Epi-neoverrucosane- and epi-homoverrucosane-type diterpenoids from Fossombronia alaskana

Abstract

Fossombronia alaskana, a rare arctic liverwort, was axenically cultured. Phytochemical investigation of the gametophytes afforded five new epi-neoverrucosane-type diterpenoids (5-oxo- epi-neoverrucosane, 13-hydroxy-5-oxo- epi-neoverrucosane, 8 α-acetoxy-13-hydroxy-5-oxo- epi-neoverrucosane, 8 α,16-diacetoxy-13-hydroxy-5-oxo- epi-neoverrucosane and 8 α,13-dihydroxy-5-oxo- epi-neoverrucosane) together with the previously known 5 β-hydroxy- epi-neoverrucosane. The overall number of natural products with the epi-neoverrucosane skeleton is now seven. In addition, the new homoverrucosane-type diterpene 5,18-dihydroxy- epi-homoverrucosane was isolated. The structures were elucidated by X-ray crystallography (5-oxo- epi-neoverrucosane), two-dimensional NMR spectroscopy and chemical degradation, resulting in some unsaturated epi-neoverrucosane structures.