A simple and effective approach to the synthesis of pyrido[4,3,2-mn]pyrrolo[3,2,1-de]acridine skeleton of arnoamines A and B, pentacyclic marine alkaloids from the ascidian Cystodytes sp.

Starting from ethyl 5-hydroxy-2-methyl-1-phenylindole-3-carboxylate, a simple and effective approach to the synthesis of pyrido[4,3,2-mn]pyrrolo[3,2,1-de]acridine skeleton of arnoamines A and B, unique pentacyclic alkaloids from the ascidian Cystodytes sp., has been developed. Synthesis of this ring system involves seven steps and produces ethyl 4-methoxy-1-methylpyrido[4,3,2-mn]pyrrolo[3,2,1-de]acridine-2-carboxylate in 41.5% overall yield.