ChemInform Abstract: Synthesis of 3,7-Anhydro-D-glycero-D-ido-octitol 1,5,6-Trisphosphate as an IP3 Receptor Ligand Using a Radical Cyclization Reaction with a Vinylsilyl Tether as the Key Step. Conformational Restriction Strategy Using Steric Repulsion B

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3,7-Anhydro-d-glycero-d-ido-octitol 1,5,6-trisphosphate (5) was designed as a novel IP3-receptor ligand having a C-glycosidic structure and was synthesized via a radical cyclization reaction with a temporary connecting vinylsilyl tether as the key step. The phenyl 2-O-dimethylvinylsilyl-3,4,6-tri-O-benzyl-1-seleno-β-d-glucopyranoside (7), in the usual 4C1-conformation, was successively treated with Bu3SnH/AIBN and under Tamao oxidation conditions to give a mixture of five C-glycosidic products. On the other hand, similar successive treatment of the corresponding 3,4-di-O-TBS-protected substrates 13 and 24, which were in an unusual 1C4-conformaion due to the steric repulsion between the bulky silyl protecting groups, gave the desired 1α-C-glycosides 18 and 25, respectively, as the major products. Thus, the course of the radical cyclization was effectively controlled by a change in the conformation of the pyranose ring into a 1C4-form due to steric repulsion between the adjacent bulky TBS-protecting groups ...