Anodic fragmentation of catharanthine and coupling with vindoline. Formation of anhydrovinblastine

摘要

The anodic oxidation of catharanthine (Cath) in the presence of vindoline (Vind) performed in MeCN-Et_4NCIO_4 at a controlled potential yields (16'S)- and (16'R)-anhydrovinblastine (AVBL) in S 4.3:1 ratio. The favorable stereoselectivity found at room temperature is rationalized by proposing The coupling of generated dication 1a++ and Vind at the electrode surface. The mechanism of the Overall fragmentation/coupling reaction was studied using electrochemical techniques and the Technique of homogeneous redox catalysis.