Beyond heparin and warfarin: the new generation of anticoagulants

To stop or not to stop novel oral anticoagulants prior to performing joint interventional maneuvers? Evidence from a prospective study that the therapy can be maintained

Anticoagulation is common in patients undergoing routine musculoskeletal interventional maneuvers. Previous retrospective studies have established the safety of continuing anticoagulation with novel oral anticoagulants (NOACs) when performing this kind of interventions. Indeed, ultrasound (US)-guided interventional maneuvers have shown a superior safety profile compared to blind anatomical maneuvers. To evaluate prospectively the periprocedural bleeding events in NOAC-anticoagulated patients undergoing interventional articular or periarticular procedures. Consecutive patients diagnosed with inflammatory or degenerative rheumatologic pathology requiring interventional maneuvers were prospectively recruited. Group 1 was treated with NOACs, group 2 was treated with vitamin K antagonists, and group 3 was not anticoagulated. Prior to the international maneuver, NOAC therapy was continuously administered, in regimens dictated by the underlying anticoagulation indication. Demographics, comorbidities, laboratory parameters, locally administered medication (corticosteroids or viscosupplementation), interventional maneuver location, needle size, and local bleeding events were recorded. Post-procedural control was performed at 30 min, 48 h, and 7 days. No articular/periarticular bleeding event occurred in patients treated with NOACs, regardless of their type and dosage, locally administered medication, needle size, location, and number of interventions per individual. Several patients in all groups developed small superficial ecchymoses at the injection site. Our results suggest that NOACs are safe to be used in a continuous regimen prior to US-guided injections, even as dual antithrombotic therapy (in combination with aspirin). The use of lower gauge needles, chosen for viscosupplementation therapy, was not burdened with adverse effects on the procedural outcome. Key Points • Currently, no prospective studies have been performed to establish the safety of continuous NOAC anticoagulation when performing routine intra- or periarticular interventional maneuvers. • The study offers an extensive view on a wide spectrum of intra- and periarticular interventional maneuvers including anatomic targets and needle sizes that were not previously assessed. • The study offers a perspective into performing repetitive maneuvers in the same patient, both over a short time and at longer intervals. • The zero periprocedural bleeding risk observed in our study may reassure practitioners and suggest that US-guided interventional therapeutic interventions are safe in patients treated with a continuous regimen of different NOACs.

Design and Synthesis of Neutralizable Fondaparinux

Fondaparinux, a clinically approved anticoagulant pentasaccharide for the treatment of thrombotic diseases, displays better efficacy and biosafety than other heparin-based anticoagulant drugs. However, there is no suitable antidote available for fondaparinux to efficiently manage its potential bleeding risks, thereby precluding its widespread use. Herein, we describe a convergent and stereocontrolled approach to efficiently synthesize an aminopentyl-functionalized pentasaccharide, which is further used to prepare fondaparinux-based biotin conjugates and clusters. Biological activity evaluation demonstrates that the anticoagulant activity of the fondaparinux-based biotin conjugate and trimer is, respectively, neutralized by avidin and protamine as effective antidotes. This work suggests that our synthetic biotin conjugate and trimer have potential for the development of neutralizable and safe anticoagulant drugs.

Efficacy of traditional Chinese medicine combined with rivaroxaban in the treatment of lower extremity deep vein thrombosis: A meta-analysis

BACKGROUND

Despite the usefulness of traditional Chinese medicine (TCM) in the treatment of lower deep vein thrombosis (DVT), there is no consensus on safety and efficacy. We aim to systematically evaluate the safety and efficacy of TCM combined with Rivaroxaban in the treatment of lower limb DVT.

METHODS

An online search of databases such as Cochrane Library, Embase, Pubmed, and Web of science, as well as CBM, China Science and Technology Journal Database, China Knowledge Network (CNKI) and Wanfang Data (from inception to July, 2021) was performed. All published clinical randomized controlled trials (RCTs) were screened manually, evaluated for quality and considered for meta-analysis using RevMan 5.3.

RESULTS

Nine RCTs with a total of 730 cases were included, 368 cases in the trial group were treated with TCM combined with Rivaroxaban, and 362 cases in the control group were treated with Rivaroxaban alone after surgery. Clinical efficiency was significantly higher in the test group [OR = 3.33, 95% CI (2.01, 5.53), P < .00001], the circumference of the affected limb was significantly lower in the thigh and calf, respectively [MD = -1.48, 95% CI (-1.88, -1.09), P < .00001], [MD = -0.54, 95% CI (-0.62, -0.46), P < .00001], pain scores were significantly lower [MD = -0.97, 95% CI (-1.58, -0.36), P = .002], coagulation index plasma fibrinogen (FIB) was significantly lower [MD = -0.85, 95% CI (-1.18, -0.52), P < .00001], coagulation function index D-2 aggregates were significantly reduced [MD = -0.69, 95% CI (-1.13, -0.24), P = .002], serum hypersensitive C-reactive protein (hs-CRP) measurements were significantly reduced [MD = -5.37, 95% CI (-9.20, -1.55), P = .006], complications measurement was significantly lower [OR = 0.60, 95% CI (0.27, 1.30), P = .20], activated partial thrombin time (ATPP) measurement was significantly lower [MD = 5.70, 95% CI (4.28, 7.12), P < .00001] and prothrombin time (PT) measurement was significantly lower [MD = 1.64, 95% CI (0.70, 2.57), P = .0006].

CONCLUSION

Based on the available evidence, TCM combined with Rivaroxaban for treating lower extremity DVT have better clinical efficacy and safety profile, reducing the risk of bleeding complications and adverse effects. Further improved studies are needed to support this inference.

Therapeutic Journey and Recent Advances in the Synthesis of Coumarin Derivatives

BACKGROUND

Coumarin is an oxygen-containing compound in medicinal chemistry. Coumarin plays an important role in both natural systems like plants and also in synthetic medicinal applications as drug molecules. Many structurally different coumarin compounds were found to show a big range of similarity with the vital molecular targets for their pharmacological action and small modifications in their structures resulted insignificant changes in their biological activities.

OBJECTIVE

This review gives detailed information about the studies of the recent advances in various pharmacological aspects of coumarins.

