For example, the most effective inhibitor of thrombin reported to date is N-alpha-(2-naphthyl-sulfonyl-glycyl)-4-amidinophenylalanine piperidine which a Ki of 6 nM. Compounds of the present invention almost completely inhibit thrombin at a concentration of 5 nM indicating a Ki of <1 nM, and thus provide excellant candidates for the control of thrombin mediated processes such as blood coagulation.