to the present invention avoids the laborious separation of the diastereoisomer mixtures by chromatography.

In particular the present invention relates to the manufacture of the compounds of formula (I)

(D whereby

A) a compound of formula (II)

(H)

is reacted with a compound of formula (III)

KS-R (HI),

in the presence of triethylammonium chloride in a suitable solvent, whereby said compound of formula (III) is being used as such or can be generated in situ by reacting a compound of formula (IU-A)

(iii-A) in the presence of potassium bases; and

the compounds of formula (I) are obtained by cleavage of R² in the -COOR² ester group, followed by the addition of an amine of the formula NHR⁴R⁵ to the resulting carboxylic acid, to form an ammonium salt of formula (IV)

(IV)

and decomposition of said salt of formula (IV);

or

B) a compound of formula (V)

is reacted with a compound of formula (III), or (III- A) together with a potassium base as described above; and the compounds of formula (I) are obtained from the reaction product by addition of hydrochloric acid to form a compound of formula (VI)

followed by re-protection of the N-atom by reaction with a ferf-butoxycarbonyl- delivering reagent;

and wherein

R¹, R³ and R⁶ independently from each other represent alkyl;

R² is benzyl or substituted benzyl; and

R⁴ and R⁵ are independently selected from cycloalkyl or alkyl, which alkyl can be unsubstituted or substituted one, two or three times with hydroxy, alkoxy, amino, mono- or di-alkylamino, acetoxy, alkylcarbonyloxy, carbamoyloxy, alkoxycarbonyl, carbamoyl, alkylcarbamoyloxy, halogen, cycloalkyl or phenyl.

The compounds of the general formulae (IV) and (VI) are new and a further embodiment of the present invention.

The term "alkyl" as used herein means a straight- chain or branched-chain hydrocarbon group containing a maximum of 8, preferably a maximum of 5, carbon atoms, e.g., methyl, ethyl, n-propyl, 2-methylpropyl (iso-butyl), 1-methylethyl (iso- propyl), n-butyl, 1,1-dimethylethyl ( t-butyl or tøt-butyl ) or t-pentyl, and more preferably a maximum of 4 carbon atoms. The alkyl group maybe unsubstituted or may be substituted with one or more substituents, preferably with one to three substituents, most preferably with one substituent. The substituents are selected from the group consisting of hydroxy, alkoxy, amino, mono- or di-alkylamino, acetoxy, alkylcarbonyloxy, carbamoyloxy, alkoxycarbonyl, carbamoyl, alkylcarbamoyloxy, halogen, cycloalkyl or phenyl.

The term "alkoxy" means -O-alkyl, wherein "alkyl" has the meaning given above.

The term "acetoxy" refers to the group -0-C(O)-CH₃.

The term "cycloalkyl" as used herein means a saturated mono- or bicyclic hydrocarbon group, containing from 3 to 10, preferably from 3 to 7 and more preferably 5 or 6 carbon-atoms. Examples of such cycloalkyls are cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl or decahydro-naphthalene.

The term "carbamoyl" refers to the group -CO-NH₂ and the term "carbamoyloxy" to the group -Q-C(O)-NH. The term "alkylcarbamoyloxy" refers to an alkyl group as defined above attached to a parent structure via a carbymoyloxy radical, such as alkyl-NH-C(O)-O~.

The term "alkylcarbonyloxy" refers to an alkyl group as defined above attached to a parent structure via a carbonyloxy radical, such as alkyl-C(O)-O-.

The term "halogen" refers to fluorine, bromine, iodine and chlorine.

The term "substituted benzyl" as used herein means a benzyl group, wherein the phenyl ring is one, two or three times substituted with a substituent independently selected from methyl, methoxy, phenyl, nitro, halogen or methylene- dioxy. Especially preferred are the following substitution patterns: 2,4,6-trimethyl, 3-methoxy, 4-methoxy, 2,4-dimethoxy, 3,4-dimethoxy, 3,5-dimethoxy, 2-nitro, 4-nitro, 2,4-dinitro, 4-bromo, 4-phenyl and 3,4- methylene- dioxy.

The term "potassium bases" as used herein means basic potassium compounds, which are generally well known to the skilled artisan. Such potassium bases are for example potassium amides, -alkoxides or potassium hydroxide. Especially preferred according to the present invention is the use of potassium ethoxide.

The term "terf-butoxycarbonyl-delivering reagent" as used herein means a reagent for the introduction of the N-Boc group as described below. Such "te/t-butoxycarbonyl- delivering reagents" are well known to the skilled artisan and for example described in "Protective Groups in Organic Synthesis, 3^rd. Edition; Eds. T. W. Greene, P.G.M-Wuts, John Wiley & Sons, Inc., New York (1999); p.518. A preferred "te/t-butoxycarbonyl-delivering reagent" according to the present invention is di~tert-butyl dicarbonate.

The term "suitable solvent" as used herein needs to be differentiated according to the different reaction sequences A) and B) as well as the different reaction steps within each sequence, according to scheme 1 further below. In particular, the following solvents are "suitable" according to the various reaction steps of each sequence:

sequence A)

The β-addition is preferably carried out in ethers, such as tetrahydrofuran, methyl- tetrahydrofuran,

methyl ether, dimethylether, diethylether and at temperatures from -20⁰C to the reflux temperature of the respective solvent, most preferably between O⁰C to room temperature. The ester cleavage is preferably carried out by hydrogenolysis in alcohols such as ethanol, methanol, isopropanol and the like; esters such as ethyl acetate, methyl acetate or isopropyl acetate; hydrocarbons such as toluene; or mixtures of the above solvents. This reaction requires temperatures between 0⁰C to reflux temperature of the respective solvent, preferably from 0⁰C to room temperature, whereby room temperature is most preferred.

The ammonium salt formation preferably takes place in solvents which provide suitable solubilities for compounds of formulae (I), NHR⁴R⁵ and (IV). In this connection ethers such as tert-butyl methyl ether, tetrahydrofuran, methyl-tetrahydrofuran, dimethylether, diethylether;_;alkanes such as hexane, cyclohexene, heptane; or aromatic solvents such as toluene, xylene; or mixtures of all the above-mentioned solvents are especially preferred. The temperature can vary between -20⁰C and 50⁰C, whereby the crystallization preferably occurs at temperatures between room temperature and -20⁰C; most preferred at temperatures between 0⁰C and -20⁰C.

The final decomposition of the isolated salt can take place under basic or acidic conditions. If basic conditions are used, inorganic bases such as alkali-hydroxides,

-hydrogencarbonates or -carbonates are especially preferred. If acidic conditions are used, mineral acids such as hydrochloric acid, sulfuric acid are especially preferred. Said decomposition is carried out in any inert organic solvent immiscible with water, preferably in terf-butyl methyl ether, toluene or ethyl acetate and at temperatures between 0⁰C and room temperature, most preferably at room temperature.

sequence B)

The solvents for the β-addition are as defined above under sequence A).

The reaction -with hydrochloric acid takes place in solvents wherein the compounds of formula (VT) crystallize, preferably in esters, ethers or haloalkanes such as dichloromethane, more preferably in esters such as ethyl acetate; and at temperatures from 50⁰C to -20⁰C, preferably from room temperature to -20⁰C. The crystallization preferably occurs at temperatures between O⁰C and -20⁰C.