METHOD

Various oxygen-containing heterocyclic compounds represented remarkable biological significances. The fused aromatic oxygen-heterocyclic nucleus is able to change its electron density; thus changing the chemical, physical and biological properties respectively due to its multiple binding modes with the receptors, which play crucial role in pharmacological screening of drugs. A number of heterocyclic compounds have been synthesized which have their nucleus derived from various plants and animals. In coumarins, benzene ring is fused with pyrone nucleus which provides stability to the nucleus. Coumarins have shown a wide range of pharmacological activities such as anti-tumour, anti-coagulant, anti-inflammatory, anti-oxidant, antiviral, anti-malarial, anti-HIV and antimicrobial activity etc. Results: Reactive oxygen species like superoxide anion, hydroxyl radical and hydrogen peroxide are a type of unstable molecule that contains oxygen, which reacts with other molecules in the cell during the metabolism process but it may produce cytotoxicity when reactive oxygen species increase in number, by the damage of biological macromolecules. Hydroxyl radical (˙OH), is a strong oxidizing agent and it is responsible for the cytotoxicity by oxygen in different plants, animals and other microbes. coumarin is the oldest and effective compound having antimicrobial activity, anti-inflammatory, antioxidant, antidepressant activity, analgesic, anticonvulsant activity, etc. Naturally existing coumarin compounds act against SARS-CoV-2 by preventing viral replication through the targeting on active site against the Mpro target protein.

CONCLUSION

This review highlights the different biological activities of coumarin derivatives. In this review we provide an updated summary of the researches which are related to recent advances in biological activities of coumarins analogue and their most recent activities against COVID -19. Natural compounds act as a rich resource for novel drug development against various SARS-CoV-2 viral strains including viruses like herpes simplex virus, influenza virus, human immunodeficiency virus, hepatitis B and C viruses, middle east respiratory syndrome and severe acute respiratory syndrome.

A validated UPLC-MS/MS method for the determination of CX3002 in human plasma and its application to a pharmacokinetic study

A simple, selective, rapid, and reliable ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to determine CX3002 in human plasma using CX3002-d3 as the internal standard (IS). After a rapid protein precipitation with acetonitrile (3:1, v/v), the chromatographic separation of CX3002 and IS was performed on a Thermo Hypersil GOLD C18 column (2.1 mm × 50 mm, 1.9 μm) with gradient elution at a flow rate of 0.4 ml/min. Gradient elution was achieved with mobile phase A consisting of water containing 0.1% formic acid and 5 mmol/L ammonium formate and mobile phase B consisting of methanol containing 0.1% formic acid. The detection was performed on AB SCIEX QTRAP® 5500 tandem mass spectrometry in the positive ion mode. Multiple reactions monitoring (MRM) was used for quantitative analysis at transition of m/z 460.3 → 199.3 for CX3002 and m/z 463.3 → 202.3 m/z for IS. The method was fully validated and displayed good linearity over a concentration range of 0.2-400 ng/mL with the correlation coefficient above 0.997. The intra-run and inter-run precision (coefficient of variation, CV) ranged from 0.60%-16.46% and the accuracy bias ranged from -7.09%-9.75%. The mean IS-normalized extraction recovery ranged from 98.30% to 104.52%. The CV(%) of IS-normalized matrix factors at the low and high QC concentration were 4.09% and 1.68%, respectively. The storage stability under different conditions was in accordance with the bioanalytical guidelines. The method was successfully applied to the pharmacokinetic study of CX3002 (30 mg) in healthy Chinese subjects.

Design, synthesis, and biological evaluation of 4-methoxy-3-arylamido-N-(substitutedphenyl)benzamide derivatives as potential antiplatelet agents

A series of 4-methoxy-3-arylamido-N-(substitutedphenyl)benzamides 6a-u were designed according to the splicing principle of structural design in the medicinal chemistry theory and were synthesized in five steps: nitration, acylation, ammoniation, reduction, and secondary ammoniation. The structures of the target compounds were characterized and verified by infrared, ¹ H nuclear magnetic resonance (NMR), ¹³ C NMR, and electron spray ionization spectroscopy. Their in vitro antiplatelet aggregation activities induced by adenosine diphosphate (ADP) or arachidonic acid (AA) were assessed by Born's method. The biological evaluation revealed that all compounds exhibited certain levels of activities in both of the antiplatelet aggregation assays; compounds 6c (IC₅₀  = 3.84 μM) and 6f (IC₅₀  = 3.12 μM) displayed the strongest antiplatelet aggregation activities in the ADP-induced and AA-induced assay, separately. Moreover, compounds that had stronger activities were chosen for cell toxicity testing via the cell counting kit-8 assay. The results indicated that none of the compounds had obvious cell toxicity against L929 cells at the doses of 10 and 20 μM. It is worth pointing out that compound 6c showed the highest antiplatelet activity and the lowest cell toxicity. In general, 4-methoxy-3-arylamido-N-(substitutedphenyl)benzamides have the potential to become a kind of safer and more effective antiplatelet agents.

An Efficient Modular One-Pot Synthesis of Heparin-Based Anticoagulant Idraparinux

Idraparinux is a fully O-sulfated α-methyl glycoside of heparin pentasaccharide motif known to interact with the antithrombin III domain and act as anticoagulant. The current most effective synthesis of Idraparinux is complicated and nonstereoselective, requiring numerous stepwise procedures with low yields. We report here an efficient modular one-pot synthesis of Idraparinux involving the use of a glycosyl phosphate with 6- O- tert-butyl diphenyl silyl group and a d-glucuronic acid-containing disaccharide thioglycoside with 6- O-acetyl group as donor building blocks for the α-directing one-pot glycosylations with an l-iduronic acid-containing disaccharide acceptor building block. The uronic acid was incorporated in a disaccharide module used in the one-pot synthesis to avoid the complicated late-stage installation of these acidic sugars. The one-pot synthesis of Idraparinux demonstrated here is an effective strategy and should be applicable to the modular assembly of other heparan sulfates with regiodefined sulfation pattern for functional study.

