Characterization of a class of peptide boronates with neutral P1 side chains as highly selective inhibitors of thrombin.

Z-D-Phe-Pro-boroMpg-OPin (9a)1,2 has been shown previously to be a highly specific inhibitor of thrombin in spite of lacking an arginine-like guanidino group at the P1 site. A range of compounds have been synthesized based upon this lead compound, varying the neutral side chain at the P1 site. Of the 20 examples based upon the structures at P2 and P3 of Z-D-X-Pro (X being Phe or beta,beta-diphenylalanine), all were found to be effective inhibitors of thrombin (Ki's between 10 and 100 nM).

Structure/function aspects of neutral P1 residue peptide inhibitors of thrombin.

Control of thrombin by its inhibition in indications such as myocardial infarction, unstable angina or stroke has been demonstrated to be therapeutically valuable. However restoration of hemostasis by targeting thrombin while avoiding its fellow serine proteinases, (e.g.

Synthetic peptides and peptidomimetics as substrates and inhibitors of thrombin and other proteases in the blood coagulation system.

The synthesis of peptides as imitations of the thrombin cleavage site of fibrinogen has led to sequences with affinity for the enzyme. These peptides were first developed as chromogenic and fluorogenic substrates for thrombin. The same idea was also used to generate peptide substrates for other serine proteases in blood coagulation and fibrinolysis.

In vitro and in vivo characterization of a neutral boron-containing thrombin inhibitor.

Peptide boronic acid derivatives have proven to be very potent inhibitors of serine proteases with boroarginine derivatives being particularly potent thrombin inhibitors. The importance of the charged side chain of arginine has been investigated by synthesizing a derivative in which this side chain has been replaced by a neutral one. This boronic acid derivative, D-benzyloxycarbonyl (Z)-Phe-Pro-methoxypropylglycine-pinanediol (MpgC10H16), inhibited thrombin by a competitive mechanism with an inhibition constant (Ki) of 8.

Benzyloxycarbonyl-D-Phe-Pro-methoxypropylboroglycine: a novel inhibitor of thrombin with high selectivity containing a neutral side chain at the P1 position.

Thrombin, the blood-clotting enzyme, is a serine proteinase with trypsin-like specificity and is able to cleave Arg-Xaa peptide bonds but only in a very limited number of substrates (and sites therein). For the prevention and treatment of thrombosis the control of thrombin activity is a key target, and a variety of synthetic inhibitors have been introduced recently, all of which have a positive charge at the P1 site. We report the synthesis of the first example of a new class of inhibitor containing a neutral side chain at the P1 site, the peptide benzyloxycarbonyl-D-Phe-Pro- methoxypropylboroglycine.