Mo-catalyzed Cyclization of N-vinylindoles and Skatoles: Synthesis of Dihydroindolo[1,2-C]-quinazolines and Dihydroindolo[3,2-B]-indoles, and Evaluation of Their Anticancer Activities

A novel approach has been developed for synthesizing unexpected dihydroindolo[1,2-c]-quinazolines (DINQ) and dihydroindolo[3,2-b]indole (DINI) compounds using N-vinylazoles as starting materials. The presence of a Mo-catalyst was found to be essential for the formation of DINQs from skatole derivatives and for accelerating the cyclization of DINI precursors. Biological evaluation revealed that compound 3o, a 2-phenyl-1-(1-phenylvinyl)-1H-indole derivative and DINI analog 6g exhibited nanomolar cytotoxic effects in vitro against a human colon cancer cell line (HCT-116).