Pharmacokinetics and pharmacodynamics of oral anticoagulants used in atrial fibrillation

INTRODUCTION

The availability of non-vitamin K antagonist oral anti-coagulants alongside vitamin K antagonists has offered a variety of options for anti-coagulation, but has also necessitated a good understanding of the pharmacological properties of each of these drugs prior to their use, to maximise the therapeutic benefit and minimise patient harm Areas covered: This review article outlines the pharmacokinetic and pharmacodynamic profiles of the currently licensed VKAs and NOACs that are most commonly used in clinical practice, with the aim of demonstrating how variations in these characteristics influence their use in clinical practice. A literature search was conducted on PubMed using keywords and relevant articles published by the 31^st of December 2018 were included. Expert opinion: The effect of a drug is determined by a combination of elements which include patient characteristics and external factors, in addition to its pharmacokinetic and pharmacodynamic properties. A good understanding of these is essential. Despite the wealth of information available, particularly on VKAs, our knowledge on the pharmacology responsible for certain drug effects and inter-individual variations is still limited. Increasing efforts are being made to understand these and include focus on pharmacogenomics and drug transporter proteins.

Preactivation-based, iterative one-pot synthesis of anticoagulant pentasaccharide fondaparinux sodium

A one-pot, three-component synthetic strategy was designed to rapidly assemble fondaparinux, using a monosaccharide donor and two disaccharide acceptors.

Hospital length of stay in patients initiated on direct oral anticoagulants versus warfarin for venous thromboembolism: a real-world single-center study

This study was conducted to describe the real-world hospital length of stay in patients treated with all of the U.S. Food and Drug Administration approved direct oral anticoagulants (DOACs) versus warfarin for new-onset venous thromboembolism (VTE) at a large, tertiary, academic medical center. A retrospective cohort analysis of all adult patients diagnosed with acute onset VTE was conducted. Of the 441 patients included, 261 (57%) patients received DOACs versus 180 (41%) patients received warfarin. In the DOAC group, a total of 92 (35%) patients received rivaroxaban, followed by 83 (32%) patients received apixaban, 50 (19%) patients received dabigatran, and 36 (14%) patients received edoxaban. Patients initiated on DOACs had a statistically significant shorter hospital length of stay compared to patients initiated on warfarin (median 3 days, [IQR 0-5] vs. 8 days [IQR 5-11], P < 0.05). Despite the shorter hospital length of stay in patients receiving DOACs, the overall reported differences between the DOACs group and the warfarin group in terms of recurrent VTE, major bleeding, intracranial bleeding, and gastrointestinal bleeding at 3 and 6 months were deemed to be statistically insignificant.

Antithrombotic potential of esculin 7, 3', 4', 5', 6'-O-pentasulfate (EPS) for its role in thrombus reduction using rat thrombosis model

Currently available anticoagulants for prevention and treatment of thrombosis have several limitations, thus, small organic scaffolds that can dissolve clots in vivo in a dose dependent manner with lesser side effects are highly desirable. Here we report the synthesis of esculin pentasulfate (EPS) and assessment of its in vitro, in vivo and ex vivo anticoagulant and antithrombotic potential. Assessment of in vitro clotting times showed prolonged activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) in the presence of EPS. EPS also showed remarkable reduction in thrombus formation when administered in occlusion induced thrombotic rats at a low dose (2.5 mg/kg). Further, assessment of clot rate with plasma isolated from EPS treated rats confirmed its anticoagulation potential. EPS at varying concentrations showed no significant cytotoxic effect on HEK293 cell line. Further, molecular docking analysis of EPS with known anticoagulant proteins [(antithrombin (ATIII) and heparin cofactor II (HCF II)] that require heparin revealed good binding affinity (-7.9 kcal/mol) with ATIII but not with HCF II. ATIII when incubated with EPS showed increased fluorescence intensity, with no change in secondary structure. Overall, our results clearly show the in vivo modulation of thrombus formation using a modified natural scaffold EPS.

Novel venous thromboembolic disease (VTED) prophylaxis for total knee arthroplasty-aspirin and fish oil

Background

Despite the demonstrated success of multiple anticoagulation therapies for post-operative prophylaxis of thromboembolic disease in lower extremity arthroplasties, each modality comes with a unique set of limitations. Thus, the ideal anticoagulation medication which provides adequate therapy with minimal cost, complications, or added patient work is yet to be defined. One promising novel thrombophylactic supplement is fish oil, as many preliminary clinical trials have demonstrated a protective effect of fish oil against thrombosis in multiple clinical settings. In addition, others have demonstrated synergistic effect when combined with aspirin. However, there are paucity of studies that compared combined aspirin and fish oil therapy for venous thromboembolism prophylaxis with other pharmacological agents, especially in the field of orthopaedics. Therefore, this study evaluated: (I) risk of post-operative deep vein thrombosis (DVT) and pulmonary embolism (PE), and (II) bleeding complications; among patients who had primary total knee arthroplasty (TKA) and received one of the following regimens: (i) 325 mg aspirin and mechanical pulsatile stocking; (ii) rivaroxaban; or (iii) 325 mg aspirin and 1,000 mg fish oil.

Methods

This was a 6-year prospective study analyzing the postoperative thromboembolic prophylaxis received by patients who underwent primary TKA. Patients who had a previous history of thromboembolic disease were excluded from the study due to an increased risk of recurrent clot formation. A total of 850 patients were enrolled. A total of 300 patients enrolled between October 2011 and June 2013 received 325 mg aspirin and mechanical pulsatile stocking, while 250 patients enrolled between June 2013 and December 2014 received rivaroxaban. A total of 300 patients enrolled between January 2015 and July 2017 received 325 mg aspirin and 1,000 mg fish oil. Major venous thromboembolic events (VTEs) and bleeding complications within the first 90 days post-operatively were recorded in each cohort. The odds ratios (ORs) and 95% confidence intervals (CIs), for thromboembolic and bleeding events were calculated and compared between the aspirin and fish oil cohort vs. aspirin and pulsatile stocking cohort, and aspirin and fish oil cohort vs. rivaroxaban cohort. A P value of <0.05 was used to determine statistical significance.

