Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Resolution of optical isomers or purification of organic...
Reexamination Certificate
2001-05-30
2002-08-27
Saucier, Sandra E. (Department: 1651)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Resolution of optical isomers or purification of organic...
Reexamination Certificate
active
06440721
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for preparing an R- or S-form &agr;-substituted heterocyclic carboxylic acid (hereinafter referred to as “&agr;-HCCA”) and a counter enantiomeric form of &agr;-HCCA ester. More particularly, the present invention pertains to a method for preparing R- or S-form &agr;-HCCA and S- or R-form &agr;-HCCA ester, respectively using an enzyme catalyst with enantioselectivity from a racemate of &agr;-HCCA ester obtained by reacting a racemic &agr;-HCCA and alcohol.
2. Description of the Prior Art
Divided into optical isomers, R- and S-form, tetrahydro-2-furoic acid (hereinafter referred to as “THFA”), a kind of &agr;-HCCA, is an important chiral building block which has various applications in chemistry. Of the optical isomers, R-(+)-THFA is used as a side chain intermediate for the synthesis of penem type antibiotics while S-(−)-THFA is useful as a chiral intermediate for organic synthesis. Thus, THFA is different in use from R form to S form. However, because THFA is obtained in the form of racemate when chemically synthesized, additional processes are required to separate THFA into enantiomers thereof: R and S forms.
Optical resolution has been usually used to divide racemic THFA into R- and S-forms thereof. In 1983, Belanger successfully separated THFA racemate into enantiomers thereof by use of brucine and ephedrine as resolving agents (Can. J. Chem., 61, 1383 (1983)). However, the resolving agents are not economical because of their being very expensive. Another problem with this process is low in enantiomeric excess value.
Japanese Pat. Laid-Open Publication No. 89-216983 discloses the use of a chiral amine(1-(4-halogenophenyl)ethylamine) as a resolving agent, in which diastereomer salts are prepared from R,S-THFA and optically resolved. This method is also economically unfavorable owing to the high price of the chiral amine. Additionally, only low production yields can be obtained because the amount of R,S-THFA to be added in the early reaction is limited to as low as 4 mmol. Furthermore, the chiral THFA finally obtained is poor in enantiomeric excess value.
Japanese Pat. Laid-Open Publication. No. 97-71576 refers to a method of synthesizing R- or S-THFA by treating R- or S-THFA salts with hydrogen halide, which is different from optical resolving methods.
It has been well known for some time that racemates could be optically resolved using enzyme catalysts, such as esterases, lipases, and proteases, to enantioselectively hydrolyze one of the two enantiomers present. For example, U.S. Pat. No. 5,928,933 discloses an enzyme with an enantiomeric excess value of 95% as a result of extensive experiments for reaction specificity of 44 enzymes, including proteases, lipases and esterases. The enzyme catalyst is very useful for the separation of enantiomeric racemates, but because the selectivity for enantiomers and the optical purity of products may vary depending on the choice of enzyme and the chemical structures of substrates, intensive efforts are required to find combinations of enzymes suitable for substrates. Especially, nowhere is found a method for optical resolution of &agr;-HCCA using an enzyme.
SUMMARY OF THE INVENTION
Leading to the present invention, the intensive and through research on the optical resolution of &agr;-HCCA, conducted by the present inventors aiming to develop an optically highly pure &agr;-HCCA and a counter enantiomeric form of &agr;-HCCA ester thereto by an economical procedure, resulted in the finding that some of microorganism- or animal-derived hydrolyzing enzymes may enantioselectively hydrolyze the ester functionality of particular optical isomers of &agr;-HCCA esters at high efficiency.
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a method for preparing a highly pure R- or S-form &agr;-HCCA and a counter enantiomeric form of &agr;-HCCA ester thereto using an enzyme, which is economically favorable.
