Bipolaristeroid A, a 5,6-seco-9,10-seco-steroid with cytotoxic activity from the fungus Bipolaris maydis

Abstract

Eleven undescribed steroids, bipolaristeroids A–K, and one known compound, demethylincisterol A₃, were isolated from the fungus Bipolaris maydis. Bipolaristeroid A is a 5,6-seco-9,10-seco-steroid with a rearranged B ring, in which the A and C rings are connected by an ester bond. Bipolaristeroid B is a rearranged 1(10 → 6)-abeosteroid with an aromatic B ring. Their planar structures and absolute configuration were determined using NMR, HRESIMS, DP4+ analysis, ECD calculation, and single-crystal X-ray diffraction. Bipolaristeroid A shows excellent inhibitory effects against the cancer cell lines HepG2, A549, SW620, and C4–2B with IC₅₀ values of 7.94, 5.11, 5.13, and 3.83 μM, respectively.