5,6-de-epoxy-5-en-7-one-17-hydroxy withaferin A, a new cytotoxic steroid from Withania somnifera L. Dunal leaves.

From the leaves of Withania somnifera L. Dunal, a new withasteroid named as 5,6-de-epoxy-5-en-7-one-17-hydroxy withaferin A (6) was isolated along with several known compounds, namely 16ß-acetoxy-6α,7α-epoxy-5α-hydroxy-1-oxowitha-2,17(20),24-trienolide (1), withanone (2), 16-en-27-deoxy withaferin A (3), 27-deoxy withaferin A (4), withaferin A (5), withanolide D (7) and 27-hydroxy withanone (8). Its structure was determined using spectroscopic methods, namely IR, (1)H NMR, (13)C NMR, COSY, HMBC and HRMS. Among the known compounds, 16ß-acetoxy-6α,7α-epoxy-5α-hydroxy-1-oxowitha-2,17(20),24-trienolide (1) was previously reported from the roots of W. somnifera. Now, it has been isolated from the leaves, as well. The cytotoxic activity of the new steroid was carried out using the MTT assay against a panel of cancer cell lines, namely MCF-7 (breast), WRL-68 (liver), PC-3 (prostate) and CACO-2 (colon). The results showed that the new compound possesses strong cytotoxic activity against liver and breast cancer with an IC50 of 1.0 µg/mL and a moderate activity against colon (IC50 3.4 µg/mL) and prostate (IC50 7.4 µg/mL) cancer cells.

Epoxide group relationship with cytotoxicity in withanolide derivatives from Withania somnifera.

Withania somnifera is one of the highly reputed medicinal plants of India. Its steroidal constituents exist in the form of two major substitution patterns, viz. withaferin A (1) and withanone (5). Withaferin A with oxidation at carbons 4, 5, and 6 is considered as an active type, especially as anticancer, whereas the withanones with oxidation at carbons 5, 6, and 7 rarely show any activity. We prepared a series of derivatives with modifications at carbons 5, 6, and 7 in ring B of these withanolides to study the role of the epoxide group towards the cytotoxic property of these bioactive steroids. We have converted withanolides into the respective thiiranes, amino alcohols and alcohols by selective reactions at the epoxide ring and were evaluated for in vitro anticancer activity against four cancer cell lines to study the structure activity relationships. The transformations of the epoxide group in withanolides of the withaferin A type showed moderate reduction in their cytotoxicity whereas the almost inactive withanones have shown some improvements in their alcohol derivatives.