Phosphono Bisbenzguanidines as Irreversible Dipeptidomimetic Inhibitors and Activity-Based Probes of Matriptase-2

Matriptase-2, a type II transmembrane serine protease, plays a key role in human iron homeostasis. Inhibition of matriptase-2 is considered as an attractive strategy for the treatment of iron-overload diseases, such as hemochromatosis and β-thalassemia. In the present study, synthetic routes to nine dipeptidomimetic inactivators were developed. Five active compounds (41-45) were identified and characterized kinetically as irreversible inhibitors of matriptase-2. In addition to a phosphonate warhead, these dipeptides possess two benzguanidine moieties as arginine mimetics to provide affinity for matriptase-2 by binding to the S1 and S3/S4 subpockets, respectively. This binding mode was strongly supported by covalent docking analysis. Compounds 41-45 were obtained as mixtures of two diastereomers and were therefore separated into the single epimers. Compound 45 A, with S configuration at the N-terminal amino acid and R configuration at the phosphonate carbon atom, was the most potent matriptase-2 inactivator with a rate constant of inactivation of 2790 m(-1)  s(-1) and abolished the activity of membrane-bound matriptase-2 on the surface of intact cells. Based on the chemotyp of phosphono bisbenzguanidines, the design and synthesis of a fluorescent probe (51 A) by insertion of a coumarin label is described. The in-gel fluorescence detection of matriptase-2 was demonstrated by applying 51 A as the first activity-based probe for this enzyme.