Isolation and structure elucidation of new sesquiterpenes of protoilludane origin from the fungus Clavicorona divaricata

Four novel sesquiterpenes of protoilludane origin, divaricatines A 3a and B 3b, 7-epitsugicoline H 4a and tsugicoline M 5a have been isolated from agar cultures of the fungus Clavicorona divaricata (Basidiomycetes). Their structures were elucidated by means of NMR studies and chemical correlations. All the metabolites are weakly active on bacteria but inhibited the germination of the water cress Lepidium sativum. A possible mechanism of their formation from the protoilludane tsugicoline A 1 is suggested. A fifth metabolite, the norsesquiterpene tsugicoline L 2b, was also isolated from the same fungus together with the known tsugicoline I 2a.