Mihály Herczeg

Synthesis of S-Linked Glycoconjugates and S-Disaccharides by Thiol–Ene Coupling Reaction of Enoses

Free-radical hydrothiolation of the endocyclic double bond of enoses is reported. Reaction between 2-acetoxy-D-glucal and a range of thiols including amino acid, peptide, glycosyl thiols, and sugars with primary or secondary thiol functions gave S-linked α-glucoconjugates and S-disaccharides with full regio- and stereoselectivity. Addition of glycosyl thiols to a 2,3-unsaturated glycoside also proceeded with good selectivity and afforded a series of 3-deoxy-S-disaccharides.

Synthesis and anticoagulant activity of bioisosteric sulfonic-Acid analogues of the antithrombin-binding pentasaccharide domain of heparin.

Two pentasaccharide sulfonic acids that were related to the antithrombin-binding domain of heparin were prepared, in which two or three primary sulfate esters were replaced by sodium-sulfonatomethyl moieties. The sulfonic-acid groups were formed on a monosaccharide level and the obtained carbohydrate sulfonic-acid esters were found to be excellent donors and acceptors in the glycosylation reactions. Throughout the synthesis, the hydroxy groups to be methylated were masked in the form of acetates and the hydroxy groups to be sulfated were masked with benzyl groups. The disulfonic-acid analogue was prepared in a [2+3] block synthesis by using a trisaccharide disulfonic acid as an acceptor and a glucuronide disaccharide as a donor. For the synthesis of the pentasaccharide trisulfonic acid, a more-efficient approach, which involved elongation of the trisaccharide acceptor with a non-oxidized precursor of the glucuronic acid followed by post-glycosidation oxidation at the tetrasaccharide level and a subsequent [1+4] coupling reaction, was elaborated. In vitro evaluation of the anticoagulant activity of these new sulfonic-acid derivatives revealed that the disulfonate analogue inhibited the blood-coagulation-proteinase factor Xa with outstanding efficacy; however, the introduction of the third sulfonic-acid moiety resulted in a notable decrease in the anti-Xa activity. The difference in the biological activity of the disulfonic- and trisulfonic-acid counterparts could be explained by the different conformation of their L-iduronic-acid residues.

Synthesis of disaccharide fragments of the AT-III binding domain of heparin and their sulfonatomethyl analogues

d-Glucuronate and l-iduronate-containing disaccharides related to the antithrombin-binding domain of heparin were prepared. The carboxylic function of the uronic acid unit was formed on a disaccharide level in the case of the glucuronate, while on a monosaccharide level in the case of the iduronate derivatives. Synthesis of their sulfonic acid analogues was carried out analoguosly applying sulfonatomethyl-containing acceptors in the form of either salts or methyl esters. Significant difference could be observed in the methyl ether formation reactions of the sulfonatomethyl-containing uronate disaccharides and the non-sulfonic acid uronates.

Toward synthesis of the isosteric sulfonate analogues of the at-iii binding domain of heparin

D-glucuronate and l-iduronate containing disaccharides related to the antithrombin-binding pentasaccharide of heparin, in which one of the sulfate esters is systematically replaced by a sodium sulfonatomethyl moiety, were synthesized. The sulfonic acid group was introduced by stereoselective radical addition onto the exomethylene moiety of the appropriate glycoside derivatives, and the resulting sulfonatomethyl glucosides were used as acceptors.

Systematic study on free radical hydrothiolation of unsaturated monosaccharide derivatives with exo- and endocyclic double bonds

Exo- and endocyclic double bonds of glycals and terminal double bonds of enoses were reacted with various thiols by irradiation with UV light in the presence of a cleavable photoinitiator. The photoinduced radical-mediated hydrothiolation reactions showed highly varying overall conversions depending not only on the substitution pattern and electron-density of the double bond but also on the nature and substitution pattern of the thiol partner. Out of the applied thiols thiophenol, producing the highly stabilized thiyl radical, exhibited the lowest reactivity toward each type of alkene. In most cases, the hydrothiolations took place with full regio- and stereoselectivities. Successful addition of 1,2 : 3,4-di-O-isopropylidene-6-thio-α-d-galactopyranose to a 2,3-unsaturated N-acetylneuraminic acid derivative, providing a (3 → 6)-S-linked pseudodisaccharide, demonstrated that the endocyclic double bond of Neu5Ac-2-ene, bearing an electron-withdrawing substituent, shows sufficient reactivity in the photoinduced thiol-ene coupling reaction.

