On the selectivity of oxynitrilases towards alpha-oxygenated aldehydes

Different alpha -alkoxy and alpha,beta -di-alkoxy substituted aldehydes hav e been submitted to the catalytic action of the oxynitrilases from almond ( PaHNL) or from Hevea brasiliensis (HbHNL), in order to explore the possibil ity of using these enzymes for the preparation of complex cyanohydrins. The selectivity of both enzymes towards these compounds was found to be largel y dependent on the substitutents, being low with the aldehydes carrying the sterically more demanding phenyl substituent. Contrary to the chemical add ition of HCN, which always occurs with a slight preference for the formatio n of the anti diastereoisomers, the enzymatic cyanuration-occurring with a facial preference, Si or Re according to the biocatalyst used-gave a mixtur e of cyanohydrins that, depending on the starting enantiomeric aldehyde, ca n be enriched in the syn diastereoisomers. (C) 2001 Elsevier Science Ltd. A U rights reserved.