Synthesis and optimization of furano[3,2-d]pyrimidines as selective spleen tyrosine kinase (Syk) inhibitors

A series of furano[3,2-d]pyrimidine Syk inhibitors were synthesized and optimized for their enzyme potency and selectivity versus other kinases. In addition, ADME properties were assessed and compounds were prepared with optimized profiles for in vivo experiments. Compound 23 was identified as having acceptable pharmacokinetic properties and demonstrated efficacy in a rat collagen induced arthritis model.

Enabling structure-based drug design of Tyk2 through co-crystallization with a stabilizing aminoindazole inhibitor

Background

Structure-based drug design (SBDD) can accelerate inhibitor lead design and optimization, and efficient methods including protein purification, characterization, crystallization, and high-resolution diffraction are all needed for rapid, iterative structure determination. Janus kinases are important targets that are amenable to structure-based drug design. Here we present the first mouse Tyk2 crystal structures, which are complexed to 3-aminoindazole compounds.

Results

A comprehensive construct design effort included N- and C-terminal variations, kinase-inactive mutations, and multiple species orthologs. High-throughput cloning and expression methods were coupled with an abbreviated purification protocol to optimize protein solubility and stability. In total, 50 Tyk2 constructs were generated. Many displayed poor expression, inadequate solubility, or incomplete affinity tag processing. One kinase-inactive murine Tyk2 construct, complexed with an ATP-competitive 3-aminoindazole inhibitor, provided crystals that diffracted to 2.5–2.6 Å resolution. This structure revealed initial “hot-spot” regions for SBDD, and provided a robust platform for ligand soaking experiments. Compared to previously reported human Tyk2 inhibitor crystal structures (Chrencik et al. (2010) J Mol Biol 400:413), our structures revealed a key difference in the glycine-rich loop conformation that is induced by the inhibitor. Ligand binding also conferred resistance to proteolytic degradation by thermolysin. As crystals could not be obtained with the unliganded enzyme, this enhanced stability is likely important for successful crystallization and inhibitor soaking methods.

Conclusions

Practical criteria for construct performance and prioritization, the optimization of purification protocols to enhance protein yields and stability, and use of high-throughput construct exploration enable structure determination methods early in the drug discovery process. Additionally, specific ligands stabilize Tyk2 protein and may thereby enable crystallization.

Discovery of thienopyridines as Src-family selective Lck inhibitors

We describe the identification, SAR, and in vivo pharmacology of a new series of Src-family selective Lck inhibitors. These thienopyridines were designed based on a desire to access the unique residues in the extended hinge region of Lck.

Discovery of A-770041, a src-family selective orally active lck inhibitor that prevents organ allograft rejection

We describe the identification, SAR, and pharmacology of the src-family selective lck inhibitor A-770041 that prolongs the survival of major histocompatibility mismatched allografts in models of solid organ transplant rejection for greater than 65 days.