Design, synthesis and SAR of a series of 1,3,5-trisubstituted benzenes as thrombin inhibitors

The Research Progress of Direct Thrombin Inhibitors

Blood coagulation is the process of changing the blood from the flowing state to the gel state. It is an important part of the hemostatic function. Coagulation is a process by which a series of coagulation factors are sequentially activated, and finally thrombin is formed to form fibrin clot. Direct thrombin inhibitors are important anticoagulant drug. These drugs can selectively bind to the active site of thrombin, inhibit thrombin activity, have strong action and high specificity, and have important significance in the clinical treatment of thrombus diseases. Some of them come from natural products of animals or plants, and many of them have been applied in the clinic. The other part is derived from the design, synthesis and activity studies of small molecule inhibitors. This review discusses the progress of direct thrombin inhibitors in recent years.

Development of Orally Active Thrombin Inhibitors for the Treatment of Thrombotic Disorder Diseases

Thrombotic disorders represent the major share of the various cardiovascular diseases, and significant progress has been made in the development of synthetic thrombin inhibitors as new anticoagulants. In addition to the development of highly potent and selective inhibitors with improved safety and suitable half-life, several allosteric inhibitors have been designed and synthesized, that did not fully nullify the procoagulant signal and thus could result in reduced bleeding complications. Furthermore, natural products with thrombin inhibitory activity have been isolated, and some natural products have been modified in order to improve their inhibitory activity and metabolic stability. This review summarizes the development of orally active thrombin inhibitors for the treatment of thrombotic disorder diseases, which could serve as a reference for the interested researchers.

Prolinamide derivatives as thrombin inhibitors for the treatment of thrombin-mediated diseases: a patent evaluation of US2013296245

INTRODUCTION

Thrombotic disorders can lead to deep vein thrombosis, myocardial infarction and stroke. Thrombin plays a vital role in cascade reaction of blood coagulation, inhibition of the activity of thrombin can block the formation of thrombus and direct thrombin inhibitor has a prospect to overcome the limitations in application of the traditional anticoagulant drugs.

AREAS COVERED

The current patent US2013296245 describes a series of prolinamide derivatives with formula (I) as thrombin inhibitors. These new compounds are defined to be pharmaceutically acceptable salts derived from pharmaceutically acceptable inorganic acid and organic acid, and pharmaceutically acceptable prodrug where N-alkoxycarbonyl is protected or carboxylic acid is protected by ester.

EXPERT OPINION

The patent used formamidine and its N-alkoxycarbonyl-protected derivatives as the P1 group; these groups were less basic compared with the traditional guanidine group, so their lipophilicity could be optimized to achieve oral absorption. Furthermore, these pharmaceutically acceptable prodrugs where N-alkoxycarbonyl is protected or carboxylic acid is protected by ester could achieve prolonged half-life for a convenient once- or twice-daily oral dosing. These efforts gave a new hope and confidence to treat thrombotic disorders with selective and orally active thrombin inhibitors.

Biomimetic Aerobic C-H Olefination of Cyclic Enaminones at Room Temperature: Development toward the Synthesis of 1,3,5-Trisubstituted Benzenes

A green and mild protocol for the dehydrogenative olefination of cyclic enaminones was devised via palladium catalysis at room temperature using oxygen as the terminal oxidant. The synthetic utility of the olefinated cyclic enaminones afforded a series of unique 1,3,5-trisubstituted benzenes via an unanticipated Diels-Alder tandem reaction. The broad substrate scope and good yields achieved with this new protocol provide an alternative pathway for arene functionalization.

Rational design and characterization of D-Phe-Pro-D-Arg-derived direct thrombin inhibitors

The tremendous social and economic impact of thrombotic disorders, together with the considerable risks associated to the currently available therapies, prompt for the development of more efficient and safer anticoagulants. Novel peptide-based thrombin inhibitors were identified using in silico structure-based design and further validated in vitro. The best candidate compounds contained both l- and d-amino acids, with the general sequence d-Phe(P3)-Pro(P2)-d-Arg(P1)-P1′-CONH₂. The P1′ position was scanned with l- and d-isomers of natural or unnatural amino acids, covering the major chemical classes. The most potent non-covalent and proteolysis-resistant inhibitors contain small hydrophobic or polar amino acids (Gly, Ala, Ser, Cys, Thr) at the P1′ position. The lead tetrapeptide, d-Phe-Pro-d-Arg-d-Thr-CONH₂, competitively inhibits α-thrombin's cleavage of the S2238 chromogenic substrate with a K_i of 0.92 µM. In order to understand the molecular details of their inhibitory action, the three-dimensional structure of three peptides (with P1′ l-isoleucine (fPrI), l-cysteine (fPrC) or d-threonine (fPrt)) in complex with human α-thrombin were determined by X-ray crystallography. All the inhibitors bind in a substrate-like orientation to the active site of the enzyme. The contacts established between the d-Arg residue in position P1 and thrombin are similar to those observed for the l-isomer in other substrates and inhibitors. However, fPrC and fPrt disrupt the active site His57-Ser195 hydrogen bond, while the combination of a P1 d-Arg and a bulkier P1′ residue in fPrI induce an unfavorable geometry for the nucleophilic attack of the scissile bond by the catalytic serine. The experimental models explain the observed relative potency of the inhibitors, as well as their stability to proteolysis. Moreover, the newly identified direct thrombin inhibitors provide a novel pharmacophore platform for developing antithrombotic agents by exploring the conformational constrains imposed by the d-stereochemistry of the residues at positions P1 and P1′.