Synthesis, Chemical Reactivity as Michael Acceptors, and Biological Potency of Monocyclic Cyanoenones, Novel and Highly Potent Anti-inflammatory and Cytoprotective Agents

Abstract

Novel monocyclic cyanoenones examined to date display unique features regarding chemical reactivity as Michael acceptors and biological potency. Remarkably, in some biological assays, the simple structure is more potent than pentacyclic triterpenoids (e.g., CDDO and bardoxolone methyl) and tricycles (e.g., TBE-31). Among monocyclic cyanoenones, 1 is a highly reactive Michael acceptor with thiol nucleophiles. Furthermore, an important feature of 1 is that its Michael addition is reversible. For the inhibition of NO production, 1 shows the highest potency. Notably, its potency is about three times higher than CDDO, whose methyl ester (bardoxolone methyl) is presently in phase III clinical trials. For the induction of NQO1, 1 also demonstrated the highest potency. These results suggest that the reactivity of these Michael acceptors is closely related to their biological potency. Interestingly, in LPS-stimulated macrophages, 1 causes apoptosis and inhibits secretion of TNF-α and IL-1β with potencies that are higher than those of bardoxolone methyl and TBE-31.

New Monocyclic, Bicyclic, and Tricyclic Ethynylcyanodienones as Activators of the Keap1/Nrf2/ARE Pathway and Inhibitors of Inducible Nitric Oxide Synthase

“…We designed and synthesized a preliminary set of eight monocylic cyanoenones, including 2 and 3, and then evaluated the chemical reactivity as Michael acceptors and biological potency. 6 Among monocyclic cyanoenones, ethynylcyanodienone 3 is a highly reactive Michael acceptor with thiol nucleophiles. Furthermore, an important feature of 3 is that its Michael addition is reversible.…”

Electron affinity of tricyclic, bicyclic, and monocyclic compounds containing cyanoenones correlates with their potency as inducers of a cytoprotective enzyme

“…However, reversible covalent drugs have been largely ignored because of the lack of reactive compounds to produce the reversible covalent adducts with protein targets. Based on previously published evidence, 8,9 the nonenolizable cyanoenone functionality is considered to be one of the best fragments that can be used for exploring reversible covalent drugs which are targeting the Keap1/Nrf2/ARE pathway. Although the reversible Michael adducts involved in equilibrium mixtures have been observed in solution by NMR, UV, and mass spectrometry, they have never been isolated and structurally characterized because of the rapid equilibrium that favors the reverse reaction.…”

“…Although the reversible Michael adducts involved in equilibrium mixtures have been observed in solution by NMR, UV, and mass spectrometry, they have never been isolated and structurally characterized because of the rapid equilibrium that favors the reverse reaction. [8][9][10] Most recently, a 3D structure of a reversible thiol Michael adduct was observed in situ in a crystalline sponge. 11 A RT I C L E I N F O A BS T RA C T Presently, a Nrf2 activator, bardoxolone methyl (Figure 1), which is a semisynthestic triterpenoid with cyanoenone functionality in ring A and a reversible covalent drug, 8 has been evaluated in Phase II clinical trials for the treatment of PAH (pulmonary arterial hypertension) in the USA 12 and diabetic nephropathy in Japan 13 .…”

“…During the development of bardoxolone methyl and its analogues, tri-, bi-, and monocyclic compounds with cyanoenones have been designed and explored. 9,10,14 They are also highly potent Nrf2 activators and reversible covalent drugs. Amongst them, tricyclic compound 1 (TBE-31, Figure 1 and Table 1) is the most potent Nrf2 activator.…”

“…The potency of tri-, bi-, and monocyclic compounds containing cyanoenones as Nrf2 activators was evaluated using a prototypic cytoprotective enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1) in Hepa1c1c7 murine hepatoma cells by CD values (the concentration required to double the specific enzyme activity of NQO1). 9,10,14 For this study, the pCD values (logarithm of the reciprocal of CD values expressed in M (mol/L) units) are employed for inducer potency. NQO1 is the prototypical Nrf2 target gene, and the NQO1 bioassay is widely recognized as a highly quantitative readout for Nrf2 activity.…”