New Chromogenic Substrates for Thrombin with Increased Specificity

Synthesis of peptide p-nitroanilides mimicking fibrinogen- and hirudin-binding to thrombin. Design of slow reacting thrombin substrates

The design and synthesis of 20 peptide p-nitroanilides is described. The nitroanilides are used as thrombin substrates that share uncommon properties. These substrates are tested for their applicability to measure thrombin generation in activated plasma. This technique requires substrates that must slowly but selectively be hydrolyzed by thrombin. To ensure selectivity, thrombin's natural substrate and its most potent inhibitor were used as lead compounds. Eighteen peptide p-nitroanilides were synthesized using human fibrinogen A alpha [7-16] decapeptide as lead structure since this fragment constitutes the minimal sequence which binds to thrombin with high affinity. Two other chromogenic substrates were designed using 5-amino-2-nitrobenzoic acid as the chromophore. A peptide giving subsite interactions with the fibrinogen recognition exosite was coupled to the carboxylic function. As the peptide segment, the carboxyl terminal part of hirudin (residues 50-65) was chosen to ensure highly specific thrombin recognition. From the 20 nitroanilides synthesized, we indeed obtained a number of compounds which can be used as substrate in the thrombin generation assay.

Chromogenic substrates in haemostasis

Advances in knowledge of the structure-function relationships of the proteins involved in haemostatic pathways, have made it possible to synthesize small peptides which mimic the active site of many of the serine proteases concerned. Attachment to the cleavage site of such synthetic peptides, of a detector molecule such as para-nitroaniline which, when released, produces a coloured compound has enabled many of the enzyme reactions of haemostasis, and most of the co-factors and naturally-occurring inhibitors, to be individually and sensitively quantitated. Chromogenic substrate assays are very specific and overcome the criticism levelled at many conventional assays that, being based on the speed of formation or the rate of destruction of a fibrin clot, they frequently involve enzymatic reactions in addition to that being examined. Moreover, chromogenic substrate assays are generally simple and quick to perform and are readily automated. They are thus economical of manpower and, more importantly from the point of view of patient care, they permit the rapidly-changing status of those with acute derangements of haemostasis to be monitored more frequently and comprehensively than is possible using some conventional assays. Chromogenic substrate assays have some limitations, however. Since they mimic only a small portion of the natural substrate, they may not be sensitive to structural defects elsewhere in the molecule, and may thus not totally reflect biological activity. Though technically simple to perform, the defined incubation times and temperatures must be rigidly adhered to if reliable results are to be obtained.(ABSTRACT TRUNCATED AT 250 WORDS)