Disclosed is a compound represented by the general formula (1) e.g. (E)-3-[1-alpha, 3-alpha, 4-alpha)-3,4-difluorocyclopentyl]-N-(5-fluorothiazol-2-yl)-2-(4-(methylsulfonyl)phenyl)acrylamide,or a pharmaceutically acceptable salt thereof wherein the substituents are defined in the specification for treatment or prevention of diabetes.