Enzymatic resolution of .alpha.-tertiary carboxylic acid esters

A method of separating the enantiomers of racemic carboxylic acid esters of general formula ##STR4## wherein R.sub.1 represents alkyl, substituted alkyl, arylalkyl or substituted arylalkyl;

• R.sub.2 represents alkyl, haloalkyl or substituted alkyl;
• R.sub.3 represents an alkyl moiety having from 1 to 8 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, substituted aryl, arylalkyl or substituted arylalkyl;
• and X represents amino, alkylamino, arylalkylamino, arylamino, acylamino, hydrazino, alkylhydrazino, arylalkylhydrazino, arylhydrazino, acylhydrazino, hydroxyl, or alkoxy;
• and Y represents oxygen or sulfur;
• provided that R.sub.1 and R.sub.2 and X are different from each other, by the preferential enzymatic hydrolysis of the (S)-enantiomer of the ester, said method comprising contacting the racemic ester in an aqueous medium with a serine carboxypeptidase selected from the group consisting of serine carboxypeptidase % serine carboxypeptidase P and serine carboxypeptidase W to hydrolyze from about 5% to about 95% of the ester, and separating the hydrolysis product from the unreacted starting material.