The subsequent N-bocylation can be carried out with a ferf-butoxycarbonyl- delivering reagent as defined above. A preferred method for the introduction of the N-Boc group involves the use of di-tert-butyl dicarbonate as reagent in the presence of a base, e.g. an inorganic base such as alkali metal hydroxide, -hydrogencarbonate, -carbonate; or tertiary amine bases such as trialkylamines, e.g. triethylamine. Suitable solvents for this reaction are polar solvents, especially water; alcohols; ethers such as tetrahydrofuran, dioxane and the like; haloalkanes such as dichloromethane; acetonitrile etc. The temperature can range from O⁰C to 50⁰C, whereby room temperature is especially preferred.

An embodiment of the present invention, is the process for the manufacture of the compounds of formula (I)

whereby

the compounds of formula (H-A)

are reacted with a compound of formula (III), or (III-A) together with a potassium base as defined above, in the presence of triethylammonium chloride in tetrahydrofuran; and

the compounds of formula (I) are obtained by benzyl-ester cleavage from the product of said reaction, followed by addition of an amine of the formula NHR⁴R⁵ to the resulting carboxylic acid, and further followed by base addition and subsequent addition of mineral acids; and

R¹, R⁴ and R⁵ have the meanings given herein before.

Another embodiment of the present invention is the process as described above, wherein the amines of formula NHR⁴R⁵ are selected from

dicyclohexylamine, diisopropylamine, (jRj-α-phenylethylamine, benzyl- (R)-a- phenylethylamine and fi^-α-cyclohexylethylamine. Still another embodiment of the present invention, is the process as described above,

whereby the compound of formula (2)

is reacted with S-methyl thioacetate together with potassium ethoxide, in the presence of triethylammonium chloride in tetrahydrofuran; and

the compound of formula (Ia)

is obtained by benzyl-ester cleavage from the product of said reaction, followed by addition of dicyclohexylamine, and further followed by sodium carbonate addition and subsequent addition of sulfuric acid.

Yet another embodiment of the present invention, is the process for the manufacture of the compounds of formula (I)

whereby

a compound of formula (V-A)

is reacted with a compound of formula (III), or (HI-A) together with a potassium base as defined above, in the presence of triethylammonium chloride in tetrahydrofuran, and

the compounds of formula (I) are obtained by further reacting the product of the above reaction with dry hydrochloric acid in ethyl acetate, followed by addition of sodium carbonate and subsequent reaction with di-tert-butyl dicarbonate; and wherein

R¹ is as defined above:

Still another embodiment of the present invention is the process as described above, wherein

a compound of formula (4)

(4)

is reacted with S-methyl thioacetate together with potassium ethoxide, in the presence of triethylammonium chloride in tetrahydrofuran, and

the compound of formula (Ia)

(Ia)

is obtained by further reacting the product of the above reaction with dry hydrochloric acid in ethyl acetate, followed by addition of sodium carbonate and subsequent reaction with di-tert-butyl dicarbonate.

Still another embodiment of the present invention is the process as described above, wherein the compounds of formula (I) are further reacted to give the compounds of formula (A),

wherein

a) the compounds of formula (I) are reacted with an alcohol or an amine, followed by cleavage of the tert-butoxycarbonyl group at the pyrrolidine N-atom, to give the compounds of formula (B)

b) the compounds of formula (B) are further reacted with the compounds of formula (C)

to give the compounds of formula (A); and

R¹ and R³ are as defined herein before;

R⁸ and R⁹ independently from each other represent alkyl; and

R⁷ is phenylalkyl-, or phenyldialkylamino or phenylalkyloxy, having (Ci-C₄)-alkylene and wherein the phenyl group optionally may be substituted with one, two or three substituents selected from the group consisting of halogen, aUkoxycarbonyl, sulfamoyl, alkylcarbonyloxy, carbamoyloxy, cyano, mono- or di-alkylamino, alkyl, alkoxy, phenyl, phenoxy, trifluoromethyl, trifluoromethoxy, alkylthio, hydroxy, alkylcarbonylamino, 1,3- dioxolyl, 1,4-dioxolyl, amino and benzyl.

If desired, the compounds of formula (A) can also be turned into their pharmaceutically acceptable salts as described in WO 03/008378 or using other methods well known to the skilled artisan.

Still another embodiment of the present invention is the process as described above for the manufacture of the compound of formula (A-I)

wherein

a) the compound of formula (Ia)

(Ia)

is reacted with 3- (2-methylamino-ethyl) -phenol, followed by cleavage of the tert- butoxycarbonyl group at the pyrrolidine N-atom, to give the compound of formula (B-I)

b) the compound of formula (B-I) is further reacted with the compound of formula (C-I)

to give the compound of formula (A-I).

Yet another embodiment of the present invention is the use of the process according to the present invention in the manufacture of the compounds of formula (A) as defined above. Yet another embodiment of the present invention is the use of the process according to the present invention in the manufacture of the compound of formula (A-I) as defined above.

In another embodiment of the present invention, there are provided the compounds of formula (IV)

wherein

R¹ and R³ independently from each other represent alkyl; and

R⁴ and R⁵ independently represent cycloalkyl or alkyl, which alkyl can be unsubstituted, or substituted one, two or three times with hydroxy, alkoxy, amino, mono- or di-alkylamino, acetoxy, alkylcarbonyloxy, carbamoyloxy, alkoxycarbonyl, carbamoyl, alkylcarbamoyloxy, halogen, cycloalkyl or phenyl.

In yet another embodiment of the present invention, there are provided the compounds as defined above, wherein

R¹ and R³ are methyl; and

the group ⁺NH₂R⁴R⁵ represents a cation selected from dicyclohexylammonium, diisopropylammonium, (X)-α-phenylethylammonium, benzγl-(R)-a- phenylethylammonium or (X)-α-cyclohexylethylammonium. In still another embodiment of the present invention, there are provided the compounds of formula (Vl),

wherein

R¹ and R³ independently from each other represent alkyl.

In still another embodiment of the present invention, there are provided the compounds as described above, wherein

R¹ and R³ are methyl.

Yet another embodiment of the present invention is the compound

(5)-2-((liR,2S)-2-Carboxy-l-methylsulfanyl-propyl)-pyrrolidine-l-carboxylic acid t erf-butyl ester (Ia).

Consequently, a further embodiment of the present invention is the use of a compound of the formulae (IV), (VI) or (Ia) as defined above in a process as described herein before.

Still another embodiment of the present invention is the use of a compound of the formulae (IV), (Vl) or (Ia) as defined above in the manufacture of the compounds of formula (A) as defined herein before

Still another embodiment of the present invention is the use of a compound of the formula (IV), wherein R¹ and R³ are methyl, or formula (Ia) as defined above in the manufacture of the compound of formula (A-I) as defined herein before. The process of the present invention can be performed according to the following general reaction scheme ( scheme 1 ), wherein unless explicitly otherwise stated R¹, R³, R⁴ and R⁵ have the significances given herein before. R¹⁰ is benzyl, substituted benzyl or alkyl, preferably benzyl or tert-butγl.

