Pictet-spengler/transamination cascade reaction of indoles for modular synthesis of marinoquinoline analogues

The Pictet-Spengler/transamination cascade reaction enables modular synthesis of marinoquinoline analogues through three-component indole ring-expansion/cyclization in the manner of novel N1–C2 cleavage of indoles. This metal-free protocol exhibits very broad functional group tolerance with up to quantitative yields. Preliminary studies on the antitumor activity of the resultant marinoquinoline analogues reveal that the indolyl-attached pyrrolo[2,3-c]quinoline product (5d) shows great potential (IC50of 0.32 μg/mL to HeLa cells) as a promising anticancer agent in clinic.