Withapubesides A–D: natural inducible nitric oxide synthase (iNOS) inhibitors from Physalis pubescens†
Four new steroid glycosides, withapubesides A–D (1–4), were isolated from the stems of Physalis pubescens L. Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1 and 2 were deduced by single-crystal X-ray diffraction and ECD data analysis, respectively. Compound 3 has shown significant inhibitory activity against LPS-induced nitric oxide production in RAW 264.7 macrophages with an IC50 value of 12.8 μM and moderate cytostatic activity against human carcinoma cells (786-O, C4-2B, 22Rvl, A375 and A375S2) with IC50 values in the range of 3.05–9.47 μM. Molecular docking simulation demonstrated that 3 is bound in the inducible nitric oxide synthase (iNOS) active site heme pocket very well, which suggests that 3 might be a candidate for the development of iNOS inhibitors.