Berberine–INF55 hybrids are a promising class of antibacterials that combine berberine and the NorA multidrug resistance pump inhibitor INF55 (5-nitro-2-phenylindole) together in one molecule via a chemically stable linkage. Previous studies demonstrated the potential of these compounds for countering efflux-mediated antibacterial drug resistance but they didn’t establish whether the compounds function as originally intended, i.e. with the berberine moiety providing antibacterial activity and the attached INF55 component independently blocking multidrug resistance pumps, thereby enhancing the activity of berberine by reducing its efflux. We hypothesised that if the proposed mechanism is correct, then hybrids carrying more potent INF55 pump inhibitor structures should show enhanced antibacterial effects relative to those bearing weaker inhibitors. Two INF55 analogues showing graded reductions in NorA inhibitory activity compared with INF55 were identified and their corresponding berberine–INF55 hybrids carrying equivalent INF55 inhibitor structures synthesised. Multiple assays comparing the antibacterial effects of the hybrids and their corresponding berberine–INF55 analogue combinations showed that the three hybrids all show very similar activities, leading us to conclude that the antibacterial mechanism(s) of berberine–INF55 hybrids is different from berberine–INF55 combinations.
小檗碱-INF55 杂交化合物是一类前景广阔的抗菌药,通过化学稳定连接将小檗碱和 NorA 多药耐药泵抑制剂 INF55(5-硝基-2-苯基吲哚)结合在一个分子中。以前的研究证明了这些化合物在对抗外流介导的抗菌药耐药性方面的潜力,但它们并没有确定这些化合物是否按照最初的设想发挥作用,即小檗碱分子提供抗菌活性,而附着的 INF55 成分则独立阻断多药耐药泵,从而通过减少小檗碱的外流来增强其活性。我们假设,如果所提出的机制是正确的,那么携带较强 INF55 泵抑制剂结构的杂交化合物应比携带较弱抑制剂的杂交化合物显示出更强的抗菌效果。我们确定了两种 INF55 类似物,与 INF55 相比,它们对 NorA 的抑制活性呈梯度降低,并合成了相应的小檗碱-INF55 杂交化合物,它们具有等效的 INF55 抑制剂结构。多重检测比较了这些杂交种及其相应的小檗碱-INF55 类似物组合的抗菌效果,结果表明这三种杂交种的抗菌活性非常相似,因此我们得出结论:小檗碱-INF55 杂交种的抗菌机制与小檗碱-INF55 类似物组合不同。