The invention provides a compound of formula1 or a pharmaceutically-acceptable salt thereof, that is useful as a JAK inhibitor. The invention also provides crystalline forms of the compound, pharmaceutical compositions comprising the compound, methods of using the compound to treat diseases amenable to a JAK inhibitor, and processes and intermediates useful for preparing the compound.本發明提供一種用作JAK抑制劑之式1化合物或其醫藥學上可接受之鹽。本發明亦提供該化合物之結晶形式、包含該化合物之醫藥組合物、使用該化合物治療適合於JAK抑制劑之疾病之方法及適用於製備該化合物之方法及中間物。