CA1179329A - METHOD OF PRODUCING .alpha.-L-ASPARTYL-L-PHENYLALANINE METHYLESTER - Google Patents
METHOD OF PRODUCING .alpha.-L-ASPARTYL-L-PHENYLALANINE METHYLESTERInfo
- Publication number
- CA1179329A CA1179329A CA000387729A CA387729A CA1179329A CA 1179329 A CA1179329 A CA 1179329A CA 000387729 A CA000387729 A CA 000387729A CA 387729 A CA387729 A CA 387729A CA 1179329 A CA1179329 A CA 1179329A
- Authority
- CA
- Canada
- Prior art keywords
- compound
- ester
- amino
- aspartate
- alkyl
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/55—Design of synthesis routes, e.g. reducing the use of auxiliary or protecting groups
Landscapes
- Peptides Or Proteins (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method for preparing an .alpha.-L-aspartyl-L-phenylalanine alkyl ester, which method comprises: reacting a divalent alkali salt of aspartic acid, having an amino-protective group, with an organic halo ester compound, to form a monovalent, alkali-salt, mixed-anhydride aspartate compound; and condensing the mixed-anhydride aspartate compound with an alkyl ester of L-phenylalanine under alkaline conditions and reducing the pH to an acidic condition after condensation to free the amino and carboxyl groups, to form a mixture consist-ing essentially of the alpha and beta alkyl ester of L-aspartyl-L-phenylalanine.
A method for preparing an .alpha.-L-aspartyl-L-phenylalanine alkyl ester, which method comprises: reacting a divalent alkali salt of aspartic acid, having an amino-protective group, with an organic halo ester compound, to form a monovalent, alkali-salt, mixed-anhydride aspartate compound; and condensing the mixed-anhydride aspartate compound with an alkyl ester of L-phenylalanine under alkaline conditions and reducing the pH to an acidic condition after condensation to free the amino and carboxyl groups, to form a mixture consist-ing essentially of the alpha and beta alkyl ester of L-aspartyl-L-phenylalanine.
Description
~7~
The discovery of the sweetness of the dipeptide ~-L-aspartyl-L-phenylalanine methylester was reported in 1969 by R.H. Mazur et al ~Jour.
Amer. Chem. Soc., 91, 2684, 1969). Since then, several methods have been develo-ped for preparing the compound ~see, for example, United States Patents 3,475,403;
3,833,553; 3,798,206; 3,769,333; and 3J933,781).
In United States Patent 3,475,403, Mazur et al react N-benzyloxy-carbonyl-L-aspartic acid ~-p-nitrophenol and ~-benzylester and L-tyrosine methylester, to produce the ~-benzyl-N- benzyloxycarbonyl-l.-aspartyl-L-tyrosine methylester. In United States Patent 3,933,781, L-phenylalanine and N-formyl-L-aspartic anhydride are used to form N-formyl-N-L-aspartyl-L-phenylalanine which is deformylated and then esterified to obtain the methylester compound.
The prior-art methods typically require a number oE process steps and the use of various expensive reagents, resulting in a high cost for the ~-L-aspartyl-L-phenylalanine dipeptide ester.
Applicant's copending Canadian patent application Serial ~o. 377,175, iled May 8, 1981) discloses the preparation of ~-I.-aspartyl-L-phenylalanine alkyl esters, particularly the methylester sweetener compouncl, in high yields;
for example, over 70%, and without substantial racemization and isomer forma-tion of the nonsweetener isomeric compound. The process comprises: reacting the free alpha-carboxyl group of an L-aspartate compound in which the ~-carboxyl group and the amino group are blocked with the free amino group of an alkyl ester of l,-phenylalanine, to provide an L-aspartyl-L-phenylalanine-coupl-ed compound; and hydrogenating the coupled compound, to provide an ~-L-aspartyl-L-phenylalanine alkyl ester~
The present invention relates to an improved method for the prepara-tion of the sweet~ner~-L-aspartyl-L-phellylalanine methylester.
~793~9 In one aspect, the PXesent inv.ention xel~tes to ~n impxoved methcd for the pXepaXa.tion of an aIkyl ester of ~-L-aspartyl-L-phenylalanine which method comprises condensing a monovalent alkali-ester mixed anhydride aspartate compound hav m g an amino-pxotective group under alkaline oondition with an alkyl ester of phenylalanine to produce an a~ino~pro-tected ester condensate co~pound;
and wherein the improvement comprises:
~ a) prDvlding an amlno-protective group which is acid-re~,ovable with the ester group; and (b) reducing the pH of the amino-protected ester condensate compound to an acidic condi-tion to rem~ve the amino-pxotective ester group and to form the alpha and beta mixture of the alkyl ester of ~-L-aspartyl-L-phenylalanine.
