Potent Trivalent Inhibitors of Thrombin through Hybridization of Salivary Sulfopeptides from Hematophagous Arthropods.

Blood feeding arthropods, such as leeches, ticks, flies and mosquitoes, provide a privileged source of peptidic anticoagulant molecules. These primarily operate through inhibition of the central coagulation protease thrombin by binding to the active site and either exosite I or exosite II. Herein, we describe the rational design of a novel class of trivalent thrombin inhibitors that simultaneously block both exosites as well as the active site. These engineered hybrids were synthesized using tandem diselenide-selenoester ligation (DSL) and native chemical ligation (NCL) reactions in one-pot. The most potent trivalent inhibitors possessed femtomolar inhibition constants against α-thrombin and were selective over related coagulation proteases. A lead hybrid inhibitor possessed potent anticoagulant activity, blockade of both thrombin generation and platelet aggregation in vitro and efficacy in a murine thrombosis model at 1 mg kg-1 . The rational engineering approach described here lays the foundation for the development of potent and selective inhibitors for a range of other enzymatic targets that possess multiple sites for the disruption of protein-protein interactions, in addition to an active site.

Short Communication - Synthesis of drug metal complexes and their influence on human platelet aggregation.

During the past few decades the emergence of inorganic medicinal chemistry has been developed novel therapeutic agents. Researcher's perseverance in this branch of chemistry has led them to explore further valuable chemical spaces by synthesizing metal complexes already known pharmacological agents for their potential use. However, it is in its early stage, this methodology has demonstrated metal complexes with better bioactivities than the parent ligand molecules. In this study, transition metal complexes of pyrazinamide (PZ), isoniazid (INH), fluconazole (FCZ), metformin (dimethylbiguanide, DMBG) and losartan potassium (LS-K) were selected to evaluate for their possible anti-platelets aggregation in the light of reports on divalent and trivalent cations like calcium, copper, manganese, magnesium, and cadmium may influence the process of thrombocytic activity and aggregation. The required evaluation was carried out on human plasma through an APACT 4004 platelet aggregation analyzer. Arachidonic acid (ADP) was used to gauge any alteration in platelet shape and aggregation process. The parent drugs showed some anti-platelets aggregation, however, their metal complexes demonstrated better efficacy.

Development of Novel High Density Gastroretentive Multiparticulate Pulsatile Tablet of Clopidogrel Bisulfate Using Quality by Design Approach.

Myocardial infarction, i.e., heart attack, is a fatal condition which is on the increase all over the world. It is reported that a large number of heart attack occur in morning hours which are attributable to platelet aggregation. Chronotherapy at this stage can be crucial. Clopidogrel bisulfate (CLB) is an antiplatelet agent and has become a drug of choice for prevention of heart attack. It is soluble in acidic pH and has a narrow absorption window. So, its long residence time in stomach is desirable. Therefore, a novel high density tablet was developed comprising multiparticulate pellets with pulsatile release necessary to maintain chronotherapy of heart attack. The pellets were prepared by extrusion-spheronization and coated in fluidized bed processor with different coating material to achieve pulsatile release. The size, shape of pellets, and drug release were evaluated. High density tablet containing coated pellets was formulated and evaluated for retention in stomach. Quality by design tools was used to design and optimize the processes. Timed release observed by dissolution study showed lag time of 6 h followed by burst release of drug up to 94% in 1 h. Density of tablets was found to be 2.2 g cm-3 which is more than gastric fluid. In vivo x-ray studies in rabbit revealed 8 h of gastric retention of tablet at the bottom of the stomach. Thus, CLB high density pulsatile system looks to open up a window of opportunity for developing formulations with drugs that are stable in gastric region and needed chronotheraupetic activity.

Synthesis, Anticlotting and Antiplatelet Effects of 1,2,3-Triazoles Derivatives.

