Hydroxynitrile lyase catalyzed enantioselective HCN addition to O-protected alpha-hydroxyaldehydes

Various O-protected glycol- and racemic lactaldehydes 3 and 6 as well as O- allyl protected racemic alpha-hydroxyaldehydes 7 (R-1=Et Pr, Bu) have been prepared to investigate and perform a stereoselective Kiliani-Fischer synth esis by hydroxynitrile lyase (HNL) catalyzed addition of HCN. From all prot ecting groups investigated the allyl moiety was most suitable. (R)-PaHNL fr om bitter almonds (Prunus amygdalus), yielding the (2S)-cyanohydrins 8-10, was found to be a more stereoselective catalyst than (S)-MeHNL from maniok (Manihot esculenta). While (R)-PaHNL led to enantiomeric excesses greater t han or equal to 93%, with (S)-MeHNL the (2R)-cyanohydrins 8-10 were obtaine d with enantiomeric excesses less than or equal to 78%. (C) 1999 Elsevier S cience Ltd. All rights reserved.