Asepterpenedol A, a novel indole sesquiterpene with a rare 7/6/5/5/6/6-hexacyclic scaffold from a marine-derived fungus Chloridium sp. NBU3282

Asepterpenedol A (1), a novel indole sesquiterpene with a rare scaffold, was isolated from the seaweed-derived endophytic fungus Chloridium sp. NBU3282. The structure was elucidated by extensive spectroscopic analysis, and the stereochemical configuration was established through analysis of ROESY spectra as well as quantum chemical calculations including DP4+ probability analysis and electronic circular dichroism (ECD) calculations. Notably, compound 1 represents the first indole sesquiterpene featuring a unique seven-membered ether ring motif, forming the rare 7/6/5/5/6/6 hexacyclic skeleton. Asepterpenedol A (1) exhibited cytotoxicity against three tumor cell lines (HL-60, HepG2 and CCRF-CEM) as well as antimicrobial activity against Candida Albicans. In addition, a plausible biosynthetic pathway for compound 1 was also proposed.