A partial synthesis of the skeleton of deoxypumiloside, a putative intermediate in camptothecin biosynthesis

Ajmalicine (3) was used as the starting material for the synthesis of a camptothecin-like skeleton. After C-21 activation through allylic conjugation, regiospecific, tertiary amine oxidation was achieved with mercury salts. Subsequent biomimetic oxidation of the indole nucleus then gave quinolone lactam 14. A two-step process finally afforded 4, a close analogue of deoxypumiloside (5), one of the putative intermediates in the biosynthesis of camptothecin.