Seven chromanoid norbisabolane derivatives from the marine-alga-endophytic fungus Trichoderma asperellum A-YMD-9-2

Abstract

An examination of the endophytic fungus Trichoderma asperellum A-YMD-9-2 obtained from the marine red alga Gracilaria verrucosa led to the isolation of seven new chromanoid norbisabolane derivatives, trichobisabolins I–L (1–4) and trichaspsides C–E (5–7). Their structures and relative configurations were established on the basis of spectroscopic techniques, mainly including 1D/2D NMR and MS, and the absolute configuration of 1 was assigned by X-ray crystallographic analysis using Cu Kα radiation. All of these isolates feature a 1,9-epoxy ring system, and 5–7 represent the second occurrence of norbisabolane aminoglycosides. Compounds 1–7 exhibited potent inhibition of several marine phytoplankton species.