A compound having the general formula (I) (wherein R 1 represents C1-C6 alkyl, etc., R 2 represents hydrogen, C2-C7 alkanoyl, C7-C11 arylcarbonyl, the formula R 4 -(CH 2 ) 1 -, etc., R 3 represents C6-C10 aryl, etc., X 1 , X 2 , X 3 , X 4 and X 5 each independently represents hydrogen, halogen, etc., and n represents an integer of 0 to 2), pharmacologically acceptable salts thereof or prodrugs thereof. They have excellent inhibition of platelet activation, etc. and are useful as a prophylactic or therapeutic agents for diseases related to thrombus or embolus formation. |