Cationic, Steroid-Based Imidazolium Amphiphiles Show Tunable Backbone-Dependent Membrane Selectivity in Fungi

Cationic amphiphiles have been reported to show broad antimicrobial activity. The potential for antimicrobial resistance to these molecules is low owing to their general cell membrane permeabilizing mode of action. However, their applications are often limited by toxicity resulting from their low selectivity for microbial cell membranes. Herein, we report a library of cationic, steroid-based imidazolium amphiphiles that show tunable antifungal activity in a variety of fungal pathogens of the genus Candida. We show that adoption of an ergosterol-derived backbone increases antifungal activity while modestly affecting hemolytic activity, thereby increasing overall selectivity by more than 8-fold in comparison to cholesterol-derived imidazolium salts. We hypothesize that this effect is caused by a privileged integration of the ergosterol-derived salts into fungal membranes leading to increased membrane disorder. We propose that these findings offer a useful platform for the development of improved amphiphilic fungicides.