Biomedical subjects

J M Mallet

Publications and source records attributed to J M Mallet.

12 recordsLinked to original sources

PubMed2001

Synthesis of conformationally locked L-iduronic acid derivatives: direct evidence for a critical role of the skew-boat 2S0 conformer in the activation of antithrombin by heparin.

We have used organic synthesis to understand the role of L-iduronic acid conformational flexibility in the activation of antithrombin by heparin. Among known synthetic analogues of the genuine pentasaccharidic sequence representing the antithrombin binding site of heparin, we have selected as a reference compound the methylated anti-factor Xa pentasaccharide 1. As in the genuine original fragment, the single L-iduronic acid moiety of this molecule exists in water solution as an equilibrium between three conformers 1C4, 4C1 and 2S0. We have thus synthesized three analogues of 1, in which the L-iduronic acid unit is locked in one of these three fixed conformations. A covalent two atom bridge between carbon atoms two and five of L-iduronic acid was first introduced to lock the pseudorotational itinerary of the pyranoid ring around the 2S0 form. A key compound to achieve this connection was the D-glucose derivative 5 in which the H-5 hydrogen atom has been replaced by a vinyl group, which is a progenitor of the carboxylic acid. Selective manipulations of this molecule resulted in the 2S0-type pentasaccharide 23. Starting from the D-glucose derivative 28, a covalent two atom bridge was now built up between carbon atoms three and five to lock the L-iduronic acid moiety around the 1C4 chair form conformation, and the 1C4-type pentasaccharide 43 was synthesized. Finally the L-iduronic acid containing disaccharide 58 which, due to the presence of the methoxymethyl substituent at position five adopts a 4C1 conformation, was directly used to synthesize the 4C1-type pentasaccharide 61. The locked pentasaccharide 23 showed about the same activity as the reference compound 1 in an antithrombin-mediated anti-Xa assay, whereas the two pentasaccharides 43 and 61 displayed very low activity. These results clearly establish the critical importance of the 2S0 conformation of L-iduronic acid in the activation of antithrombin by heparin.

Antithrombins↗

PubMed2001

Ultraweak sugar-sugar interactions for transient cell adhesion.

Carbohydrate-carbohydrate interactions are rarely considered in biologically relevant situations such as cell recognition and adhesion. One Ca(2+)-mediated homotypic interaction between two Lewis(x) determinants (Le(x)) has been proposed to drive cell adhesion in murine embryogenesis. Here, we confirm the existence of this specific interaction by reporting the first direct quantitative measurements in an environment akin to that provided by membranes. The adhesion between giant vesicles functionalized with Le(x) was obtained by micropipette aspiration and contact angle measurements. This interaction is below the thermal energy, and cell-cell adhesion will require a large number of molecules, as illustrated by the Le(x) concentration peak observed at the cell membranes during the morula stage of the embryo. This adhesion is ultralow and therefore difficult to measure. Such small interactions explain why the concept of specific interactions between carbohydrates is often neglected.

Calcium↗

PubMed1999

NMR study of a Lewis(X) pentasaccharide derivative: solution structure and interaction with cations.

The structure and conformation of the synthetic pentasaccharide Gal(beta 1-4){Fuc(alpha 1-3)}GlcNAc(beta 1-3)Gal(beta 1-4)Glc-beta OMe of the Lewis(X) family has been determined by NMR spectroscopy in dimethyl sulfoxide and methanol. In these solvents, the binding constants with calcium have been evaluated as 9.5 and 29.6 M-1, respectively. Study of the interaction sites has been achieved through the use of paramagnetic divalent cations and distance triangulation methods. Two regions have been found, the first one in the vicinity of the fucose unit, the second one closer to the lactose part.

Calcium↗

PubMed1999

Oligosaccharides corresponding to the regular sequence of heparin: chemical synthesis and interaction with FGF-2.

It has been proposed that oligosaccharides corresponding to the so-called regular region of heparin/heparan sulfate (HS) bind to fibroblast growth factor-2 (FGF-2). In order to explore the molecular basis of FGF/HS interaction, we describe here the chemical synthesis of a tetra and a hexasaccharide, prepared as methyl glycosides, corresponding to the regular sequence of heparin. The strategy relies on the efficient preparation of three building blocks: a seeding block, an elongating block and a capping block. The hexasaccharide inhibited the binding of FGF-2 on its receptor on human aorta vascular smooth muscle cells with an IC50 value (16+/-1.2 microg/mL) close to that of standard heparin (14.8+/-0.5 microg/mL) whereas the tetrasaccharide was much less potent (IC50 = 127+/-10.5 microg/mL). The hexasaccharide and heparin, inhibited in a dose-dependent manner FGF-2 (30 nM) induced proliferation (IC50 = 23.7+/-1.6 and 30.1+/-1.3 microg/mL, respectively). Under the same experimental conditions, the tetrasaccharide only slightly inhibited the mitogenic effect of FGF-2 (IC50 > 100 microg/mL).

Carbohydrate Conformation↗

PubMed1999

Synthesis of a highly hydrophobic dimeric Lewis X containing glycolipid: a model for the study of homotypic carbohydrate--carbohydrate interaction.

