Lipooligosaccharide (LOS) structures in the outer core of Gram-negative mucosal pathogens such as Neisseria meningitidis and Haemophilus influenzae contain characteristic glycoepitopes that contribute significantly to bacterial virulence. An important example is the digalactoside epitope generated by the retaining α-1,4-galactosyltransferase LgtC. These digalactosides camouflage the pathogen from the host immune system and increase its serum resistance. Small molecular inhibitors of LgtC are therefore sought after as chemical tools to study bacterial virulence, and as potential candidates for anti-virulence drug discovery. We have recently discovered a new class of non-substrate-like inhibitors of LgtC. The new inhibitors act via a covalent mode of action, targeting a non-catalytic cysteine residue in the LgtC active site. Here, we describe, for the first time, structure-activity relationships for this new class of glycosyltransferase inhibitors. We have carried out a detailed analysis of the inhibition kinetics to establish the relative contribution of the non-covalent binding and the covalent inactivation steps for overall inhibitory activity. Selected inhibitors were also evaluated against a serum-resistant strain of Haemophilus influenzae, but did not enhance the killing effect of human serum.

革兰氏阴性黏膜病原体（如脑膜炎奈瑟氏球菌和流感嗜血杆菌）外核中的脂寡糖（LOS）结构含有特征性的糖表位，对细菌的毒力有显着贡献。一个重要的例子是由保留的α-1,4-半乳糖基转移酶LgtC生成的半乳糖苷表位。这些半乳糖苷会掩盖宿主免疫系统中的病原体，并增加其血清抵抗力。因此，人们寻求LgtC的小分子抑制剂作为研究细菌毒力的化学工具，并作为抗毒力药物发现的潜在候选者。我们最近发现了一类新的非底物样LgtC抑制剂。新的抑制剂通过共价作用方式起作用，靶向LgtC活性位点的非催化性半胱氨酸残基。在这里，我们首次描述了这种新型糖基转移酶抑制剂的结构-活性关系。我们已经对抑制动力学进行了详细的分析，以建立非共价结合和相对于总抑制活性共价失活步骤的相对贡献。还评估了所选抑制剂的抗血清抗性菌株流感嗜血杆菌，但没有增强人类血清的杀伤作用。