It has been found that ~-L-aspartyl-L-phenylalal~Lne alkyl esters, particulaxly the methylester sweetenercompound, may be produced in high yields, without racemization and isomer f~rmati~n of the nonsweetener isomeric compound, and at low cost.
We have discovered that the ~-dipeptide aIkyl esters, particularly the methyl ester representing the sweetener compound, can be obtained directly in good yield by reacting a divalent alkali metal salt of aspartlc acid, where-in the amlno group is protected, with a carboxyl blocking compound, such as a halo ester compound, to form a mixed alkali-ester, anhydride aspartate com-pound, and, therea:Eter, reacting through a condensation reaction, the mixed anhydride aspartate compound with an alkyl ester of the L-phenylalanine or any am m o-acid este~, to ~oxm the deslred dipeptide, and particularly the methyl -.ester sweetener compound.
The method, ~irstly, comprises .~orm m g the divalent alkali ~alt oE
the L-aspartic acid typically by reacting an alkali hydroxide, such as an alkali metal hydroxlde of potassi~n, sodium and lithiwm, ~or example~ in an alcohol
The discovery of the sweetness of the dipeptide ~-L-aspartyl-L-phenylalanine methylester was reported in 1969 by R.H. Mazur et al ~Jour.
Amer. Chem. Soc., 91, 2684, 1969). Since then, several methods have been develo-ped for preparing the compound ~see, for example, United States Patents 3,475,403;
3,833,553; 3,798,206; 3,769,333; and 3J933,781).
In United States Patent 3,475,403, Mazur et al react N-benzyloxy-carbonyl-L-aspartic acid ~-p-nitrophenol and ~-benzylester and L-tyrosine methylester, to produce the ~-benzyl-N- benzyloxycarbonyl-l.-aspartyl-L-tyrosine methylester. In United States Patent 3,933,781, L-phenylalanine and N-formyl-L-aspartic anhydride are used to form N-formyl-N-L-aspartyl-L-phenylalanine which is deformylated and then esterified to obtain the methylester compound.
The prior-art methods typically require a number oE process steps and the use of various expensive reagents, resulting in a high cost for the ~-L-aspartyl-L-phenylalanine dipeptide ester.
Applicant's copending Canadian patent application Serial ~o. 377,175, iled May 8, 1981) discloses the preparation of ~-I.-aspartyl-L-phenylalanine alkyl esters, particularly the methylester sweetener compouncl, in high yields;
for example, over 70%, and without substantial racemization and isomer forma-tion of the nonsweetener isomeric compound. The process comprises: reacting the free alpha-carboxyl group of an L-aspartate compound in which the ~-carboxyl group and the amino group are blocked with the free amino group of an alkyl ester of l,-phenylalanine, to provide an L-aspartyl-L-phenylalanine-coupl-ed compound; and hydrogenating the coupled compound, to provide an ~-L-aspartyl-L-phenylalanine alkyl ester~
The present invention relates to an improved method for the prepara-tion of the sweet~ner~-L-aspartyl-L-phellylalanine methylester.
~793~9 In one aspect, the PXesent inv.ention xel~tes to ~n impxoved methcd for the pXepaXa.tion of an aIkyl ester of ~-L-aspartyl-L-phenylalanine which method comprises condensing a monovalent alkali-ester mixed anhydride aspartate compound hav m g an amino-pxotective group under alkaline oondition with an alkyl ester of phenylalanine to produce an a~ino~pro-tected ester condensate co~pound;
and wherein the improvement comprises:
~ a) prDvlding an amlno-protective group which is acid-re~,ovable with the ester group; and (b) reducing the pH of the amino-protected ester condensate compound to an acidic condi-tion to rem~ve the amino-pxotective ester group and to form the alpha and beta mixture of the alkyl ester of ~-L-aspartyl-L-phenylalanine.
It has been found that ~-L-aspartyl-L-phenylalal~Lne alkyl esters, particulaxly the methylester sweetenercompound, may be produced in high yields, without racemization and isomer f~rmati~n of the nonsweetener isomeric compound, and at low cost.
We have discovered that the ~-dipeptide aIkyl esters, particularly the methyl ester representing the sweetener compound, can be obtained directly in good yield by reacting a divalent alkali metal salt of aspartlc acid, where-in the amlno group is protected, with a carboxyl blocking compound, such as a halo ester compound, to form a mixed alkali-ester, anhydride aspartate com-pound, and, therea:Eter, reacting through a condensation reaction, the mixed anhydride aspartate compound with an alkyl ester of the L-phenylalanine or any am m o-acid este~, to ~oxm the deslred dipeptide, and particularly the methyl -.ester sweetener compound.
