Several clinical candidates have now emerged as a result of an intense search for orally available, antithrombotic factor Xa inhibitors. This review highlights the discovery of XareltoTM (Rivaroxaban) starting from an initial tetrahydrophthalimide screening hit. The major breakthrough was the finding that a chlorothiophene moiety can undergo an interaction in the S1 binding site thus leading to high potency combined with favorable oral bioavailability. The binding mode of this P1 moiety is discussed, and further non-basic S1 binders of this new type are reviewed.