"

Boc-L-prolinal

2 minor dia- stereoisomers

(VIIIc ₁ VIIId) -I

(Villa) (VIIIb)

sequence A)

(I) scheme 1 Step 1: This step represents a Wittig reaction starting from commercially available tert-butoxycarbonyl protected L-prolinal ( Boc-L-prolinal ) with the ylide (VΙI)and using methods known to the skilled artisan ( see e.g. Heterocycles, 36 (9), 1993, 2073-2080 and WO 03/008378 ). Said ylide wherein R¹ is methyl and R¹⁰ is benzyl can be obtained according to the synthesis described in "Y. Ito, M. Okano, R.Oda, Tetrahedron, 23, 1967, 2137."

Said ylide wherein R¹ is methyl and R¹⁰ is tert-bntγl can be obtained according to the synthesis described in "Y. Guindon, L. Murtagh, V. Caron, S.R. Landry, G. Jung, M. Bencheqroun, A.-M. Faucher, B. Guerin, /. Org. Chem., 66, 2001, 5427" or "P.L. Stotter, K.A. Hill, Tetrahedron Lett., 16, 1975, 1679." \

Step 2: This reaction is a β-addition of alkyl-mercaptanes, especially methyl mercaptane, wherein the potassium salts of formula (III) can be used as such, or generated in situ by adding the compounds of formula (III- A) in the presence of potassium bases, especially potassium ethoxide. According to the present invention, improvement of diastereoselectivity in this addition reaction is achieved by using triethylammonium chloride ( Et₃N x HCl ) as the proton source, compared to other common proton sources tested (see Table 1).

Table 1: Diastereoselectivity of β-Addition: Influence of Proton Source

a) Ratio determined by GC analysis.

b) Methyl mercaptan (6 equiv.) used instead of S-methyl thioacetate ( IH-A, scheme 1 ), no additional proton source.

c) Methyl mercaptan (3 equiv.) used instead of S-methyl thioacetate ( III-A, scheme 1 ); Et₃N x HCl (1.0 equiv.) as additional proton source. With respect to reaction sequence A), the crude ester (mixture of VIII a, b, c and d, scheme 1 with R¹⁰ being benzyl or substituted benzyl) is now hydrogenolyzed, preferably in the presence of 20% Pd-C (30% w/w) in ethanol. According to the present invention, further treatment with the amines mentioned herein before, especially dicyclohexylamine in tert-butyl methyl ether, furnish the respective ammonium salts in good diastereoisomeric purities and high yields.

With respect to reaction sequence B) the crude ester (mixture of VIII a, b, c and d, scheme 1 with R¹⁰ being alkyl, preferably tert-butyl) can also be treated with dry hydrochloric acid in ethyl acetate at room temperature. The hydrochloride of the desired diastereoisomer precipitates directly from the reaction mixture in high diastereoisomeric purity and yield.

Step 4: The compounds of formula (I) can finally be obtained by standard decomposition methods of the salts obtained from step 3a) or by N-bocylation of the salts obtained from step 3b). Such decomposition and bocylation methods are well known to the skilled artisan.

The salts of formula (IV), as obtained from step 3 of reaction sequence A) can be decomposed in the presence of an inorganic base, such as for example but not limited to an alkali metal hydroxide, -hydrogencarbonate or -carbonate, preferably in the presence of sodium carbonate; followed by removal of the amine base by extraction with an organic solvent; followed by addition of a mineral acid, preferably sulfuric acid, to the remaining aqueous phase and extraction of the compounds of formula (I) into an organic solvent. Alternatively said decomposition can be achieved by direct addition of said mineral acid to the reaction mixture containing the compounds of formula (IV), followed by extraction of the compounds of formula (I) into an organic solvent.

The salts of formula (VI), as obtained from step 3 of reaction sequence B) can be further N-bocylated using methods well known to the skilled artisan, preferably in the presence of an inorganic base, such as for example but not limited to an alkali metal hydroxide or -carbonate, more preferably in the presence of sodium carbonate, followed by further reaction with di-tert -butyl dicarbonate; or alternatively with di- tert-butyl dicarbonate in dichloromethane and in the presence of amine bases such as triethylamine. Subsequently to each of the aforementioned procedures the compounds of formula (I) can finally be obtained and/or purified by crystallization from organic solvents, preferably from hexane or heptane.

The following examples are provided to aid the understanding of the present invention. It is understood that modifications can be made without departing from the spirit of the invention.

If not explicitly otherwise stated, the following abbreviations are used:

min minute(s)

h hour(s)

rt room temperature

NMR nuclear magnetic resonance

GC gas chromatography

TLC thin layer chromatography

HPLC high performance liquid chromatography

dr distereosiomer ratio

er enantiomer ratio

ee enantiomeric excess

mp melting point

Reaction Sequence A)

Example 1

Synthesis of (S)-2-(2-Benzyloxycarbonyl-proρenyl)-pyrrolidine-l-carboxylic acid tert- butyl ester (2) (Synthesis with Preformed Wittig Ylide)

a) The Wittigγlide (benzyl 2-(triphenylphosphoranylidene)propionate) can be obtained according to the synthesis disclosed in "Y. Ito, M. Okano, R. Oda, Tetrahedron, 23, 1967, 2137".

b) To a solution of 135.7 g benzyl 2-(triphenylphosphoranylidene)propionate (320 mmol) in 440 ml tet-butyl methyl ether was added at rt a solution of 45.5 g Boc-L-prolinal (228.4 mmol) in 62 ml tert-butyl methyl ether. The yellow solution was heated under reflux for 1.5 h upon which a white precipitate of triphenylphosphine oxide formed. From the suspension 230 ml of tert-butyl methyl ether solvent were removed by distillation using a Dean-Stark trap. Then 360 ml heptane were added drop by drop at reflux temperature to further promote the triphenylphosphine oxide precipitation. The suspension was cooled to rt, stirred at rt overnight, then cooled to 0-5⁰C and stirred at this temperature for 30 min. The suspension was filtered over a pre-cooled (0-5⁰C) G3 glass filter funnel and the filter cake washed portion-wise with 250 ml pre-cooled (0-5⁰C) heptane. The yellow filtrate and the wash solution were combined and evaporated (40⁰C/ 10 mbar) to provide 86.8 g of yellow oil as the crude product. GC: 4.67% Z-2, 91.55% £-2, 3.78% triphenylphosphine oxide; E/Z = 95.15 : 4.85. Of this material 86.6 g were filtered over 434 g silica gel using ca. 3 1 hexane/ethyl acetate (2:1) as the eluent to provide, after evaporation and dηάng in vacuo, 81.38 g (103% w/w) of the title compound (2) as light yellow oil. The material by GC analysis contained 4.59% Z-2, 90.58% E-2, and 1.12% triphenylphosphine oxide; E/Z = 95.2 : 4.8. The material by chiral HPLC analysis contained 4.19% Z-2, 0.31% ent-E-2, and 95.50% E-2; er = 99.7 : 0.3; E/Z = 95.7 : 4.3. ¹H-NMR: (400 MHz, CDCl₃): 7.4-7.3 (m, 5 arom. H); 6.65 (br. d, J = 7, vinyl. H of (E)-2); 5.9-5.8 (br., vinyl. H of (Z)-2); 5.3-5.1 (br. m, PhCH₂O); 4.7-4.4 (br. m, 1 H); 3.6-3.35 (br. m, 2 H); 2.13 (m, 1 H); 2.0-1.3 [m, in total 15 H, with 1.43 (br. s, tBu)].

