Total syntheses of novel cytocidal β-carboline alkaloids, oxopropalines D and G

Abstract

A new type of β-carboline nucleus, N-methoxymethyl-4-methyl-β- carboline (4) was synthesized by thermal electrocyclic reaction of a 1- azahexatriene system, involving the indole 2,3-bond. The key compound N- methoxymethyl-1-methoxycarbonyl-4-methyl-β-carboline (2) was then prepared in a four-step sequence. The total synthesis of oxopropaline G (1e) was achieved from this key compound in four steps. Furthermore, the enantioselective total syntheses of (+)-oxopropaline D (1c) and its enantiomer were also achieved by application of the Sharpless oxidation- procedure in nine steps from 2.