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Starting with the natural product vulgarin, isolated from Artemisia canariensis , several acetylated, acetonated and oxidized polyhydroxylated eudesmanes and eudesmenes were semisynthesized. Some of these derivatives were biotransformed with the fungus Rhizopus nigricans and thus metabolites with new hydroxylation, reduction and/or deacetylation were isolated. Incubation of 1β,6α-diacetoxy-12-hydroxy-5α,11β- H -eudesm-4(15)-ene gave a 2-hydroxyselinane derivative in high yield (60%). Microbiological transformations of 1-oxo- and 6-oxoeudesmanes gave other useful hydroxyselinane derivatives in high proportions as the result of a stereoselective reduction of the carbonyl groups at these positions by the fungus on the β-face. Moreover, R. nigricans gave occasionally, regioselective deacetylated and/or hydrolyzed isopropylidene compounds. |
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