JPS59130846A - Synthesis of aspartame - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for the unregulated synthesis of aspartame, α-L-7 subartyl-L-phenylalanine methyl ester. Aspartame has sweetening properties like sucrose and beet sugar, and is used as a sweetening agent in foods and beverages, as in Belky Patent (BE) No. 717,373.
, aspartame is dibepged and is formed using an amide bond between the activated carboxyl group of one amino acid and the amino group of another amino acid. Activation is necessary to increase the rate and yield of condensation.

To obtain the desired pure peptide, all other functional groups not involved in peptide bond formation must be protected. Finally the protecting group is removed.

Aspartame can be made pl by reacting N-protected L-asnoξlagic anhydride with L-phenylalanine methyl ester.

Thereby L-α-aspartyl and 1. A mixture of -β-aspartyl-L-phenylalanine methyl ester is obtained, which requires resolution of the isomers.

The primary groups used are benzyloxycarbonyl (Z) (see FR 2.040,473) and tert-butyloxycarbonyl (see GB 1.339.101). ) of N-protecting groups commonly used in peptide chemistry, such as
or simple protonation to avoid the final removal of the N-protecting group (see US Pat. No. 3,901.El 71). German Patent No. 2,064,482 describes the resolution of the α- and β-isomers (the β-isomer has no sweetening properties), but this leads to a reduction in yield3 and leading to an increase in price. German patent number 2
, 608,174 and European Patent No. 27
．． No. 319 describes the use of charcoal palladium as a catalyst for the removal of protecting groups by catalytic hydrogenation. During the removal of 2, carbon dioxide is formed and must be removed to avoid stopping the reaction.

This is done under a constant stream of hydrogen, resulting in the loss of a large and dangerous amount of this explosive gas.

The method for synthesizing aspartame involves converting a fully protected L-aspartic acid derivative into L-phenylalanine methyl ester in the presence of a condensing agent obtained by reacting a nitrogen-containing heterocyclic compound with a nitrogen or inorganic acid chloride. It consists of condensation and removal of the protecting group by hydrogenation using a hydrogen donor other than molecular hydrogen in the presence of an acid.

By using fully protected L-aspartic acid derivatives the formation of β-isomers is avoided. Condensing agents of the type described above are readily available, inexpensive and effective under mild conditions. Removal of protecting groups using hydrogen donors other than molecular hydrogen can be done easily without the use of dangerous gaseous reagents.
It can be carried out in a simple candy cane. The formation of diketopiperazine, an undesirable by-product due to the presence of acid in the final protecting group removal step, is avoided.

The present invention is represented by the following formula: γ Pi-Asp-Phe-QC)i5. Here, in the above formula,
is a carboxyl holding group, A is a condensing agent, and B is a hydrogen donor other than molecular hydrogen.

Preferred terminal nitrogen-retaining groups X include benzyloxycarbonyl, 2,4-dichlorobenzyloxycarbonyl, 2-bromobenzyloxycarbonyl, 4-nitrobenzyloxycarbonyl and 4-methoxy in aromatic urethane types. Includes benzyloxycarbonyl,
Preferred carboxyl protecting groups Y include benzyl ester, 4-methoxybenzyl ester and 4-nitrobenzyl ester.Among the aralkyl types include benzyl, benzhydryl and trityl. Preferred condensing agents A are the general 2R-W-R [wherein R is imidazole, 2-methylimitazole, penzimitazole, pyrazole, 3,5-dimethylpyrazole, triazole or benzotriazole and W is C
O, Ca, SO, SO2t or P-OR1 (here R
1 represents phenyl, 4-chlorophenylmatahapendyl). Hydrogen donor B is preferably @
ammonium acid, cyclohexane or cyclohexadiene.

The condensation of L-aspartic acid derivatives with L-phenylalanine methyl ester monophenol is carried out in excess (50%
(up to 1) can be carried out using equimolar reagents in the presence of a condensing agent. Dichloromethane, lyoform or tetrahydrofuran are preferred.

