Are D- 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 1D- and 1L-chiro-inositol have been synthesized. 1D-2-O-(1,2-O-Dipalmitoyl-sn-glycero-3-phospho)-chiro-inositol (1D-chiro-PI) was synthesized in 12 steps starting from 1D-2,3,4,5-O-tetrakis(methoxymethylene)-myo-inositol by the inversion of the hydroxyl group at the 1-position of inositol followed by several protection/deprotection and phosphorylation steps. IL-2-O-(1,2-O-Dipalmitoyl-sn-glycero-3-phospho)-chiro-inositol (1L-chiro-PI) was synthesized in eight steps starting from 1L-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 1L-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, 1D-chiro-PI was found to be resistant to PI-PLC. These results suggest that the natural chiro-inositol derivatives should have the 1L-configuration if they are produced by PI-PLC, which is in contrast to the 1D-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 1L-configuration, with the enantiomeric purity exceeding 99%.