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 bioconversion of the corresponding alkylfumarates (mesaconate and 3-isopropylfumarate) using beta-methylaspartase from cell-free extracts of Clostridium tetanornorphum. Optically pure (2S,3S)-3-alkylaspartic acids were transformed in several steps to benzyl (3S,4R) 3-alkylmalolactonates without any racemization of the two chiral centers. These optically active alpha,beta-substituted-beta-lactones were polymerized by anionic ring opening polymerization yielding optically active semi-crystalline polyesters. C-13 NMR analysis of poly[benzyl beta-3-isopropylmalate] in CDCl3 has shown that only the iso-type stereosequence is present in the polymer, indicating that the macromolecular chain is constituted by the only units of benzyl beta-(2S,3S)-3-isopropylmalate monomer. The polymerization reaction was done without any racemization of the two stereogenic centers as in the case of benzyl (3S,4R)-3-methylmalolactonate. (C) 1996 Wiley-Liss, Inc.