Regiospecific, enantiospecific total synthesis of the alkoxy-substituted indole bases, 16-epi-N(a)-methylgardneral, 11-methoxyaffinisine, and 11-methoxymacroline as well as the indole alkaloids alstophylline and macralstonine.
A regiospecific, enantiospecific approach to the synthesis of ring-A-substituted indole alkaloids was developed via a doubly convergent strategy. The asymmetric Pictet-Spengler reaction and enolate-driven palladium cross-coupling processes were both executed in stereospecific fashion and served as the stereochemical basis of this approach. The synthesis of 16-epi-N(a)-methylgardneral (15), 11-methoxyaffinisine (16), and 11-methoxymacroline (22) has been accomplished in high yield and in enantiospecific fashion. Moreover, the key C-19 ketosarpagine system (borane adducts) 19a,b employed for the construction of 11-methoxymacroline (22) was also transformed into alstophylline 25, which resulted in completion of the total synthesis of the bisindole macralstonine (1). [reaction: see text]
D000470:Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry*; D031051:Alstonia / Q000737:chemistry; D000962:Antimalarials / Q000138:chemical synthesis / Q000737:chemistry; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry*; D007536:Isomerism; D015394:Molecular Structure; D010946:Plants, Medicinal / Q000737:chemistry
D000470:Alkaloids; D000962:Antimalarials; D007211:Indoles