The present invention is directed to compounds of formula I and pharmaceutically acceptable salts, esters, and prodrugs thereof which are inhibitors of JAK kinase. The present invention is also directed to intermediates used in making such compounds, the preparation of such a compound, pharmaceutical compositions containing such a compound, methods of inhibition JAK kinase activity, methods ofinhibition the platelet aggregation, and methods to prevent or treat a number of conditions mediated at least in part by JAK kinase activity, such as undesired thrombosis and Non Hodgkin’s Lymphoma.本發明係關於式I化合物及其醫藥學上可接受之鹽、酯及前藥,其為JAK激酶抑制劑。本發明亦係關於用於製造該等化合物之中間物、該化合物之製備、含有該化合物之醫藥組合物、抑制JAK激酶活性之方法、抑制血小板聚集之方法及預防或治療至少部分由JAK激酶活性介導之許多種病狀(諸如不希望出現的血栓症及非霍奇金氏淋巴瘤(Non Hodgkin's Lymphoma))的方法。