Synthesis of part of a proposed insulin second messenger glycosylinositol phosphate and the inner core of glycosylphosphatidylinositol anchors

Chemical synthesis and functionalization of clickable glycosylphosphatidylinositol anchors

Glycosylphosphatidylinositol (GPI) anchorage is a common posttranslational modification of eukaryotic proteins. Chemical synthesis of structurally defined GPIs and GPI derivatives is a necessary step toward understanding the properties and functions of these molecules in biological systems. In this work, the synthesis of several functionalized GPI anchors was accomplished using the para-methoxybenzyl (PMB) group for permanent hydroxyl protection, which allowed the incorporation of functionalities that are incompatible with permanent protecting groups traditionally used in carbohydrate synthesis. A flexible convergent-divergent assembly strategy enabled efficient access to a diverse set of target structures, including "clickable" Alkynyl-GPIs 1 and 2 and Azido-GPI 3. For global deprotection, a one-pot reaction was employed to afford the target GPIs in excellent yields (85-97%). Fully deprotected clickable GPIs 2 and 3 were readily conjugated to imaging and affinity probes via Cu(I)-catalyzed and Cu-free strain-promoted [3+2] cycloaddition, respectively, resulting in GPI-Fluor 4 and GPI-Biotin 5.

Synthesis of oligosaccharides corresponding to Vibrio cholerae O139 polysaccharide structures containing dideoxy sugars and a cyclic phosphate

A spacer-equipped tetrasaccharide, p-aminocyclohexylethyl alpha-l-Colp-(1-->2)-beta-d-Galp-(1-->3)-[alpha-l-Colp-(1-->4)]-beta-D-GlcpNAc, containing a 4,6-cyclic phosphate in the galactose residue, has been synthesised. The structure corresponds to a part of the repeating unit of the capsular (and lipo-) polysaccharide of the endemic bacteria Vibrio cholerae type O139 synonym Bengal. The synthetic strategy allows continuous syntheses of the complete O139 hexasaccharide repeating unit as well as of the structurally related repeating unit of serotype O22. Starting from ethyl 2-azido-4,6-O-benzylidene-2-deoxy-1-thio-beta-D-glucopyranoside, a thioglycoside tetrasaccharide donor block was constructed through two orthogonal glycosylations with glycosyl bromide donors. First, a properly protected galactose moiety was introduced using silver triflate as promoter and subsequently the two colitose residues, carrying electron-withdrawing protecting groups for stability reasons, under halide-assisted conditions. The tetrasaccharide block was then linked to the spacer in a NIS-TMSOTf-promoted coupling. Transformation of the azido group into an acetamido group using H2S followed by removal of temporary protecting acetyl groups gave a 4',6'-diol, which was next phosphorylated with methyl dichlorophosphate and deprotected to yield the 4,6-cyclic phosphate tetrasaccharide target structure.

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.

Enzyme-catalysed synthesis of galactosylated 1d- and 1l-chiro-inositol, 1d-pinitol, myo-inositol and selected derivatives using the β-galactosidase from the thermophile Thermoanaerobacter sp. strain TP6-B1

The products from the enzymatic beta-D-galactopyranosylation of 1D-chiro-inositol, 1D-pinitol, 1D-3-O-allyl-4-O-methyl-chiro-inositol, 1D-3,4-di-O-methyl-chiro-inositol, 1L-chiro-inositol and myo-inositol in combined yields ranging from 46% to 64% have been obtained using the beta-galactosidase isolated from an anaerobic extreme thermophile, Thermoanaerobacter sp. strain TP6-B1 and p-nitrophenyl beta-D-galactopyranoside as the donor. Analysis of the products from these reactions reveals information about the acceptor preferences of the enzyme.

First total synthesis of a GPI-anchored peptide

A GPI-anchored dipeptide of sperm CD52 antigen was prepared through a convergent synthesis. First, the dipeptide with its C-terminus free and the GPI with its nonreducing end phosphoethanolamine bearing a free amino group were synthesized separately. Then, the two building blocks were coupled with use of EDC/HOBt as the condensation reagent. Finally, the GPI-anchored peptide was deprotected to give the target molecule 1.

Convergent synthesis of an inner core GPI of sperm CD52

An inner core of the GPI anchor of sperm CD52 antigens was synthesized by a highly convergent process using specially modified inositol, glucosamine and phospholipid as key building blocks. This paper also presents a new and efficient procedure to prepare 1,2,6-differentiated derivatives of inositol for GPI syntheses.

NMR spectra of fluorinated carbohydrates

Recent advances in structural and conformational analysis of fluorinated carbohydrates by NMR spectroscopy are reviewed. Characteristic 1H, 13C, and 19F NMR chemical shifts and coupling constants for selected examples are given and the spectral data of a series of fluorinated carbohydrates were collected in continuation of the review of Csuk and Glänzer [Adv. Carbohydr. Chem. Biochem., 46 (1988) 73-177].