Aspersterols A-D, ergostane-type sterols with an unusual unsaturated side chain from the deep-sea-derived fungus Aspergillus unguis

Abstract

Four previously undescribed ergostane-type sterols, aspersterols A？D (1？4), were isolated from a deep-sea-derived fungus, Aspergillus unguis IV17-109. The structures of the new compounds were determined by extensive analyses of their spectroscopic data, pyridine-induced deshielding effect, Mosher’s method, and electronic circular dichroism calculations. The key feature of these sterols is the presence of a rare unsaturated side chain with conjugated double bonds at Δ17 and Δ22. The absolute configuration of C-24 in the side chain was determined by hydrogenation and comparing 13C NMR chemical shifts of the hydrogenated products with literature values. In addition, aspersterol A (1) is the second representative of anthrasteroids with a hydroxy group at the C-2 position. Compound 1 showed cytotoxicity against six cancer cell lines, with GI50 values of 3.4 ± 0.3 to 4.5 ± 0.7 μM, while 2？4 showed anti-inflammatory activity, with IC50 values ranging from 11.6 ± 1.6 to 19.5 ± 1.2 μM.