Large-scale synthesis of 6-deoxy-6-sulfonatomethyl glycosides and their application for novel synthesis of a heparinoid pentasaccharide trisulfonic acid of anticoagulant activity

Multigram-scale syntheses of three 6-deoxy-6-sulfonatomethyl α-glucosides were accomplished via reactions of the corresponding primary triflate derivatives with the lithiated ethyl methanesulfonate. Chemoselective glycosylation reactions of different 6-C-sulfonatomethyl glucoside donors were studied. The sulfonic acid-containing building blocks were utilised in a novel [2+3] block synthesis of a trisulfonic acid isoster of the anticoagulant pentasaccharide idraparinux.

Synthesis and antibacterial evaluation of some teicoplanin pseudoaglycon derivatives containing alkyl- and arylthiosubstituted maleimides

Bis-alkylthio maleimido derivatives have been prepared from teicoplanin pseudoaglycon by reaction of its primary amino group with N-ethoxycarbonyl bis-alkylthiomaleimides. Some of the new derivatives displayed excellent antibacterial activity against resistant bacteria.

Investigation of glycosylating properties of 1-deoxy-1-ethoxysulfonyl-hept-2-ulopyranosyl derivatives. Synthesis of a new sulfonic acid mimetic of the sialyl Lewis X tetrasaccharide.

Glycosylation reactions of the ethylthio, bromo and chloro derivatives of 1-deoxy-1-ethoxysulfonyl-hept-2-ulopyranose were studied applying different acceptors under different conditions. Elimination side-reactions affording exo- and endoglycals occured in all cases, however, with different proportions. Glycosyl chloride donor was applied to glycosylate a trisaccharide acceptor obtaining a new sulfonic acid mimetic of the sialyl Lewis X tetrasaccharide in high yield.

Preparation of synthetic oligosaccharide-conjugates of poly-β- (1→6)-N-acetyl glucosamine

Staphylococcus aureus and Staphylococcus epidermidis are prominent bacterial pathogens of nosocomial infections. Both microorganisms colonize medical devices by forming adherent biofilms. Poly-β-D-(1→6)-N-acetyl-glucosamine (PNAG) is a surface polysaccharide antigen which was found on both S. aureus and S. epidermidis. Animal studies have proved that PNAG can elicit antibodies which protect against staphylococcal infections. We have presented the synthesis of di-, tetra- and hexasaccharide fragments of PNAG with formyl-heptyl aglycone and their attachment to bovine serum albumin (BSA) by reductive amination.

Inhibitory Effect of Multivalent Rhamnobiosides on Recombinant Horseshoe Crab Plasma Lectin Interactions with Pseudomonas aeruginosa PAO1.

To evaluate the molecular interaction of recombinant horseshoe crab plasma lectin (rHPL) with Pseudomonas aeruginosa PAO1, multivalent rhamnobioside derivatives were designed. Eight rhamnoclusters with three or four α(1-3)-rhamnobiosides attached to different central cores, such as methyl gallate, pentaerythritol, and N-Boc Tris, through either an ethylene glycol or a tetraethylene glycol linker, were assembled in two consecutive azide-alkyne cycloaddition click reactions. The synthetic method embraced the preparation of two α(1-3)-rhamnobiosides with different linker arms and their conjugation, in stoichiometric or substoichiometric amounts, to propargyl ether-functionalized tri- or tetravalent scaffolds. A divalent derivative and two self-assembling rhamnobiosides were also prepared. The different architectures and valences of the rhamnoclusters provided an opportunity to evaluate the impact of topology and valency on the binding properties toward rHPL. Inhibitory ELISA data showed that all covalently linked rhamnoclusters could inhibit P. aeruginosa PAO1 recognition activity of rHPL with high efficacy. Trivalent rhamnobiosides showed a stronger inhibitory effect on P. aeruginosa PAO1 binding, and the more flexible clusters on a pentaerythritol or a Tris core were superior to the less flexible methyl gallate-based clusters. Interestingly, the length of the linker arms had a very low impact on the binding ability of the rhamnoclusters. Herein, the two trivalent derivatives on an N-Boc protected Tris central core were the best inhibitors. The self-assembling amphiphilic rhamnobioside derivatives were found to display no multivalent effect.