This article reports a novel virtual screening algorithm seeking the rational identification of novel lead anticoagulants. Seven 5-(3-methyl-1-aryl-1H-pyrazol-4-yl)-1H-tetrazoles and seven novel 1-aryl-4-(4,5-dihydro-1H-imidazol-2-yl)-3-methyl-1H-pyrazoles were obtained in three steps starting from arylhydrazine hydrochlorides as raw materials in good yields: 50-72% and 50-85%, respectively. All compounds were submitted to an in silico target-base pipeline named integrated multiplex analysis virtual screening (IMA-VS), which comprises the evaluation of their (i) fitting physicochemical properties to the chemical environment of the target enzyme; (ii) active-site homing electrostatic potential to the target enzyme; (iii) structural fitting to the target active site through molecular docking; and (iv) overall absorption, distribution, metabolism, excretion and toxicity (ADMET) profile. After the virtual selection of potential anticoagulant hits, all molecules were synthesized and candidates were evaluated in vitro for their anticoagulant and hemolytic profile. The most promising candidate pointed out by IMA-VS was compound 1-(3',4'-dichlorophenyl)-4-(4,5-dihydro-1H-imidazol-2-yl)-3-methyl-1H-pyrazole that shown to display factor Xa (FXa)-specific inhibitory activity in vitro, acting as an uncompetitive inhibitor with an inhibition constant (Ki) = 61.16 ± 12.96 µM, in addition to the lowest hemolytic activity of the series. Further experiments revealed the antithrombotic activity of this compound in an in vivo model of arterial thrombosis induced by FeCl3.

A alta especificidade das proteases da coagulação tem sido atribuída não somente aos resíduos que cercam o sítio ativo, mas também a outros domínios de superfície que estão envolvidos no reconhecimento e interação com substratos macromoleculares e inibidores. Inibidores específicos da coagulação sanguínea obtidos de fontes exógenas como glândulas salivares de animais hematófagos e venenos de serpentes têm sido identificados. Alguns desses inibidores interagem com os exosítios das enzimas da coagulação. Dois exemplos são discutidos nesta curta revisão. A Botrojaracina é uma proteína derivada de veneno de serpente que se liga aos exosítios 1 e 2 da trombina. A formação do complexo impede várias atividades da trombina dependentes do exosítio 1 incluindo a clivagem do fibrinogênio e a ativação plaquetária. A Botrojaracina também interage com o proexosítio 1 da protrombina diminuindo a ativação do zimogênio pelo complexo protrombinase (FXa/FVa). O ixolaris é um inibidor com dois domínios Kunitz obtido da glândula salivar de carrapato, homólogo ao inibidor da via do fator tecidual. Recentemente foi demonstrado que o ixolaris se liga ao exosítio de ligação à heparina do FXa, impedindo o reconhecimento da protrombina pela enzima. Além disso, o ixolaris interage com o FX, possivelmente através do proexosítio de ligação à heparina. Diferentemente do FX, o complexo ixolaris-FX não é reconhecido como substrato pelo complexo tenase intrínseco (FIXa/FVIIIa). Nós concluimos que esses inibidores podem servir como ferramentas para o estudo dos exosítios da coagulação, assim como protótipos para novas drogas anticoagulantes.

The high specificity of blood coagulation proteases has been attributed not only to residues surrounding the active site but also to other surface domains that are involved in recognizing and interacting with macromolecular substrates and inhibitors. Specific blood coagulation inhibitors obtained from exogenous sources such as blood sucking salivary glands and snake venoms have been identified. Some of these inhibitors interact with exosites on coagulation enzymes. Two examples are discussed in this short revision. Bothrojaracin is a snake venom-derived protein that binds to thrombin exosites 1 and 2. Complex formation impairs several exosite-dependent activities of thrombin including fibrinogen cleavage and platelet activation. Bothrojaracin also interacts with proexosite 1 on prothrombin thus decreasing the zymogen activation by the prothrombinase complex (FXa/FVa). Ixolaris is a two Kunitz tick salivary gland inhibitor, that is homologous to tissue factor pathway inhibitor. Recently it was demonstrated that ixolaris binds to heparin-binding exosite of FXa, thus impairing the recognition of prothrombin by the enzyme. In addition, ixolaris interacts with FX possibly through the heparin-binding proexosite. Differently from FX, the ixolaris-FX complex is not recognized as substrate by the intrinsic tenase complex (FIXa/FVIIIa). We conclude that these inhibitors may serve as tools for the study of coagulation exosites as well as prototypes for new anticoagulant drugs.