Example 2

Synthesis of (S)-2-(2-Benzyloxycarbonyl-proρenyl)-pyrrolidine-l-carboxylic acid tert- butyl ester (2); (Synthesis with in situ Formation of Wittig Ylide)

A solution of 378 g (l-benzyloxycarbonyl-ethyO-triphenylphosphonium bromide (82.9%, 619.9 mmol) in 1.451 dichloromethane was azeotropically distilled while keeping the volume constant by addition of 1.20 1 dichloromethane. To the solution was added slowly at an internal temperature of 10-12.5⁰C a solution of 71.0 g potassium tøt-butoxide (98%, 620 mmol) in 640 ml tetrahydrofuran. The yellowish turbid solution was allowed to attain rt and stirred at rt for 75 min. Then, a solution of 127.4 g Boc-L-prolinal (97%, 620.3 mmol) in 640 ml tetrahydrofuran was added, whereby the reaction temperature rose to 25 ⁰C. The yellow solution was heated under reflux for 18 h upon which a white precipitate of triphenylphosphine oxide formed. The tetrahydrofuran/dichloromethane solvent mixture was exchanged for 3.6 1 heptane. The suspension was then cooled to 0⁰C, stirred at 0⁰C for 1 h, and the triphenylphosphine oxide was filtered and washed with 1 1 heptane (pre- cooled at 0⁰C). The combined yellow filtrate and wash solution were washed with 2 x 2.5 1, a total of 5 1 water and evaporated (40°C/100 mbar) to provide as crude product 233.9 g of the title compound (2) as yellow oil. This material by HPLC analysis contained 89.6% E-2 and 5.4% Z-2; E/Z = 94.3 : 5.7. The material by chiral HPLC analysis contained 5.5% Z-2, 0.0% βnt-E-2, and 94.50% E-2; er = 100 : 0; E/Z = 94.5 : 5.5. Example 3

Synthesis of (S)-2- (( 2i?,2S)-2-Benzyloxycarbonyl- 1 ~methylsulfanyl-propyl)-pyrrolidine- 1-carboxylic acid tørt-butyl'ester (3a) in mixture with (S)-2-((lR,2R)-2- Benzyloxycarbonyl-l-methylsulfanyl-propy^-pyrrolidine-l-carboxylic acid tert-butyl ester (3b) and two further diastereoisomers of (S)-2-(2-Benzyloxycarbonyl-l- methylsulfanyl-propyl)-pyrrolidine-l-carboxylic acid tert-butyl ester of partially undetermined configuration (3c and 3d)

¬

S-methyl thioacetate (64.09 g , 703 mmol) was dissolved under argon with stirring in 700 ml tetrahydrofuran. To the clear colorless solution potassium ethoxide (59.16 g, 703 mmol) was added as solid with the aid of a glass funnel and the funnel was rinsed with 100 ml tetrahydrofuran. The temperature of the yellow-orange suspension rose to 41°C then returned to rt within 30 min. The suspension was stirred at rt for 2.75 h. After a total reaction time of 3.25 h, 48.39 g triethylamine hydrochloride (351.5 mmol) were added at once followed by dropwise addition of a solution of 80.97 g (S)~2-(2-benzyloxycarbonyl- propenyl) -pyrrolidine- 1-carboxylic acid tert-butyl ester (2, from example 1) in 344 ml tetrahydrofuran. The yellow-orange suspension was stirred at rt for 5 h. For work-up 344 ml ethyl acetate and 690 ml 5M ammonium chloride solution were added at rt to the reaction mixture. The two phase system was stirred at rt for 2 min, and then transferred into a separatory funnel. The phases were separated, and the organic phase was dried over sodium sulfate, filtered and evaporated (40°C/10 mbar) to yield 93.91 g of the crude product as yellow oil. Subsequently, 93.0 g of the crude product were subjected to filtration over 465 g silica gel with ca. 21 heptane/ ethyl acetate 1:1 mixture. Evaporation and drying in vacuo afforded 91.8 g of the title compound (3) as clear yellow oil. This material by GC analysis contained 1.2% (E)-2, 84.1% 3a, 1.4% 3c, 1.5% 3d and 8.7% 3b; dr 3a/3b/3c/3d = 87.8 : 9.1 : 1.5 : 1.6. ¹H-NMR (400 MHz, CDCl₃): 7.45-7.25 (m, 5 arom. H); 5.3-5.05 (br. m, PhCH₂O); 4.2-3.8 (br. m, 1 H); 3.75-3.15 (br. m, 3 H); 2.6 (br. m, 1 H); 2.07 (s, SCH₃); 1.9 (m, 3 H); 1.7 (m, 1 H); 1.46 and 1.43 (2 s, tBu, of 2 rotamers); 1.34 (d, J = 6.5, CH₃).

Example 4:

Synthesis of (S)-2-((2jR,25)-2-Carboxy-l-methylsulfanyl-propyl)-pyτrolidine-l-carboxylic acid t erf-butyl ester (Ia)

1a x Cy₂NH 1a

a) Synthesis of (S)-2-((2i?,2S)-2-Carboxy-l-methylsulfanyl-propyl)-pyrrolidine-l- carboxylic acid terf-butyl ester (Ia) in mixture with (5)-2-((2i?,2i?)-2-Carboxy-l- methylsulfanyl-propyl)-pyrrolidine-l-carboxylic acid terf-butyl ester (Ib) and two further diastereoisomers of (5)-2-(2-Carboxy-l-methylsulfanyl-propyl)-pyrrolidine-l-carboxylic acid fert-butyl ester of partially undetermined configuration (Ic and Id)

91.8 g (S)-2-(2-Benzyloxycarbonyl-l-methylsulfanyl-propyl)-pyrrolidine-l-carboxylic acid text -butyl ester (3, diastereoisomer mixture, see example 3; derived from 224.5 mmol Boc-L-prolinal) were dissolved under argon in an Erlenmeyer flask in 920 ml ethanol and treated with 46.0 g Raney-Ni. The suspension was stirred at rt for 1 h, then filtered and the filter cake was thoroughly Washed with 360 ml ethanol. The combined filtrate and wash solutions were divided in two parts of roughly equal volume (ca. 640 ml) which were hydrogenated separately over 13.75 g, a total of 27.5 g 20% Pd on charcoal with hydrogen at 10 bar pressure and at 30⁰C for 18 h. The hydrogen uptake was 2.741 and 2.41 1 (theor. 2 x 2.82 1). The black suspensions of the two runs were filtered and the filter cakes were washed each with 300 ml, a total of 600 ml ethanol. The filtrates and wash solutions of both runs were combined and the solution was divided in two parts of exactly equal volumes. One part was evaporated (40 ⁰C/ 10 mbar/4 h) to provide, after drying in vacuo, 33.85 g of light yellow oil. The other part was concentrated to a volume of ca 150 ml, filtered to remove some traces of charcoal, and then evaporated to provide, after drying in vacuo, 33.13 g of light yellow oil. Combined yield 66.98 g of crude acid 1 (diastereoisomer mixture). This material by GC analysis contained 84.4% Ia, 1.4% Ic, 8.8% Ib and 1.65% Id; dr la/lb/lc/ld = 87.7 : 9.2 : 1.5 : 1.6. Assays of 78.1% Ia and of 7.1% Ib were determined by HPLC with internal standard.

