Laccase-catalyzed coupling of catharanthine and vindoline : an efficient approach to the bisindole alkaloid anhydrovinblastine

The efficient enzyme-catalyzed coupling of the indolic alkaloids catharanthine and vindoline was carried out by exploiting the oxidoreductases laccases and atmospheric oxygen. Following NaBH4 reduction of the eniminium cationic intermediate, the synthetically useful dimer anhydrovinblastine (AVBL) was isolated and characterized. Several reaction parameters were investigated in detail and, under the optimized reaction conditions, AVBL was isolated in 56% yield. The practicability of this bioconversion was further confirmed through the condensation of catharanthine with the vindoline analogue 11-methoxy-dihydrotabersonine.