The method, ~irstly, comprises .~orm m g the divalent alkali ~alt oE
the L-aspartic acid typically by reacting an alkali hydroxide, such as an alkali metal hydroxlde of potassi~n, sodium and lithiwm, ~or example~ in an alcohol
2 -93~
solution, such as a methanol, ethanol or other lower alkanol, with L-aspartic acid, and heating and refluxing the mixture, to form the divalent alkali salt of the L-aspartic acid. Particularly preferred is the reaction of the L-aspart-ic acid in a methanol-potassium hydroxide solution, to form the divalent potassium salt.
The amino group of the divalent alXali salt is protected by reacting one hydrogen of the amino group, typically in si~u, after the formation of the divalent alkali salt, with an organic compound which would react with the hydro-gen group. A wide variety of organic compounds may be employed to react with and protect the amino group. The amino-protective compound employed should be reacted, typically in situ, with the amino group, to protect the amino site from further reaction during the reaction with the halo ester to form the anhydride, and yet the amino-protective group should be removed easily after the condensation step throu~h a reduction in pH to an acid pH or by hydrogena-tion, to reform the free-amino group and the free-carhoxyl group of the desired aspartate. For example, the amino-group site may be protected by reaction with a carbobenzoxy halide, such as a carbobenzoxy chloride, as in the parent application. However, the use of this compound requires a separate hydrogena-tion step, as in the parent process. A preferred compound to protect the amino-group site is an alkyl acetoacetate compound, such as the methyl, e~hyl and propyl acetoacetate.
The amino-protect ~d divalent alkali salt o~ the aspartate is reacted with a halo ester in a quantity sufficient to displace one of the dialkali salt groups and to form the mixed alkali-halo ester anhydride aspartate com-pound. The mixed anhydricle aspartate compo~md thus provides for protection for 'ootll carboxyl groups - one by the alkali salt and one by the halo ester, and ~9~29 also protection for the amino group. Typically, the halo ester may comprise an alkyl; for example, Cl-C6, halo; for example, chloro or bromo alkanoate, such as a Cl-C4 al~anoate, with one preferred compound being an alkylchlorofor-mate, such as a methyl, ethyl, propyl, chloro or bromoformate.
The mixed anhydride aspartate compound is then reacted in a condensa-tion reaction carried out under alkaline conditions; for example, from about 8 to 9 pH, and at a low temperature; for example~ below -20C, ~ith an alkyl ester of the phenylalanine, and particularly the methylester where the desired sweetener compound is to be produced. The reaction mixture is then reduced in pH to an acidic pH of 2.0 or less, and typically 1.5 or less~ to free the amino and carboxyl groups, thereby forming an alpha-beta mixture of the desired alkyl ester of the L-aspartyl-L-phenylalanine. The method provides ~or the direct formation of the alpha-beta mixture of the dipeptide compound in good yield, without interfering by-products and at a low cost, through the use of low-cost reagents.
Thus, the method provides ~r the preparation of the desired ~-dipeptide ester directly in good yield, by reacting the alkali salt of aspartic acid with the amino site protected, in situ, and reacting the mixed anhydride with L phenyl:alanine methylester and subsequent deprotection by reduction of the p}l, to free the amine. This method yields alpha and beta dipeptide esters simultaneously. The desired isomer formed af the dipeptide ester is formed pre~crentially in a larger yieldl depending on the reaction conditions employed.
Typically, such reaction conditions include carrying out the condensation reac-tion at a temperature of from -20C to -60C; for example, -30C to ~40C, and at a ptl of from about 8 to 9, and typically 8.5 to 8.9 pH, with the subsequent regeneration of the free amino and carboxyl groups by reducing the pH. The ~7~
reaction mixture essentially is all alpha and beta dipeptide, with the alpha isomer having a larger yield. The undesired beta dipeptide ester can be separa-ted readily from the alpha isomer by methods known in the art. The method does not require many steps and expensive reagents and is easily adapted for industrial application.
The process conditions o each step of the method may be varied.
However, in the formation of the alkali ester of the aspartic acid, sufficient stoichiometric concentration of the monovalent alkali should be employed, to prepare the divalent alkali ester aspartate, and sufficient quantities of the amino-protective compound used to provide for protection of the amino group of alkali aspartate compound. Thereafter, a sufficient stoichiometric amount of the halo ester should be employed, to react and displace one of the alkali salt groups, to form the mono-alkali-monohalo ester, mixed-anhydride compound.
Thereafter, the condensation reaction is carried out, using a stoichiometric concentration of the l.-phenylalanine under alkaline conditions and low tempera-tures, and the subsequent reduction to free both the amino ~roup and the carbox-yl group to form the dipeptide.
