Synthesis of β-galactosylamides as ligands of the peanut lectin. Insights into the recognition process

Abstract

The synthesis of mono and divalent β-galactosylamides linked to a hydroxylated chain having a C2 symmetry axis derived from l-tartaric anhydride is reported. Reference compounds devoid of hydroxyl groups in the linker were also prepared from β-galactosylamine and succinic anhydride. After functionalization with an alkynyl residue, the resulting building blocks were grafted onto different azide-equipped scaffolds through the copper catalyzed azide-alkyne cycloaddition. Thus, a family of structurally related mono and divalent β-N-galactopyranosylamides was obtained and fully characterized. The binding affinities of the ligands towards the model lectin PNA were measured by the enzyme-linked lectin assay (ELLA). The IC values were significantly higher than that of galactose but the presence of hydroxyl groups in the aglycone chain improved lectin recognition. Docking and molecular dynamics experiments were in accordance with the hypothesis that a hydroxyl group properly disposed in the linker could mimic the Glc O3 in the recognition process. On the other hand, divalent presentation of the ligands led to lectin affinity enhancements.

Crystal structures of peanut lectin in the presence of synthetic β-N- and β-S-galactosides disclose evidence for the recognition of different glycomimetic ligands

“…S2). As expected, these ligand atoms face the solvent and do not contact the protein (Cano et al, 2017). Moreover, the simultaneous presence of two -galactoside recognition elements from divalent ligands in two distinct binding sites of a PNA tetramer was not observed, which could be attributed to the short linkers of the glycoclusters.…”

“…The ligands used in this work were synthesized as described previously (Cagnoni et al, 2014;Cano et al, 2017). They can be structurally classified into two distinct subgroups: the first includes the compounds NGS, diNGS and diNGT, in which the -galactose moieties are N-linked through amide functional groups (Fig.…”

“…under the crystallization conditions employed; Greenber et al, 2002;Tron et al, 2008). Furthermore, N-and S-glycosidic bonds have been shown to be resistant to enzymatic hydrolysis (Cagnoni et al, 2014;Cano et al, 2017;Sulzenbacher et al, 1996;Driguez et al, 1994;Driguez, 2001). Consequently, this observation is attributed to the fact that a significant portion of the ligand molecules lies outside the sugar-binding site and is thus totally disordered, as explained in detail below.…”

“…However, most of the PNA ligands reported to date correspond to O-linked carbohydrates, which are expected to have a limited half-life in biological media since they are sensitive to glycosidase-mediated hydrolysis. Conversely, aminoglycosides (N-glycosides) and thioglycosides (S-glycosides) are more resistant towards enzymatic and acidic hydrolysis, and therefore present a better bioavailability under physiological conditions (Cagnoni et al, 2011(Cagnoni et al, , 2014Cano et al, 2017;Wang et al, 2018). For this purpose, we used a set of previously synthesized glycoclusters, namely NGS, diNGS, diNGT, STG, STGD and diSTGD ( Fig.…”

“…1). These ligands possess -linked galactose residues and have been shown to be ligands of PNA with different binding affinities (Cagnoni et al, 2014;Cano et al, 2017).…”