Complex sentence: DX-9065a was the first compound to inhibit FXa without inhibiting thrombin, this was attained by having a carboxyl group in R1 which seemed to be the most important moiety for a selective binding to FXA (need a picture of DX-9065a).
Split into simpler sentences: DX-9065a was the first compound to inhibit FXa without inhibiting thrombin. That was attained by having a carboxyl group in R1 which seemed to be the most important moiety for a selective binding to FXa (need a picture of DX-9065a).