Syntheses of the marine alkaloids 6-oxofascaplysin, fascaplysin and their derivatives

A simple approach towards the pyrido[1,2-a:3,4-b′]diindole system via the reaction of indigo with methylene active compounds was used for the syntheses of the marine alkaloids 6-oxofascaplysin, fascaplysin, and their derivatives. It was also demonstrated that the reaction with ketones led to indigo decomposition and the formation of isatin derivatives. The derivative of fascaplysin with a phenyl substituent at C-7 demonstrated 2–3 times greater inhibitory activity against selected cancer cell lines than fascaplysin.