D-chiro-Inositol Ribophostin: A Highly Potent Agonist of D-myo-Inositol 1,4,5-Trisphosphate Receptors: Synthesis and Biological Activities

摘要

Analogues of the Ca2+-releasing intracellular messenger D-myoinositol 1,4,5-trisphosphate [1, Ins(1,4,5)P-3] are important synthetic targets. Replacement of the a-glucopyranosyl motif in the natural product mimic adenophostin 2 by D-chiro-inositol in D-chiro-inositol adenophostin 4 increased the potency. Similar modification of the non-nucleotide Ins(1,4,5)P-3 mimic ribophostin 6 may increase the activity. D-chiro-Inositol ribophostin 10 was synthesized by coupling as building blocks suitably protected ribose 12 with L-(+)-3-O-trifluoromethylsulfonyl-6-O-p-methoxybenzyl-1,2:4,5-di-O-isopropylidene-myo-inositol 11. Separable diastereoisomeric 3-O-camphanate esters of (+/-)-6-O-p-methoxy-benzyl-1,2:4,5-di-O-isopropylidene-myo-inositol allowed the preparation of 11. Selective trans-isopropylidene deprotection in coupled 13, then monobenzylation gave separable regioisomers 15 and 16. p-Methoxybenzyl group deprotection of 16, phosphitylation/oxidation, then deprotection afforded 10, which was a full agonist in Ca2+-release assays; its potency and binding affinity for Ins(1,4,5)P3R were similar to those of adenophostin. Both 4 and 10 elicited a store-operated Ca2+ current ICRAC in patch-clamped cells, unlike Ins(1,4,5)P-3 consistent with resistance to metabolism. D-chiro-Inositol ribophostin is the most potent small-molecule Ins(1,4,5)P-3 receptor agonist without a nucleobase yet synthesized.