Metabolites of Cyathus helenae. A New Class of Diterpenoids

Allocyathin B3 and cyathin A3, metabolites of the bird's nest fungus Cyathus helenae Brodie are shown to possess structures [Formula: see text] and [Formula: see text], respectively. In the solid state allocyathin B3 exists in the hydroxyketone form 2a, while cyathin A3 is in the hemiketal form 6a. In each case acetylation gives the diacetyl derivative of the hydroxyketone form whereas treatment with methanolic HCl gives an internal ketal. Allocyathin B3 and cyathin A3 have been correlated by hydrogénation to the common product 13a, and by transformation of each to the aldehyde 12a. These compounds are representatives of a new class of diterpenoids. Their biogenesis from geranylgeranyl pyrophosphate is discussed.