Total syntheses of novel cytocidal beta-carboline alkaloids, oxopropalinesD and G

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