Molluscicidal acridone alkaloids from Angostura paniculata: isolation, structures, and synthesis

Two novel acridone alkaloids, cuspanine [1] and cusculine [2], were isolated from the CH2Cl2 extract of the leaves of Angostura paniculata (Rutaceae). Their structures were established as 1-hydroxy-2,3,5,6-tetramethoxy-9-acridone for 1 and 1,2,3,5,6-pentamethoxy-9-acridone for 2 by means of spectroscopic studies, in particular nmr. These structural assignments were confirmed by synthesis, using a direct metallation method as a key reaction. Both alkaloids exhibited moderate molluscicidal activity against an aquatic snail, Biomphalaria glabrata, and cytotoxicity against several types of carcinoma cell lines.