Synthesis of the tumour-inhibitory alkaloids, ellipticine, 9-methoxyellipticine, and related pyrido[4,3-b]carbazoles

Abstract

Orthophosphoric acid has been found to accomplish the previously unsuccessful cyclization of azomethines of 3-formylcarbazoles and aminoacetal to substituted pyrido[4,3-b]carbazoles according to a scheme proposed by Cranwell and Sexton. By this method, there have been prepared 6,11-dimethyl-(ellipticine), 5,6,11-trimethyl-, 5,9,11- trimethyl-, 9-methoxy-5,11-dimethyl- (9-methoxyellipticine), 9-methoxy- 5,6,11-trimethyl-, 9-bromo-6,11-dimethyl-, and 9-nitro-5,11-dimethyl- 6H-pyrido[4,3-b]carbazole.