Randomisation and apparent regiospecificity in the incorporation of acetate into the monoterpenoid segment of the Corynanthe alkaloids

Abstract

Incorporation of ¹³C-enriched acetates into ajmalicine (3) by tissue cultures of Catharanthus roseus shows that, although administered [2-¹³C]-and [1,2-¹³C₂]-acetates are extensively randomised prior to incorporation, the 16-, 17-, 18-, 19-, and 22-positions of monoterpene skeleton are selectively enriched as a result of equilibration of ¹³C enrichment in the intermediate 3-hydroxy-3-methylglutaryl (HMG) CoA pool; in contrast, DL-[2-¹³C]mevalonic acid was incorporated preferentially into dimethylailylpyrophosphate-derived unit of the monoterpene moiety.