Inositol Adenophostin: Convergent Synthesis of a Potent Agonist of d-myo-Inositol 1,4,5-Trisphosphate Receptors

d- myo -Inositol 1,4,5-trisphosphate receptors (IP 3 Rs) are Ca 2+ channels activated by the intracellular messenger inositol 1,4,5-trisphosphate (IP 3 , 1 ). The glyconucleotide adenophostin A (AdA, 2 ) is a potent agonist of IP 3 Rs. A recent synthesis of d- chiro -inositol adenophostin (InsAdA, 5 ) employed suitably protected chiral building blocks and replaced the d-glucose core by d- chiro -inositol. An alternative approach to fully chiral material is now reported using intrinsic sugar chirality to avoid early isomer resolution, involving the coupling of a protected and activated racemic myo -inositol derivative to a d-ribose derivative. Diastereoisomer separation was achieved after trans -isopropylidene group removal and the absolute ribose-inositol conjugate stereochemistry assigned with reference to the earlier synthesis. Optimization of stannylene-mediated regiospecific benzylation was explored using the model 1,2- O -isopropylidene-3,6-di- O -benzyl- myo -inositol and conditions successfully transferred to one conjugate diastereoisomer with 3:1 selectivity. However, only roughly 1:1 regiospecificity was achieved on the required diastereoisomer. The conjugate regioisomers of benzyl derivatives 39 and 40 were successfully separated and 39 was transformed subsequently to InsAdA after amination, pan-phosphorylation, and deprotection. InsAdA from this synthetic route bound with greater affinity than AdA to IP 3 R1 and was more potent in releasing Ca 2+ from intracellular stores through IP 3 Rs. It is the most potent full agonist of IP 3 R1 known and .equipotent with material from the fully chiral synthetic route.