Chromone and isocoumarin derivatives from the endophytic fungus <i>Xylomelasma</i> sp. Samif07, and their antibacterial and antioxidant activities

Abstract

Five chromone derivatives, including 2,6-dimethyl-5-methoxyl-7-hydroxylchromone (<b>1</b>), 6-hydroxymethyleugenin (<b>2</b>), 6-methoxymethyleugenin (<b>3</b>), chaetoquadrin D (<b>4</b>), and isoeugenitol (<b>5</b>), and three isocoumarin congeners, namely diaporthin (<b>6</b>), 8-hydroxy-6-methoxy-3-methylisocoumarin (<b>7</b>), and 6-methoxymellein (<b>8</b>), were isolated from the culture of the endophytic fungus <i>Xylomelasma</i> sp. Samif07 derived from the medicinal plant <i>Salvia miltiorrhiza</i> Bunge. Among them, compound <b>1</b> was a new natural product. Their structures were determined by spectroscopic methods and comparison with the literature. The isolated compounds were evaluated for their antibacterial and antioxidant activities. Compound <b>5</b> showed notable antitubercular activity against <i>Mycobacterium tuberculosis</i> with MIC value of 10.31 µg/mL, while compounds <b>1</b>-<b>3</b>, and <b>5</b>-<b>7</b> displayed inhibitory activities against the other bacteria with MIC range of 25 ∼ 100 µg/mL. Meanwhile, compound <b>6</b> showed potent hydroxyl radical-scavenging activity with EC₅₀ value of 15.1 µg/mL, while compounds <b>5</b>-<b>7</b> showed certain ferric reducing ability.