Both d- and l‑Glucose Polyphosphates Mimic d-<i>myo</i>-Inositol 1,4,5-Trisphosphate: New Synthetic Agonists and Partial Agonists at the Ins(1,4,5)P₃ Receptor

Chiral sugar derivatives are potential cyclitol surrogates of the Ca2+-mobilizing intracellular messenger d-myo-inositol 1,4,5-trisphosphate [Ins­(1,4,5)­P3]. Six novel polyphosphorylated analogues derived from both d- and l-glucose were synthesized. Binding to Ins­(1,4,5)­P3 receptors [Ins­(1,4,5)­P3R] and the ability to release Ca2+ from intracellular stores via type 1 Ins­(1,4,5)­P3Rs were investigated. β-d-Glucopyranosyl 1,3,4-tris-phosphate, with similar phosphate regiochemistry and stereochemistry to Ins­(1,4,5)­P3, and α-d-glucopyranosyl 1,3,4-tris-phosphate are full agonists, being equipotent and 23-fold less potent than Ins­(1,4,5)­P3, respectively, in Ca2+-release assays and similar to Ins­(1,4,5)­P3 and 15-fold weaker in binding assays. They can be viewed as truncated analogues of adenophostin A and refine understanding of structure-activity relationships for this Ins­(1,4,5)­P3R agonist. l-Glucose-derived ligands, methyl α-l-glucopyranoside 2,3,6-trisphosphate and methyl α-l-glucopyranoside 2,4,6-trisphosphate, are also active, while their corresponding d-enantiomers, methyl α-d-glucopyranoside 2,3,6-trisphosphate and methyl α-d-glucopyranoside 2,4,6-trisphosphate, are inactive. Interestingly, both l-glucose-derived ligands are partial agonists: they are among the least efficacious agonists of Ins­(1,4,5)­P3R yet identified, providing new leads for antagonist development.