¹H-NMR (300 MHz, CDCl₃): ca. 10 (br. s, COOH); 4.15-3.95 (br. m, 1 H); 3.65-3.1 (br. m, 3 H); 2.6 (br. m, 1 H); 2.12 (s, SCH₃); 2.0-1.65 (m, 4 H); 1.46 and 1.43 (2 s, tBu of 2 rotamers), 1.39 (d, J = 6.5, CH₃).

b) Formation of (S)-2-((2J?,25)-2-Carboxy-l-methylsulfanyl-propyl)-pyrrolidine-l- carboxylic acid tert-butyl ester; compound with dicydohexylamine (Ia x Cy₂NH)

A quantity of 33.5 g crude acid [1, diastereoisomer mixture from a), derived from 112.3 mmol Boc-L-prolinal] was dissolved in 170 ml tert-butyl methyl ether. The solution was filtered to remove some residual solid (charcoal), and then treated with 23.73 ml dicydohexylamine (119 mmol). The solution was cooled to 0-5⁰C under stirring whereby a white solid started to precipitate at ca. 8°C. The suspension was stirred at 0-5⁰C for 3 h. The solid was collected by nitration over a pre-cooled glass filter funnel, washed with 100 ml pre-cooled (0-5⁰C) tert-butyl methyl ether and dried (4O⁰C/ 10 mbar/4 h) to furnish 38.55 g (70.8%, based on Boc-L-prolinal) of the title compound (Ia x Cy₂NH) as white powder; m.p. 141-142°C; [α]o²⁰ -20.56 (c 1.04, ethanol). The composition of this material as derived from GC analysis was 44.6% Cy₂NH, 54.1% Ia, 0.33% Ic, 0.69% Ib and 0.13% Id; dr la/lb/lc/ld = 97.9 : 1.25 : 0.6 : 0.25. An assay of 61% Ia (theor. 62.6%) was determined by HPLC with internal standard. Chiral HPLC analysis showed Ia to be enantiomerically pure (ent-la not detectable).

¹H-NMR (CDCl₃, 400 MHz): 8.55 (br. s, NH₂ ⁺); 4.2-4.0 (br. m, 1 H); 3.75-3.2 (br. m, 3 H); 2.S7 (m, 1 H); 2.27 (m, .l H); 2.2-1.1 [m, total 39 H, with 2.12 (s, SCH₃), 1.48 and 1.44, (2 s, tBu of 2 rotamers)]. ..

c) Isolation and Crystallization of (S)-2-(Ji?,2S)-2-Carboxy-l-methylsulfanyl-propyl)- pyrrolidine-1-carboxylic acid tert-butyl ester (Ia)

A quantity of 38.5 g lax Cy₂NH (derived from 112.1 mmol Boc-L-prolinal) was treated with 160 ml tert-butyl methyl ether and 160 ml IM sodium carbonate solution. The organic phase was separated and extracted with 160 ml IM sodium carbonate solution. The combined aqueous phases were acidified to pH 2 by addition of 175 ml 2M sulfuric acid and the resulting mixture was extracted 3 times with 175 ml, a total of 525 ml tert- butyl methyl ether. The combined extracts were dried over ca. 90 g sodium sulfate_, filtered and evaporated (40°C/10 mbar/ 0.5 h) to provide 24.16 g of crude acid Ia as colorless viscous oil. Assays of 95.2% Ia and of 1.2% Ib were determined by HPLC with internal standard. The crude acid Ia was dissolved at rt in 120 ml hexane and the solution stirred at -20⁰C for 16 h. The white precipitate was filtered over a pre-cooled (-20⁰C) glass filter funnel, washed portion-wise with 60 ml hexane (pre-cooled at -20⁰C) and dried (40°C/10 mbar/2 h) to furnish 19.94 g (58.5 % based on Boc-L-prolinal) of the title compound (Ia) as white crystals; m.p. 64.5-66°C. The material by GC analysis contained 97.9% Ia, 0.53% Ic, 0.98% Ib and 0.13% Id; dr la/lb/lc/ld = 98.4 : 1.0 : 0.5 : 0.1. Chiral HPLC analysis showed Ia to be enantiomerically pure (βnt-la not detectable).

¹H-NMR (400 MHz, CDCl₃): 4.15-3.95 (br. m, 1 H); 3.65-3.15 (br. m, 3 H); 2.6 (br. m, 1 H); 2.12 (s, SCH₃); 1.94 (br! m, 3 H); 1.75 (m, 1 H); 1.47 and 1.45 (2 s, tBu of 2 rotamers), 1.39 (d, J = 6.5, CH₃).

Example 5

(S)-2-((li?,2S)-2-Carboxy-l-methylsulfanyl-propyl)-pyrrolidine-l-carboxylic acid fert- butyl ester; compound with (R)-l-phenyl-ethylamine (Ia x (PhEt)NH₂)

Analogously to the salt formation described in example 4b) the (-R)-l-phenylethyl- ammonium salt was obtained:

A quantity of 30.34 g of the crude acid 1 [diastereoisomer mixture, dr la/lb/lc/ld = 87.7 : 9.2 : 1.5 : 1.6, see example 4a), derived from 101.7 mmol Boc-L-prolinal] was dissolved in 166.9 ml heptane, resulting in a slightly turbid, greenish solution. Then 12.98 g (105 mmol) (β)-(+)-l-pheriyl-ethylarnine were injected in one portion from a syringe resulting in a temperature increase from 25 to 35°C. The reaction mixture was stirred overnight ( 16 h) at rt. The precipitated crystals were separated by filtration, washed with heptane and dried in vacuo at rt, yielding 31.43 g of the crude (R)-I- phenylethylammonium salt of Ia. The crude product was purified by recrystallization from diisopropyl ether leading to 27.4 g (63% based on Boc-L-prolinal) white crystals; m.p. 99-100⁰C. The material contained, as derived from GC analysis, 97.7 % Ia, 0.9 % Ib, and 0.2 and 0.1 % of the minor diastereoisomers Ic and Id. A sample for analysis was obtained by further recrystallization, white crystals; m.p. 103-104⁰C; [α]_D ²⁰ -22.4 (c 1.04, ethanol).

¹H-NMR: (300 MHz, CDCl₃): 7.5-7.2 (m, NH₃ ⁺ and 5 arom. H); 4.33 (q, J = 6.8, PhCH(Me)); 3.97 (br. m, IH); 3.50 (br. t, J = 8, 1 H); 3.24 (m, 2 H); 2.45-1.15 [m, in total 23 H with 2.03 (s, SCH₃), 1.58 (d, J = 6.8, PHCH-CH₃1, 1-34 (s, tBu), 1.20 (d, J = 6.5, CH₃CH-COO^")].

The isolation and crystallization of Ia can be carried out analogously to the description given in example 4c).

Example 6

(5)-2- ( ( 1R,2S) -2-Carboxy- 1 -methylsulfanyl-propyl)-pyrrolidine- 1 -carboxylic acid tert- butyl ester; compound with diisopropyl-amine (Ia x (1Pr)₂NH)

Analogously to the salt formation described in examples 4b) or 5 the diisopropyl- ammonium salt was obtained:

A quantity of 1.10 g of the crude acid 1 [diastereoisomer mixture with assays of 69.9% Ia and 8.0% Ib as determined by HPLC with internal standard; cf. example 4a)] and 370 mg (3.62 mmol) of diisopropylamine were dissolved at 6O⁰C in 10 ml cyclohexane. The hot solution was allowed to cool to rt overnight while stirring. The precipitated white crystals were collected by filtration, washed with cyclohexane and dried at rt in vacuo to yield 700 mg (68.5%) of the diisopropyl ammonium salt of Ia as white crystals; m.p. 125-128 ⁰C; [α]_D ²⁰ -26.9 (c 1.98, ethanol).

