Progress in the Synthesis and Biological Activities of the Calothrixin and Topyrone Natural Products

Natural products represent a rich source of structurally diverse and biologically potent compounds. Among these are the calothrixins (cyanobacterial indolo[3,2-j]phenanthridine alkaloids) and the topyrones (fungal anthraquinone-type polyketides). While originating from different kingdoms of life and possessing distinct overall architectures, both scaffold families share a crucial quinone pharmacophore that is intrinsically linked to their potent cytotoxic activities, often involving DNA interaction and reactive oxygen species (ROS) generation. This review provides a comprehensive overview of the progress in the total synthesis and biological characterization of these two intriguing natural product classes. We discuss the various synthetic strategies developed to access their complex cores.