Emerging targets in the bioactivity of ellipticines and derivatives

The tetracyclic natural product ellipticine 1 (5,11-dimethyl-6H-pyrido[4,3- b]carbazole) was first isolated from the plant material of Ochrosia elliptica Labill in 1959. Woodward et al. reported the first synthesis of ellipticine later the same year, and this was followed by many different synthetic strategies in subsequent decades. Investigation of the biological activity of ellipticines uncovered potent anticancer properties, and several ellipticine derivatives have been the subject of clinical trials. The ellipticine family of compounds exert their biological activity via several modes of action, the most well-established of which are intercalation with DNA and topoisomerase II inhibition. In recent times, however, other modes of action have been discovered such as kinase inhibition, interaction with p53 transcription factor, biooxidation, and adduct formation. This opens up a new chapter in the bioactivity of the ellipticines and hence a comprehensive review of the synthesis and biology of ellipticines is timely. Early reviews of the synthesis of ellipticine were published by Sainsbury (1977), Hewlins et al. (1984), Gribble and Saulnier (1985), and Kansal et al. (1986). The biological activity of ellipticine has also been reviewed by Auclair (1987) and Garbett and Graves (2004). This review covers key features of the biological activity of ellipticine along with synthetic routes from 1986 onward.