recently reported the discovery of orally active sulfonylalkylamide Factor Xa (FXa) inhibitors, as typified by compound 1 (FXa IC(50)=0.061 microM). Since the pyridylpiperidine moiety was not investigated in our previous study, we conducted detailed structure-activityrelationship studies on this S4 binding element. This investigation led to the discovery of piperazinylimidazo[1,2-a]pyridine 2b as a novel