The present invention provides for compounds of formula (I) wherein R1, R2, R3, and R4 have any of the values defined in the specification, and pharmaceutically acceptable salts thereof, that are useful as agents in the treatment of diseases and conditions mediated and modulated by CFTR, including cystic fibrosis, Sjögren's syndrome, pancreatic insufficiency, chronic obstructive lung disease, and chronic obstructive airway disease. Also provided are pharmaceutical compositions comprised of one or more compounds of formula (I).本發明提供式(I)化合物其中R1、R2、R3及R4具有本說明書中所定義之值中之任一者,及其醫藥學上可接受之鹽,其適用作治療藉由CFTR介導及調節之疾病及病況,包括囊腫性纖維化、休格連氏症候群(Sjögren's syndrome)、胰臟功能不全、慢性阻塞性肺病及慢性阻塞性呼吸道疾病之藥劑。亦提供包含一或多種式(I)化合物之醫藥組合物。