THE BIOTRANSFORMATION OF 2 3,15-OXYGENATE ENT-KAURANE DERIVATIVES BY GIBBERELLA-FUJIKUROI

The incubation of 3 alpha,15 beta-dihydroxy-ent-kaur-16-ene (1) with t he fungus Gibberella fujikuroi gave 3 alpha,7 alpha,15 beta-tribydroxy -ent-kaur-16-ene (5), 3 alpha,11 beta,15 beta-trihydroxy-ent-kaur-16-e ne (13), and 3 alpha,7 alpha,11 beta,15 beta-tetrahydroxy-ent-kaur-16- ene (17). The ether 3 alpha,15 beta-dihydroxy-11 beta,16 beta-epoxy-en t-kaurane (15) and the isomerized compounds 3 alpha,7 alpha-dihydroxy- 15-oxo-ent-(16S)-kaurane (8) and 3 alpha,7 alpha,11 beta-trihydroxy-15 -oxo-ent-(ISS)-kaurane (10) were also obtained. The incubation of 3 al pha-hydroxy-15-oxo-ent-(16S)-kaurane (7) with the fungus also afforded compounds 8 and 10, as well as 3 alpha,11 beta-dihydroxy-15-oxo-ent-( 16S)-kaurane (20), 3 alpha,6 alpha,11 beta-trihydroxy-15-oxo-ent-(16S) -kaurane, (22) 3 alpha,6 beta,7 alpha-trihydroxy-15-oxo-ent-(16S)-kaur ane (25), and 3 alpha,11 beta,16 alpha-trihydroxy-15-oxo-ent-(16S)-kau rane (27). These results indicate that in 3,15-oxygenated ent-kaurane derivatives the presence of a 3 alpha-hydroxyl inhibits oxidation at C -19, while a 15 beta-hydroxyl or a 15-oxo group directs hydroxylation at C-11(beta) and C-7(alpha).