The improved method of the invention is set forth in a general schematic sequence as ollows:
solution, such as a methanol, ethanol or other lower alkanol, with L-aspartic acid, and heating and refluxing the mixture, to form the divalent alkali salt of the L-aspartic acid. Particularly preferred is the reaction of the L-aspart-ic acid in a methanol-potassium hydroxide solution, to form the divalent potassium salt.
The amino group of the divalent alXali salt is protected by reacting one hydrogen of the amino group, typically in si~u, after the formation of the divalent alkali salt, with an organic compound which would react with the hydro-gen group. A wide variety of organic compounds may be employed to react with and protect the amino group. The amino-protective compound employed should be reacted, typically in situ, with the amino group, to protect the amino site from further reaction during the reaction with the halo ester to form the anhydride, and yet the amino-protective group should be removed easily after the condensation step throu~h a reduction in pH to an acid pH or by hydrogena-tion, to reform the free-amino group and the free-carhoxyl group of the desired aspartate. For example, the amino-group site may be protected by reaction with a carbobenzoxy halide, such as a carbobenzoxy chloride, as in the parent application. However, the use of this compound requires a separate hydrogena-tion step, as in the parent process. A preferred compound to protect the amino-group site is an alkyl acetoacetate compound, such as the methyl, e~hyl and propyl acetoacetate.
The amino-protect ~d divalent alkali salt o~ the aspartate is reacted with a halo ester in a quantity sufficient to displace one of the dialkali salt groups and to form the mixed alkali-halo ester anhydride aspartate com-pound. The mixed anhydricle aspartate compo~md thus provides for protection for 'ootll carboxyl groups - one by the alkali salt and one by the halo ester, and ~9~29 also protection for the amino group. Typically, the halo ester may comprise an alkyl; for example, Cl-C6, halo; for example, chloro or bromo alkanoate, such as a Cl-C4 al~anoate, with one preferred compound being an alkylchlorofor-mate, such as a methyl, ethyl, propyl, chloro or bromoformate.
The mixed anhydride aspartate compound is then reacted in a condensa-tion reaction carried out under alkaline conditions; for example, from about 8 to 9 pH, and at a low temperature; for example~ below -20C, ~ith an alkyl ester of the phenylalanine, and particularly the methylester where the desired sweetener compound is to be produced. The reaction mixture is then reduced in pH to an acidic pH of 2.0 or less, and typically 1.5 or less~ to free the amino and carboxyl groups, thereby forming an alpha-beta mixture of the desired alkyl ester of the L-aspartyl-L-phenylalanine. The method provides ~or the direct formation of the alpha-beta mixture of the dipeptide compound in good yield, without interfering by-products and at a low cost, through the use of low-cost reagents.
Thus, the method provides ~r the preparation of the desired ~-dipeptide ester directly in good yield, by reacting the alkali salt of aspartic acid with the amino site protected, in situ, and reacting the mixed anhydride with L phenyl:alanine methylester and subsequent deprotection by reduction of the p}l, to free the amine. This method yields alpha and beta dipeptide esters simultaneously. The desired isomer formed af the dipeptide ester is formed pre~crentially in a larger yieldl depending on the reaction conditions employed.
Typically, such reaction conditions include carrying out the condensation reac-tion at a temperature of from -20C to -60C; for example, -30C to ~40C, and at a ptl of from about 8 to 9, and typically 8.5 to 8.9 pH, with the subsequent regeneration of the free amino and carboxyl groups by reducing the pH. The ~7~
reaction mixture essentially is all alpha and beta dipeptide, with the alpha isomer having a larger yield. The undesired beta dipeptide ester can be separa-ted readily from the alpha isomer by methods known in the art. The method does not require many steps and expensive reagents and is easily adapted for industrial application.
The process conditions o each step of the method may be varied.
However, in the formation of the alkali ester of the aspartic acid, sufficient stoichiometric concentration of the monovalent alkali should be employed, to prepare the divalent alkali ester aspartate, and sufficient quantities of the amino-protective compound used to provide for protection of the amino group of alkali aspartate compound. Thereafter, a sufficient stoichiometric amount of the halo ester should be employed, to react and displace one of the alkali salt groups, to form the mono-alkali-monohalo ester, mixed-anhydride compound.
Thereafter, the condensation reaction is carried out, using a stoichiometric concentration of the l.-phenylalanine under alkaline conditions and low tempera-tures, and the subsequent reduction to free both the amino ~roup and the carbox-yl group to form the dipeptide.
The improved method of the invention is set forth in a general schematic sequence as ollows:
3~29 1) 0 0 " monovalent "
H2-C-OH alkali lH2 C-OR
.. . ..
