Microbial Transformation of Sesquiterpenes, (−)‐ Ambrox ® and (+)‐Sclareolide

The microbial transformation of (−)‐ Ambrox ® ( 1 ), a perfumery sesquiterpene, by a number of fungi, by means of standard two‐stage‐fermentation technique, afforded ambrox‐1 α ‐ol ( 2 ), ambrox‐1 α ,11 α ‐diol ( 3 ), ambrox‐1 α ,6 α ‐diol ( 4 ), ambrox‐1 α ,6 α ,11 α ‐triol ( 5 ), ambrox‐3‐one ( 6 ), ambrox‐3 β ‐ol ( 7 ), ambrox‐3 β ,6 β ‐diol ( 8 ), 13,14,15,16‐tetranorlabdane‐3,8,12‐triol ( 9 ), and sclareolide ( 10 ) ( Schemes 1 and 2 ). Further incubation of compound 10 with Cunninghamella elegans afforded 3‐oxosclareolide ( 11 ), 3 β ‐hydroxysclareolide ( 12 ), 2 α ‐hydroxysclareolide ( 13 ), 2 α ,3 β ‐dihydroxysclareolide ( 14 ), 1 α ,3 β ‐dihydroxysclareolide ( 15 ), and 3 β ‐hydroxy‐8‐episclareolide ( 16 ) ( Scheme 3 ). Metabolites 2 – 5, 12, 13 , and 16 were found to be new compounds. The major transformations include a reaction path involving hydroxylation, ether‐bond cleavage and inversion of configuration. Metabolites 11 – 16 of sclareolide showed significant phytotoxicity ( Table 1 ). The structures of the metabolites were characterized on the basis of spectroscopic techniques.