Based on the present invention the above object could be accomplished by providing a method for preparing an R- or S-form &agr;-HCCA and a counter enantiomeric form of &agr;-HCCA ester thereto, comprising the steps of:
reacting a racemic &agr;-HCCA with alcohol to give a racemic &agr;-HCCA ester represented by the following chemical formula 1:
wherein R
1
is selected from the group consisting of substituted or unsubstituted alkyl or alkenyl containing 1 to 6 carbon atoms, benzyl, cycloalkyl containing 3 to 6 carbon atoms, substituted or unsubstituted arylalkyl, and substituted or unsubstituted heteroarylalkyl, X represents O, S or N—H, and n is an integer of 1 to 3;
optically resolving the racemate of the formula 1 by use of an enzyme with enantioselectivity to hydrolyze either R-form or S-form of the racemate, thereby producing a pure R-form or S-form of &agr;-HCCA and a counter enantiomeric form of &agr;-HCCA ester thereto, said enzyme existing as a powder or an aqueous solution; and
extracting the unhydrolyzed &agr;-HCCA ester with an organic solvent.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is characterized by the enantioselective hydrolysis of esters of racemic &agr;-HCCA by an enzyme to produce a certain enantiomeric form of &agr;-HCCA and a counter enantiomeric form of the esters of &agr;-HCCA, at once. The separation of the hydrolyzed &agr;-HCCA and the remaining esters of &agr;-HCCA can be achieved by extracting with an organic solvent.
In detail, &agr;-HCCA is reacted with an alcohol at an equivalent amount to produce an &agr;-HCCA ester, which is then enantioselectively hydrolyzed at a constant temperature and pH in an aqueous solution in the presence of an enzyme with enantioselectivity. As a result, the reaction produces an R- or S-form &agr;-HCCA, along with the ester of &agr;-HCCA which has an enantiomeric form counter to that of the hydrolyzed &agr;-HCCA. After the completion of the enantioselective hydrolysis, addition of an organic solvent extracts the ester of &agr;-HCCA thereinto, leaving the &agr;-HCCA in the aqueous phase only. Removal of the organic solvent from the organic phase results in acquisition of an optically pure S- or R-form of &agr;-HCCA ester. Poor in optical purity, the &agr;-HCCA remaining in the aqueous solution may be increased in purity through a purification process using, for example, a column, or may be reused as a starting material in the present invention.
Using a non-enantioselective enzyme or a palladium catalyst, the S- or R-form of &agr;-HCCA ester obtained can be hydrolyzed to an S- or R-form of &agr;-HCCA with a high enantiomeric excess value (>99%). Additionally, the S- or R-form of &agr;-HCCA ester may be reduced to a chiral alcohol which is useful as an intermediate for the synthesis of various medicines.
For instance, the enantiomeric &agr;-HCCA ester is hydrolyzed at a constant pH and temperature in an aqueous solution in the presence of an enzyme that shows no enantioselectivity and non-specifically hydrolyzes &agr;-HCCA ester. After completion of the enzymatic hydrolysis, the aqueous layer is controlled to pH 2-3 with hydrochloric acid and extracted several times with an organic solvent to yield an S- or R-form of &agr;-HCCA. In the case of an palladium catalyst (Pd/C), the obtained S- or R-form of &agr;-HCCA ester is dissolved in an organic solvent and subjected to hydrogenation at a constant temperature under a predetermined partial hydrogen pressure to produce an S- or R-form of &agr;-HCCA with a high optical purity (>99%).
In accordance with a preferred embodiment of the present invention, THFA, which belongs to an &agr;-HCCA, is reacted with alcohol at an equivalent amount to give a THFA ester adduct which is then subjected to optical resolution in the presence of an enantioselectively hydrolyzing enzyme to afford an R- or S-form of THFA while leaving a counter enantiomeric form of the THFA ester, which is extracted with an organic solvent. Using a non-enantioselective enzyme or
Lim Jong-Ho
Lim Sang-Chul
Uhm Ki-Nam
Abelman ,Frayne & Schwab
Afremova Vera
Saucier Sandra E.
SK Corporation
LandOfFree
Method for preparing an R- or S-form of &agr;-substituted... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for preparing an R- or S-form of &agr;-substituted..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for preparing an R- or S-form of &agr;-substituted... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2899739