Cardiovascular diseases, such as thrombosis and stroke, represent the major cause of disability and death worldwide; and dysfunctions in platelet aggregation and blood coagulation processes are involved. The regular antithrombotic drugs have unsatisfactory results and may produce side effects. Therefore, alternative therapies have been extensively investigated. OBJECTIVE: The anticoagulant and antiplatelet aggregation potential of a series of six synthetic 1,2,3-triazole derivatives were investigated through in vitro models. METHODS: Coagulation tests included the prothrombin time (PT), activated partial thromboplastin time (APTT) and thrombin time (TT) assays, and were performed on a multichannel coagulometer, using human plasma. The platelet aggregation assays were carried out using human platelet-rich-plasma (PRP). Aggregation was initiated by adding ADP or collagen and monitored turbidimetrically on a Whole Blood Aggregometer. Toxicity of derivatives was evaluated on platelets and red blood cells, by measuring the release of lactate dehydrogenase and hemoglobin, respectively. Moreover, theoretical toxicity of derivatives was calculated using the software Osiris® Property Explorer. RESULTS: All the six derivatives tested inhibited, but with different potencies, the plasma coagulation assessed by the PT and TT assays, and also inhibited platelet aggregation of PRP induced by collagen or ADP. The derivatives did not interfere in the aPTT assay and did not affect the viability of platelets or red blood cells. Theoretical studies also revealed that all derivatives will likely to have low toxicity, great pharmacological and oral bioavailability profiles, and a Druglikeness and Drug score similar to some commercial anticoagulant and antiplatelet drugs. CONCLUSION: 1,2,3-triazoles are potential candidates for molecular modeling of new antithrombotic drugs.

Synthesis and biological evaluation of nitric oxide (NO)-hydrogen sulfide (H2S) releasing derivatives of (S)-3-n-butylphthalide as potential antiplatelet agents.

In the present study, a series of novel nitric oxide-hydrogen sulfide releasing derivatives of (S)-3-n-butylphthalide ((S)-NBP) were designed, synthesized, and evaluated as potential antiplatelet agents. Compound NOSH-NBP-5 displayed the strongest activity in inhibiting the arachidonic acid (AA)- and adenosine diphosphate (ADP)-induced platelet aggregation in vitro, with 3.8- and 7.0-fold more effectiveness than (S)-NBP, respectively. Furthermore, NOSH-NBP-5 could release moderate levels of NO and H2S, which would be beneficial in improving cardiovascular and cerebral circulation. Moreover, NOSH-NBP-5 could release (S)-NBP when incubated with rat brain homogenate. In conclusion, these findings may provide new insights into the development of novel antiplatelet agents for the treatment of thrombosis-related ischemic stroke.

[Synthesis and biological evaluation of novel chalcone aromatic oxygen alkyl acids compounds].

Six novel ligustrazine chalcone aromatic oxygen alkyl acids compounds and two pyridine chalcone aromatic oxygen alkyl acids ester compounds were synthesized according to the traditional Chinese medicine theory removing blood stasis. The structures of target compounds were identified by IR, NMR and ESI-MS. The inhibitory activities of platelet aggregation induced by adenosine diphosphate (ADP) and arachidonic acid(AA) were measured by the liver microsomal incubation method in vitro. Hypolipidemic activities of compounds were tested in vivo for better inhibitory activities of platelet aggregation. Preliminary pharmacological results showed that compounds 7c, 8a and 11 a had potent inhibitory activity against platelet aggregation induced by AA, compounds 7c, 7d, 8a and 11 b showed significant inhibitory activity against platelet aggregation induced by ADP. Compounds 7c and 8a exhibited good hypolipidemic activities in high-fat-diet(HFD) induced hyperlipidemia C57/BL6 mice and worthy for further investigation.

Design, Synthesis and Pharmacological Evaluation of Novel Piperlongumine derivatives as Potential Antiplatelet Aggregation Candidate.

A series of novel piperlongumine derivatives (4a-i, 6a-i) were designed and synthesized. The inhibitory activities of platelet aggregation induced by ADP and AA in vitro have been evaluated by bron turbidimetry and liver microsomal incubated assay. The assay results show that compounds 4e and 6e exhibited remarkable potency to that of the positive control piplartine and aspirin.

Design, Virtual Screening, and Synthesis of Antagonists of αIIbß3 as Antiplatelet Agents.

This article describes design, virtual screening, synthesis, and biological tests of novel αIIbß3 antagonists, which inhibit platelet aggregation. Two types of αIIbß3 antagonists were developed: those binding either closed or open form of the protein. At the first step, available experimental data were used to build QSAR models and ligand- and structure-based pharmacophore models and to select the most appropriate tool for ligand-to-protein docking. Virtual screening of publicly available databases (BioinfoDB, ZINC, Enamine data sets) with developed models resulted in no hits. Therefore, small focused libraries for two types of ligands were prepared on the basis of pharmacophore models. Their screening resulted in four potential ligands for open form of αIIbß3 and four ligands for its closed form followed by their synthesis and in vitro tests. Experimental measurements of affinity for αIIbß3 and ability to inhibit ADP-induced platelet aggregation (IC50) showed that two designed ligands for the open form 4c and 4d (IC50 = 6.2 nM and 25 nM, respectively) and one for the closed form 12b (IC50 = 11 nM) were more potent than commercial antithrombotic Tirofiban (IC50 = 32 nM).

