Synthesis of a potentially insulin-mimetic phosphodisaccharide

An anionic inositol phosphate glycan pseudotetrasaccharide exhibits high insulin-mimetic activity in rat adipocytes

Inositol phosphate glycan pseudotetrasaccharides consisting of man-(alpha1-6)-man-(alpha1-4)-glcN-(alpha,beta1-6)-myo-inositol-1,2-cyclic phosphate possessing a sulfate group at either O-6 (compounds 3alpha,beta) or O-2 (compounds 4alpha,beta) of the terminal mannose have been prepared. Compound 4alpha was able to stimulate lipogenesis in native rat adipocytes to 78% of the maximal insulin response (MIR) with an EC50 of 1.1 microM. The other compounds exhibited lower maximal stimulations (47-63% MIR) and higher EC50 values (9.5-10.6 microM).

Synthesis of the Core Tetrasaccharide of Trypanosoma cruzi Glycoinositolphospholipids: Manp(α1→6)-Manp(α1→4)-6-(2-aminoethylphosphonic acid)-GlcNp(α1→6)-myo-Ins-1-PO4

[structure: see text] Synthesis of the core tetrasaccharide Manp(alpha1-->6)-Manp(alpha1-->4)-6-(2-aminoethylphosphonic acid)-GlcNp(alpha1-->6)-myo-Ins-1-PO4, found in glycoinositolphospholipids of Trypanosoma cruzi parasites, is described. The key building block, 6-O-(2-azido-3-O-benzyl-6-O-((2-benzyloxycarbonylaminoethyl)phosphonic acid benzyl ester)-2-deoxy-alpha-D-glucopyranosyl)-1-di-O-benzylphosphoryl-4,5-O-isopropylidene-2,3-O-(D-1,7,7-trimethyl[2,2,1]bicyclohept-6-ylidene)-D-myo-inositol, was synthesized using a partially protected glucosyl D-camphorinositolphosphate and a (2-benzyloxycarbonylaminoethyl)phosphonic acid derivative in a regioselective phosphonate esterfication. Elongation with ethyl 2-O-benzoyl-3,4,6-tri-O-benzyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzyl-1-alpha-D-thiomannopyranoside using dimethyl(methylthio)sulfonium trifluoromethanesulfonate gave a fully protected tetrasaccharide which was successfully deprotected subsequently with sodium methoxide, sodium in liquid ammonia, and aq hydrochloric acid to give title compound.

Synthesis, structure-activity relationships, and the effect of polyethylene glycol on inhibitors of phosphatidylinositol-specific phospholipase C from Bacillus cereus

Substrate analog inhibitors of Bacillus cereus phosphatidylinositol-specific phospholipase C (PI-PLC) were synthesized and screened for their suitability to map the active site region of the enzyme by protein crystallography. Analogs of the natural substrate phosphatidylinositol (PI) were designed to examine the importance of the lipid portion and the inositol phosphate head group for binding to the enzyme. The synthetic compounds contained pentyl, hexyl, or hexanoyl and octyl lipid chains at the sn-1 and sn-2 positions of the glycerol backbone and phosphonoinositol, phosphonic acid, methyl phosphonate, phosphatidic acid, or methyl phosphate at the sn-3 position. The most hydrophobic compound, dioctyl methyl phosphate 14, was also the best inhibitor with an IC50 of 12 microM. In a series of dihexyl lipids, compounds with phosphonoinositol head groups inhibited more strongly than those that do not contain inositol but are otherwise identical. Compound 29, a short-chain lipid with a phosphonoinositol head group, was found to be a competitive inhibitor and the most potent in this series with an IC50 of 18 microM (Ki = 14 microM). Analogs with dihexyl chains were better inhibitors than those with dihexanoyl chains, presumably because the ether-linked lipids are more hydrophobic than the ester-linked lipids. No appreciable difference in inhibition was found between a phosphonoinositol lipid and the corresponding difluorophosphonoinositol lipid. Inositols and inositol derivatives that do not contain lipid moieties show IC50s about 3 orders of magnitude above those of the short-chain lipids. In this group, glucosaminyl(alpha 1-->6)-D-myo-inositol inhibited more strongly than myo-inositol, which in turn is a better inhibitor than inositol phosphate. The addition of polyethylene glycol (PEG-600) resulted in a marked decrease in inhibition by the short-chain lipids, but had little effect on the water-soluble head group analogs. This is accounted for in terms of solubilization of the amphipathic inhibitors by PEG. Since PEG is required in the crystallization, these data indicate that the best strategy for obtaining enzyme inhibitor complexes is to start by cocrystallizing PI-PLC with the head group analogs. The next step is to synthetically add the shortest possible hydrophobic moieties to the analogs and cocrystallize these with the enzyme. This strategy may be applicable to other lipolytic enzymes.

