Marine pyridoacridine, pyridoacridone and pyrroloacridine alkaloids

The families of pyridoacridine, pyridoacridone, and pyrroloacridine alkaloids are fascinating classes of natural products that have attracted the attention of chemists for over 80 years. Since the first purification of a brightly colored molecule isolated from the sea anemone Calliactis parasitica in 1940, over 110 examples of these alkaloids have been reported from marine organisms. While the paucity of numbers of protons relative to carbons and nitrogens in these molecules presents challenges in structure solution, the chemist is rewarded by their bright pigmented colors and typically diverse biological activities. In the past, several authors have proposed biosynthetic relationships within the pyridoacridine family of alkaloids, formulating a family tree derived from the reaction of dopaminequinone and kynuramine to tie together over 75 alkaloids. Inclusion of two additional quinones, and one homologous diamine, building blocks, for which there is biomimetic synthesis support, is suggestive of a more expansive connected biogenesis that encompasses not only pyridoacridines, but also pyridoacridone, and pyrroloacridine alkaloids. This review covers the isolation, structure elucidation, and proposed biosynthesis and biogenesis of pyridoacridine, pyridoacridone and pyrroloacridine marine alkaloids published to the end of 2022. Biomimetic or bio-inspired syntheses of the compound classes are described and new biological activities reported since 2004 are updated.