Microbial Transformations of Gelomulide G: A Member of the Rare Class of Diterpene Lactones

Microbial transformation of gelomulide G (3 β ,6 β‐ diacetoxy‐8 β ,14 β‐ epoxyabiet‐13(15)‐en‐16,12‐olide, 1 ) was carried out. Incubation of 1 with Aspergillus niger afforded two new metabolites, 3 β ,6 β‐ diacetoxy‐8 β ,14 β‐ dihydroxyabiet‐13(15)‐en‐16,12‐olide ( 2 ) and 3 β ,6 β‐ diacetoxy‐14 β‐ hydroxyabieta‐8(9),13(15)‐dien‐16,12‐olide ( 3 ). While Cunninghamella elegans afforded the 14‐epimer of 2 , i.e. , 3 β ,6 β‐ diacetoxy‐8 β ,14 α‐ dihydroxyabiet‐13(15)‐en‐16,12‐olide ( 4 ), along with 3 β ‐acetoxy‐6 β‐ hydroxy‐8 β ,14 β‐ epoxyabiet‐13(15)‐en‐16,12‐olide ( 5 ). The structures of the transformed products 2 – 5 were deduced to be new on the basis of MS and NMR data.