The biotransformation of two 3,15-oxygenate ent-kaurane derivatives by Gibberella fujikuroi

Abstract

The incubation of 3a,15B-dihydroxy-ent-kaur-16-ene (1) with the fungus Giobberella fujikuroi gave 3a,7a,15B-trihydroxy-ent-kaur-16-ene (5), 3a,11B,15B-trihydroxy-ent-kaur-16-ene (13), and 3a,7a,11B,15B-tetrahydroxy-ent-kaur-16-ene (17). The ether 2a,15B-dihydroxy-11B,16B-epoxy-ent-kaurane (15) and the isomerized compounds 3a,7a-dihydroxy-15-oxo-ent-(16S)-kaurane (8) and 3a,7a,11B-trihydroxy-15-oxo-ent-(16S)-kaurane (10) were also obtained. The incubationof 3a-hydroxy-15-oxo-ent-(16S)-kaurane (7) with the fungus also afforded compounds 8 and10, as well as 3a,11B-dihydroxy-15-oxo-ent-(16S)-kaurane (20), 3a,6a,11B-trihydroxy-15-oxo-ent-(16S)-kaurane, (22) 3a,6B,7a-trihydroxy-15-oxo-ent-(16S)-kaurane (25), and 3a,11B,16a-trihydroxy-15-oxo-ent-(16S)-kaurane (27). These results indicate that in 3,15-oxygenated ent-kaurane derivatives the presence of a 3a-hydroxyl inhibits oxidation at C-19, whilw a 15B-hydroxyl or a 15-oxo group directs hydroxylation at C-11(B) and C-7(a).