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-β-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.

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