Enzymic Coupling of Catharanthine and Vindoline to form 3′,4′-Anhydrovinblastine by Horseradish Peroxidase

Abstract

The synthesis of 3′, 4′- anhydrovinblastine (AVLB) from catharanthine and vindoline was achieved through the enzymic action of horseradish peroxidase (HRP), followed by sodium borohydride reduction. It is proposed that the peroxidase enables the condensation of catharanthine and vindoline to an iminium intermediate, which is then reduced by the borohydride to AVLB. Catharanthine was apparently involved in other reactions, in addition to the coupling with vindoline, and the time at which its utilization was complete corresponded with the initiation of degradation of the putative iminium intermediate. There was an absolute requirement for either hydrogen peroxide or FMN and manganese chloride, but the latter combination is thought to generate hydrogen peroxide in situ by a light-activated mechanism. HRP types of varying purities and isozymic compositions all exhibited comparable coupling activities. AVLB yields of between 40 and 50% were reached under optimized conditions.