Chemical semisynthesis and biotransformation with Rhizopus nigricans of several sesquiterpenes: Obtention of new 1 alpha- and 2 alpha-hydroxyselinanederivatives

Starting with the natural product vulgarin, isolated from Artemisia canarie nsis, several acetylated, acetonated and oxidized polyhydroxylated eudesman es and eudesmenes were semisynthesized. Some of these derivatives were biot ransformed with the fungus Rhizopus nigricans and thus metabolites with new hydroxylation, reduction and/or deacetylation were isolated. Incubation of 1 beta,6 alpha-diacetoxy- 12-hydroxy-5 alpha,11 beta-H-eudesm-4(15)-ene ga ve a 2-hydroxyselinane derivative in high yield (60%). Microbiological tran sformations of 1-oxo- and 6-oxoeudesmanes gave other useful hydroxyselinane derivatives in high proportions as the result of a stereoselective reducti on of the carbonyl groups at these positions by the fungus on the beta-face . Moreover, R. nigricans gave occasionally, regioselective deacetylated and /or hydrolyzed isopropylidene compounds. (C) 2000 Elsevier Science Ltd. All rights reserved.