(L-aspartic acid) 2) O
amino-protective CH2-C-OR
+ compound R ~ ¦ 0 H-N
R' 3) ~ O
R"X ____~ CH2-C-OR
lo CH-C-OR"
H-N
1, .
mixed anhydride ~) ,~ O
~ ~ -CH2-CH C-OR" ' -~, alkaline condi.tions later O
C~12- C- 0~1 rcduce pll ~ o 112N-CH-C-NH-Ctl-C~12- ~) COOR" ' and ~ dipeptide ~9 wherein R is a monovalent metal alkali; R' is an amino reactive compound; R"
is an ester group of halo ester; X is a halo group; and R" ' is an alkyl group.
A preferred specific reaction sequence, employing a specific compound, is shown as follows:
O O O O
.. .. .. ..
1) 0 CH2-C-OK CH3 C CH2 C O CH3 " methanol ¦ O -H2N-(:}I-C-OH KOH H2N-CH-C-OKreflux (L-aspartic acid) 2) 0 -CH -C-OK few drops of CH2-C-OK
l 20, ~ Cl COOC2 H5 N-methyl morpholine ¦
CH-C-OK -40 to -60C O O
I ~ '~I-C-O-C
NH O
~ OC2H5 H3C-C=CH-C-OC~13 1 ~H
(dipotassium-L-aspartyl N-3-ketobutenoate) O
H3C-C=CH-C-OCH3 ~7~Z9 3~ 0 O
I " "0 ~3 -CH2-CH-C-OCH3 CH-C-O-C
~ OC2H5 N~2 NH (L-phenylalanine methylester) l O
~13C-C=CII-C-OCH3 -30 to -40C
triethylamine "
pH 8-9 0 then reduce to ¦ "
pH 1.5 H2N-CH-C-NH-CH-CH2-and ~ mixture (L-aspa~tyl-L-phenylalanine me~hylest-er) The method of the invention will be described in connection with certain preferred embodiments; however, it is recognized that those persons skilled in the art may make various changes and modifications in the embodi-ments shown, all within the spirit and scope of the invention.
~xample 1.
Preparat:Lon of dipotassium-L-aspa~ L~ L~g -A three-necked ~lask was charged with 360 ml of methanol (distilled over molecular sieves~ and 44.8 g potassium hydroxide. The flask was attached with a condenser and a motored stirrer. The contcnts were heated with stirring ~L~7~3~
to ~5C, when a clear solution was obtained. It was coc>led to room temperature and 45.2 g of L-aspartic acid were added slowly with stirring. The contents were again refluxed for 15 minutes. It was cooled to room temperature, and 40.l ml of methylacetoacetate in 197 ml of anhydrous methanol were slowly added and refluxed for l/2 hour.
Methanol was stripped off completely under vacuum and the contents were added to 500 ml of 2-propanol. While precipitate was formed and was filtered off and dried in a vacuum desiccator over potassium hydroxide. Overall yield of this product was 91 to 98%.
Example 2.
Condensation of the potassium salt of L-aspartyl with the ester of phenylalanine ~.6 g of dipotassium~L-aspartyl N-3-ketobutenoate were added to a 500-ml three-necked flask attached with a stirrer, a thermometer and a calcium-chloride guard tube. Acetone ~40 ml~ was added and stirred at -55C for 10 minutes. Ethyl chloroformate (2.0 ml) was added while stirring, followed by 5 drops of N-methyl morpholine. Coolin~ was discontinued, and the temperature was allowed to rise to -30C, and the mixture was stirred between -30C to -~0C for 30 to 60 minutes, preferably ~5 minutes. At the end of this period, it was coo~ed to -70C and filtered through a celite pad. The filtrate was kept at -55C.
To the mixed anhydride maintained at -55C, phenylalanine methylester hydrochloride (~.2 g) in lO ml of water neutralized with triethylamine was added, and thc p~l was adjuste~ to ~.5 to 8.9. The contents were stirred at -~0C to -30C for 1 1/2 hours. At the end of the reaction period, 25 ml of water were added, Eollowed by concentrated hydrochloric acid to bring the p~l to 1.5, and the mixture ~as stirrecl at 0C for 10 minutes. 'I'he mixture was ~L7~3;29 extracted with dichloromethane (2 x 70 ml), and the aqueous layer was adjusted to p~l 4.1.
The resulting aqueous solution was chromatographed on a silica-gel column, to obtain pure ~-L-aspartyl-L-phenylalanine methylester. A portion of the aqueous solution crystallized at 0C, to give ~-L-aspartyl-L-phenylalanine methylester.
The product was identified by melting point ~235~C to236C) m. mpt and TLC comparison with an authentic commercial sample.
