Light-dependent decomposition of FICZ, an endogenous ligand of the aryl hydrocarbon receptor

An efficient and scalable synthesis of 6-formylindolo[3,2-b]carbazole (FICZ) has been developed to provide large quantities of this physiologically important ligand of the aryl hydrocarbon receptor. Photo-decomposition of FICZ revealed a new non-enzymatic light-assisted mechanism for its conversion to a biologically less active quinone. The light-dependent synthesis and decomposition of FICZ makes it a candidate hormone to link sun exposure to regulation of biological pathways in peripheral tissues.