New insight in cyclic monoterpenoids mechanism of action: an in silico approach

Clarifying the mechanism of action of natural terpenoids is challenging. Further, their efficacy is inspiring in developing new antimycotic agents. Among all, thymol, carvacrol and thymyl acetate are largely scrutinized, while the new brominate thymol, namely bromothymol (4-bromo-2-isopropyl-5-methylphenol), needs deeper investigation. Here its antimycotic efficacy was evaluated and, in parallel, a careful in silico investigation of the mechanism of action was proposed. In vivo experiments, on species of acclaimed resistance, demonstrated that bromothymol had a Minimum Inhibitory Concentration (MIC) equal [~]40 g/ml, 6 times more active than thymol. Partition coefficient (LogP) in heptane, determined through density functional theory (DFT), and Molecular Dynamics (MD) simulations, based on a Minimum Bias Approach, in the presence of neutral bilayers, indicated that bromothymol inserts into cellular membrane, such as thymol, carvacrol, and Thymyl acetate. Monoterpenoids bearing the hydroxyl group induces a shrinkage of the membrane thickness, while only thymol affected membrane density of the leaflets in which it inserted. Thymol, carvacrol, and bromothymol interacted with the polar head of the lipids causing an electrostatic imbalance into the membrane, justifying their biological activity. For the first time a detailed in silico characterization on the mechanism of these compounds is afforded, returning a coherent and clear picture of their mechanism of action.