Total synthesis of the second messenger analogue D-myo-inositol 1-phosphorothioate 4,5-bisphosphate: optical resolution of DL-1-O-allyl-2,3,6-tri-O-benzyl-myo-inositol and fluorescent labelling of myo-inositol 1,4,5-trisphosphate

Abstract

Two routes for the synthesis of the myo-inositol 1,4,5-triphosphate analogue myo-inositol 1-phosphorothioate 4,5-bisphosphate have been devised. DL-2,3,6-Tri-O-benzyl-1-O-(cis-prop-1-enyl)-myo-inositol was prepared from DL-1-O-allyl-2,3,6-tri-O-benzyl-myo-inositol and phosphorylated to the protected 4,5-biphosphate. Removal of the propenyl group generated DL-1,2,4-tri-O-benzyl-5,6-bis[bis(2-cyanoethoxy)phospho]-myo-inositol which was thiophosphorylated to give DL-2,3,6-tri-O-benzyl-1-O-[bis(2-cyanoethoxy)thiophospho]-4,5-bis[bis(2-cyanoethoxy)phospho]-myo-inositol. Deblocking afforded racemic myo-inositol 1-phosphorothioate 4,5-bisphosphate, which was reacted with the iodoketone of a fluorescent label to generate a fluorescently labelled inositol 1,4,5-trisphosphate analogue. DL-1-O-Allyl-2,3,6-tri-O-benzyl-myo-inositol was resolved into its enantiomers by means of the crystalline 4,5-biscamphanate ester. 1 D-(+)-1-O-Allyl-2,3,6-tri-O-benzyl-myo-inositol was used to prepare D-myo-inositol 1-phosphorothioate 4,5-bisphosphate in a fashion analogous to the racemic modification via1 D-(+)-2,3,6-tri-O-benzyl-1-O-(cis-prop-1-enyl)-4,5-bis[bis(2-cyanoethoxy)phospho]-myo-inositol.

In a second route, DL-1,2-O-isopropylidene-3,6-di-O-benzyl-myo-inositol was converted into the corresponding 4,5-dibutyrate. Removal of the isopropylidene group gave DL-1,4,-di-O-benzyl-5,6-di-O-butyryl-myo-inositol which was converted into the corresponding 1-O-p-methoxybenzyl ether via the 1,2-O-dibutylstannylidene derivative. Benzylation of the 2-position and removal of the butyrates yielded DL-1-O-p-methoxybenzyl-2,3,6-tri-O-benzyl-myo-inositol which was phosphorylated to DL-1-O-p-methoxybenzyl-2,3,6-tri-O-benzyl-4,5-bis[bis(2-cyanoethoxy)phospho]-myo-inositol.

Removal of the p-methoxybenzyl group gave the key intermediate DL-1,2,4-tri-O-benzyl-5,6-bis[bis(2-cyanoethoxy)phospho]-myo-inositol, which could be further elaborated to myo-inositol 1-phosphorothioate 4,5-bisphosphate.