The Microbiological Transformation of Two 15β-Hydroxy-ent-kaurene Diterpenes by Gibberella fujikuroi

The incubation of 15 beta -hydroxy-3-oxo-ent-kaur-16-ene (1) with the fungus Gibberella fujikuroi afforded 11 beta -hydroxy-3,15-dioxo-ent-kaurane (6), 11 beta ,15 beta -dihydroxy-3-oxo-ent-kaur-16-ene (8), 7 beta ,11 beta ,15 beta -trihydroxy-3-oxo-ent-kaur-16-ene (9), 7 alpha ,11 beta -dihydroxy-3,15-dioxo-ent-kaurane (7), and 7 alpha ,11 beta ,15 beta -trihydroxy-3-oxo-ent-kaur-16-ene (10). The incubation of 15 beta -hydroxy-ent-kaur-2,16-diene (3) with the same fungus yielded 70 alpha ,11 beta -dihydroxy-15-oxo-ent-kaur-2-ene (12), 70 alpha ,11 beta ,15 beta -trihydroxy-ent-kaur-2,16-diene (13), 7 beta ,15 beta -dihydroxy-ent-kaur-2,16-dien-19,6-olide (14), 1 beta ,7 beta ,15 beta -trihydroxy-ent-kaur-2,16-dien-19-oic acid (15), 7 alpha ,11 beta ,16 alpha -trihydroxy-15-oxo-ent-kaur-2-ene (17), and 7 alpha ,15 beta ,17-trihydroxy-11 beta ,16 beta -epoxy-ent-kaur-2-ene (19). These results indicated that a 3-oxo group in ent-kaur-16-ene derivatives inhibits the oxidation at C-19, typical of the biosynthetic pathway of gibberellins and kaurenolides, while a 2,3-double bond or a 15 beta -OH does not. In both substrates a 15 beta -alcohol directs hydroxylations at C-11( beta ) and C-7( alpha ), while in those with a 2,3-double bond the functionalization of C-1( beta ) is favored.