Thrombin active site inhibitors: chemical synthesis, in vitro and in vivo pharmacological profile of a novel and selective agent BMS-189090 and analogues

Enantioselective Synthesis of trans-4-Methylpipecolic Acid

An asymmetric synthesis for the preparation of both enantiomers of trans-methylpipecolic acids is described. It is based on Sharpless epoxidation as a chirality source, regioselective ring opening with allylamine, and ring-closing metathesis to construct the piperidine ring. The stereogenic center at C-4 is set by stereoselective hydrogenation that is directed by the alcohol functionality of an intermediate and proceeds with good diastereomeric control (trans/cis 16/1). Crystallization of the Boc-protected amino acid afforded the target products with excellent chemical (98% de) and enantiomeric purity (99% ee).

Stereoselective Preparation of a Cyclopentane-Based NK1 Receptor Antagonist Bearing an Unsymmetrically Substituted Sec−Sec Ether

A highly efficient synthesis of the potent and selective NK-1 receptor antagonist 1 is described. The key transformation involved the etherification reaction between cyclopentanol 12 and chiral imidate 30 which was catalyzed by HBF4 to initially give ether 14 as a 17:1 mixture of diastereomers and in 75% combined yield. The diastereoselectivity was upgraded to 109:1 by crystallization of the triethylamine solvate 44 which was isolated in 54% yield from 12. Mechanistic studies confirmed that the etherification reaction proceeds through an unprecedented S(N)2 reaction pathway under typical S(N)1 reaction conditions.

Progress in the design of low molecular weight thrombin inhibitors

Intravascular thrombosis and its complication, embolism, is a leading cause of morbidity and mortality throughout the world. Past few decades have seen a great deal of progress in the development of antithrombotic agents, though the current treatment options are limited to heparin, LMW heparins, and warfarin. Detailed understanding of the biochemical and biophysical mechanisms of activation and regulation of blood coagulation have helped in developing specific inhibitors of enzymes, especially thrombin, within the coagulation cascade. Thrombin plays a central role in the coagulation cascade and so has become the primary target for the development of antithrombotic drugs. The review covers the main pharmacological aspects of haemostasis and thrombosis and provides an update on low molecular weight thrombin inhibitors along with the limitations of the prevalent antithrombotic agents. Recent developments in small molecule inhibitors of Protease Activated Receptor-1 (PAR-1) which can be helpful for the treatment of thrombotic and vascular proliferative disorders, have also been discussed.

Long duration of anticoagulant activity and protective effects of acharan sulfate in vivo

INTRODUCTION

We previously reported that a new glycosaminoglycan, acharan sulfate (AS) from the African giant snail Achatina fulica showed anticoagulant activity in vitro, but was much less active when compared to heparin. In the present study, the anticoagulant activity of AS was investigated in vivo.

METHODS

AS and heparin were administered to mice and rats in various doses and the anticoagulant activities were measured by aPTT assay. Both were also compared in a thrombin-induced lethality animal model. As one of the possible mechanisms, AS-thrombin interaction was studied by using surface plasmon resonance spectroscopy.

RESULTS

Intravenous administration of AS to mice prolonged the clotting time (aPTT) in a time and dose-dependent manner. Although the anticoagulant activity was low in rats, it steadily increased over 5 h after administration of AS (30 mg/kg). In contrast, the increase in aPTT induced by 5 mg/kg of heparin was restored to a normal level after 3 h. In a thrombin-induced lethality model in mice, AS (20 mg/kg) protected against lethality by 80%, while heparin (20 mg/kg) did not show any protective activity beyond 3.5 h post-administration. AS could be also detected in plasma even 5 h after i.v. administration to rats. The binding constant (K(D)) of AS to thrombin was 7.27 x 10(-6) M, corresponding to moderate binding affinity.

CONCLUSIONS

These results show that the longer duration of AS in blood could prolong the clotting time determined by aPTT and offering protection against thrombin-induced lethality. One possible mechanism may result from AS-thrombin interaction.

Retro-binding thrombin active site inhibitors: identification of an orally active inhibitor of thrombin catalytic activity

A series of retro-binding inhibitors of human alpha-thrombin was prepared to elucidate structure-activity relationships (SAR) and optimize in vivo performance. Compounds 9 and 11, orally active inhibitors of thrombin catalytic activity, were identified to be efficacious in a thrombin-induced lethality model in mice.

Molecular design and structure--activity relationships leading to the potent, selective, and orally active thrombin active site inhibitor BMS-189664

A series of structurally novel small molecule inhibitors of human alpha-thrombin was prepared to elucidate their structure-activity relationships (SARs), selectivity and activity in vivo. BMS-189664 (3) is identified as a potent, selective, and orally active reversible inhibitor of human alpha-thrombin which is efficacious in vivo in a mouse lethality model, and at inhibiting both arterial and venous thrombosis in cynomolgus monkey models.