Discovery of a JAK1/3 Inhibitor and Use of a Prodrug To Demonstrate Efficacy in a Model of Rheumatoid Arthritis.

The four members of the Janus family of nonreceptor tyrosine kinases play a significant role in immune function. The JAK family kinase inhibitor, tofacitinib 1, has been approved in the United States for use in rheumatoid arthritis (RA) patients. A number of JAK inhibitors with a variety of JAK family selectivity profiles are currently in clinical trials. Our goal was to identify inhibitors that were functionally selective for JAK1 and JAK3. Compound 22 was prepared with the desired functional selectivity profile, but it suffered from poor absorption related to physical properties. Use of the phosphate prodrug 32 enabled progression to a murine collagen induced arthritis (CIA) model. The demonstration of a robust efficacy in the CIA model suggests that use of phosphate prodrugs may resolve issues with progressing this chemotype for the treatment of autoimmune diseases such as RA.

Discovery of potent and efficacious pyrrolopyridazines as dual JAK1/3 inhibitors.

A series of potent dual JAK1/3 inhibitors have been developed from a moderately selective JAK3 inhibitor. Substitution at the C6 position of the pyrrolopyridazine core with aryl groups provided exceptional biochemical potency against JAK1 and JAK3 while maintaining good selectivity against JAK2 and Tyk2. Translation to in vivo efficacy was observed in a murine model of chronic inflammation. X-ray co-crystal structure determination confirmed the presumed inhibitor binding orientation in JAK3. Efforts to reduce hERG channel inhibition will be described.

Discovery of pyrrolo[1,2-b]pyridazine-3-carboxamides as Janus kinase (JAK) inhibitors.

A new class of Janus kinase (JAK) inhibitors was discovered using a rationally designed pyrrolo[1,2-b]pyridazine-3-carboxamide scaffold. Preliminary studies identified (R)-(2,2-dimethylcyclopentyl)amine as a preferred C4 substituent on the pyrrolopyridazine core (3b). Incorporation of amino group to 3-position of the cyclopentane ring resulted in a series of JAK3 inhibitors (4g-4j) that potently inhibited IFNγ production in an IL2-induced whole blood assay and displayed high functional selectivity for JAK3-JAK1 pathway relative to JAK2. Further modifications led to the discovery of an orally bioavailable (2-fluoro-2-methylcyclopentyl)amino analogue 5g which is a nanomolar inhibitor of both JAK3 and TYK2, functionally selective for the JAK3-JAK1 pathway versus JAK2, and active in a human whole blood assay.

Discovery of 4-(5-(cyclopropylcarbamoyl)-2-methylphenylamino)-5-methyl-N-propylpyrrolo[1,2-f][1,2,4]triazine-6-carboxamide (BMS-582949), a clinical p38α MAP kinase inhibitor for the treatment of inflammatory diseases.

The discovery and characterization of 7k (BMS-582949), a highly selective p38α MAP kinase inhibitor that is currently in phase II clinical trials for the treatment of rheumatoid arthritis, is described. A key to the discovery was the rational substitution of N-cyclopropyl for N-methoxy in 1a, a previously reported clinical candidate p38α inhibitor. Unlike alkyl and other cycloalkyls, the sp(2) character of the cyclopropyl group can confer improved H-bonding characteristics to the directly substituted amide NH. Inhibitor 7k is slightly less active than 1a in the p38α enzymatic assay but displays a superior pharmacokinetic profile and, as such, was more effective in both the acute murine model of inflammation and pseudoestablished rat AA model. The binding mode of 7k with p38α was confirmed by X-ray crystallographic analysis.

Benzothiazole based inhibitors of p38alpha MAP kinase.

Rational design, synthesis, and SAR studies of a novel class of benzothiazole based inhibitors of p38alpha MAP kinase are described. The issue of metabolic instability associated with vicinal phenyl, benzo[d]thiazol-6-yl oxazoles/imidazoles was addressed by the replacement of the central oxazole or imidazole ring with an aminopyrazole system. The proposed binding mode of this new class of p38alpha inhibitors was confirmed by X-ray crystallographic studies of a representative inhibitor (6a) bound to the p38alpha enzyme.

5-Cyanopyrimidine derivatives as a novel class of potent, selective, and orally active inhibitors of p38alpha MAP kinase.

A novel class of 5-cyanopyrimidine-based inhibitors of p38alpha MAP kinase has been investigated. Analogues optimized through SAR iterations display low nanomolar enzymatic and cellular activity. The in vivo efficacy of this class of p38 inhibitors was demonstrated by 3a and 3b (>50% reduction in TNF levels when orally dosed at 5 mg/kg, 5 h prior to LPS administration in an acute murine model of inflammation). For 3a and 3b, the previously identified N-methoxybenzamide moiety (1) was replaced with N-(isoxazol-3-yl)benzamide, thereby providing increased metabolic stability. Cyanopyrimidine 3a demonstrated 100% oral bioavailability in mouse. High p38 kinase selectivity versus over 20 kinases was observed for analogue 3b. Direct hydrogen bonding of the cyano nitrogen of the 5-cyanopyrimidine core to the backbone NH of Met109 was confirmed by X-ray crystallographic analysis of 3a bound to p38alpha.