Systematic SAR studies of in vitro factor Xa inhibitory activity around compound 
1 were performed by modifying each of the three phenyl rings. A class of highly 
potent, selective, efficacious and orally bioavailable direct factor Xa 
inhibitors was discovered. These compounds were screened in hERG binding assays 
to examine the effects of substitution groups on the hERG channel affinity. From 
the leading compounds, betrixaban (compound 11, PRT054021) has been selected as 
the clinical candidate for development.