Gram-scale synthesis of FICZ, a photoreactive endogenous ligand of the aryl hydrocarbon receptor.

Development of an efficient and scalable synthesis of 6-formylindolo[3,2-b]carbazole (FICZ), a naturally-occurring aryl hydrocarbon receptor (AhR) ligand, allowed its biological and physical properties to be studied. FICZ was shown to be the most potent among a series of 6-substituted indolo[3,2-b]carbazoles for activation of AhR in cells. Photostability studies of FICZ revealed a non-enzymatic mechanism for its conversion to a biologically active quinone. These results further support the hypothesis that FICZ is a light-dependent hormone that links sun exposure to regulation of biological pathways in peripheral tissues.