Synthesis and polymerization of benzyl (3R,4R)-3-methylmalolactonate via enzymatic preparation of the chiral precursor.
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.
Bear
M M
MM
Laboratoire de Physico-Chimie des Biopolymères, UMR 27 CNRS-Université Paris XII, Thiais, France.
Monne
C
C
Robic
D
D
Campion
G
G
Langlois
V
V
Rimbault
A
A
Bourbouze
R
R
Guerin
P
P
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
D007783:Lactones; C115828:benzyl(3r,4)-3-methylmalolactonate; D001220:Aspartate Ammonia-Lyase