Ac-Gly-BoroPro is a selective FAP inhibitor with a K i of 23 nM. In Vitro FAP has been implicated in cancer; however, its specific role remains elusive because inhibitors that distinguish FAP from other prolyl peptidases like dipeptidyl peptidase-4 (DPP-4) have not been developed. Ac-Gly-BoroPro selectively inhibits FAP relative to other prolyl peptidases. FAP reacts readily with submicromolar concentrations of Ac-Gly-BoroPro, reaching steady state inhibition levels rapidly (K i =23±3 nM). In contrast, DPP-4 requires higher Ac-Gly-BoroPro concentrations for inhibition and a longer time to reach steady state inhibition levels (K i =377±18 nM). Ac-Gly-BoroPro inhibits other prolyl peptidases (DPP-7, DPP-8, DPP-9, prolyl oligopeptidase, and acylpeptide hydrolase) with K i values ranging from 9- to 5400-fold higher than that for FAP inhibition. The N-acyl-linkage in Ac-Gly-BoroPro blocks the N terminus of the inhibitor, making it less nucleophilic and therefore unlikely to cyclize. MCE has not independently confirmed the accuracy of these methods. They are for reference only. Form:Solid IC50& Target:Ki: 23 nM (FAP)