the present invention relates to compounds to inhibit blood coagulation , and more particularly to novel diketopiperazine derivatives , pharmaceutically acceptable salts and compositions thereof , to specifically inhibit thrombin . the compound has the following general structure , wherein r 1 , r 2 and r 4 consist of a hydrogen , alkyl or aryl moiety , r 3 consist of an alkyl or aryl moiety , wherein r 5 consists of a hydrogen , alkyl , aryl , hydroaryl , heteroaryl , hydroheteroaryl , sulfonylalkyl , sulfonylaryl , sulfonylhydroaryl , sulfonylheteroaryl or sulfonylhydroheteroaryl moiety , and wherein r 6 consists of a hydrogen , alkyl , aryl , hydroaryl , heteroaryl or hydroheteroaryl moiety . also disclosed are methods of using the compound for treating coagulation disorders such as thrombosis and heparin associated thrombocytopenia .