Ferrocene- and ruthenium arene-containing glycomimetics as selective inhibitors of human galectin-1 and -3†

Galectins are a family of β-galactoside-binding proteins with an evolutionarily conserved carbohydrate recognition domain. Their dysregulation has been implicated in physiological and pathological processes, including fibrotic disorders, inflammation, and cancer. For example, elevated levels of galectin-1 contribute to tumor cell migration and immune evasion, whereas overexpression of galectin-3 is associated with increased invasiveness and the formation of metastasis. Pharmacological inhibition of these galectins is a promising therapeutic strategy to counteract their oncogenic effects. In this study, we synthesized a novel series of galectin inhibitors with ferrocene and ruthenium arene motifs attached to lactose, N-acetyllactosamine, or thiodigalactoside scaffolds. We determined their binding affinity toward human galectin-1 (hgal-1) and the CRD domain of human galectin-3 (hgal-3-CRD) using fluorescence polarization, intrinsic fluorescence of galectin tryptophan residues, and isothermal titration calorimetry. The ferrocene analogs exhibited superior affinity for both hgal-1 and hgal-3-CRD compared with ruthenium arenes. In particular, a symmetrical diferrocene thiodigalactoside complex exhibited low nanomolar affinity for hgal-1 and selectivity over hgal-3-CRD. Asymmetrical monoferrocene thiodigalactoside complexes exhibited nanomolar affinity and good selectivity for hgal-3-CRD. Chronopotentiometric stripping analysis demonstrated that the inhibitors stabilized hgal-1 against destabilization by electric field effects. ¹⁹F{¹H} NMR experiments and molecular dynamics simulations suggested that the incorporation of the ferrocene motif limited the accessible binding modes to hgal-3-CRD whereas binding to hgal-1 remained unrestricted, resulting in attenuated binding affinities to hgal-3-CRD and selectivity for hgal-1. These results open new possibilities for the design and optimization of therapeutic organometallic galectin inhibitors.