The compounds predicted to be the most promising against FAP by docking, the N-acetyl bicyclic derivative and three of the free amines, were next tested against FAP. One of the Cbzcontaining bicycles was also tested on FAP and displayed no inhibitory activity (see Supporting Info), confirming the need for smaller side chains in FAP inhibitors we proposed previously. The results of the FAP assay are displayed in Table and. In vitro results indicate that free amine boronic acid 10f exhibits nanomolar activity in FAP and low micromolar activity in POP, making it a promising dual inhibitor for future development. However, N-acetyl boronic ester derivative 12c exhibits submicromolar activity in both enzymes and comparable potency to failed clinical trial candidate Talabostat against POP (Figure ), making it a very promising drug candidate for future studies.