Strong Binding of <i>C</i>‑Glycosylic1,2-Thiodisaccharides to Galectin-3Enthalpy-Driven Affinity Enhancement by Water-Mediated Hydrogen Bonds

Galectin-3 is involved in multiple pathways of many diseases, including cancer, fibrosis, and diabetes, and it is a validated pharmaceutical target for the development of novel therapeutic agents to address unmet medical needs. Novel 1,2-thiodisaccharides with a C-glycosylic functionality were synthesized by the photoinitiated thiol-ene click reaction of O-peracylated 1-C-substituted glycals and 1-thio-glycopyranoses. Subsequent global deprotection yielded test compounds, which were studied for their binding to human galectin-3 by fluorescence polarization and isothermal titration calorimetry to show low micromolar Kd values. The best inhibitor displayed a Kd value of 8.0 μM. An analysis of the thermodynamic binding parameters revealed that the binding Gibbs free energy (ΔG) of the new inhibitors was dominated by enthalpy (ΔH). The binding mode of the four most efficient 1,2-thiodisaccharides was also studied by X-ray crystallography that uncovered the unique role of water-mediated hydrogen bonds in conferring enthalpy-driven affinity enhancement for the new inhibitors. This 1,2-thiodisaccharide-type scaffold represents a new lead for galectin-3 inhibitor discovery and offers several possibilities for further development.半乳糖凝集素3（galectin-3）参与多种疾病的多条信号通路，涵盖癌症、纤维化与糖尿病，同时亦是针对未满足临床医疗需求开发新型治疗制剂的已验证药物靶点。研究人员通过O-全酰化1-C取代糖烯与1-硫代吡喃糖的光引发巯基-烯点击反应，合成了带有C-糖苷官能团的新型1,2-硫代二糖。经全局脱保护步骤后得到测试化合物，随后借助荧光偏振法与等温滴定量热法，评估其与人半乳糖凝集素3的结合活性，结果显示化合物的解离常数Kd处于低微摩尔级别。其中活性最优的抑制剂，其Kd值可达8.0 μM。对热力学结合参数的分析表明，新型抑制剂的结合吉布斯自由能（ΔG）主要由焓变（ΔH）主导。研究还通过X射线晶体学，解析了4种活性最优的1,2-硫代二糖的结合模式，揭示了水介导氢键在为新型抑制剂赋予焓驱动的亲和力提升过程中所发挥的独特作用。该1,2-硫代二糖类母核骨架为半乳糖凝集素3抑制剂的研发提供了全新先导方向，同时为后续开发提供了多重可行路径。