Synthesis and oxidative fragmentation of catharanthine analogs. Comparison to the fragmentation - Coupling of catharanthine and vindoline

Article abstract of DOI:10.1016/S0040-4020(98)00289-0

Two new analogs of catharanthine have been synthesized in racemic form. They differ from catharanthine in the fusion of the indole ring to the non- aromatic portion of the iboga skeleton, with the [2,3] fusion present in catharanthine being replaced by [2,1] and [3,2] fusions. The corresponding deethyl analogs were also and methodological improvements were applied to an existing synthesis of deethylcatharanthine and a formal synthesis of racemic catharanthine. The reactivity of the catharanthine analogs toward coupling with vindoline was examined. Coupling was attempted by both the amine oxide fragmentation (Potier) and Fe³⁺ methods. Under Potier conditions the [2,1] fused analogs give low yields of coupling products in which vindaline is attached to the 3-position of the indole ring. The [3,2] isomers undergo fragmentation of the C16-C21 bond, as observed for catharanthine, but no coupling to vindoline occurs. The reactivity, oxidation potentials and conformation of the analogs are compared with catharanthine, deethylcatharanthine and N-methylcatharanthine.