d-myo-Inositol 1,4,5-trisphosphate analogues substituted at the 3-hydroxyl group

d-myo-Inositol 1,4,5-trisphosphate (Ins(1,4,5)P₃) analogues derived at 3-OH with a bulky substituent were chemically synthesized and structural features of vicinity surrounding the 3-OH of Ins(1,4,5)P₃, recognized by metabolic enzymes and by the receptor were explored. 3-Benzoyl-, 3-methylbenzoyl- and 3-para-aminobenzoyl-Ins(1,4,5)P₃ inhibited the dephosphorylation of [³H]Ins(1,4,5)P₃ by the 5-phosphatase present in erythrocyte ghosts, but the potency varied. The inhibitory potency for the former two compounds was slightly lower than that for Ins(1,4,5)P₃, while that for the latter compound was higher. Transfer of the amino group to the meta-position of the benzoyl group led to a less potent analogue. In an assay of [³H]Ins(1,4,5)P₃ 3-kinase at a low Ca²⁺ concentration, catalyzed by rat brain cytosol, 3-meta-aminobenzoyl-Ins(1,4,5)P₃ was the most potent among compounds examined, including Ins(1,4,5)P₃ in inhibiting the phosphorylation, whereas both 3-benzoyl- and 3-methylbenzoyl-Ins(1,4,5)P₃ at concentrations up to 30 μM, were without effect. All analogues examined were effective in inhibiting [³H]Ins(1,4,5)P₃ binding to purified Ins(1,4,5)P₃ receptor, but all 3-derived analogues were less potent and 3-benzoyl-Ins(1,4,5)P₃ was the least potent. It would thus appear that the space in the vicinity surrounding the 3-hydroxyl group of Ins(1,4,5)P₃ is sterically restrictive with regard to recognition by metabolic enzymes and the receptor, whereas the amino group providing arms for either the electrostatic interaction or the hydrogen bond, makes the analogues more potent.