¹H-NMR: (300 MHz, CDCl₃): 8.42 (br. s, NH₂ ⁺); 4.1 (br. s, 1 H); 3.7-3.3 (br. m, 3 H); 3.24 (septet, J = 6.5, 2 CHMe₂); 2.25 (m, 1 H); 2.15-1.2 [m, in total 31 H, with 2.11 (s, SCH₃), 1.46 and 1.44 (2 s, tBu of 2 rotamers), 1.26 (d, J = 6.5, 2 CH(CHO₂I.

Example 7

(S)-2- ( ( ii?,25)-2-Carboxy- 1 -methylsulfanyl-propyl)-pyrrolidine- 1 -carboxylic acid tert- butyl ester; compound with (i?)-l-cyclohexyl-ethylamine (la x (CyEt)NH₂)

and

(5)-2-((li?,25)-2-Carboxy-l-methylsulfanyl-ρropyl)-pyrrolidine-l-carboxylic acid tert- butyl ester; compound with benzyl-((R)-l-phenyl-ethyl)-amine (Ia x (Bn)(PhEt)NH)

Analogously to the salt formation described in examples 4b), 5 and 6 the respective (.R)-I- cyclohexyl-ethylammonium salt or benzyl-((£)-l-phenyl-ethyl)-ammonium salt can be obtained. These salts were obtained as reference examples by adding the respective amine to the pure acid (Ia), which was dissolved under argon in a mixture of fert-butyl methyl ether and heptane (1:1). Stirring for 18 h at rt yields the crystalline ammonium salt which is separated by filtration, washed with heptane and dried in vacuo for about 4 h.

a) The respective (#)~l-cydohexyl-ethylammonium salt is obtained as white crystals with a melting point of 132-133 ⁰C; [α]_D ²° -23.2 (c 1.06, ethanol).

¹H-NMR: (300 MHz, CDCl₃): 7.29 (br. s, NH₃ ⁺); 4.0 (br. m, 1 H); 3.55 (br. t, J = 8, 1

H); 3.4-3.2 (m, 2 H); 3.06 (qui, J = 6, 1 H); 2.4-1.0 [m, in total 42 H with 2.09 (s, SCH₃), 1.43 (s, tBu), 1.35 (d, J = 7, 1 CH₃), 1.27 (d, J = 7, 1 CH₃)].

b) The respective benzyl-((#)-l-phenyl-ethyl)-ammonium salt is obtained as white crystals with a melting point of 71-73 ⁰C; [α]_D ²⁰ -5.1 (c 1.09, ethanol).

¹H-NMR: (300 MHz, CDCl₃): 7.4-7.2 (m, 10 arom. H); 6.97 (br. s, NH₂ ⁺); 3.99 (q, J = 5.5, 1 H); 3.90 (q, J = 7, 1 H); 3.75 and 3.65 (AB, J = 13; PhCH₂-); 3.65-3.15 (br m, 3 H); 2.47 (m, 1 H); 2.11 (s, SCH₃); 2.0-1.25 [m, in total 19 H, with 1.46 (s, tBu), 1.36 (d, J = 7, I CH₃)] .

The isolation and crystallization of Ia can be carried out analogously to the description given in example 4c). Reaction sequence B)

Example 8

Synthesis of (S)-2-(2-fert-Butoxycarbonyl-propenyl)-pyrrolidine-l-carboxylic acid tert- butyl ester (4) (Synthesis with preformed Wittig Ylide)

a) The WϊrtzgYlide ((2-triphenylphosphoranylidene)-propionic acid tert-buty\ ester) can be obtained according to the synthesis described in "Y. Guindon, L. Murtagh, V. Caron, S.R. Landry, G. Jung, M. Bencheqroun, A.-M. Faucher, B. Guerin, /. Org. Chem., 66, 2001, 5427" or

"P.L Stotter, K.A. Hill, Tetrahedron Lett., 16, 1975, 1679."

b) A quantity of 56.0 g (2-triphenylphosphoranylidene)-propionic acid tøt-butyl ester (143.4 mmol) was suspended under argon and with stirring in 160 ml tert-butyl methyl ether. A solution of 21.0 g Boc-L-prolinal (105.4 mmol) in 50 ml tot-butyl methyl ether was added drop by drop. The yellowish suspension was stirred at 50⁰C for 3.5 h. After complete conversion, the suspension was transferred with dichloromethane into a 1 1 round bottomed flask. The solvent was removed by evaporation and final drying in vacuo (0.1 mbar/rt/15 min). The residue was taken up in 400 ml heptane, the resulting yellowish suspension stirred at rt for 30 min and the white precipitate of triphenylphosphine oxide removed by filtration over ca. 20 g decalite speed plus (diatomaceous filter-aid). The filter residue was washed 3 times with 50 ml, a total of 150 ml heptane and the combined filtrate and wash solutions were evaporated. The residue was dried (0.1 mbar/rt/2 h) to afford 34.4 g of the crude product. The material by GC analysis contained 5.5% (Z)-4, 91.7% (E)-4 and 1.8% triphenylphosphine. The crude product was dissolved in ca. 20 ml hexane/ ethyl acetate (9:1 mixture) and flash-filtered over 150 g silica gel using a pressure of ca. 0.5 bar. The product was eluted with ca. 2 1 hexane/ ethyl acetate 9:1 mixture. Evaporation afforded as the filtered product 32.4 g (98.7% based on Boc-L-prolinal) of the title compound (4) as a light yellowish oil. The material by GC analysis contained 5.6% (Z)-4, 92.8% (E)-4 and 1.4% triphenylphosphine; E/Z = 94:6. The material by chiral HPLC analysis contained 0.05% CR,£)-4 and 99.95% (S,£)-4; ee = 99.9%.

¹H-NMR: (300 MHz, CDCl₃): 6.5 (br. d, J = 7, vinyl. H of (£)-4); 5.75 and 5.95 (2 br. s, vinyl. H of 2 rotamers of (Z)A); 4.65-4.35 (br. m, 1 H); 3.6-3.35 (br. m, 2 H); 2.15 (m, IH); 2.0-1.3 (m, in total 24 H, with 1.48 (s, tBu), 1.41 (br. s, tBu)].

