SCHIFF-BASES OF AMINO-ACID ESTERS AS NEW SUBSTRATES FOR THE ENANTIOSELECTIVE ENZYMATIC-HYDROLYSIS AND ACCOMPANIED ASYMMETRIC TRANSFORMATIONS IN AQUEOUS-ORGANIC SOLVENTS

The enzyme (lipases and chymotrypsin)-catalyzed hydrolysis of Schiff b ases derived from racemic amino acid esters and aromatic aldehydes has been investigated. The reactions were successfully carried out in dif ferent aqueous organic solvents at ambient temperature, but the aqueou s acetonitrile (5.4% water content by volume) was the solvent of choic e. The L-amino acid (ee 98%) precipitated out from the solution as the reaction progressed, and the liberated aldehyde and unhydrolyzed D-es ter (ee 40-98%) remained in the solution. The range of substrates incl uded amino acids having different types of side chains. The addition o f an organic base (DABCO) into the solution resulted in the racemizati on of the remaining D-ester and the additional hydrolysis of the subst rate, thus leading to the effective asymmetric transformation of the i nitial ester. Upto 87.5% of the initial racemate was converted into th e L-enantiomer.