Bioactive and other sesquiterpenes from Chiloscyphus rivularis

Bioassay-directed fractionation of the methyl ethyl ketone extract of Chiloscyphus rivularis yielded five new sesquiterpenes, 12-hydroxychiloscyphone (2), chiloscypha-2,7-dione (3), 12-hydroxychiloscypha-2,7-dione (4), chiloscypha-2,7,9-trione (5), and rivulalactone (6) in addition to the known sesquiterpenes, 4-hydroxyoppositan-7-one (7), chiloscyphone (1), and isointermedeol (8). The structure and stereochemistry of rivulalactone, a novel trinorsesquiterpene, was confirmed by its synthesis starting from 1. Compound 2 showed selective bioactivity in our yeast-based DNA-damaging assay and cytotoxicity to human lung carcinoma cells.