title: Synthesis and polymerization of benzyl (3R,4R)-3-methylmalolactonate via enzymatic preparation of the chiral precursor.
abstract: beta-methylaspartate ammonia-lyase, EC 4.3.1.2, (beta-methylaspartase) from Clostridium tetanomorphum was used to produce a 40/60 molar ratio of (2S,3R) and (2S,3S)-3-methylaspartic acids, 2a and 2b, respectively, from mesaconic acid 1 as substrate, on a large scale. To prepare (3R,4R)-3-methyl-4-(benzyloxycarbonyl)-2-oxetanone (benzyl 3-methylmalolactonate) 6, 2a and 2b were transformed, in the first step, into 2-bromo-3-methylsuccinic acids 3a and 3b and separated. After three further steps, (2S,3S)-3a yielded the alpha, beta-substituted beta-lactone (3R,4R) 6 with a very high diastereoisomeric excess (> 95% by chiral gas chromatography). The corresponding crystalline polymer, poly[benzyl beta-(2R,3S)-3-methylmalate] 8, prepared by an anionic ring opening polymerization, was highly isotactic as determined by 13C NMR. Catalytic hydrogenolysis of lactone 6 yielded (3R,4R)-3-methyl-4-carboxy-2-oxetanone (3-methylmalolactonic acid) 7, to which reactive, chiral, or bioactive molecules can be attached through ester bonds leading to polymers with possible therapeutic applications. Because of the ability of beta-methylaspartase to catalyse both syn- and anti-elimination of ammonia from (2S,3RS)-3-methylaspartic acid 2ab at different rates, the (2S,3R)-stereoisomer 2a was retained and isolated for further reactions. These results permit the use of the chemoenzymatic route for the preparation of both optically active and racemic polymers of 3-methylmalic acid with well-defined enantiomeric and diastereoisomeric compositions.
authors.affiliation: Laboratoire de Physico-Chimie des Biopolymères, UMR 27 CNRS-Université Paris XII, Thiais, France.
authors.forename: M M
authors.initials: MM
authors.lastname: Bear
authors.forename: C
authors.initials: C
authors.lastname: Monne
authors.forename: D
authors.initials: D
authors.lastname: Robic
authors.forename: G
authors.initials: G
authors.lastname: Campion
authors.forename: V
authors.initials: V
authors.lastname: Langlois
authors.forename: A
authors.initials: A
authors.lastname: Rimbault
authors.forename: R
authors.initials: R
authors.lastname: Bourbouze
authors.forename: P
authors.initials: P
authors.lastname: Guerin
mesh_terms: D001220:Aspartate Ammonia-Lyase / Q000378:metabolism; D002384:Catalysis; D002849:Chromatography, Gas; D003013:Clostridium / Q000201:enzymology; D007783:Lactones / Q000138:chemical synthesis*; D009682:Magnetic Resonance Spectroscopy; D013237:Stereoisomerism
chemical_list: D007783:Lactones; C115828:benzyl(3r,4)-3-methylmalolactonate; D001220:Aspartate Ammonia-Lyase