Two new bioactive steroids from a mangrove-derived fungus Aspergillus sp.

Two unusual naturally Diels-Alder additive steroids, ergosterdiacids A and B (1 and 2), constructing a 6/6/6/6/5 pentacyclic steroidal system, together with three known compounds (3-5) were obtained from the mangrove-derived fungus Aspergillus sp. Their structures were elucidated based on the comprehensive spectroscopic analysis, including 1D, 2D NMR and HRESIMS, as well as the quantum chemical ECD calculations. The plausible biosynthetic pathways of 1 and 2 were discussed. In the bioactivity assays, 1 and 2 exhibited potential in vitro inhibition activity against Mycobacterium tuberculosis protein tyrosine phosphatase B (MptpB) with an IC50 value of 15.1 and 30.1 μM, respectively. The inhibitory kinetic experiments indicated that both of them acted via a noncompetitive inhibition mechanism. Moreover, 1 and 2 showed strong in vitro anti-inflammatory effects by suppressing the NO production at 4.5 and 3.6 μM, respectively.