Cell signalling by inositol phosphoglycans from different species

The discovery of glycosyl-phosphatidylinositol (GPI) molecules and their products has given new insight into the field of signal transduction. In the last decade a novel mechanism of protein attachment to membranes has emerged, which involves a covalent linkage of the protein to the glycan moiety of a GPI. The discovery that GPI-anchored proteins are ubiquitous throughout the eukaryotes was followed by the observation that uncomplexed GPI molecules are implicated in signal transduction for a diversity of hormones and growth factors. The hydrolysis of free-GPI generates a novel second messenger: the inositol phosphoglycan (IPG). The aim of this article is to review the role of IPG and IPG-like molecules in signal transduction and to discuss future research directions.

Synthesis and investigation of the possible insulin-like activity of 1D-4-O- and 1D-6-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol 1-phosphate and 1D-6-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol 1,2-(cyclic phosphate)

The synthesis of the glycosyl-myo-inositol 1-phosphates 1 and 2 and of the glycosyl-myo-inositol 1,2-(cyclic phosphate) 3, starting from previously synthesized intermediates, is reported. Compound 3 was found to display proliferative effects on the early developing inner ear of chick embryo.

Enzymatic resolution of racemic 1,2:5,6-di-O-cyclohexylidene and 1,2:3,4-di-O-cyclohexylidene-myo-inositol

Enzyme-catalyzed regio- and enantioselective esterification of racemic 1,2:5,6-di-O-cyclohexylidene- and 1,2:3,4-di-O-cyclohexylidene-myo-inositol, which are key intermediates for syntheses of various naturally occurring myo-inositol phosphate derivatives, proceeded exclusively in organic solvent to give optically pure materials and selectively protected products in gram scale. Hydrolysis of mono-O-acetates of the corresponding racemic materials catalyzed by the same enzymes yielded complementary products. The present study provides a new and efficient method for obtaining optically pure myo-inositol derivatives.

Building blocks for the synthesis of glycosyl-myo-inositols involved in the insulin intracellular signalling process

Glycosylation of (+/- )-1-O-benzyl-2,3:5,6-di-O-isopropylidene-myo-inositol (4) with 6-O-acetyl-4-O-allyl-2-azido-3-O-benzyl-2-deoxy-beta-D-glucopyranosyl trichloroacetimidate (6) gave the 4-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)- myo-inositol derivative (9) as a mixture of diastereoisomers which could be resolved by chromatography. Likewise alpha-glycosylation of 4 with 6-O-acetyl-2-azido-3-O-benzoyl-2-deoxy-4-O-(2,3,4,6-tetra-O-acetyl-beta- D- galactopyranosyl)-D-glucopyranosyl trichloroacetimidate (10) gave the corresponding pseudotrisaccharide derivative 16 as a mixture of diastereomers which could be resolved partially by chromatography. alpha-Glycosylation of enantiomerically pure 2,3:5,6- (18) and 2,3:4,5-di-O-isopropylidene-1-O-menthoxycarbonyl-myo-inositol (19) with 3,4,6-tri-O-acetyl-2-azido-2-deoxy-D-glucopyranosyl trichloroacetimidate (20) gave the pseudodisaccharide derivatives 21 and 22, respectively. Likewise, alpha-glycosylation of 18 with 10 afforded a pseudotrisaccharide derivative (23).

A fluorescent substrate for the continuous assay of phosphatidylinositol-specific phospholipase C: synthesis and application of 2-naphthyl myo-inositol-1-phosphate

A fluorescent water-soluble substrate for phosphatidylinositol-specific phospholipase C was synthesized. The diacylglycerol moiety of the natural substrate, phosphatidylinositol, was replaced by the fluorescent moiety, 2-naphthol, resulting in the synthetic substrate, racemic 2-naphthyl myo-inositol-1-phosphate. The synthetic substrate provided a continuous fluorometric assay for the phosphatidylinositol-specific phospholipase C from Bacillus cereus. Initial rates of the cleavage of the 2-naphthyl substrate by the phospholipase measured by fluorometry were linear with time and the amount of enzyme added. The specific enzyme activity at pH 8.5 and 25 degrees C was about 0.04 mumol/min mg protein at an initial substrate concentration of 0.8 mM. 31P NMR experiments suggest that, as with phosphatidylinositol itself, cleavage of the fluorescent substrate proceeds in two steps via a myo-inositol-1,2-cyclic phosphate intermediate, and that only the D-isomer is a substrate for the B. cereus phospholipase. The synthetic substrate was stable during long-term storage as a solid in the dark at -20 degrees C. It was also stable for several weeks when stored in the dark frozen in aqueous solution near neutral pH.