A new acylated flavone glycoside, <i>in vitro</i> antioxidant and antimicrobial activities from Saudi <i>Diospyros mespiliformis</i> Hochst. ex A. DC (Ebenaceae) leaves

Abstract

Phytochemical investigation of <i>Diospyros mespiliformis</i> leaves resulted in the isolation of new acylated flavone isoscutellarein 7-<i>O</i>-(4'''-<i>O</i>-acetyl)-<i>β</i>-allopyranosyl(1''' → 2'')-<i>β</i>-glucopyranoside (<b>1</b>), along with eight known flavonoid metabolites, luteolin 3',4',6,8-tetramethyl ether (<b>2</b>), luteolin 4'-<i>O</i>-<i>β</i>-neohesperidoside (<b>3</b>), luteolin 7-<i>O</i>-<i>β</i>-glucoside (<b>4</b>), luteolin (<b>5</b>), quercetin (<b>6</b>), quercetin 3-<i>O</i>-<i>β</i>-glucoside (<b>7</b>), quercetin 3-<i>O</i>-<i>α</i>-rhamnoside (<b>8</b>), and rutin (<b>9</b>). Their structures were identified by analysis of spectroscopic (UV, NMR, and MS) data, as well as by acid hydrolysis for the isolated glycosides. The antioxidant activity of <i>D. mespiliformis</i> metabolites was determined by the DPPH radical-scavenging assay. The new acylated flavone (<b>1</b>) and flavonol <i>O</i>-rhamnoside (<b>8</b>) displayed the highest antioxidant activities with IC₅₀ values 15.46 and 12.32 μg/mL, respectively, with respect to the antioxidant ascorbic acid (IC₅₀ value 10.62 μg/mL). In addition, the isolated flavonoids were evaluated against four human pathogenic bacteria where the methylated flavone (<b>2</b>) exhibited potent activity against <i>Escherichia coli</i> with inhibition zone 34 mm, and mild activity of flavonol <i>O</i>-rhamnoside (<b>8</b>) against <i>Staphylococcus aureus</i> with MIC value 9.77 μg/mL. According to the MBC/MIC ratio, the antibacterial activity of the isolated flavonoids was considered flavonoid <b>2</b> is bactericidal nature against <i>S. aureus,</i> and flavonoids <b>3</b> and <b>4</b> are bactericidal against <i>E. coli.</i>