Novel antiplatelet agent

A method for preventing or treating ischemic stroke, acute coronary syndrome, microvascular dysfunction, peripheral arterial disease, arteriosclerosis obliterans, ischemic heart disease, thrombotic microangiopathy, or unstable or stable angina, the method comprising:

• administering, to a subject in need thereof, an effective amount of a compound of formula I or a pharmaceutically acceptable salt thereof:
• wherein:
• X is N or CR1d;
• Xb1-Xb5 are the same or different, and are nitrogen or carbon;
• R1a-R1d are the same or different, and are hydrogen, an optionally substituted alkyl, an optionally substituted alkoxy, an optionally substituted alkylthio, an alkenyl, a cycloalkyl, a halogen, cyano, hydroxyl, or an amino optionally substituted with 1 or 2 alkyl;
• R2 is an optionally substituted aryl or an optionally substituted heteroaryl;
• and
• R3 is an optionally substituted aryl or an optionally substituted heteroaryl,
• provided that at least three of Xb1-Xb5 are carbon,
• when Xb1 is nitrogen, each of Xb2, Xb4, and Xb5 is carbon,
• when Xb2 is nitrogen, both Xb1 and Xb4 are carbon, and
• when Xb4 is nitrogen, Xb5 is carbon.