This paper describes the synthesis of an octasaccharidic glycolipid 1 based on a stereo- and regioselective glycosylation between a Lewis X trisaccharidic donor and a pentasaccharidic acceptor. A highly hydrophobic lipid moiety of a new type was selected, making the compound 1 a good candidate for the study of the interaction of Lewis X functionalised vesicles.

Carbohydrate Sequence↗

PubMed1998

Introducing a C-interglycosidic bond in a biologically active pentasaccharide hardly affects its biological properties.

We describe here the synthesis and the biological activity of a 'C-pentasaccharide', a new analogue of the antithrombin III (AT III) binding region of heparin containing a methylene bridge in place of an interglycosidic oxygen atom. The affinity for AT III and the anti-factor Xa activity of this compound have been compared with that of the corresponding selected 'O-pentasaccharide'. Such a structural modification slightly decreased the affinity of this compound for AT III as well as its anti-factor Xa activity (880 +/- 40 anti-Xa units versus 1180 +/- 30 anti-Xa units for the C-pentasaccharide and the O-pentasaccharide, respectively). This compound therefore represents the first example of a new class of anti-factor Xa pentasaccharides containing a C-interglycosidic bond.

Antithrombin III↗

PubMed1998

Synthesis of a 3-deoxy-L-iduronic acid containing heparin pentasaccharide to probe the conformation of the antithrombin III binding sequence.

We report in this work the total synthesis of a close analogue of the pentasaccharide active site of heparin, in which the L-iduronic acid residue has been deoxygenated at position three. 1H NMR studies demonstrated that, as anticipated, such a modification induces a shift of the conformational equilibrium toward 1C4 (contribution to the conformational equilibrium rises from 37% to 65%) and a substantial decrease of the affinity for antithrombin III (Kd 0.154 microM versus 0.050 microM).

Antithrombin III↗

PubMed1997

Transfer reactions catalyzed by cyclodextrin glucosyltransferase using 4-thiomaltosyl and C-maltosyl fluorides as artificial donors.

Cyclodextrin glycosyltransferase enzyme from Bacillus circulans catalyzed the effective conversion of 4-thio-alpha-maltosyl fluoride into cyclo-alpha-(1-->4(2))-thiomalto -tetraoside, -pentaoside, -hexaoside and linear hemithiomaltooligosaccharides. However, under the same conditions, C-maltosyl fluoride afforded only linear modified maltotetraose, maltohexaose and maltooctaose in moderate yield.

Bacillus↗

PubMed1996

L-iduronic acid derivatives as glycosyl donors.

O-[Methyl (2-O-acetyl-3-O-benzyl-4-O-levulinyl-alpha, and beta-L-idopyranosid)uronate] trichloroacetimidate and the corresponding n-pentenyl glycosides are efficient L-iduronic acid glycosyl donors. Both have been used for the high-yielding synthesis of basic disaccharide blocks which are useful for the subsequent synthesis of complex oligosaccharides related to heparin/heparan sulfate, and dermatan sulfate. In contrast, the corresponding thioethyl glycosides, thiophenyl glycosides, and fluoride, did not yield the expected disaccharides.

Carbohydrate Sequence↗

PubMed1996

Beta-1,2-linked oligomannosides inhibit Candida albicans binding to murine macrophage.

Interaction of Candida albicans with cells of the macrophage lineage was examined by using heat-killed (HK) and live yeast cells. Laminarin, an analogue of the cell wall beta-glucans, strongly inhibited HK yeasts adherence to J774 cell line but had no effect on live yeast binding. Phosphopeptidomannan (PPM) from Saccharomyces cerevisiae had a limited effect on the binding of both HK and live yeasts but significant inhibition was achieved by the use of C. albicans PPM. The role of beta-1,2-oligomannosides was examined with regard to their exclusive presence within C. albicans PPM. PPM acid labile beta-1,2-oligomannosides or a synthetic beta-1,2-mannotetraose, inhibited yeasts binding in a manner comparable to the original PPM. These latter results were confirmed by using mouse peritoneal macrophages, thus suggesting a general role for beta-1,2-oligomannosides in the adherence of the yeast to the macrophage membrane.

Animals↗

PubMed1993

Electrosyntheses of disaccharides from phenyl or ethyl 1-thioglycosides.

Constant current electrolyses of the glycosyl donors phenyl and ethyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D-glucopyranoside in dry acetonitrile in the presence of various primary and secondary sugar alcohols, performed in an undivided cell, gave beta-linked disaccharide derivatives selectively in good yields. Phenyl 2,3,4,6-tetra-O-benzoyl-1-thio-beta-D-glucopyranoside gave the beta-glucosides exclusively in good to moderate yields.

Carbohydrate Sequence↗

PubMed1992

Glycosylation using a one-electron-transfer, homogeneous reagent. Application to an efficient synthesis of the trimannosyl core of N-glycosylproteins.

Double glycosylation of methyl 2,4-di-O-benzyl-beta-D-mannopyranoside with ethyl 2-O-benzoyl-3,4,6-tri-O-benzyl-1-thio-alpha-D-mannopyranoside using as promoter tris(4-bromophenyl)ammoniumyl hexachloroantimonate, a stable, commercial, and crystalline radical cation, afforded after debenzoylation methyl 2,4-di-O-benzyl-3,6-di-O-(3,4,6-tri-O-benzyl-alpha-D-mannopyranoside in excellent yield. Other mannosyl donors were also investigated.

Carbohydrate Sequence↗