The yields of the ~ and ~ -isomers were qualitatively found to be 60:35 percent.
H2-C-OH alkali lH2 C-OR
.. . ..
(L-aspartic acid) 2) O
amino-protective CH2-C-OR
+ compound R ~ ¦ 0 H-N
R' 3) ~ O
R"X ____~ CH2-C-OR
lo CH-C-OR"
H-N
1, .
mixed anhydride ~) ,~ O
~ ~ -CH2-CH C-OR" ' -~, alkaline condi.tions later O
C~12- C- 0~1 rcduce pll ~ o 112N-CH-C-NH-Ctl-C~12- ~) COOR" ' and ~ dipeptide ~9 wherein R is a monovalent metal alkali; R' is an amino reactive compound; R"
is an ester group of halo ester; X is a halo group; and R" ' is an alkyl group.
A preferred specific reaction sequence, employing a specific compound, is shown as follows:
O O O O
.. .. .. ..
1) 0 CH2-C-OK CH3 C CH2 C O CH3 " methanol ¦ O -H2N-(:}I-C-OH KOH H2N-CH-C-OKreflux (L-aspartic acid) 2) 0 -CH -C-OK few drops of CH2-C-OK
l 20, ~ Cl COOC2 H5 N-methyl morpholine ¦
CH-C-OK -40 to -60C O O
I ~ '~I-C-O-C
NH O
~ OC2H5 H3C-C=CH-C-OC~13 1 ~H
(dipotassium-L-aspartyl N-3-ketobutenoate) O
H3C-C=CH-C-OCH3 ~7~Z9 3~ 0 O
I " "0 ~3 -CH2-CH-C-OCH3 CH-C-O-C
~ OC2H5 N~2 NH (L-phenylalanine methylester) l O
~13C-C=CII-C-OCH3 -30 to -40C
triethylamine "
pH 8-9 0 then reduce to ¦ "
pH 1.5 H2N-CH-C-NH-CH-CH2-and ~ mixture (L-aspa~tyl-L-phenylalanine me~hylest-er) The method of the invention will be described in connection with certain preferred embodiments; however, it is recognized that those persons skilled in the art may make various changes and modifications in the embodi-ments shown, all within the spirit and scope of the invention.
~xample 1.
Preparat:Lon of dipotassium-L-aspa~ L~ L~g -A three-necked ~lask was charged with 360 ml of methanol (distilled over molecular sieves~ and 44.8 g potassium hydroxide. The flask was attached with a condenser and a motored stirrer. The contcnts were heated with stirring ~L~7~3~
to ~5C, when a clear solution was obtained. It was coc>led to room temperature and 45.2 g of L-aspartic acid were added slowly with stirring. The contents were again refluxed for 15 minutes. It was cooled to room temperature, and 40.l ml of methylacetoacetate in 197 ml of anhydrous methanol were slowly added and refluxed for l/2 hour.
Methanol was stripped off completely under vacuum and the contents were added to 500 ml of 2-propanol. While precipitate was formed and was filtered off and dried in a vacuum desiccator over potassium hydroxide. Overall yield of this product was 91 to 98%.
Example 2.
Condensation of the potassium salt of L-aspartyl with the ester of phenylalanine ~.6 g of dipotassium~L-aspartyl N-3-ketobutenoate were added to a 500-ml three-necked flask attached with a stirrer, a thermometer and a calcium-chloride guard tube. Acetone ~40 ml~ was added and stirred at -55C for 10 minutes. Ethyl chloroformate (2.0 ml) was added while stirring, followed by 5 drops of N-methyl morpholine. Coolin~ was discontinued, and the temperature was allowed to rise to -30C, and the mixture was stirred between -30C to -~0C for 30 to 60 minutes, preferably ~5 minutes. At the end of this period, it was coo~ed to -70C and filtered through a celite pad. The filtrate was kept at -55C.
To the mixed anhydride maintained at -55C, phenylalanine methylester hydrochloride (~.2 g) in lO ml of water neutralized with triethylamine was added, and thc p~l was adjuste~ to ~.5 to 8.9. The contents were stirred at -~0C to -30C for 1 1/2 hours. At the end of the reaction period, 25 ml of water were added, Eollowed by concentrated hydrochloric acid to bring the p~l to 1.5, and the mixture ~as stirrecl at 0C for 10 minutes. 'I'he mixture was ~L7~3;29 extracted with dichloromethane (2 x 70 ml), and the aqueous layer was adjusted to p~l 4.1.
The resulting aqueous solution was chromatographed on a silica-gel column, to obtain pure ~-L-aspartyl-L-phenylalanine methylester. A portion of the aqueous solution crystallized at 0C, to give ~-L-aspartyl-L-phenylalanine methylester.
