Preparation and reactions of optically active cyanohydrins using the (R)-hydroxynitrile lyase from Prunus amygdalus

Cyanuration of 2-naphthaldehyde (1) and 5-methyl-2-furaldehyde (2) yielded the racemic 2-hydroxy-2-(β-naphthyl)ethanenitrile (R,S)-3 and 2-hydroxy-2-(5-methyl-2-furyl)ethanenitrile (R,S)-5, respectively. The same reaction can be completed by using acetone cyanohydrin (4) as a transcyanating agent. The optically active (R)-3 and (S)-5 could be respectively obtained by hydrocyanation of 1 and 2 using (R)-hydroxynitrile lyase (R)-PaHNL [EC 4.1.2.10] from almonds (Prunus amygdalus) as a chiral catalyst. Cyanohydrins 3 and 5 in their racemic and optically active forms undergo a number of transformations which involve either the hydroxyl group or the cyanide function. Moreover, derivatization of 3 and 5 with (S)-Naproxen®chloride (S)-14 gave the respective diastereoisomers. The optical activity of (R)-3 and (S)-5 as well as their derivatives were recorded. The postulated structures for the new products were supported with compatible elementary and spectroscopic (IR, ¹H NMR, ¹³C NMR, MS, and single crystal X-Ray crystallography) analyses. The antimicrobial activity of some selected racemic new products and their respective optically active analogues were also undertaken.