The reaction temperature is -60°C [-to ambient temperature.

The reaction time is generally less than 5 hours. The condensing agent is H, A,
5taab IJAngew, Chem, J Vol. 74, p. 407 (1962)].

Recovery of the intercalated dibutide is accomplished by removal of the reaction solvent, followed by solution of the residue in a solvent such as dimethylformamide, -dimethylacetamide, dimethylsulfoxide or N-methylpyrrolidone, lower alkyl (preferably methyl) or ethyl) alcohol and precipitation by addition of water. Recrystallization may be carried out from a mixture of dimethylformamide and lower alkyl (preferably methyl or ethyl) alcohol. The protecting group can be systematically removed from the protected dipeptide by catalytic transfer hydrogenation using an appropriate amount of catalyst. The catalyst may be any suitable noble metal (preferably palladium or platinum) alone, in combination or in supported form. Ammonium chloride is the preferred hydrogen donor. Hydrogenation can be carried out using mMc (preferably formic acid or acetic acid) or inorganic acids (preferably JIA acid) and lower alkyl (preferably methyl or ethyl) alcohols such as dimethylformamide, dimethylacetamide, dimethylsulfoxide or N-methylpyrrolidone. It can be carried out in a suitable solvent. One reaction source may be at a temperature of 0°C to 65°C.

For the final recovery of aspartame, any (j'i Jf
One method can be used.

Symbols and abbreviations used herein include: Acp)J=
Glacial acetic acid, B, t=benzyl, dec-decomposition, DMF=dimethylborumamide, Me-methyl, 1r1. p-””
Melting point, 'I' LC-thin layer chromatography included. Rf Xian is a lower fertilizer development solvent thread (all the compacts are Yongzhoudu), i.e. Solvent U, System A: bennanone/benzine 60-80)/ethyl acetate (25':5 nia 0), solvent system B: Benzene/ethyl acetate/acetic acid ice water 10:1
0:2:1) (upper layer), solvent system C: n-butanol/acetic acid/water (4:1:1), fluid system = chloroform/
Methanol 762% ammonium hydroxide (+55:45
:20) on a precoated plate of silica gel 60 F254 (Merck product) with a layer redness of 0.25 m and a plate length of 20 m.

Since the 'r'Lc analysis was not performed under standard conditions,
Rf(ii> changes especially at different temperatures5o, m
, p.

is ui (measured in the discharge capillary and uncorrected).

A high-pressure sheet of paper η is transmitted through the Ferrograph-Original Frankfurt (Pherograph-Original,
Schleicher and Schull (5Chleicher and Schull)
5C11ii11) T)H on j-f paper m2317
l, 2 (mW (Q', / 'Cj't: acid/water (
cloth, ratio 123:100 near 77)) and 1600
V (40V/cIn).

The electrophoretic mobility (El,2) is expressed in relation to that of glutamic acid.

Example 1 [1st step] Z-Asp'(OBzA)-P by condensation
Preparation of he-OMe(V) thionyldiimitazoe/in dichloromethane 3DOm/
LD, 2? Z-Asp(OBzt) in a solution of
-0H35,7Y, RC/l・)] -Phe-(
Me 216? and N-methylmorpholine 1l-2
rA was added continuously at 0°C. After stirring at this temperature for 1 hour and at room temperature for 6 minutes, the solvent was evaporated off under vacuum. The residue was dimethylformamide 400m7! The solution was concentrated to a solid solution and diluted with ethyl alcohol. The product was precipitated by adding water and one portion of the precipitate was collected. Recrystallize the crude compound from a mixture of dimethylformamide and ethyl alcohol to obtain (1) 4
6.19 was obtained (yield 89%) o m, p, 115~
116℃, [α]ru2=-13,1 (C==1, DMF
), RfA=0.86, Rf13=0.89゜ [Second stage] ■ Co-Asp-Phe-O by hydrogenation
Preparation of Me(I) Z-Asp(OBzt)-Phe-OMe(V)41
．． 59 was dissolved in dimethylformamide 300- and acetic acid 150 me and methyl alcohol//150 m
Diluted with 1.

