Crinatusins, Bioactive Diels–Alder Adducts from Cyathocalyx crinatus

Abstract From the stems of Cyathocalyx crinatus , a rain forest plant in Borneo, six new Diels–Alder adducts, named crinatusins A 1 , A 2 , B 1 , B 2 , C 1 , and C 2 , together with a known chalcone derivative, 4′,6′-dihydroxy-3′,5′-dimethyl-2′-methoxychalcone, have been obtained. Their structures were determined on the basis of spectroscopic data and chemical methods. Crinatusins showed a lethal toxicity against brine shrimp.