Phytochemical Study and Antioxidant Activities of the Water-Soluble Aerial Parts and Isolated Compounds of Thymus munbyanus subsp. ciliatus (Desf.) Greuter & Burdet

Abstract

The present study aimed to determine the phenolic compounds present in the water-soluble extracts of Thymus munbyanus subsp. ciliatus using high pressure liquid chromatography-time-of-flight mass spectrometry (MS). These phenolic compounds were further isolated and characterized for their antioxidant activities. The aerial parts of T. munbyanus subsp. ciliatus were air dried, powdered, and extracted using water:methanol three times. The concentrated hydromethanolic extract was further dissolved in H2O, filtered, and successively extracted using ethyl acetate, chloroform, and n-butanol. T. munbyanus extracts were further purified using column chromatography, and the purified extracts were subjected to in vitro antioxidant assays. Two previously undescribed compounds, namely methyl 2,3,5,6-tetrahydroxybenzoate and 4-hydroxy-5-methoxy-2-oxo-2H-pyran-3-carboxylic acid, and 14 known compounds, including 3 flavonoids; namely 3',5,5',7-tetrahydroxyflavanone, luteolin, and isorhamnetin-3-O-β-glucoside; a sterol glucoside named daucosterol; and 10 phenolic compounds, namely salicylic acid, ferulic acid, pluchoic acid, ethyl caffeate, methyl caffeate, protocatechuic acid, rosmarinic acid, p-coumaric acid, tyrosol, and protocatechuic aldehyde, were isolated from ethyl acetate and n-butanol extracts. The isolated compounds were characterized using 1D-2D-1H-13C nuclear magnetic resonance and MS methods. The compounds isolated from ethyl acetate and n-butanol extracts exhibited excellent antioxidant and 2,2-diphenyl-1-picrylhydrazyl scavenging activities. All these results highlighted the antioxidant potential of the isolated phenolic compounds and extracts, which could be further utilized for different pharmacological applications.