Design and SAR of Withangulatin A Analogues that Act as Covalent TrxR Inhibitors through the Michael Addition Reaction Showing Potential in Cancer Treatment.

The thioredoxin system plays an important role in cancer cells. Inhibiting thioredoxin reductase (TrxR) has emerged as an effective strategy to selectively target cancer cells. Withangulatin A (), a natural product extracted from the whole herb of L. (Solanaceae), exhibits potent anticancer activity and other diverse pharmacological activities. To improve activity and targeting, we designed and prepared 41 semisynthetic analogues of WA. Biological evaluation indicated that the most promising compound displayed the most significant effect on HT-29 cells (human colon cancer cells) (IC = 0.08 μM). A structure-activity relationship study indicated that α,β-unsaturated ketones and ester are necessary groups, allowing to undergo Michael addition reactions with mercaptan and selenol. Liquid chromatography-mass spectrometry (LC-MS) analysis confirmed that modified selenocysteine 498 (U) residues in the redox centers of TrxR, resulting in enzyme inhibition. Therefore, compound acts as a novel TrxR inhibitor and may be a promising candidate for cancer intervention.