The product was identified by melting point ~235~C to236C) m. mpt and TLC comparison with an authentic commercial sample.
The yields of the ~ and ~ -isomers were qualitatively found to be 60:35 percent.
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method for the preparation of an alkyl ester of .alpha.-L-aspartyl-L-phenylalanine which method comprises:
condensing a monovalent alkali-ester mixed anhydride aspartate com-pound having an amino-protective group under alkaline condition with an alkyl ester of phenylalanine to produce an amino-protected ester condensate compound;
the improvement which comprises:
(a) providing an amino-protective group which is acid-removable with the ester group; and (b) reducing the pH of the amino-protected ester condensate compound to an acidic condition to remove the amino-protective ester group and to form the alpha and beta mixture of the alkyl ester of .alpha.-L-aspartyl-L-phenylalanine.
condensing a monovalent alkali-ester mixed anhydride aspartate com-pound having an amino-protective group under alkaline condition with an alkyl ester of phenylalanine to produce an amino-protected ester condensate compound;
the improvement which comprises:
(a) providing an amino-protective group which is acid-removable with the ester group; and (b) reducing the pH of the amino-protected ester condensate compound to an acidic condition to remove the amino-protective ester group and to form the alpha and beta mixture of the alkyl ester of .alpha.-L-aspartyl-L-phenylalanine.
2. The method of claim 1 which comprises reducing the pH to about 2.0 or less.
3. The method of claim 1 which includes separating the alpha isomer from the alpha and beta alkyl ester mixture.
4. The method of claim 1 wherein the acid-removable amino-protective group of the mixed anhydride aspartate compound is an alkyl acetoacetate group.
5. The method of claim 1 wherein the alkali salt is a potassium or sodium salt.
6. The method of claim 1 wherein the ester group of the mixed anhydride aspartate compound is an alkanoate group.
7. The method of claim 1 wherein the ester group of the mixed anhydride aspartate compound is an alkyl formate group.
8. The method of claim 1 wherein the alkyl ester is the methylester of phenylalanine to form the alpha and beta mixture of the methylester sweetener compound.
9. The method of claim 1 wherein the condensing step is carried out at an alkaline pH of from about 8 to 9 and at a temperature of about -20°C to -60°C.
10. The method of claim 1 which includes forming the mixed anhydride aspartate compound by:
(a) reacting aspartic acid with a monovalent alkali hydroxide to form the aspartate salt compound;
(b) reacting the aspartate salt compound with an acid-removable amino-protected compound, in situ, to form the amino-protected divalent alkali salt of aspartic acid;
and (c) reacting the amino-protected alkali salt of aspartic acid with an organic halo alkyl formate to form the monoalkali monoester mixed anhydride aspartate compound.
(a) reacting aspartic acid with a monovalent alkali hydroxide to form the aspartate salt compound;
(b) reacting the aspartate salt compound with an acid-removable amino-protected compound, in situ, to form the amino-protected divalent alkali salt of aspartic acid;
and (c) reacting the amino-protected alkali salt of aspartic acid with an organic halo alkyl formate to form the monoalkali monoester mixed anhydride aspartate compound.
11. The method of claim 10 wherein the free amino group of the salt of the aspartic acid is reacted in situ, with an alkyl acetoacetate to form an amino protective group.
12. The method of claim 11 wherein the alkali hydroxide is potassium hydroxide, the alkyl formate is a chloro alkyl formate, and the alkyl aceto-acetate is methyl acetoacetate.
13. In a method for the preparation of the methyl ester of .alpha.-L-aspartyl-L-phenylalanine which method comprises;
condensing a monovalent alkali-ester mixed anhydride aspartate compound having an amino-protective group under alkaline condition with the methyl ester of phenylalanine to produce an amino-protected ester condensate compound;
the improvement which comprises:
(a) providing an alkyl acetoacetate group as an amino-protective group;
(b) reducing the pH of the condensate compound to a pH of about 2.0 or less to remove the alkyl acetoacetate ester groups, and to form the alpha and beta methyl ester of .alpha.-L-aspartyl-L-phenylalanine; and (c) recovering the alpha methyl ester.
condensing a monovalent alkali-ester mixed anhydride aspartate compound having an amino-protective group under alkaline condition with the methyl ester of phenylalanine to produce an amino-protected ester condensate compound;
the improvement which comprises:
(a) providing an alkyl acetoacetate group as an amino-protective group;
(b) reducing the pH of the condensate compound to a pH of about 2.0 or less to remove the alkyl acetoacetate ester groups, and to form the alpha and beta methyl ester of .alpha.-L-aspartyl-L-phenylalanine; and (c) recovering the alpha methyl ester.
