Abstract

Halogenation reactions of vindoline and 14,15-dihydrovindoline and its hydrochloric salt were investigated and the anomalous reductions were discussed. Performing the hydrogenation in the presence of chlorine-containing solvent, e.g. dichloromethane, hydrogenolysation reaction of chlorine also took place. In this case unexpected chlorinated product could be observed. Performing the hydrogenation reaction only in the presence of methanol, the expected reduced derivative was obtained. Upon bromination of vindoline with excess NBS, oxidation products with ring contraction and developing an oxygen bridge were isolated. The fluorination reactions of vinblastine using Selectfluor^® and xenon difluoride as the fluorination reagents were unsuccessful because of the decomposition of the starting material. Reactions of vindoline with Selectfluor^® a mixture of products were obtained. Using xenon difluoride as fluorination agent resulted in a pure quinoidal product containing the fluorine atom in the bridgehead carbon atom of the indole ring. The fluorination of catharanthine gave an anomalous indolenine type product.

Keywords: Vindoline, catharanthine, halogenation, Selectfluor^®, xenon difluoride, quinoidal products.

Graphical Abstract