ARE D-CHIRO AND L-CHIRO PHOSPHOINOSITIDES SUBSTRATES OF PHOSPHATIDYLINOSITOL-SPECIFIC PHOSPHOLIPASE-C

Derivatives of chiro-inositol have been recently shown to mediate many important biological processes. This work addresses the question of whether phosphatidylinositol-specific phospholipase C (PI-PLC) could be involved in the generation of these chiro-inositol derivatives. Two diastereomers of the analog of phosphatidylinositol containing 1(D)- and 1(L)-chiro-inositol have been synthesized. 1(D)-2-O-(1,2-O-Dipalmitoyl-sn-glycero-3-phospho)-chio inositol(1(D)-chiro-PI) was synthesized in 12 steps starting from 1(D)-2,3,4,5-O-tetrakis(methoxymethylene)-myo-inositol the inversion of the hydroxyl group at the 1-position of inositol followed by several protection/deprotection and phosphorylation steps. 1(L)-2-O-(1,2-O-Dipalmitoyl-sn-glycero-3-phospho)-chiro-inositol (1(L)-chiro-PI) was synthesized in eight steps starting from 1(L)-chiro-inositol using regioselective silylation of the hydroxyl group at the 2-position of chiro-inositol in a key synthetic stage. Both diastereomers were subjected to cleavage by PI-PLC from Bacillus thuringiensis. The reaction of 1(L)-chiro-PI produced chiro-inositol 1,2-cyclic phosphate, however, at the rate of 10(-3) of that attained with the natural substrate, phosphatidylinositol. On the other hand, 1(D)-chiro-PI was found to be resistant to PI-PLC. These results suggest that the natural chiro-inositol derivatives should have the 1(L)-configuration if they are produced by PI-PLC, which is in contrast to the 1(D)-configuration reported by others. We therefore have isolated chiro-inositol from the total bovine liver lipid and determined its absolute configuration. The obtained chiro-inositol was found to be exclusively of the 1(L)-configuration, with the enantiomeric purity exceeding 99%.