Abstract-We report here the synthesis of a series of mono-to trivalent N-acetylglucosamine (GlcNAc) derivatives as ligands for the plant lectin wheat germ agglutinin (WGA). Their WGA binding potencies were determined by an established enzyme-linked lectin assay (ELLA) employing microtiter plates with non-covalently immobilized porcine stomach mucin (PSM) as reference ligand and an ELLA with a new GlcNAc derivative covalently immobilized via a thiourea linkage. Comparison of both assays revealed that the type of presentation of GlcNAc residues on the microtiter plates either as part of a glycoprotein or as a covalently immobilized monosaccharide derivative strongly influences the outcome of the assay. Although the apparent dissociation constants K ELLA D for the interaction of peroxidase-labeled WGA with the microtiter plates are comparable for both surfaces, IC 50 values obtained with the PSM-free ELLA were substantially lower. Even more strikingly, this ELLA displayed a better differentiation between ligands of different valency leading to significantly higher relative inhibitory potencies of multivalent ligands compared to monovalent. Additionally, problems associated with the use of PSM, such as maximum inhibition at considerably less than 100% and poor reproducibility of IC 50 values could be overcome with this type of ELLA.
The reaction of thiocarboxylic acids with azides (thioacid‐azide ligation, TAL) is a chemoselective transformation, leading to the formation of amide bonds. Especially in the case of electron‐deficient sulfonyl azides, the reaction occurs in excellent yields, within minutes at room temperature, in a broad range of solvents. In this article, the application of TAL for the synthesis of glycosylated and dansylated amino acids is reported. 2‐Azidosulfonylethyl glycosides were prepared from peracetylated monosaccharides and reacted with thioacid‐containing derivatives of aspartic acid and glutamic acid. Likewise, aromatic sulfonyl azides were employed. Ligation products were obtained in yields of up to 96 %. Different conditions for the generation of the thioacids were compared. Whereas reaction of succinimidyl esters with sodium hydrogen sulfide led to concomitant formation of diacyl disulfides, trityl thioesters turned out to be suitable precursors for the in situ preparation of thioacids by mild acidolysis.
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