Progress in the synthesis of canthine alkaloids and ring-truncated congeners.

The canthines represent a fairly large subclass of β-carboline alkaloids, with the first members described 75 years ago. Over the last 60 years, many members of the parent compound, canthin-6-one (1), have been isolated from various plant sources, principally the Rutaceae and Simaroubaceae families, and recently from fungi. Structures isolated from these sources have been the subject of total synthesis, which continues to the present day. This review gives a broad overview of synthetic approaches to canthines over a 30-year period from 1982 to 2012 and summarizes recent reports on the synthesis of less well known ring-truncated congeners. These include C-ring-truncated ("ABD", 2) and A-ring-truncated ("BCD", 3) ring systems, which are providing new scaffolds for potentially useful therapeutic applications.