New indole glucosides as biosynthetic intermediates of camptothecin from the fruits of Camptotheca acuminata

Six new indole glucosides (1-6) and fifteen known alkaloids (7-21) were isolated from the fruit of Camptotheca acuminata. The planar structures of 1-6 were determined on the basis of spectroscopic data analysis and their absolute configurations were established by CD. The isolated indole glucosides showed a clear biosynthetic pathway of camptothecin (7), which started from tryptamine and secologanin and was proposed by synthetic chemists previously. Particularly, compound 1 supplemented the process of the transformation from pumiloside (20) or 3-epi-pumiloside (21) to camptothecin (7). In addition, camptothecin 10-O-beta-D-glucopyranoside (13) and norcamptothecin (17), synthesized in the early structural modification of 7, were first isolated from the natural resources. The new compounds 1-6 were screened for their in vitro cytotoxicity but they did not show any exciting result. (C) 2015 Elsevier B.V. All rights reserved.