Unambiguous total synthesis of the enantiomers of myo-inositol 1,3,4-trisphosphate: 1L-myo-inositol 1,3,4-trisphosphate mobilizes intracellular Ca2+ in Limulus photoreceptors.

Syntheses of the enantiomers of myo-inositol 1,3,4-trisphosphate are described. 1,4-Di-O-allyl-myo-inositol was regioselectively p-methoxybenzylated at the 3-position to give 1,4-di-O-allyl-3-O-(p-methoxybenzyl)-myo-inositol followed by benzylation of the remaining free hydroxyl groups to give the key intermediate 1,4-di-O-allyl-2,5,6-tri-O-benzyl-3-O-(p-methoxybenzyl)-myo-inositol. Removal of the p-methoxybenzyl and allyl groups gave 2,4,5-tri-O-benzyl-myo-inositol which was phosphitylated with bis(benzyloxy)(diisopropylamino)phosphine to give the fully protected trisphosphite triester. Oxidation using tert-butyl hydroperoxide gave 2,5,6-tri-O-benzyl-1,3,4-tris(dibenzylphospho)-myo-inositol, and deprotection using sodium in liquid ammonia gave racemic myo-inositol 1,3,4-trisphosphate. Deprotection of the key intermediate 1,4-di-O-allyl-2,5,6-tri-O-benzyl-3-O-(p-methoxybenzyl)-myo-inositol by isomerization of allyl groups followed by mild acid hydrolysis gave 2,4,5-tri-O-benzyl-1-O-(p-methoxybenzyl)-myo-inositol, which was converted to the diastereoisomeric (bis-(-)-camphanates. The diastereoisomers were separated by column chromatography and the camphanates and the p-methoxybenzyl group removed by saponification and acid hydrolysis, respectively, for each diastereoisomer to give the enantiomers of 2,4,5-tri-O-benzyl-myo-inositol. The absolute configurations of the latter were established by conversion of 1L-2,5,6-tri-O-benzyl-3-O-(p-methoxybenyl)-myo-inositol to the known 1L-1,2,4,5,6-penta-O-benzyl-myo-inositol. Phosphorylation and deblocking gave the D- and L-enantiomers of myo-inositol 1,3,4-trisphosphate. Biological evaluation in Limulus photoreceptors showed that 1L-myo-inositol 1,3,4-trisphosphate was much more active than the D-enantiomer, producing repetitive bursts of depolarization due to mobilization of intracellular calcium.