Novel derivatives of ent-17,19-dihydroxy-16betaH-kaurane obtained by biotransformation with Verticillium lecanii

In the search for new routes in the synthesis of hydroxylated kaurane diterpenoids, Verticillium lecanii, grown in a mineral liquid medium for 48 h, was fed with ent-17,19-dihydroxy-16betaH-kaurane, obtained by hydroboration/oxidation of kaurenoic acid, a natural product easily isolated from plants of the genera Xylopia (Annonaceae) and Wedelia (Asteraceae). After 14 days, the culture medium was extracted with ethyl acetate, and the metabolites were purified by column chromatography on silica gel. The results show that V. lecanii biotransformed the starting material into three novel compounds: ent-11alpha,17,19-trihydroxy-16betaH-kaurane; ent-7alpha,17,19-trihydroxy-16betaH-kaurane; and ent-7beta,17,19-trihydroxy-16betaH-kaurane, the structures of which were fully elucidated by using classical and modern two-dimensional NMR techniques.