Synthesis of Electrophilic Cyclopent-2-enone Conjugates With Modulatory Effects on Inflammatory Responses Mediated by Nrf2/Keap1, NF-κB and IL-6

Cyclopent-2-enone bearing natural products possess anti-inflammatory, cytotoxic, antiproliferative, and antimicrobial activities attributed to the presence of a Michael acceptor enone group acting as a bait for protein targets. To explore the biological activity of synthetic small molecules bearing the cyclopent-2-enone moiety, a collection of 4-substituted cyclopent-2-enones (3 a–3 i) was prepared synthetically using Lewis acid-catalyzed Mukaiyama-Michael reaction (MMR) in modest to high yields. These derivatives were screened for their effect on inflammatory response mediators, namely Nrf2, NF-κB, and IL-6 through cell-based reporter assays. The results show that 5-(4-oxocyclopent-2-en-1-yl)furan-2(5H)-one (3 g) is a potent Nrf2 activator in HaCaT cells. The mechanism of Nrf2 activation by 3 g was investigated through an MS/MS-directed proteomic analysis and have shown the formation of a Michael adduct via cysteine-613 on Keap1, an inhibitor of Nrf2. Density functional theory calculations show favorable Michael adduct formation between 3 g and the truncated Keap1 tripeptide Pro-Cys613-Ala at the β-carbon of the cyclopent-2-enone moiety. On the other hand, the derivative 4-(2-oxo-2-phenylethyl)cyclopent-2-en-1-one (3 a) exhibited selective Nrf2 inhibition in the cancer cell line Huh7, and inhibitory activity along with 3 g against NF-κB, and IL-6 in RAW 264.7 cells. This points to the cyclopent-2-enone group being an effective scaffold for anti-inflammatory drug designs.