Diphenyl ethers from Aspergillus sp. and their anti-Aβ₄₂ aggregation activities.

Two new compounds with the character of diphenyl ether structure, oxisterigmatocystin D (1) and 9-acetyldiorcinol B (6), were isolated from the endolichenic fungal strain Aspergillus sp. (No. 16-20-8-1), along with six known compounds, oxisterigmatocystin A (2), oxisterigmatocystin C (3), sterigmatocystin (4), diorcinol B (5), violaceol-I (7), and violaceol-II (8). The structures of the new compounds were determined by extensive NMR spectroscopic data, and the absolute configuration of 1 was established by single-crystal X-ray diffraction analysis. Moreover, the Aβ42 aggregation inhibitory activities of 5-8 were evaluated by the standard thioflavin T (ThT) fluorescence assay using epigallocatechin gallate (EGCG) as the positive control. Compounds 7 and 8 displayed significant anti-Aβ42 aggregation activity with IC50 values of 5.1 and 2.3μM, respectively. Preliminary structure-activity relationship of these diphenyl ethers as anti-Aβ42 aggregation inhibitors was proposed.