Example 9

Synthesis of (S)-2-((l.R₎2S)-2-iterf-Butoxycarbonyl -l-methylsulfanyl-propyl)-pyrrolidine- 1-carboxylic acid tert-butyl ester (5a) in mixture with (S)-2-((lR,2R)-2- tert- Butoxycarbonyl-l-methylsulfanyl-propy^-pyrrolidine-l-carboxylic acid tert-butyl ester (5b) and two further diastereoisomers of (S)-2-(2-tert-Butoxycarbonyl- 1-methylsulfanyl- propyl) -pyrrolidine- 1-carboxylic acid tert-butyl ester of partially undetermined configuration (5c and 5d)

-

54.6 g S-methyl thioacetatei ( 606 mmol ) were dissolved under argon with stirring in 310 ml tetrahydrofuran. To the clear colorless solution 50.4 g potassium ethoxide (599 mmol) were added at once as a yellow solid with the aid of a glass funnel. The funnel was rinsed with 50 ml tetrahydrofuran; The suspension was stirred at rt for an additional 4 h. After a total reaction time of 5 h, 41.3 g triethylamine hydrochloride were added at once followed by dropwise addition of a solution of 31.1 g (S)-2-(2-te7t-butoxycarbonyl~propenyl)- pyrrolidine-1-carboxylic acid terf-butyl ester (100 mmol, see example S) in 160 ml tetrahydrofuran. The yellow suspension was stirred at rt for 22 h. After 22 h, 120 ml ethyl acetate and 350 ml 5M ammonium chloride solution were added to the reaction mixture. The two phase-system was stirred at rt for 10 min, then transferred into a separatory funnel and the phases were separated. The aqueous phase was extracted with 100 ml ethyl acetate. The combined organic phases were dried over ca. 40 g sodium sulfate, filtered and evaporated to yield 37.7 g of the crude product. The material by GC analysis contained 1.3% (Z)-4, 3.3% (_5)-4, 81.8% 5a, 2.0% 5c and 9.5% of the co-eluting 5b and 5d. The crude product was dissolved in 20 ml hexane/ ethyl acetate (9:1 mixture) and flash-filtered over 100 g silica gel using a pressure of ca. 0.5 bar. The product was eluted with ca. 2 1 hexane/ ethyl acetate 9:1 mixture. Evaporation and drying (0.1 mbar/rt/2 h) afforded as the filtered product 35.5 g of the title product 5 (99% based on Boc-L-prolinal) as a clear yellow oil. This material consisted by GC analysis of 1.3% (Z)-4, 2.6% (E) Λ, 82.5% 5a, 2.2% 5c, 7.5% 5b and 2.2%.5d; dr 5a/5b/5c/5d = 87.4. 8.0 : 2.3 : 2.3.

¹H-NMR: (300 MHz, CDCl₃): 4.2-3.1 (br. m, 4 H); 2.45 (m, 1 H); 2.3-1.15 (m, in total 28 H, with 2.11 (s, SCH₃), 1.48 and 1.46 (2 s, tBu of 2 rotamers), 1.29 (br. d, J = 6.5, CH₃)].

Example 10

Synthesis of (5)-2-(( Jl?,2S)-2-Carboxy-l-methylsulfanyl-propyl)-pyrrolidinium chloride (6a x HCl)

A quantity of 33.5 g (S)-2-(2-terf-butoxycarbonyl-l-methylsulfanyl-propyl)-pyrrolidine-l- carboxylic acid tert-butyl ester (5, 93.3 mmol, from example 9; diastereoisomer mixture, 5a/5b/5c/5d = 87.4 : 8.0 : 2.3 : 2.3) was dissolved under argon with stirring in 185 ml of a 4.44M solution of dry hydrochloric acid in ethyl acetate (821 mmol). The solution was stirred at rt for 30 min, then seed crystals were added whereby crystallization started. The suspension was stirred at rt for 2 h and at 0⁰C for 2 h. The precipitate was isolated by filtration, washed two times with 10 ml, a total of 20 ml cold ethyl acetate (0⁰C ) and dried in vacuo (0.1 mbar) at rt for about 18 h to afford 15.5 g (69% based on 5) of the title compound (lax HCl) as white crystals; m.p. 169-170⁰C. ¹H-NMR (300 MHz, d₆-DMSO): 12.5 (br. s, COOH); 9.9 and 8.9 (2 br. s, NH₂ ⁺); 3.57 (q, J = 6.7, 1 H); 3.34 (dxd, J = 9 and 4.5, 1 H); 3.21 (m, 2 H); 2.86 (m, 1 H); 2.25 (m, 1 H); 2.19; (s, SCH₃); 2.0-1.65 (m, 3 H); 1.15 (d, J = 6.9, CH₃).

Example 11

Synthesis of (S)-2-(Ii?,2S)-2-Carboxy-l-methylsxdfanyl-propyl)-pyrrolidine-l-carboxylic acid tert-butyl ester (Ia)

A quantity of 15.2 g (S)-2-((Ji?,2S)-2-carboxy-l-methylsulfanyl-propyl)-pyτrolidinium chloride (6a x HCl, 63.4 mmol, from example 10) was suspended under argon with stirring in 280 ml dioxane. A solution of 9.4 g sodium carbonate (89 mmol ) in 205 ml deionized water was added. Upon addition of approximately half of the volume, a clear solution formed which after completion of the addition turned into a milky solution. Then 17.3 g di-fert-butyl dicarbonate (79.3 mmol) were added and the slightly turbid solution was stirred at rt for 5.5 h. For 'work-up 100 ml førf-butyl methyl ether/heptane 1:1 mixture were added and the two phases were separated. The organic phase was evaporated to afford 4.4 g of a colorless oil containing product by TLC and HPLC. The aqueous phase was overlaid with 150 ml tert-butyl methyl ether and acidified under stirring with 57.5 ml 2N hydrochloric acid to pH 2. After phase separation, the water phase was extracted 3 times with 40 ml, a total of 120 ml tert-butyϊ methyl ether. The combined organic phases were washed 2 times with 40 ml, a total of 80 ml saturated sodium chloride solution, dried over ca. 40 g sodium sulfate, filtered and evaporated. The residue was taken up in little dichloromethane and combined with the 4.4 g material obtained above. The solution was evaporated and the residue dried in vacuo (0.1 mbar) at a temperature of 70⁰C for 2 h to yield 21.5 g of crude product as thick colorless oil. The material by GC analysis consisted of 96.0% Ia, 0.35% Ic, 0.43% Ib and 0.17% Id; dr la/lb/lc/ld = 99.0 : 0.5 : 0.4 : 0.1. HPLC analysis with internal standard indicated an assay of 85.0 w% Ia. For crystallization the crude material was dissolved in 60 ml heptane at 70°. The clear solution was stirred and allowed to cool to rt whereby crystallization started after ca. 20 min. The suspension was stirred at O⁰C for 3h, and the resulting thick suspension placed in the refrigerator at 4°C for 24 h and finally in the freezer at -18⁰C for 72 h. The precipitate was isolated by filtration, washed 2 times with 10 ml,, a total of 20 ml cold heptane and dried in vacuo (0.1 mbar) at rt for 2h to afford as the 1^st crop product 15.6 g (81%) of Ia as white crystals; m.p. 71- 72°C. The material by GC analysis consisted of 98.9% Ia, 0.25% Ic, 0.04% Ib and 0.00 % Id; dr la/lb/lc/ld = 99.7 : 0.05 : 0.25 : 0.0.

¹H-NMR (300 MHz, CDCl₃): ca. 10 (br. s, COOH); 4.15-3.95 (br. m, 1 H); 3.65-3.1 (br. m, 3 H); 2.6 (br. m, 1 H); 2.12 (s, SCH₃); 2.0-1.65 (br. m, 4 H); 1.46 (br. s, tBu), 1.39 (br. d, J = 6.5, CH₃). Microanalysis calc. for CuH₂₅NOdS (303.42): C 55.42, H 8.30, N 4.62, S 10.57; found: C 55.34/55.25, H 7.88/7.88, N 4.64/4.64, S 10.56/10.59.

