Structure-activity modelling of essential oils, their components, and key molecular parameters and descriptors

Many essential oil components are known to possess broad spectrum antimicrobial activity, including against antibiotic resistant bacteria. These compounds may be a useful source of new and novel antimicrobials. However, there is limited research on the structure-activity relationship (SAR) of essential oil compounds, which is important for target identification and lead optimization. This study aimed to elucidate SARs of essential oil components from experimental and literature sources. Minimum Inhibitory Concentrations (MICs) of essential oil components were determined against Escherichia colt and Staphylococcus aureus using a microdilution method and then compared to those in published in literature. Of 12 essential oil components tested, carvacrol and cuminaldehyde were most potent with MICs of 1.98 and 2.10 mM, respectively. The activity of 21 compounds obtained from the literature, MICs ranged from 0.004 mM for limonene to 36.18 mM for alpha-terpineol. A 3D qualitative SAR model was generated from MICs using FORGE software by consideration of electrostatic and steric parameters. An r(2) value of 0.807 for training and cross-validation sets was achieved with the model developed. Ligand efficiency was found to correlate well to the observed activity (r(2) = 0.792), while strongly negative electrostatic regions were present in potent molecules. These descriptors may be useful for target identification of essential oils or their major components in antimicrobial/drug development.