α-Glucosidase Inhibitors: Diphenyl Ethers and Phenolic Bisabolane Sesquiterpenoids from the Mangrove Endophytic Fungus Aspergillus flavus QQSG-3

Abstract

Two new diphenyl ethers (<b>1</b> and <b>2</b>) and four new phenolic bisabolane sesquiterpenoids (<b>3</b>⁻<b>6</b>), together with five known related derivatives, were isolated from the culture of the endophytic fungus <i>Aspergillus flavus</i> QQSG-3 obtained from a fresh branch of <i>Kandelia obobata</i>, which was collected from Huizhou city in the province of Guangdong, China. The structures of compounds <b>1</b>⁻<b>6</b> were determined by analyzing NMR and HRESIMS data. The absolute configurations of <b>5</b> and <b>6</b> were assigned by comparing their experimental ECD spectra with those reported for similar compounds in the literature. All isolates were evaluated for their α-glucosidase inhibitory activity, of which compounds <b>3</b>, <b>5</b>, <b>10</b>, and <b>11</b> showed strong inhibitory effects with IC₅₀ values in the range of 1.5⁻4.5 μM.