Design and synthesis of novel 3-triazolyl-1-thiogalactosides as galectin-1, -3 and -8 inhibitors

Abstract

Galectins are galactoside-binding proteins that play a role in various pathophysiological conditions, making them attractive targets in drug discovery. We have designed and synthesised a focused library of aromatic 3-triazolyl-1-thiogalactosides targeting their core site for binding of galactose and a subsite on its non-reducing side. Evaluation of their binding affinities for galectin-1, -3, and -8N identified acetamide-based compound 36 as a suitable compound for further affinity enhancement by adding groups at the reducing side of the galactose. Synthesis of its dichlorothiophenyl analogue 59 and the thiodigalactoside analogue 62 yielded promising pan-galectin inhibitors.

Fig. 1. (A): Alignment of galectin CRD crystal structures indicating binding subsites A–E. Residues are shown as green (galectin-1, PDB code: 5MWX), cyan (galectin-3, PDB code: 6QLN), and salmon (galectin-8N, PDB code: 7AEN) coloured sticks. (B): Crystal structure of galectin-1 in complex with ligand JB60 (PDB code 5MWK). (C): Crystal structure of galectin-3 in complex with a fluoroaryltriazole disaccharide (PDB code 6QLN). (D): Crystal structure of galectin-8N in complex with a quinolinyl galactopyranoside (PDB code 7AEN). In all structures, the ligand is shown in sticks with white carbons, with the galactose moiety shown in purple to emphasise the predominant binding of the sugar moiety in subsite C. This galactose moiety of the ligands binds between a Trp68 and Arg48 in galectin-1; Trp181 and Arg162 in galectin-3; and Trp86 and Arg69 in galectin-8N.

Fig. 2. Selected known galectin inhibitors with triazolyl groups or related functionalities.

Scheme 1. Synthesis of optimised acetamide ligands.

Fig. 3. Schematic representation of interaction analysis from MD simulations. (A) Galectin-1, (B) galectin-3 and (C) galectin-8N. Hydrogen and halogen bonds are shown as black and pink dashed lines, respectively. Cation–π interaction is presented as red line, while hydrophobic interactions are presented as grey curved line. For clarity of presentation, interactions with galactose moieties are not shown.

Fig. 4. Molecular dynamics snapshots of compounds 62 and 59 in galectin-1, -3, and -8N. (A) and (D) The CRD of galectin-1 with compounds 62 and 59, respectively. (B) and (E) The CRD of galectin-3 with compounds 62 and 59, respectively. (C) and (F) The CRD of galectin-8N with compounds 62 and 59, respectively. Ligands are shown as white sticks with standard atom colouring. Residues are shown as sticks carbon-coloured green (galectin-1), cyan (galectin-3), and salmon (galectin-8N).