SYNTHESIS OF (R)-2-HYDROXY-3-ENOIC AND (S)-2-HYDROXY-3-ENOIC ACID-ESTERS

The synthesis of (R)- and (S)-2-hydroxy-3-enoic acid esters [(R)-1a-d and (S)-1a-c] is described. The (R) enantiomers were prepared by a Pin ner synthesis from the corresponding (R)-cyanohydrins [(R)-2a-d], whic h in turn were obtained by R-oxynitrilase- (E.C. 4.1.2.10)-catalyzed a ddition of HCN to the alpha,beta-unsaturated aldehydes 3a-d. For the p reparation of the (S) enantiomers an inversion of the configuration ha d to be implemented. A critical evaluation of the two possible sequenc es: inversion of the configuration of the cyanohydrins followed by sol volysis of the nitrile function, and solvolysis of the cyanohydrins fo llowed by inversion of the configuration of the resulting alpha-hydrox y esters, came out in favor of the latter pathway.