Medicinal chemistry and pharmacology of cyclic ADP-ribose

Cyclic ADP-ribose (cADPR) is a signaling molecule that has been shown to regulate calcium mobilization from intracellular stores in a wide variety of biological systems. Synthesis of structural analogs of cADPR has provided insights into structure-activity relationships as well as produced pharmacological research tools with useful properties such as, hydrolysis-resistance and cell permeability. The first generation of cADPR analogs was synthesized by a chemo-enzymatic approach that took advantage of the broad substrate specificity of Aplysia ADP-ribosyl cyclase. Analogs synthesized by this approach provided useful structure-activity information, including the importance of the 8-position of the adenine in determining agonistic or antagonistic activity and of the 3'-hydroxyl group of the southern ribose for activity. Hydrolysis resistant analogs were generated by replacing the southern ribose with a carbocyclic structure or by replacing the adenine ring with 7-deaza- or 3-deaza-adenine. Approaches to synthesize cADPR analogs by total chemical approaches have been recently reported. These approaches allow the synthesis of analogs with stable linkages between N1 of adenine and the northern ribose (or surrogate) that are not possible with the enzymatic strategy. This review will focus on the synthesis and properties of analogs that have been shown to have utility in dissecting the role of cADPR in calcium signaling.