Results

A total of 25 DVT events were recorded including 1 of 300 (0.33%) in the aspirin and fish oil cohort, 22 of 300 (7.33%) in the aspirin and pulsatile stocking cohort and 2 of 250 (0.8%) in the rivaroxaban cohort. When comparing ORs, patients who received aspirin and fish oil demonstrated significantly lower risk for thromboembolic events when compared to the aspirin and pulsatile stocking group (OR: 0.045; 95% CI: 0.0061-0.3394; P<0.05). When compared to the rivaroxaban cohort the ORs did not differ significantly (OR: 0.416; 95% CI: 0.0376-4.6223; P>0.05). In addition, no PE events were recorded in any of the cohorts. When compared to rivaroxaban, the fish oil and aspirin cohort demonstrated significantly lower incidence of bleeding episodes (1 of 300, 0.33% vs. 30 of 250 patients, 12%; OR: 0.0278; 95% CI: 0.0038-0.2051; P<0.05). No bleeding events were recorded in the aspirin and pulsatile stocking cohort.

Conclusions

This study demonstrated the potentially synergistic anti-thromboembolic effect of aspirin and fish oil in the prevention of post-operative venous thromboembolism in primary TKA patients. Based on the results from this study, the authors conclude that the combination of aspirin and fish oil maybe an excellent thromboprophylactic modality for patients to use after TKA. These results warrant further, larger prospective studies analyzing the use of fish oil supplements in VTE prophylaxis.

Functional characterisation of Vizottin, the first factor Xa inhibitor purified from the leech Haementeria vizottoi

The strategic position of factor Xa (FXa) in blood coagulation makes it a compelling target for the development of new anticoagulants. Bloodsucking animals have in their salivary glands mixtures of anticoagulants, which could be used for designing novel antithrombotic compounds. Herein, we describe Vizottin, the first FXa inhibitor from the salivary complex of the leech Haementeria vizottoi. Vizottin was purified by gel filtration and reverse-phase chromatography, and shown to have anticoagulant effects in human plasma, prolonging the recalcification time in a dose-dependent manner (IC50 40 nM). Vizottin induced blood incoagulability in FX-deficient plasma, whereas in normal and reconstituted plasma, Vizottin doubled the prothrombin time at 160 nM. This peptide competitively inhibited human FXa (Ki 2 nM) like FXa inhibitors from other leeches, albeit via a distinct mechanism of action. At high concentrations, vizottin inhibited the amidolytic activity of factor VIIa/tissue factor (IC50 96.4 nM). Vizottin inhibited FXa in the prothrombinase complex and Gla-domainless FXa. Moreover, vizottin did not interfere with FX activation induced by RVV-X, a known enzyme that requires the Gla-domain of FX for activation. Competition experiments in the presence of FXa and GGACK-FXa (active site blocked) demonstrated that the inhibition of FXa by vizottin is through binding to the active site rather than an exosite. This novel inhibitor appears to exert its inhibitory effects through direct binding to the active site of FXa in a time-dependent manner, but not involving a tight-binding model. In this context, vizottin is a promising model for designing novel anticoagulants for the treatment of thrombotic diseases.

Synthesis and in Vitro and in Vivo Anticoagulant and Antiplatelet Activities of Amidino- and Non-Amidinobenzamides

Three amidino- and ten non-amidinobenzamides were synthesized as 3-aminobenzoic acid scaffold-based anticoagulant and antiplatelet compounds. The anticoagulant activities of thirteen synthesized compounds 1-13, and 2b and 3b as prodrugs were preliminary evaluated by screening the prolongation of activated partial thromboplastin time (aPTT) and prothrombin time (PT) in vitro. From the aPTT results obtained, two amidinobenzamides, N-(3'-amidinophenyl)-3-(thiophen-2''-ylcarbonylamino) benzamide (1, 33.2 ± 0.7 s) and N-(4'-amidinophenyl)-3-(thiophen-2''-ylcarbonylamino) benzamide (2, 43.5 ± 0.6 s) were selected to investigate the further anticoagulant and antiplatelet activities. The aPTT results of 1 (33.2 ± 0.7 s) and 2 (43.5 ± 0.6 s) were compared with heparin (62.5 ± 0.8 s) in vitro at 30 μM. We investigated the effect of 1 and 2 on blood anticoagulant activity (ex vivo) and on tail bleeding time (in vivo) on mice. A tail cutting/bleeding time assay revealed that both 1 and 2 prolonged bleeding time in mice at a dose of 24.1 g/mouse and above. Compounds 1 and 2 dose-dependently inhibited thrombin-catalyzed fibrin polymerization and platelet aggregation. In addition, 1 and 2 were evaluated on the inhibitory activities of thrombin and FXa as well as the generation of thrombin and FXa in human umbilical vein endothelial cells (HUVECs). Collectively, 1 and 2 possess some antiplatelet and anticoagulant activities and offer a basis for development of a novel antithrombotic product.

Formal Synthesis of Anticoagulant Drug Fondaparinux Sodium

The practical formal synthesis of the anticoagulant drug fondaparinux sodium 1 was accomplished using an optimized modular synthetic strategy. The important pentasaccharide 2, a precursor for the synthesis of fondaparinux sodium, was synthesized on a 10 g scale in 14 collective steps with 3.5% overall yield from well-functionalized monosaccharide building blocks. The strategy involved a convergent [3 + 2] coupling approach, with excellent stereoselectivity in every step of glycosylation from the monosaccharide building blocks. Efficient routes to the syntheses of these fully functionalized building blocks were developed, minimizing oligosaccharide stage functional-group modifications. The syntheses of all building blocks avoided rigorous reaction conditions and the use of expensive reagents. In addition, common intermediates and a series of one-pot reactions were employed to enhance synthetic efficiency, improving the yield considerably. In the monosaccharide-to-oligosaccharide assembly reactions, cheaper activators (e.g., NIS/TfOH, TESOTf, and TfOH) were used to facilitate highly efficient glycosylations. Furthermore, crystallization of several monosaccharide and oligosaccharide intermediates significantly simplified purification procedures, which would be greatly beneficial to the scalable synthesis of fondaparinux sodium.