New platelet aggregation inhibitors based on pyridazinone moiety.

New series of pyridazinone derivatives (4, 5 and 6) were synthesized in good yields following a synthetic strategy based on singlet oxygen oxidation of alkyl furans, in which a suitable ß(α)-substituted γ-hydroxybutenolide (10 or 11) or a bicyclic lactone (12 or 13) was the key intermediate. The synthesized compounds were tested in vitro as antiplatelet agents and some of them (compounds 4b, 4d and 5b) exhibited potent inhibitory effects on collagen-induced platelet aggregation with IC50 values in the low µM range. Studies performed with the most active compound of these series (4b) demonstrated its lack of activity as inhibitor of platelet aggregation induced by other agonists as thrombin, ionomycin or U-46619 suggesting a selective action on the biochemical mechanisms triggered by collagen in the platelets.

Synthetic analogues of flavonoids with improved activity against platelet activation and aggregation as novel prototypes of food supplements.

We investigated the ability of quercetin and apigenin to modulate platelet activation and aggregation, and compared the observed efficacy with that displayed by their synthetic analogues 2-phenyl-4H-pyrido[1,2-a]pyrimidin-4-ones, 1-4, and 2,3-diphenyl-4H-pyrido[1,2-a]pyrimidin-4-ones, 5-7. Platelet aggregation was explored through a spectrophotometric assay on platelet-rich plasma (PRP) treated with the thromboxane A2 mimetic U46619, collagen and thrombin in presence/absence of various bioisosteres of flavonoids (12.5-25-50-100 µM). The platelet density, (mean platelet component, MPC), was measured by the Advia 120 Hematology System as a marker surrogate of platelet activation. The induced P-selectin expression, which reflects platelet degranulation/activation, was quantified by flow cytometry on PRP. Our synthetic compounds modulated significantly both platelet activation and aggregation, thus turning out to be more effective than the analogues quercetin and apigenin when tested at a concentration fully consistent with their use in vivo. Accordingly, they might be used as food supplements to increase the efficacy of natural flavonoids.

Synthesis of analogues of gingerol and shogaol, the active pungent principles from the rhizomes of Zingiber officinale and evaluation of their anti-platelet aggregation effects.

The present study was aimed at discovering novel biologically active compounds based on the skeletons of gingerol and shogaol, the pungent principles from the rhizomes of Zingiber officinale. Therefore, eight groups of analogues were synthesized and examined for their inhibitory activities of platelet aggregation induced by arachidonic acid, collagen, platelet activating factor, and thrombin. Among the tested compounds, [6]-paradol (5b) exhibited the most significant anti-platelet aggregation activity. It was the most potent candidate, which could be used in further investigation to explore new drug leads.

Novel furfurylidene N-acylhydrazones derived from natural safrole: discovery of LASSBio-1215, a new potent antiplatelet prototype.

We describe herein the discovery of (E)-N-methyl-N'-((5-nitrofuran-2-yl)methylene)benzo[d]( 1 , 3 ) dioxole-5-carbohydrazide (9e), named LASSBio-1215, as a novel antiplatelet agent belonging to the N-methyl-N-acylhydrazone class, which exert their antiaggregating actions on human and rabbit platelets induced by different agonists, through cyclooxygenase-1 (COX-1) or thromboxane synthase inhibition. This compound was elected after screening of a series of functionalized furyl N-acylhydrazone derivatives, synthesized from natural safrole 10. In vitro assays showed that compound 9e presents platelet-aggregating activity in rabbit platelet-rich plasma (PRP) induced by arachidonic acid (IC(50) = 0.7 µM) and collagen (IC(50) = 4.5 µM). Moreover, LASSBio-1215 also inhibited almost completely the second wave of adenosine diphosphate-induced platelet aggregation in human PRP, and this effect was correlated with their ability to block the production of pro-aggregating autacoid thromboxane A(2).

RGD mimetics containing phthalimidine fragment as novel ligands of fibrinogen receptor.

The novel RGD mimetics with phthalimidine central fragment were synthesized with the use of 4-piperidine-4-yl-butyric, 4-piperidine-4-yl-benzoic, 4-piperazine-4-yl-benzoic and 1,2,3,4-tetrahydroisoquinoline-7-carboxylic acids as surrogates of Arg motif. The synthesized compounds potently inhibited platelet aggregation in vitro and blocked FITC-Fg binding to α(IIb)ß(3) integrin in a suspension of washed human platelets. The key α(IIb)ß(3) protein-ligand interactions were determined in docking experiments.

[Synthesis of ferulic acid derivatives and their inhibitory effect on platelet aggregation].

