The microbiological transformation of 7alpha-hydroxy-ent-kaur-16-ene derivatives by Gibberella fujikuroi

The biotransformation of 7alpha-hydroxy-ent-kaur-16-ene (epi-candol A) by the fungus Gibberella fujikuroi gave 7alpha,16alpha,17-trihydroxy-ent-kaur-16-ene and a seco-ring B derivative, fujenoic acid, whilst the incubation of candicandiol (7alpha,18-dihydroxy-ent-kaur-16-ene) and canditriol (7alpha,15alpha,18-trihydroxy-ent-kaur-16-ene) afforded 7alpha,18,19-trihydroxy-ent-kaur-16-ene and 7alpha,11beta,15alpha,18-tetrahydroxy-ent-kaur-16-ene, respectively. The presence of a 7alpha-hydroxyl group in epi-candol A avoids its biotransformation along the biosynthetic pathway of gibberellins, and directs it to the seco-ring B acids route. The 15alpha-hydroxyl group in canditriol inhibits oxidation at C-19 and direct hydroxylation at C-11(beta). The formation of fujenoic acid, from 7alpha-hydroxy-ent-kaur-16-ene, probably occurs via 7alpha-hydroxykaurenoic acid and 7-oxokaurenoic acid, with subsequent hydroxylation at the C-6(beta) position.