Chemoenzymatic synthesis of heparan sulfate and heparin

Heparan sulfate is a polysaccharide that plays essential physiological functions in the animal kingdom. Heparin, a highly sulfated form of heparan sulfate, is a widely prescribed anticoagulant drug worldwide. The heparan sulfate and heparin isolated from natural sources are highly heterogeneous mixtures differing in their polysaccharide chain lengths and sulfation patterns. The access to structurally defined heparan sulfate and heparin is critical to probe the contribution of specific sulfated saccharide structures to the biological functions as well as for the development of the next generation of heparin-based anticoagulant drugs. The synthesis of heparan sulfate and heparin, using a purely chemical approach, has proven extremely difficult, especially for targets larger than octasaccharides having a high degree of site-specific sulfation. A new chemoenzymatic method has emerged as an effective alternative approach. This method uses recombinant heparan sulfate biosynthetic enzymes combined with unnatural uridine diphosphate-monosaccharide donors. Recent examples demonstrate the successful synthesis of ultra-low molecular weight heparin, low-molecular weight heparin and bioengineered heparin with unprecedented efficiency. The new method provides an opportunity to develop improved heparin-based therapeutics.

Synthesis and anticoagulant activity of polyureas containing sulfated carbohydrates

Polyurea-based synthetic glycopolymers containing sulfated glucose, mannose, glucosamine, or lactose as pendant groups have been synthesized by step-growth polymerization of hexamethylene diisocyanate and corresponding secondary diamines. The obtained polymers were characterized by gel permeation chromatography, nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy. The nonsulfated polymers showed similar results to the commercially available biomaterial polyurethane TECOFLEX in a platelet adhesion assay. The average degree of sulfation after reaction with SO₃ was calculated from elemental analysis and found to be between three and four −OSO₃ groups per saccharide. The blood-compatibility of the synthetic polymers was measured using activated partial thromboplastin time, prothrombin time, thrombin time, anti-IIa, and anti-Xa assays. Activated partial thromboplastin time, prothrombin time, and thrombin time results indicated that the mannose and lactose based polymers had the highest anticoagulant activities among all the sulfated polymers. The mechanism of action of the polymers appears to be mediated via an anti-IIa pathway rather than an anti-Xa pathway.

Synthetic oligosaccharides as active pharmaceutical ingredients: lessons learned from the full synthesis of one heparin derivative on a large scale

Covering: up to November 2013. Heparin and heparan sulfate are natural polysaccharides with strong structural variations, which are responsible for their numerous specific biological properties. One key target of heparin, among others, is antithrombin, a serine protease inhibitor that, upon activation, mainly targets anticoagulation factors IIa and Xa. It is well documented that inhibition of the latter is due to a specific pentasaccharidic sequence, its synthetic analog being the registered drug fondaparinux. The replacement of hydroxyls by methoxy groups, N-sulfates by O-sulfonates and the modulation of the sulfation pattern gave rise to both idraparinux and its neutralizable form, idrabiotaparinux, two pentasaccharides with a significantly increased half-life compared to fondaparinux. Although numerous efforts have been devoted to improving the chemoenzymatic preparation of heparin fragments, enzymes are usually selective for their natural substrates, which limits the generation of some specific non-natural structures. Up to now, total synthesis has proved to be a valuable approach for the preparation of tailor-made and pure saccharides in the milligram to gram scale. This highlight will focus on the synthesis and the technical challenges associated with the development and the production of complex carbohydrates which will be exemplified with idrabiotaparinux. Particular attention will be paid to the process improvements needed in order to implement the production in a pilot plant, achieving batch generation on a multi-kilogram scale with a purity higher than 99.5%, and with no unknown impurity over 0.1%.

Synthesis of the heparin-based anticoagulant drug fondaparinux

Fondaparinux, a synthetic pentasaccharide based on the heparin antithrombin-binding domain, is an approved clinical anticoagulant. Although it is a better and safer alternative to pharmaceutical heparins in many cases, its high cost, which results from the difficult and tedious synthesis, is a deterrent for its widespread use. The chemical synthesis of fondaparinux was achieved in an efficient and concise manner from commercially available D-glucosamine, diacetone α-D-glucose, and penta-O-acetyl-D-glucose. The method involves suitably functionalized building blocks that are readily accessible and employs shared intermediates and a series of one-pot reactions that considerably reduce the synthetic effort and improve the yield.

Novel serine protease inhibitors

The pursuit of serine protease inhibitors as anticoagulants and anti-hepatitis C virus drugs continues to be an active area of research. Compounds such as P1-P3 macrocyclic peptides and linear peptides have been registered as potent hepatitis C virus protease inhibitors and compounds such as phenylglycinamide derivatives, substituted biaryls, tetrahydroquinoline derivatives, arylpropionamides, arylacrylamides, arylpropynamides, arylmethylurea analogs and peptides as factor XIa inhibitors. Given the recent US FDA approval of telaprevir and boceprevir for the treatment of hepatitis C virus, the development of new serine protease inhibitors is likely to be one of the hottest areas in the pharmaceutical industry. This review covers the patent literature on serine protease inhibitors during the period between 2009 and 2010.

Homogeneous low-molecular-weight heparins with reversible anticoagulant activity

Low-molecular-weight heparins (LMWHs) are carbohydrate-based anticoagulants clinically used to treat thrombotic disorders, but impurities, structural heterogeneity or functional irreversibility can limit treatment options. We report a series of synthetic LMWHs prepared by cost-effective chemoenzymatic methods. The high activity of one defined synthetic LMWH against human factor Xa (FXa) was reversible in vitro and in vivo using protamine, demonstrating that synthetically accessible constructs can have a critical role in the next generation of LMWHs.

Fabricating a novel porous releaser of heparin

Reduced graphene oxide (rGO) could adsorb heparin of 112 mg g⁻¹ and released 80% of them within 30 days.

Rivaroxaban: a novel oral anticoagulant for the prevention and treatment of several thrombosis-mediated conditions

The development of rivaroxaban (XARELTO®) is an important new medical advance in the field of oral anticoagulation. Thrombosis-mediated conditions constitute a major burden for patients, healthcare systems, and society. For more than 60 years, the prevention and treatment of these conditions have been dominated by oral vitamin K antagonists (such as warfarin) and the injectable heparins. Thrombosis can lead to several conditions, including deep vein thrombosis, pulmonary embolism, myocardial infarction, stroke, and/or death. Prevention and treatment of thrombosis with an effective, convenient-to-use oral anticoagulant with a favorable safety profile is critical, especially in an aging society in which the risk of thrombosis, and the potential for bleeding complications, is increasing. Rivaroxaban acts to prevent and treat thrombosis by potently inhibiting coagulation Factor Xa in the blood. Factor Xa converts prothrombin to thrombin, which initiates the formation of blood clots by converting fibrinogen to clot-forming fibrin and leads to platelet activation. After a large and novel clinical development program in over 75,000 patients to date, rivaroxaban has received approval for multiple indications in the United States, European Union, and other countries worldwide to prevent and treat several thrombosis-mediated conditions. This review will highlight some of the unique aspects of the rivaroxaban development program.

