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

Abstract 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 Aβ 42 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-Aβ 42 aggregation activity with IC 50 values of 5.1 and 2.3 μM, respectively. Preliminary structure–activity relationship of these diphenyl ethers as anti-Aβ 42 aggregation inhibitors was proposed.