Anti-acetylcholinesterase activity of essential oils and their major constituents from four Ocimum species.

Ocimum is a genus of considerable importance in traditional medicine worldwide. The goal of this study was to examine the anti-acetylcholinesterase activity of Ocimum essential oils and to correlate the activity with their chemical profiles using a metabolome based GC-MS approach coupled to chemometrics. Further, molecular docking was adopted to rationalize the activity of some essential oil isolates. Essential oil prepared from the four species O. basilicum, O. africanum, O. americanum, and O. minimum exhibited significant anti-acetylcholinesterase activity with (IC50 0.22, 0.175, 0.57 and 0.152 mg/mL, respectively) comparable to that of physostigmine (IC50 0.27 mg/mL). The phenylpropanoids (i.e. estragole) constituted the most dominant chemical group in O. basilicum (sweet basil) and O. minimum, whereas camphor (a ketone) was the most abundant in O. africanum and O. americanum. Supervised and unsupervised multivariate data analyses clearly separated O. africanum and O. americanum from other accessions, with estragole, camphor and, to less extent, β-linalool contributing to species segregation. Estragole was found the most active AchE inhibitor (IC50 0.337 µM) followed by cineole (IC50 2.27 µM), camphor (IC50 21.43 µM) and eugenol (IC50 40.32 µM). Molecular docking revealed that these compounds bind to key amino acids in the catalytic domain of AchE, similar to standard drugs.