Use of Molecular Dynamics for the Refinement of an Electrostatic Model for the In Silico Design of a Polymer Antidote for the Anticoagulant Fondaparinux

Molecular dynamics (MD) simulations results are herein incorporated into an electrostatic model used to determine the structure of an effective polymer-based antidote to the anticoagulant fondaparinux. In silico data for the polymer or its cationic binding groups has not, up to now, been available, and experimental data on the structure of the polymer-fondaparinux complex is extremely limited. Consequently, the task of optimizing the polymer structure is a daunting challenge. MD simulations provided a means to gain microscopic information on the interactions of the binding groups and fondaparinux that would have otherwise been inaccessible. This was used to refine the electrostatic model and improve the quantitative model predictions of binding affinity. Once refined, the model provided guidelines to improve electrostatic forces between candidate polymers and fondaparinux in order to increase association rate constants.

Oral direct factor Xa inhibitors

Vitamin K antagonists, such as warfarin, have been the mainstay of oral anticoagulation for many decades. Although effective, warfarin has numerous limitations, including a variable dose requirement from patient to patient because of differences in dietary vitamin K intake, common genetic polymorphisms, and multiple drug interactions that affect its pharmacodynamics and metabolism. Consequently, warfarin requires frequent monitoring to ensure that a therapeutic anticoagulant effect has been achieved because excessive anticoagulation can lead to bleeding, and because insufficient anticoagulation can result in thrombosis. Such monitoring is burdensome for patients and physicians and is costly for the health care system. These limitations have prompted the development of new oral anticoagulants that target either factor Xa or thrombin. Although the path to the development of these drugs has been long, the new drugs are at least as effective and safe as warfarin, but they streamline clinical care because they can be administered in fixed doses without routine coagulation monitoring. This article focuses on rivaroxaban, apixaban, and edoxaban, the oral factor Xa inhibitors in the most advanced stages of development. After 20 years of discovery research, these agents are already licensed for several indications. Thus, the long path to finding replacements for warfarin has finally reached fruition. Therefore, development of the oral factor Xa inhibitors represents a translational science success story.

In situ crosslinkable heparin-containing poly(ethylene glycol) hydrogels for sustained anticoagulant release

Low-molecular weight heparin (LMWH) is widely used in anticoagulation therapies and for the prevention of thrombosis. LMWH is administered by subcutaneous injection usually once or twice per day. This frequent and invasive delivery modality leads to compliance issues for individuals on prolonged therapeutic courses, particularly pediatric patients. Here, we report a long-term delivery method for LMWH via subcutaneous injection of long-lasting hydrogels. LMWH is modified with reactive maleimide groups so that it can be crosslinked into continuous networks with four-arm thiolated poly(ethylene glycol) (PEG-SH). Maleimide-modified LMWH (Mal-LMWH) retains bioactivity as indicated by prolonged coagulation time. Hydrogels comprising PEG-SH and Mal-LMWH degrade via hydrolysis, releasing bioactive LMWH by first-order kinetics with little initial burst release. Separately dissolved Mal-LMWH and PEG-SH solutions were co-injected subcutaneously in New Zealand White rabbits. The injected solutions successfully formed hydrogels in situ and released LMWH as measured via chromogenic assays on plasma samples, with accumulation of LMWH occurring at day 2 and rising to near-therapeutic dose equivalency by day 5. These results demonstrate the feasibility of using LMWH-containing, crosslinked hydrogels for sustained and controlled release of anticoagulants.

Synthesis and evaluation of anti-thrombotic activity of benzocoumarin amide derivatives

A series of novel benzocoumarin amide derivatives have been synthesized and evaluated for their anti-thrombotic activity. Amongst these, compounds 5, 7 and 8 exhibited promising anti-thrombotic profile in an established model of mouse thrombosis. Hence, comprehensive profiling on platelet aggregation and coagulation parameters was carried out to assess its potential as a lead candidate. In vitro treatment of these compounds in mice plasma resulted into significant reduction in ADP (p<0.01) and collagen (p<0.001) induced platelet aggregation. Moreover, Compounds 5, 7 and 8 also significantly increased thrombin time (p<0.05). Thus, in the present study, these benzocoumarin amide derivatives exhibited anti-thrombotic profile via both anti-platelet as well as anti-coagulant action.

The cardioprotective effects of marrubiin, a diterpenoid found in Leonotis leonurus extracts

ETHNOPHARMACOLOGICAL RELEVANCE

Leonotis leonurus L. (Lamiaceae) is used as a traditional medicine for a variety of ailments in South Africa. The diterpene marrubiin is the major product constituent in specimens of this plant occurring in South Africa.

MATERIALS AND METHODS

Marrubiin isolated from South African specimens of L. leonurus in addition to an organic extract of L. leonurus were tested in vivo, ex vivo and in vitro for their anticoagulant, antiplatelet and anti-inflammatory activities.

RESULTS

Marrubiin and the organic extract suppressed coagulation, platelet aggregation and inflammatory markers. For the coagulation markers it was found that the organic extract and marrubiin significantly prolonged activated partial thromboplastin time (APTT). Fibrin and D-dimer formation were drastically decreased. These findings were observed in an ex vivo model and an obese rat model. Chemokines enhance leukocyte recruitment to inflammatory sites. TNF-α and RANTES secretion were significantly reduced by the extract and marrubiin when determined in the obese rat model relative to the controls. Calcium mobilization and TXB(2) synthesis were suppressed by the extract and marrubiin. An in vitro model was used to elucidate the antiplatelet mechanism and it was found that the extract and marrubiin inhibited platelet aggregation by inhibiting the binding of fibrinogen to glycoprotein (GP) IIb/IIIa receptor in a concentration dependent manner.

CONCLUSION

The findings reflect that marrubiin largely contributes to the extract's anticoagulant, antiplatelet and anti-inflammatory effects observed.

