Structure-based design and synthesis of 1H-pyrazolo[3,4-d]pyrimidin-4-amino derivatives as Janus kinase 3 inhibitors.

Janus kinases (JAKs) regulate various inflammatory and immune responses and are targets for the treatment of inflammatory and immune diseases. Here we report the discovery and optimization of 1H-pyrazolo[3,4-d]pyrimidin-4-amino as covalent JAK3 inhibitors that exploit a unique cysteine (Cys909) residue in JAK3. Our optimization study gave compound 12a, which exhibited potent JAK3 inhibitory activity (IC of 6.2 nM) as well as excellent JAK kinase selectivity (>60-fold). In cellular assay, 12a exhibited potent immunomodulating effect on IL-2-stimulated T cell proliferation (IC of 9.4 μM). Further, compound 12a showed efficacy in delayed hypersensitivity assay. The data supports the further investigation of these compounds as novel JAKs inhibitors.