The present invention provides a compound represented by the formula (I) wherein X is a hydrogen atom or a fluorine atom； R is a hydrogen atom or alkyl； R1 is (1) cyclopropyl optionally substituted by 1 to 3 halogen atoms or (2) phenyl optionally substituted by 1 to 3 halogen atoms； R2 is alkyl, alkoxy, haloalkoxy, a halogen atom, cyano, etc.； and R3 is 7-oxo-7,8-dihydro-1,8-naphthyridinyl, 3-pyridyl, etc., or a salt thereof. The compound of the present invention has excellent antimicrobial activity against Clostridium difficile and is useful for the prevention or treatment of intestinal infection such as Clostridium difficile-associated diarrhea.本發明提供一種式(I)表示之化合物或其鹽其中，X係氫原子或氟原子；R係氫原子或烷基；R1係(1)視需要經1至3個鹵素原子取代之環丙基或(2)視需要經1至3個鹵素原子取代之苯基；R2係烷基、烷氧基、鹵烷氧基、鹵素原子、氰基等；及R3係7-側氧基-7,8-二氫-1,8-啶基、3-吡啶基等。本發明之化合物對難養芽胞梭菌具有優越的抗微生物活性，及有用於預防或治療如難養芽胞梭菌相關的腹瀉之腸道感染。
