Indoloquinolines as scaffolds for drug discovery

Traditional medicines have contributed greatly over the centuries to the discovery and development of new therapeutic agents and indoloquinoline alkaloids may represent a new class of drug leads. Cryptolepine (5-methyl-5Hindolo[3,2-b]quinoline), neocryptolepine (5-methyl-5H-indolo[2,3-b]quinoline), isocryptolepine (5-methyl-5H-indolo[3,2-c]quinoline, extracted from the African medicinal plant Cryptolepis sanguinolenta, and isoneocryptolepine (5-methyl-5Hindolo[2,3-c]quinoline), which has never been found in nature, are isomeric tetracyclic compounds of particular interest due to their broad spectrum of biological activities including antiparasitic, antifungal, antibacterial, cytotoxic, anti-inflammatory and antihyperglycaemic. As a result, in the last 30 years hundreds of indoloquinoline analogues were synthesized and their biological activities evaluated. In this paper, we present an overview of the potential of indoloquinolines as scaffolds in drug discovery by reviewing the in vitro and in vivo biological activities of natural and synthetic analogues, as well as the proposed mechanisms of action and structure-activity relationships.