ENANTIOSPECIFIC ENZYMATIC PREPARATION OF (2S,3S)-3-ALKYLASPARTIC ACIDS OF CURRENT INTEREST IN THE SYNTHESIS OF STEREOREGULAR POLY[BETA-(2S,3S)-3-ALKYLMALIC ACIDS] AS NEW OPTICALLY-ACTIVE FUNCTIONAL POLYESTERS

(2S,3S)-3-methyl- and 3-isopropylaspartic acids were synthesized by bi oconversion of the corresponding alkylfumarates (mesaconate and 3-isop ropylfumarate) using beta-methylaspartase from cell-free extracts of C lostridium tetanornorphum. Optically pure (2S,3S)-3-alkylaspartic acid s were transformed in several steps to benzyl (3S,4R) 3-alkylmalolacto nates without any racemization of the two chiral centers. These optica lly active alpha,beta-substituted-beta-lactones were polymerized by an ionic ring opening polymerization yielding optically active semi-cryst alline polyesters. C-13 NMR analysis of poly[benzyl beta-3-isopropylma late] in CDCl3 has shown that only the iso-type stereosequence is pres ent in the polymer, indicating that the macromolecular chain is consti tuted by the only units of benzyl beta-(2S,3S)-3-isopropylmalate monom er. The polymerization reaction was done without any racemization of t he two stereogenic centers as in the case of benzyl (3S,4R)-3-methylma lolactonate. (C) 1996 Wiley-Liss, Inc.