Biotransformation of monoterpenoid ketones by yeasts and yeast-like fungi

A large number of yeasts were screened for the biotransformation of (-)-piperitone, (+)- and (-)-carvone, (-)menthone, (+)-pulegone and (-)-verbenone. A relatively small number of yeasts gave hydroxylation products of (-)-piperitone. Products obtained from (-)-piperitone were 7-hydroxy-piperitone, cis-6-hydroxy-piperitone, trans-6-hydroxy-piperitone and 2-isopropyl-5 -methyl -hydroquinone. Yields for the hydroxylation reactions varied between 84b and 60%, corresponding to product concentrations of 0.04 g/l to 0.3 g/l. Not one of the yeasts tested reduced (-)-piperitone. In contrast, almost all the yeasts tested gave reduction of carvone, although the enzyme activity varied. Reduction of (-)-carvone was often much faster than reduction of (+)-carvone. Some yeasts only reduced the carbon=carbon double bond to yield the dihydrocarvone isomers with the stereochemistry at C-l always R, while others also reduced the ketone to give the dihydrocarveols with the stereochemistry at C-2 always S for(-)-carvone, but sometimes S and sometimes R for (+)-carvone. In the case of(-)-carvone yields of up to 90% were obtained within 2 h. Only one organism, a Hormonema isolate (UOFS Y-0067), quantitatively reduced(-)-menthone and(+)-pulegone to(+)-neomenthol. This same organism reduced (4S)-isopiperitenone to (3R,4S)-isopiperitenol, a precursor of (-)-menthol. (C) 1998 Elsevier Science B.V. All rights reserved.