Tethered IP₃. Synthesis and Biochemical Applications of the 1-O-(3-Aminopropyl) Ester of Inositol 1,4,5-Trisphosphate

A phosphodiester analogue of the second messenger Ins(1,4,5)P₃ has been synthesized and used to prepare a novel photoaffinity label and a selective bioaffinity matrix. A selectively protected inositol precursor was first converted by phosphite ester chemistry to an N-protected 1-O-(3-aminopropyl-l-phospho)-DL-myo-inositol and then phosphorylated to give a fully benzylated IP₃ derivative. Hydrogenolysis gives the title compound, which was converted to a photolabile analogue and was immobilized on a polymeric resin. The analogues all competed with [³H] Ins(1,4,5)P3 for binding to purified IP₃ receptors from rat brain. Reconstituted receptor liposomes showed calcium release when stimulated by the tethered IP₃ materials. None of the new materials were substrates for the 5-phosphatase or the 3-kinase that normally act on Ins(1,4,5)P₃.