The residue from the mother liquor (4.3 g, colorless oil) was dissolved in a round bottom flask in 9 ml heptane at 70°, and the solution was allowed to cool to rt. Seed crystals from the 1^st crop were added and the flask was placed in a freezer at -18° for 48 h. Filtration and drying as described above afforded as the 2ⁿ crop product 1.04 g (5.4%) of Ia as white crystals; m.p. 70-71°C. The material by GC analysis consisted of 98.2% Ia, 0.60% Ic, 0.13% Ib and 0.10 % Id; dr la/lb/lc/ld = 99.2 : 0.1 : 0.6 : 0.1.

¹H-NMR (300 MHz, CDCl₃): identical with ¹H-NMR of 1^st crop material. Combined yield: 16.64 g Ia (86.5%)

Claims

1. A process for the manufacture of the compounds of formula (I)

(D whereby

A) a compound of formula (II)

is reacted with a compound of formula (III)

KS- FT (HI),

in the presence of triethylammonium chloride in a suitable solvent, whereby said compound of formula (III) is being used as such or can be generated in situ by reacting a compound of formula (III -A)

O

-{ S-R (iii-A) in the presence of potassium bases; and

(IV)

and decomposition of said salt of formula (IV);

or

B) a compound of forimila (V)

is reacted with a compound of formula (III), or (III-A) together with a potassium base as described above; and the compounds of formula (I) are obtained from the reaction product by addition of hydrochloric acid to form a compound of formula (VI)

(VI) followed by re-protection of the N-atom by reaction with a tert-butoxycarbonyl- delivering reagent;

and wherein

R¹, R³ and R⁶ independently from each other represent alkyl;

R² is benzyl or substituted benzyl; and

R⁴ and R⁵ are independently selected from cydoalkyl or alkyl, which alkyl can be unsubstituted or substituted one, two or three times with hydroxy, alkoxy, amino, mono- or di-alkylamino, acetoxy, alkylcarbonyloxy, carbamoyloxy, alkoxycarbonyl, carbamoyl, alkylcarbamoyloxy, halogen, cycloalkyl or phenyl.

2. The process according to claim 1, whereby

the compounds of formula (II-A)

are reacted with a compound of formula (III), or (HI-A) together with a potassium base as defined above, in the presence of triethylammonium chloride in tetrahydrofuran; and

the compounds of formula (I) are obtained by benzyl-ester cleavage from the product of said reaction, followed by addition of an amine of the formula NHR⁴R⁵ to the resulting carboxylic acid, arid further followed by base addition and subsequent addition of mineral acids; and

R¹, R⁴ and R⁵ have the meanings given herein before.

3. The process according to claim 1 or 2, wherein the amines of formula NHR⁴R⁵ are selected from

dicyclohexylamine, diisopropylamine, (XJ-α-phenylethylamine, benzγl-(R)-a- phenyiethylamine and (.RJ-α-cyclohexylethylamine.

4. The process according to claim 3, whereby

the compound of formula (2)

the compound of formula (Ia)

5. The process according to claim 1, whereby

a compound of formula (V-A)

is reacted with a compound of formula (III), or (III- A) together with a potassium base as defined above, in the presence of triethylammonium chloride in tetrahydrofuran, and

the compounds of formula (I) are obtained by further reacting the product of the above reaction with dry hydrochloric acid in ethyl acetate, followed by addition of sodium carbonate and subsequent reaction with di-terf-butyl dicarbonate; and wherein

R¹ is as defined above.

6. The process as according to claim 5, wherein

a compound of formula (4)

is reacted with S-methyl thioacetate together with potassium ethoxide, in the presence of triethylammonium chloride in tetrahydrofuran, and the compound of formula (Ia)

is obtained by further' reacting the product of the above reaction with dry hydrochloric acid in ethyl acetate, followed by addition of sodium carbonate and subsequent reaction with di-tert-butyl dicarbonate.

7. The process according to claim 1, wherein the compounds of formula (I) are further reacted to give the compounds of formula (A),

wherein

a) the compounds of formula (I) are reacted with an alcohol or an amine, followed by cleavage of the tert-butoxycarbonyl group at the pyrrolidine N- atom, to give the compounds of formula (B)

(B); and b) the compounds of formula (B) are further reacted with the compounds of formula (C)

to give the compounds of formula (A); and

R¹ and R³ are as defined in claim 1;

R⁸ and R⁹ independently from each other represent alkyl; and

R⁷ is phenylalkyl-, or phenyldialkylamino or phenylalkyloxy, having (Q-C^-alkylene and wherein the phenyl group optionally may be substituted with one, two or three substituents selected from the group consisting of halogen, alkoxycarbonyl, sulfamoyl, alkylcarbonyloxy, carbamoyloxy, cyano, mono- or di-alkylamino, alkyl, alkoxy, phenyl, phenoxy, trifluoromethyl, trifluoromethoxy, alkylthio, hydroxy, alkylcarbonylamino, 1,3- dioxolyl, 1,4-dioxolyl, amino and benzyl.

8. The process according to claim 7 for the manufacture of the compound of formula (A-I)

wherein

a) the compound of formula (Ia)

is reacted with 3-(2-methylamino-ethyl)-phenol, followed by cleavage of the tert- butoxycarbonate group at the pyrrolidine N-atom, to give the compound of formula (B-I)

to give the compound of formula (A-I).

9. The use of the process according to claim 1 in the manufacture of the compounds of formula (A) according to claim 7.

10. The use of the process according to claim 1 in the manufacture of the compound of formula (A-I) according.to claim 8.

11. The compounds of formula (IV)

wherein

R¹ and R³ independently from each other represent alkyl; and

R and R⁵ are independently selected from cydoalkyl or alkyl, which alkyl can be unsubstituted, or substituted one, two or three times with hydroxy, alkoxy, amino, mono- or di-alkylamino, acetoxy, alkylcarbonyloxy, carbamoyloxy, alkoxycarbonyl, carbamoyl, alkylcarbamoyloxy, halogen, cycloalkyl or phenyl.

12. The compounds according to claim 11, wherein

R¹ and R³ are methyl;. and

the group ⁺NH₂R⁴R⁵ represents a cation selected from dicyclohexylammonium, diisopropylammonium, (β)-α-phenylethylammonium, benzyl-f-Rj-α- phenylethylammonium or ^J-α-cyclohexylethylammonium.

13. The compounds of formula (Vl)

^u H H S_{x 3} O

^R3 (VI),

wherein

R¹ and R³ independently from each other represent alkyl.

14. The compound according to claim 13, wherein

R¹ and R³ are methyl.

15. The compound

(S) -2- (( 1R,2S) -2-Carboxy- 1 -methylsulfanyl-propyl) -pyrrolidine- 1 -carboxylic acid tert-butyl ester.

16. The use of a compound as defined in any one of claims 11 to 15 in a process as defined in claim 1.

17. The use of a compound as defined in any one of claims 11 to 15 in the manufacture of the compounds of formula (A) according to claim 7.

18. The use of a compound according to claim 12 or 15 in the manufacture of the compound of formula (A-I) according to claim 8.

19. The novel processes, compounds and uses substantially as described herein before.