Design and synthesis of potent, selective, and orally bioavailable tetrasubstituted imidazole inhibitors of p38 mitogen-activated protein kinase.

Novel potent and selective diarylimidazole inhibitors of p38 MAP (mitogen-activated protein) kinase are described which have activity in both cell-based assays of tumor necrosis factor-alpha (TNF-alpha) release and an animal model of rheumatoid arthritis. The SAR leading to the development of selectivity against c-Raf and JNK2alpha1 kinases is presented, with key features being substitution of the 4-aryl ring with m-trifluoromethyl and substitution of the 5-heteroaryl ring with a 2-amino substituent. Cell-based activity was significantly enhanced by incorporation of a 4-piperidinyl moiety at the 2-position of the imidazole which also enhanced aqueous solubility. In general, oral bioavailability of this class of compounds was found to be poor unless the imidazole was methylated on nitrogen. This work led to identification of 48, a potent (p38 MAP kinase inhibition IC50 0.24 nM) and selective p38 MAP kinase inhibitor which inhibits lipopolysaccharide-stimulated release of TNF-alpha from human blood with an IC50 2.2 nM, shows good oral bioavailability in rat and rhesus monkey, and demonstrates significant improvement in measures of disease progression in a rat adjuvant-induced arthritis model.

Transglutaminase inhibition by 2-[(2-oxopropyl)thio]imidazolium derivatives: mechanism of factor XIIIa inactivation.

The physiologic role of several transglutaminases could be more precisely defined with the development of specific inhibitors for these enzymes. In addition, specific plasma transglutaminase (fXIIIa) inhibitors may have therapeutic utility in the treatment of thrombosis. For these purposes, the inactivation of fXIIIa and human erythrocyte transglutaminase (HET) by 2-[(2-oxopropyl)thio]imidazolium derivatives, which comprise a novel class of transglutaminase inactivators, was studied. As a specific example, 1,3,4,5-tetramethyl-2-[(2-oxopropyl)thio]imidazolium chloride (III) inactivated fXIIIa with an apparent second-order rate constant (specificity constant of inactivation) of 6.3 x 10(4) M-1 s-1, corresponding to a rate 4 x 10(7) times greater than its reaction rate with glutathione (GSH). The mechanism of fXIIIa inactivation by this class of compounds was investigated utilizing two [14C]-isotopic regioisomers of 1,3-dimethyl-2-[(2-oxopropyl)thio]imidazolium iodide (II). Structural analyses demonstrated that acetonylation of the active site cysteinyl residue of fXIIIa occurred along with the stoichiometric release of the complementary fragment of the inactivator as the corresponding thione. Kinetic analysis of the inactivation of fXIIIa by nonquarternary analogs of II and III indicated the formation of a reversible complex between the inactivator and fXIIIa prior to irreversible modification of the enzyme. At 1 mM, III displayed no detectable levels of inhibition or inactivation with several serine proteases and thiol reagent-sensitive enzymes. 2-[(2-Oxopropyl)thio]imidazolium derivatives and the related molecule 2-(1-acetonylthio)-5-methylthiazolo-[2,3]-1,3,4-thiadiazo lium perchlorate (I), when present at the time of clot formation at 1-10 microM, enhanced the rates of tissue plasminogen activator catalyzed clot lysis in vitro. These inactivators prevented the fXIIIa-catalyzed covalent incorporation of alpha 2-antiplasmin into the alpha chain of fibrin and the formation of high molecular weight fibrin alpha chain polymers, providing the basis for the observed enhancements in clot lysis rates.