Schiff Bases of Amino Acid Esters as New Substrates for the Enantioselective Enzymatic Hydrolysis and Accompanied Asymmetric Transformations in Aqueous Organic Solvents1,2

The enzyme (lipases and chymotrypsin)-catalyzed hydrolysis of Schiff bases derived from racemic amino acid esters and aromatic aldehydes has been investigated. The reactions were successfully carried out in different aqueous organic solvents at ambient temperature, but the aqueous acetonitrile (5.4% water content by volume) was the solvent of choice. The l -amino acid (ee 98%) precipitated out from the solution as the reaction progressed, and the liberated aldehyde and unhydrolyzed d -ester (ee 40−98%) remained in the solution. The range of substrates included amino acids having different types of side chains. The addition of an organic base (DABCO) into the solution resulted in the racemization of the remaining d -ester and the additional hydrolysis of the substrate, thus leading to the effective asymmetric transformation of the initial ester. Upto 87.5% of the initial racemate was converted into the l -enantiomer.