Selectivity of the (S)-oxynitrilase from Hevea brasiliensis towards α- and β-substituted aldehydes

The performance of (S)-oxynitrilase from Hevea brasiliensis (HbHNL) has been investigated with several α- and β-substituted alkyl or alkoxy aldehydes and the results have been compared to the data previously obtained with the (R)-specific enzyme from almonds (PaHNL). With both enzymes there was no chiral discrimination between the enantiomers of the racemic substrates, therefore this reaction cannot be used as a preparative method to achieve both the kinetic resolution of the starting racemic aldehyde and the production of diastereomerically pure (or enriched) cyanohydrins. Additionally, in comparison with the (R)-PaHNL the (S)-selective enzyme from Hevea gave products with higher de, but was more negatively effected by oxygenated substituents.