Total synthesis of a new stable cyclic ADP-ribose mimic

Cyclic ADP-ribose (cADPR) is a natural occurring metabolite of NAD⁺, that mobilizes Ca²⁺ ions from intracellular stores. It was firstly isolated from sea urchin eggs extract, but it was later established that it is also produced in many other mammalian cells, such as pancreatic β-cells, T-lymphocytes, smooth and cerebellar neurons. cADPR is a dinucleotide in which a pyrophosphate bridge connects two ribose residues, bonded to adenine through N1 and N9 glycosidic bonds. As the N1 glycosidic bond is very labile, cADPR is rapidly hydrolyzed in neutral aqueous solution to ADP-ribose. In the light of the the poor knowledge of the cADPR receptor binding pocket, several stable and active derivatives have been synthesized. Among them, the cyclic inosine diphosphate ribose (cIDPR), in which the adenine is isosterically replaced by the hypoxanthine, was stable in physiological conditions and showed significant Ca²⁺ mobilizing activity. In our laboratories, we have synthesized several cIDPR analogues. In particular, the analogue with the “northern” ribose replaced by a pentyl chain (cpIDP) showed interesting Ca²⁺ mobilizing activity in the neuronal PC12 cell line. We report here on the total synthesis of a new stable cADPR analogue, in which the “northern” ribose is replaced by a 2”S,3”R dihydroxy pentyl chain. The new mimic elicites Ca²⁺ ions from intracellular stores in primary cortical neurons as effectively as cADPR.