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

Two new diphenyl ethers (1 and 2) and four new phenolic bisabolane sesquiterpenoids (3–6), together with five known related derivatives, were isolated from the culture of the endophytic fungus Aspergillus flavus QQSG-3 obtained from a fresh branch of Kandelia obobata, which was collected from Huizhou city in the province of Guangdong, China. The structures of compounds 1–6 were determined by analyzing NMR and HRESIMS data. The absolute configurations of 5 and 6 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 3, 5, 10, and 11 showed strong inhibitory effects with IC(50) values in the range of 1.5–4.5 μM.