Palladium 82 by weight on charcoal and ammonium formate 24F were added to the stirrer. Once the reaction was complete, the catalyst was removed and the solvent was evaporated to dryness. The residue was taken up in water, the p month was maintained at 6 using an automatic titrator and the product precipitated on addition of triethylamine. This mixture was allowed to stand overnight in a refrigerator. The product was suspended in ethyl alcohol and stirred at room temperature for 3 hours. 20 t of pure compound (II) was obtained in a yield of 85 times. m, p, 233-235°C (dec
), □[α), j2=+33.2°(c=1,
Ac0H), E12=0.85, Rfc=0.36
, Rfl) = 0.66° Continued from page 1 0 Inventor Giuseppe Ribaldone Italy 2
1100 Gallarate 7 Vualese Viacarlo Power Tutane No. 37

Claims (1)

[Claims] 1) A compound of the formula ■ N-methylmorpholine and a completely preserved 1-1-asno-
benzimidazole, bilapur, 6,5-dimethylpyrazole, triazole or benzotriazole group and W is co, cs, so, so, or P
-OR, (wherein R1 is a phenyl, 4-chlorophenyl or benzyl group)] formed in the presence of a condensing agent carrying HCt-H-Phe-OCH3 (Ill) -t'ruphenylalanine Methyl ester hydrochloric acid base and -30℃~+
React at 25° C. for 2 to 5 hours to obtain a retained intermediate having the formula V Y(V) This is dissolved in an organic solvent such as dimethylformamide, dimethylsulfoxide or 19-methylpyrrolidone and heated from 0°C to 6°C in the presence of an organic or inorganic acid and a lower alkyl alcohol.
Catalytic transfer hydrogenation using a hydrogen donor and a noble metal as catalyst at 5° C. to remove all retaining groups gives the desired product of formula I, which is prepared by methods known in the art. The formula I J(-Asp-Phe-QC) 13 (1) is characterized in that it is isolated and purified.
rtame)) production method. 2) The N-binding X group in the intermediate compound of formula (1) is benzyloxycarbonyl, 2,4-cyclobenzylmexylcarbonyl, 2-bromobenzyloxycarbonyl, 4-nitrobenzyloxycarbonyl, 4-methoxybenzyl 2. A method according to claim 1, wherein the group is selected from the group consisting of oxycarbonyl, benzyl, benzhydryl or trityl groups. 6) The method according to claim 1, wherein the carboxyl-containing Y & in the intermediate compound of formula (1) is selected from the group consisting of benzyl, 4-methoxybenzyl or 4-nitrobenzyl groups. 4) A process according to claim 1, characterized in that the inorganic acid used during the removal of the binding group from the compound of formula V is preferably formic acid or acetic acid. 5) Process according to claims 1 and 4, characterized in that the inorganic acid alternatively used during the pre-protection removal from the compound of formula (1) is preferably hydrochloric acid. 6) Claim 1 in which the lower alkyl alcohol used during the removal of the protecting group from the compound of formula V is preferably methyl or ethyl alcohol.
The method described in section. 7) Process according to claim 1, characterized in that the hydrogen donor used for removing the protecting group from the compound of formula V is selected from the group consisting of ammonium formate, cyclohexane or cyclohexadiene. 8) The method according to claim 1, wherein the noble metal used as a catalyst for the removal of the protecting group from the compound of formula (I) is preferably palladium or platinum, alone or in complex or supported form. Method. 9) Condensation to obtain protected derivatives of formula V, the organic solvent used in the step being from the group consisting of dichloromethane, chloroform, tetrahydrone lye, toluene, dimethylformamide, dimethylacetamide, dimethylsulfoxide or N-methylpyrrolidone. 2. A method according to claim 1, comprising selecting: