The partial chemical synthesis of inositol 1,2-cyclic 4,5-trisphosphate

Appreciable amounts of inositol 1,2-cyclic 4,5-trisphosphate (cIP3) are formed on agonist stimulation of secretory cells, e.g., pancreas (1,2) and parotid (3,4). However, the physiological role of this compound is unknown. To obtain sufficient amounts of cIP3, we have developed a synthetic method to produce cIP3 from inositol 1,4,5-trisphosphate (I(1,4,5)P3). The method is an adaptation of the dicyclohexylcarbodiimide (DCCD) method of Khorana et al. (5), which was originally developed to synthesize 2',3'-cyclic ribonucleotides. The method involves treatment of the pyridinium salt of I(1,4,5)P3 with DCCD in pyridine water, which cyclizes part of the 1-phosphate on the inositol ring to the 1,2-cyclic phosphate. The compound identified as cIP3 cochromatographed with authentic cIP3 in two HPLC systems and on ionophoresis. It was converted to I(1,4,5)P3 on mild acid treatment--a characteristic of cyclic inositol phosphates. Inositol 1,2-cyclic 4,5-trisphosphate is then purified by HPLC. Sufficient amounts of cIP3 can be prepared by this method to carry out numerous experiments on its possible cellular role.