Chemoenzymatic synthesis of homogeneous ultralow molecular weight heparins

Ultralow molecular weight (ULMW) heparins are sulfated glycans that are clinically used to treat thrombotic disorders. ULMW heparins range from 1500 to 3000 daltons, corresponding from 5 to 10 saccharide units. The commercial drug Arixtra (fondaparinux sodium) is a structurally homogeneous ULMW heparin pentasaccharide that is synthesized through a lengthy chemical process. Here, we report 10- and 12-step chemoenzymatic syntheses of two structurally homogeneous ULMW heparins (MW = 1778.5 and 1816.5) in 45 and 37% overall yield, respectively, starting from a simple disaccharide. These ULMW heparins display excellent in vitro anticoagulant activity and comparable pharmacokinetic properties to Arixtra, as demonstrated in a rabbit model. The chemoenzymatic approach is scalable and shows promise for a more efficient route to synthesize this important class of medicinal agent.

Factor XI-deficient mice display reduced inflammation, coagulopathy, and bacterial growth during listeriosis

In mice infected sublethally with Listeria monocytogenes, fibrin is deposited at low levels within hepatic tissue, where it functions protectively by limiting bacterial growth and suppressing hemorrhagic pathology. Here we demonstrate that mice infected with lethal doses of L. monocytogenes produce higher levels of fibrin and display evidence of systemic coagulopathy (i.e., thrombocytopenia, fibrinogen depletion, and elevated levels of thrombin-antithrombin complexes). When the hepatic bacterial burden exceeds 1×10(6) CFU, levels of hepatic fibrin correlate with the bacterial burden, which also correlates with levels of hepatic mRNA encoding the hemostatic enzyme factor XI (FXI). Gene-targeted FXI-deficient mice show significantly improved survival upon challenge with high doses of L. monocytogenes and also display reduced levels of hepatic fibrin, decreased evidence of coagulopathy, and diminished cytokine production (interleukin-6 [IL-6] and IL-10). While fibrin limits the bacterial burden during sublethal listeriosis in wild-type mice, FXI-deficient mice display a significantly improved capacity to restrain the bacterial burden during lethal listeriosis despite their reduced fibrin levels. They also show less evidence of hepatic necrosis. In conjunction with suboptimal antibiotic therapy, FXI-specific monoclonal antibody 14E11 improves survival when administered therapeutically to wild-type mice challenged with high doses of L. monocytogenes. Together, these findings demonstrate the utility of murine listeriosis as a model for dissecting qualitative differences between protective and pathological host responses and reveal novel roles for FXI in exacerbating inflammation and pathogen burden during a lethal bacterial infection.

Novel oral anticoagulants for VTE prevention in orthopedic surgery: overview of phase 3 trials

Outpatient use of anticoagulants to prevent venous thromboembolism after total hip or knee arthroplasty may be hampered either by requirements for parenteral administration or high variability and frequent monitoring of anticoagulant activity. Trials of the new oral direct factor Xa inhibitors rivaroxaban and apixaban and the direct thrombin inhibitor dabigatran indicate that they can be administered in fixed doses without monitoring and that they generally have efficacy at least equivalent to enoxaparin, although with potential minor differences in the balance of efficacy vs risk for bleeding. This article reviews the results and pharmacokinetic properties that may influence their use in clinical practice.

Effects of ketoconazole on the in vivo biotransformation and hepatobiliary transport of the thrombin inhibitor AZD0837 in pigs

Ketoconazole has been shown in clinical trials to increase the plasma exposure of the oral anticoagulant prodrug AZD0837 [(2S)-N-{4- [(Z)-amino(methoxyimino)methyl]benzyl}-1-{(2R)-2-[3-chloro-5-(difluoromethoxy)phenyl]-2-hydroxyethanoyl}-azetidine-2-carboxamide] and its active metabolite, AR-H067637 [(2S)-N-{4-[amino(imino)methyl]benzyl}-1-{(2R)-2-[3-chloro-5-(difluoromethoxy)phenyl]-2-hydroxyethanoyl}-azetidine-2-carboxamide]. To investigate the biotransformation of AZD0837 and the effect of ketoconazole on this process, we used an experimental model in pigs that allows repeated sampling from three blood vessels, the bile duct, and a perfused intestinal segment. The pigs received AZD0837 (500 mg) given enterally either alone (n = 5) or together with single-dose ketoconazole (600 mg) (n = 6). The prodrug (n = 2) and its active metabolite (n = 2) were also administered intravenously to provide reference doses. The plasma data revealed considerable interindividual variation in the exposure of the prodrug, intermediate metabolite, and active metabolite. However, AR-H067637 was detected at very high concentrations in the bile with low variability (Ae(bile) = 53 ± 6% of the enteral dose), showing that the compound had indeed been formed in all of the animals and efficiently transported into the bile canaliculi. Concomitant dosing with ketoconazole increased the area under the plasma concentration-time curve for AZD0837 (by 99%) and for AR-H067637 (by 51%). The effect on the prodrug most likely arose from inhibited CYP3A-mediated metabolism. Reduced metabolism also seemed to explain the increased plasma exposure of the active compound because ketoconazole prolonged the terminal half-life with no apparent effect on the extensive biliary excretion and biliary clearance. These in vivo results were supported by in vitro depletion experiments for AR-H067637 in pig liver microsomes with and without the addition of ketoconazole.

Biarylmethoxy isonipecotanilides as potent and selective inhibitors of blood coagulation factor Xa

New chloro-substituted biarylmethoxyphenyl piperidine-4-carboxamides were synthesized and assayed in vitro as inhibitors of the blood coagulation enzymes factor Xa (fXa) and thrombin. An investigation of effects of the amidine and isopropyl groups attached at the piperidine nitrogen and 5-(halogenoaryl)isoxazol-3-yl groups as biaryl substituents led us to identify new compounds which proved to be selective fXa inhibitors, with inhibition constants in the low nanomolar range. The most potent compound 21e, that incorporates 2-Cl-thiophen-5-yl group as the P1 motif and 1-isopropylpiperidine P4 group, inhibited fXa with K(i) value of 0.3nM and very high selectivity over thrombin and some other tested serine proteases, achieving moderate levels of anticoagulant activity in the low micromolar range, as assessed by the prothrombin time clotting assay (PT(2)=3.30μM). Based on reliable docking simulations, molecular modeling provided a rationale for interpreting structure-activity relationships. The predicted binding modes highlighted the structural requirements for addressing the subsites S1 and S4 of the fXa enzyme.

