Total syntheses of mitragynine, paynantheine and speciogynine via an enantioselective thiourea-catalysed Pictet–Spengler reaction

Abstract

The pharmacologically interesting indole alkaloids (–)-mitragynine, (+)-paynantheine and (+)-speciogynine were synthesised in nine steps from 4-methoxytryptamine by a route featuring (i) an enantioselective thiourea-catalysed Pictet–Spengler reaction, providing the tetrahydro-β-carboline ring and (ii) a Pd-catalysed Tsuji–Trost allylic alkylation, closing the D-ring.