Ferulic acid, an useful compound of Chinese traditional medicine, was used as leading compound. Six ferulic acid derivatives were designed and synthesized based on bioisosterism. Their structures were characterized by IR, 1H NMR, 13C NMR and mass spectra. In vivo experiment showed that ferulic acid derivatives had good inhibitory effects on adenosine diphosphate (ADP) induced platelet aggregation, which were significantly higher than that of Ozagrel.

Circular dichroism studies of type III collagen mimetic peptides with anti- or pro-aggregant activities on human platelets.

We report the synthesis of collagen related peptides containing the peptide sequence Lys-Hyp-Gly-Glu-Hyp-Gly-Pro-Lys. The anti-thrombotic activity effects of different glycine mutations in this sequence were studied in regard with their different adopted conformations. The biological results could be correlated to the glycine propensity to adopt a more stable polyproline II helix conformation. The incorporation of these sequences in "collagen-like" alpha-triple-helix peptides shows a pro-thrombotic activity compared to a scrambled negative control peptide which possesses no significant activity.

Synthesis and anti-platelet evaluation of 2-benzoylaminobenzoate analogs.

Fifty-two 2-benzoylaminobenzoate analogs were synthesized and subjected to anti-platelet aggregation assay using arachidonic acid (AA), collagen (Col), thrombin (Thr), and U46619 as inducers. The results revealed that most of 2-benzoylaminobenzoic acid derivatives showed a selectively inhibitory effect on AA-induced platelet aggregation. As a result of the 2-benzoylaminobenzoic acid derivatives (18, 44, and 46), there were no inhibitory effects on platelet aggregation induced by U46619, but these elicited an inhibitory effect on thromboxane B(2) formation at 1.0microM. These 2-benzoylaminobenzoate analogs were therefore proposed as cyclooxygenase inhibitors.

Synthesis and evaluation of N-acylsulfonamide and N-acylsulfonylurea prodrugs of a prostacyclin receptor agonist.

N-Acylsulfonamide and N-acylsulfonylurea derivatives of the carboxylic acid prostacyclin receptor agonist 1 were synthesized and their potential as prodrug forms of the carboxylic acid was evaluated in vitro and in vivo. These compounds were converted to the active compound 1 by hepatic microsomes from rats, dogs, monkeys, and humans, and some of the compounds were shown to yield sustained plasma concentrations of 1 when they were orally administered to monkeys. These types of analogues, including NS-304 (2a), are potentially useful prodrugs of 1.

Synthesis, resolution, and antiplatelet activity of 3-substituted 1(3H)-isobenzofuranone.

A series of 3-substituted-1(3H)-isobenzofuranone 6a-g and 7a-g were synthesized from phthalic anhydride. The compound 6a-g was resolved. The antiplatelet activities of these compounds were evaluated using in vitro experiment of platelet aggregation. The levels of antiplatelet activity were displayed as following sequence: l-isomer >dl-isomer>d-isomer, respectively. The alkylphthalide is more active than the corresponding alkenephthalide. All these compounds were less active than n-butylphthalide (NBP, 6c) and Aspirin (Asp).

Synthesis, identification and antiplatelet evaluation of 2-morpholino substituted benzoxazines.

A number of 2-morpholino substituted benzoxazines have been prepared in order to test their effectiveness against ADP and collagen induced platelet aggregation. The reaction of 2-thio-1,3-benzoxazines with morpholine has been generalised to enable the use of substituted benzoxazines. Two separate methods were used to prepare 7-O-2-morpholino substituted benzoxazines from 7-hydroxy-2-morpholino benzoxazines. Antiplatelet testing was carried out on 15 of the title compounds. 7-(2-Chloroethoxy)-8-methyl-2-morpholin-4-yl-4H-1,3-benzoxazin-4-one 15d and 7-[2-(4-methylpiperazin-1-yl)ethoxy]-8-methyl-2-morpholin-4-yl-4H-1,3-benzoxazin-4-one 16d showed potent activity against ADP and collagen induced platelet aggregation. The structures of the newly prepared compounds were confirmed by microanalysis as well as the analysis of IR, (1)H and (13)C NMR.

Derivatives of 7-amino-1,2,3,4-tetrahydroisoquinoline and isophthalic acids as novel fibrinogen receptor antagonists.

The novel fibrinogen receptor antagonists containing fragments of 7-amino-1,2,3,4-tetrahydroisoquinoline and isophthalic acids were synthesized and successfully tested for their ability to inhibit platelet aggregation in vitro and to block FITC-Fg binding to alpha(IIb)beta(3) on washed human platelets.