A stannylene strategy for regioselective acylation and phosphorylation of 1,2-cyclohexylidene-myo-inositol. Its convenient resolution and phosphatidylinositol synthesis

Synthesis of unsaturated phosphatidylinositol 4-phosphates and the effects of substrate unsaturation on SopB phosphatase activity

In this paper evidence is presented that the fatty acid component of an inositide substrate affects the kinetic parameters of the lipid phosphatase Salmonella Outer Protein B (SopB). A succinct route was used to prepare the naturally occurring enantiomer of phosphatidylinositol 4-phosphate (PI-4-P) with saturated, as well as singly, triply and quadruply unsaturated, fatty acid esters, in four stages: (1) The enantiomers of 2,3:5,6-O-dicyclohexylidene-myo-inositol were resolved by crystallisation of their di(acetylmandelate) diastereoisomers. (2) The resulting diol was phosphorylated regio-selectively exclusively on the 1-O using the new reagent tri(2-cyanoethyl)phosphite. (3) With the 4-OH still unprotected, the glyceride was coupled using phosphate tri-ester methodology. (4) A final phosphorylation of the 4-O, followed by global deprotection under basic then acidic conditions, provided PI-4-P bearing a range of sn-1-stearoyl, sn-2-stearoyl, -oleoyl, -γ-linolenoyl and arachidonoyl, glycerides. Enzymological studies showed that the introduction of cis-unsaturated bonds has a measurable influence on the activity (relative Vmax) of SopB. Mono-unsaturated PI-4-P exhibited a five-fold higher activity, with a two-fold higher KM, over the saturated substrate, when presented in DOPC vesicles. Poly-unsaturated PI-4-P showed little further change with respect to the singly unsaturated species. This result, coupled with our previous report that saturated PI-4-P has much higher stored curvature elastic stress than PI, supports the hypothesis that the activity of inositide phosphatase SopB has a physical role in vivo.

Synthesis and biological evaluation of phosphatidylinositol phosphate affinity probes

The synthesis of the complete family of phosphatidylinositol phosphate analogues (PIPs) from five key core intermediates A-E is described. These core compounds were obtained from myo-inositol orthoformate 1 via regioselective DIBAL-H and trimethylaluminium-mediated cleavages and a resolution-protection process using camphor acetals 10. Coupling of cores A-E with phosphoramidites 34 and 38, derived from the requisite protected lipid side chains, afforded the fully-protected PIPs. Removal of the remaining protecting groups was achieved via hydrogenolysis using palladium black or palladium hydroxide on carbon in the presence of sodium bicarbonate to afford the complete family of dipalmitoyl- and amino-PIP analogues 42, 45, 50, 51, 58, 59, 67, 68, 76, 77, 82, 83, 92, 93, 99 and 100. Investigations using affinity probes incorporating these compounds have identified novel proteins involved in the PI3K intracellular signalling network and have allowed a comprehensive proteomic analysis of phosphoinositide interacting proteins.

Catalyst-Dependent Syntheses of Phosphatidylinositol-5 Phosphate-DiC8 and its Enantiomer

Peptide-based catalysts have been applied to the enantioselective syntheses of the title compounds, with this being the first report of the synthesis of an ent-PI5P analogue. The key steps in the synthesis involve asymmetric phosphorylation catalysis. Additional maneuvers were developed with a protecting groups scheme that enabled efficient, streamlined syntheses of these important mediators of biochemical events.