title: Defining the potential of aglycone modifications for affinity/selectivity enhancement against medically relevant lectins: synthesis, activity screening, and HSQC-based NMR analysis.
abstract: The emerging significance of lectins for pathophysiological processes provides incentive for the design of potent inhibitors. To this end, systematic assessment of contributions to affinity and selectivity by distinct types of synthetic tailoring of glycosides is a salient step, here taken for the aglyconic modifications of two disaccharide core structures. Firstly we report the synthesis of seven N-linked-lactosides and of eight O-linked N-acetyllactosamines, each substituted with a 1,2,3-triazole unit, prepared by copper-catalyzed azide-alkyne cycloaddition (CuAAC). The totally regioselective β-D-(1 → 4) galactosylation of a 6-O-TBDPSi-protected N-acetylglucosamine acceptor provided efficient access to the N-acetyllactosamine precursor. The resulting compounds were then systematically tested for lectin reactivity in two binding assays of increasing biorelevance (inhibition of lectin binding to a surface-presented glycoprotein and to cell surfaces). As well as a plant toxin, we also screened the relative inhibitory potential with adhesion/growth-regulatory galectins (total of eight proteins). This type of modification yielded up to 2.5-fold enhancement for prototype proteins, with further increases for galectins-3 and -4. Moreover, the availability of (15)N-labeled proteins and full assignments enabled (1)H, (15)N HSQC-based measurements for hu- man galectins-1, -3, and -7 against p-nitrophenyl lactopyranoside, a frequently tested standard inhibitor containing an aromatic aglycone. The measurements confirmed the highest affinity against galectin-3 and detected chemical shift differences in its hydrophobic core upon ligand binding, besides common alterations around the canonical contact site for the lactoside residue. What can be accomplished in terms of affinity/selectivity by this type of core extension having been determined, the applied combined strategy should be instrumental for proceeding with defining structure-activity correlations at other bioinspired sites in glycans and beyond the tested lectin types.
authors.affiliation: PharmaQAM, Department of Chemistry, Université du Québec à Montréal, P. O. Box 8888, Succ. Centre-ville, Montréal, QC, H3C 3P8 (Canada).
authors.forename: Subhash R
authors.initials: SR
authors.lastname: Rauthu
authors.forename: Tze Chieh
authors.initials: TC
authors.lastname: Shiao
authors.forename: Sabine
authors.initials: S
authors.lastname: André
authors.forename: Michelle C
authors.initials: MC
authors.lastname: Miller
authors.forename: Élodie
authors.initials: É
authors.lastname: Madej
authors.forename: Kevin H
authors.initials: KH
authors.lastname: Mayo
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Gabius
authors.forename: René
authors.initials: R
authors.lastname: Roy
mesh_terms: D000117:Acetylglucosamine / Q000737:chemistry; D000480:Alkynes / Q000737:chemistry; D000606:Amino Sugars / Q000138:chemical synthesis / Q000737:chemistry*; D001386:Azides / Q000737:chemistry; D001798:Blood Proteins; D002240:Carbohydrate Sequence; D002384:Catalysis; D061565:Cycloaddition Reaction; D037483:Galectin 1 / Q000037:antagonists & inhibitors / Q000737:chemistry*; D037502:Galectin 3 / Q000037:antagonists & inhibitors / Q000737:chemistry*; D037161:Galectins / Q000037:antagonists & inhibitors / Q000737:chemistry*; D006027:Glycosides / Q000138:chemical synthesis / Q000737:chemistry*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009598:Nitrophenylgalactosides / Q000737:chemistry; D011485:Protein Binding; D013329:Structure-Activity Relationship; D014230:Triazoles / Q000737:chemistry
chemical_list: D000480:Alkynes; D000606:Amino Sugars; D001386:Azides; D001798:Blood Proteins; D037483:Galectin 1; D037502:Galectin 3; D037161:Galectins; D006027:Glycosides; C428445:LGALS3 protein, human; C092525:LGALS7 protein, human; D008024:Ligands; D014230:Triazoles; C008245:lactosides; C032233:lactosamine; D009598:Nitrophenylgalactosides; C059200:4-nitrophenylgalactoside; D000117:Acetylglucosamine
keywords: galectins; glycoproteins; lactose; lectins; structure-activity relationships