A dimeric thymol derivative from Arnica sachalinensis

Abstract A novel, unusual terpenoid compound was found as one of the main constituents in Arnica sachalinensis (Asteraceae). Its structure was established by NMR spectroscopic studies including COSY, HMQC, HMBC, and DEPT-135 experiments as a dimeric thymol derivative with a new spiro[benzofuran-3(2 H ),2′-pyrano[2,3- b ]benzofuran] ring system. The stereochemistry and a possible biosynthesis of this compound are discussed and its antifeedant activity was tested against 5 th instar larvae of Spodoptera litura , using leaf disk bioassays.