14. The method of claim 13 wherein the ester group of the mixed anhydride aspartate compound is an alkyl formate group.
15. The method of claim 13 which includes forming the mixed anhydride aspartate compound by:
(a) reacting aspartic acid with a monovalent alkali hydroxide to form the aspartate salt compound;
(b) reacting the aspartate salt compound with an alkyl aceto-acetate, in situ, to form the amino-protected alkali salt of aspartic acid; and (c) reacting the amino-protected alkali salt of aspartic acid with an organic halo alkyl formate to form the monoalkali monoester mixed aspartate compound.
(a) reacting aspartic acid with a monovalent alkali hydroxide to form the aspartate salt compound;
(b) reacting the aspartate salt compound with an alkyl aceto-acetate, in situ, to form the amino-protected alkali salt of aspartic acid; and (c) reacting the amino-protected alkali salt of aspartic acid with an organic halo alkyl formate to form the monoalkali monoester mixed aspartate compound.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000387729A CA1179329A (en) | 1981-10-09 | 1981-10-09 | METHOD OF PRODUCING .alpha.-L-ASPARTYL-L-PHENYLALANINE METHYLESTER |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000387729A CA1179329A (en) | 1981-10-09 | 1981-10-09 | METHOD OF PRODUCING .alpha.-L-ASPARTYL-L-PHENYLALANINE METHYLESTER |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1179329A true CA1179329A (en) | 1984-12-11 |
Family
ID=4121143
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000387729A Expired CA1179329A (en) | 1981-10-09 | 1981-10-09 | METHOD OF PRODUCING .alpha.-L-ASPARTYL-L-PHENYLALANINE METHYLESTER |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1179329A (en) |
-
1981
- 1981-10-09 CA CA000387729A patent/CA1179329A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP0127411B1 (en) | Method of preparing alpha-l-aspartyl-l-phenylalanine methyl ester and its hydrochloride | |
| US4173562A (en) | Process for the preparation of α-L-aspartyl-L-phenylalanine methyl ester | |
| US4333872A (en) | Method of producing α-L-aspartyl-L-phenylalanine methylester | |
| SE440506B (en) | PROCEDURE FOR PREPARING ALFA-L-ASPARTYL-L-PHENYLALANINE METHYL ESTER | |
| CA1179329A (en) | METHOD OF PRODUCING .alpha.-L-ASPARTYL-L-PHENYLALANINE METHYLESTER | |
| JPS61143397A (en) | Production of n-formyl-alpha-aspartylphenylalanite | |
| KR920002337B1 (en) | Process for preparing alpha-l-aspartyl-l-phenylalanine methylester of hydrochloride | |
| GB2140805A (en) | Isolation of aspartame | |
| CA1274349A (en) | L-aminodicarboxylic acid alkanes | |
| US4394308A (en) | Method of producing α-L-aspartyl-L-phenylalanine methylesters | |
| CA1244008A (en) | Aspartame synthesis | |
| CA1298432C (en) | PROCESS FOR SEPARATION OF N-PROTECTED- .alpha. L-ASPARTYL- L-PHENYLALANINES | |
| RU2205834C2 (en) | Method of synthesis of [2-((8,9)-dioxo-2,6-diazobi-cyclo-[5,2,0]non-1(7)-en-2-yl)ethyl]phosphonic acid, method of synthesis of n-[3-(tertiary butyloxy- carbonylamino)propyl]-2-aminoethylphosphonic acid di-c1-c6-alkyl ester, compounds | |
| JPS5825661B2 (en) | N-acyl-1-acyl-4-guanidinobutylamine and its acid addition salt | |
| JP2508803B2 (en) | Process for producing α-L-aspartyl-L-phenylalanine derivative | |
| KR830002205B1 (en) | Method for preparing kanamycin A derivative | |
| JPH08134088A (en) | Isolation of n-phosphonomethylglycine | |
| KR850000059B1 (en) | Process of preparing for alpha-l-aspatyl-l-phehylallanine alkylaster | |
| KR880002415B1 (en) | Process for the preparation of a-l-aspartyl-l-phenyl alanine alkyl ester | |
| JP2598467B2 (en) | Method for producing N-protected-α-L-aspartyl-L-phenylalanine methyl ester | |
| JP2598470B2 (en) | Method for producing N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester | |
| JP2647420B2 (en) | Method for producing N-protected-α-L-aspartyl-L-phenylalanine methyl ester | |
| KR900000685B1 (en) | Process for the preparation pf alpha-l-aspartyl-phenylalanine alkylester | |
| CA1240703A (en) | Preparation of o-acylaminomethylbenzyl halides | |
| JPH0514691B2 (en) |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |