Synthesis of the indole alkaloids meridianins from the tunicate Aplidium meridianum

The marine natural products meridianins A and C–E have been synthesized for the first time starting from the appropriate N-tosyl-3-acetylindole. A facile two-step conversion of N-tosyl-3-acetylindoles to the corresponding meridianins by treatment with dimethylformamide dimethylacetal and further cyclization of the resulting enaminone with aminoguanidine is described. This method has also been applied for the preparation of the 3-[(2-amino)pyrimidin-4-yl]-7-azaindole.