Novel factor Xa inhibitors: a patent review

IMPORTANCE OF THE FIELD

New oral anticoagulants with favorable safety profiles and fixed doses are required for the management of thromboembolism and stroke prevention in patients with atrial fibrillation. Among them, fXa inhibitors (the so-called xabans) are attractive options that can overcome limitations (e.g., bleeding) of the current oral antithrombotic therapy. The rational design of small-molecule direct fXa inhibitors, whose importance is testified by the growing number of publications and patents recently registered, has been fully supported by the X-ray crystallography of enzyme-ligand complexes.

AREAS COVERED IN THIS REVIEW

Pubmed, SciFinder Scholar, ISI web of knowledge(SM), http://ep.espacenet.com/ and Google websites were used as the main sources for literature retrieving, and > 100 patents filed between 2006 and April 2009, reviewed and discussed herein, highlight the variety among the P1 and P4 moieties on suitable scaffolds.

WHAT THE READER WILL GAIN

The replacement of the benzamidine P1 moiety, which characterizes the first generation, with less basic bioisosteric or nonpolar neutral P1 groups led to the disclosure of numerous fXa inhibitors with high potency, selectivity and oral bioavailability. Novel selective fXa inhibitors with stable pharmacokinetics, better therapeutic windows and ease-of-use than the existing anticoagulants are currently under advanced stage clinical trials.

TAKE-HOME MESSAGE

Available data from Phase II and Phase III studies reflect the drive towards fXa inhibitors as potentially more effective and safer antithrombotic drugs. Their development is expected to address two major needs for anticoagulation, namely safety and ease-of-use, and to significantly affect the anticoagulant market.

Antithrombotics in acute coronary syndromes

Antithrombotic agents are an integral component of the medical regimens and interventional strategies currently recommended to reduce thrombotic complications in patients with acute coronary syndromes (ACS). Despite great advances with these therapies, associated high risks for thrombosis and hemorrhage remain as the result of complex interactions involving patient comorbidities, drug combinations, multifaceted dosing adjustments, and the intricacies of the care environment. As such, the optimal combinations of antithrombotic therapies, their timing, and appropriate targeted subgroups remain the focus of intense research. During the last several years a number of new antithrombotic treatments have been introduced, and new data regarding established therapies have come to light. Although treatment guidelines include the most current available data, subsequent findings can be challenging to integrate. This challenge is compounded by the complexity associated with different efficacy and safety measures and the variability in study populations, presenting syndromes, physician, and patient preferences. In this work we review recent data regarding clinically available antiplatelet and anticoagulation agents used in the treatment of patients with ACS. We address issues including relative efficacy, safety, and timing of therapies with respect to conservative and invasive treatment strategies. In specific cases we will highlight remaining questions and controversies and ongoing trials, which will hopefully shed light in these areas. In addition to reviewing existing agents, we take a look forward at the most promising new antithrombotics currently in late-stage clinical development and their potential role in the context of ACS management.

Antithrombotic potential of GW813893: a novel, orally active, active-site directed factor Xa inhibitor

BACKGROUND

Factor Xa (FXa) has been a target of considerable interest for drug development efforts aimed at suppressing thrombosis. In this report, a new orally active, small molecule, active-site directed FXa inhibitor, GW813893, has been profiled in a succession of in vitro and in vivo assays involved in its preclinical characterization as a potential antithrombotic therapeutic.

METHODS

In vitro profiling of GW813893 consisted of assessing its inhibitory potential against FXa and a broad panel of related and unrelated enzymes and receptors. Additionally, the FXa inhibition potential of GW813893 was assessed in prothrombinase and plasma-based clotting assays. In vivo characterization of GW813893 consisted of thrombosis studies in a rat inferior vena cava model, a rat carotid artery thrombosis model, and a rabbit jugular thrombosis model. Bleeding studies were conducted in a rat tail transection model. Ex vivo determinations of compound effects on FX and clotting activity were also undertaken.

RESULTS

GW813893 was more than 90-fold selective over all enzymes tested, and it inhibited FXa and prothrombinase activity with a Ki of 4.0 nM and 9.7 nM, respectively. In vivo, GW813893 concentration-dependently suppressed thrombotic activity in all models tested. The antithrombotic activity correlated with the suppression of plasma-based clotting activity and the inhibition of plasma FX activity (P < 0.02). Over the antithrombotic dose-range, an increased bleeding diathesis was not observed.

CONCLUSION

These experiments demonstrate that GW813893 is a potent, selective, orally active inhibitor of FXa. The data suggest that GW813893 has robust antithrombotic potential at doses that have no detectable hemostasis liability. Collectively, the profile suggests that GW813893 has the preclinical pharmacology underpinnings of an oral antithrombotic therapeutic.

Characterization of total plasma glycosaminoglycan levels in healthy volunteers following oral administration of a novel antithrombotic odiparcil with aspirin or enoxaparin

Odiparcil is a novel, orally active beta-d-thioxyloside analog with antithrombotic activity associated with a reduced risk of adverse bleeding events. Its unique mechanism of action is postulated by means of an elevation in circulating endogenous chondroitin sulfate-related glycosaminoglycans (GAGs) levels. The purpose of these 2 separate clinical studies was to evaluate plasma GAG levels in healthy subjects administered odiparcil with either aspirin (ASA) or enoxaparin. Clinical plasma samples were processed and analyzed using validated HPLC bioassays that indirectly estimate GAG levels based on the simultaneous detection of the chondroitin disaccharide derivatives. The concomitant administration of odiparcil with or without ASA resulted in a significant elevation in GAG levels over baseline for both treatment groups. In the other clinical study, the concomitant administration of odiparcil with or without enoxaparin displayed significant increases in plasma DeltaDi-OS, DeltaDi-4S, and total disaccharide levels versus control group. Neither plasma GAG levels nor odiparcil plasma levels were correlated with a rise in hepatic transaminases, an adverse drug event observed in several subjects; and plasma odiparcil levels were indirectly correlated with plasma GAG levels. These clinical studies were proof of concept of preclinical rat studies indicating that chronic odiparcil treatment elevates endogenous GAG levels in human subjects.