Antiplatelet effects of KW-7, a new inhibitor of cyclic nucleotide phosphodiesterases

Unprecedented access to functionalized pyrrolo[2,1-a]isoquinolines from the domino reaction of isoquinolinium ylides and electrophilic benzannulated heterocycles

We have come across an unexpected reaction between electrophilic indoles and isoquinolinium methylides for accessing functionalized pyrrolo[2,1-a]isoquinolines. The reaction was found in general to yield the products in good yields. We also observed the formation of S-S-bridged bis-pyrrolo[2,1-a]isoquinolines from the reaction of 3-nitro benzothiophene and isoquinolinium methylides.

Pyrrolo[2,1-a]isoquinoline scaffold in drug discovery: advances in synthesis and medicinal chemistry

Pyrrolo[2,1-a]isoquinoline (PIq) is a nitrogen heterocyclic scaffold of diverse alkaloids endowed with several biological activities, including antiretroviral and antitumor activities. Several 5,6-dihydro-PIq (DHPIq) alkaloids, belonging to the lamellarins' family, have proved to be cytotoxic to tumor cells, as well as reversers of multidrug resistance. In this review, we provide an overview of the main achievements over the last decade in the synthetic approaches to access libraries of PIq compounds along with a survey, as comprehensive as possible, of bioactivity, mechanism of action, pharmacophore and structure-activity relationships of synthetic analogs of DHPIq-based alkaloids. The focus is mainly on the potential exploitation of the (DH)PIq scaffold in design and development of novel antitumor drugs.

Anti-allergic Hydroxy Fatty Acids from Typhonium blumei Explored through ChemGPS-NP

Increasing prevalence of allergic diseases with an inadequate variety of treatment drives forward search for new alternative drugs. Fatty acids, abundant in nature, are regarded as important bioactive compounds and powerful nutrients playing an important role in lipid homeostasis and inflammation. Phytochemical study on Typhonium blumei Nicolson and Sivadasan (Araceae), a folk anti-cancer and anti-inflammatory medicine, yielded four oxygenated fatty acids, 12R-hydroxyoctadec-9Z,13E-dienoic acid methyl ester (1) and 10R-hydroxyoctadec-8E,12Z-dienoic acid methyl ester (2), 9R-hydroxy-10E-octadecenoic acid methyl ester (3), and 12R^*-hydroxy-10E-octadecenoic acid methyl ester (4). Isolated compounds were identified by spectroscopic methods along with GC-MS analysis. Isolated fatty acids together with a series of saturated, unsaturated and oxygenated fatty acids were evaluated for their anti-inflammatory and anti-allergic activities in vitro. Unsaturated (including docosahexaenoic and eicosapentaenoic acids) as well as hydroxylated unsaturated fatty acids exerted strong anti-inflammatory activity in superoxide anion generation (IC₅₀ 2.14-3.73 μM) and elastase release (IC₅₀ 1.26-4.57 μM) assays. On the other hand, in the anti-allergic assays, the unsaturated fatty acids were inactive, while hydroxylated fatty acids showed promising inhibitory activity in A23187- and antigen-induced degranulation assays (e.g., 9S-hydroxy-10E,12Z-octadecadienoic acid, IC₅₀ 92.4 and 49.7 μM, respectively). According to our results, the presence of a hydroxy group in the long chain did not influence the potent anti-inflammatory activity of free unsaturated acids. Nevertheless, hydroxylation of fatty acids (or their methyl esters) seems to be a key factor for the anti-allergic activity observed in the current study. Moreover, ChemGPS-NP was explored to predict the structure-activity relationship of fatty acids. The anti-allergic fatty acids formed different cluster distant from clinically used drugs. The bioactivity of T. blumei, which is historically utilized in folk medicine, might be related to the content of fatty acids and their metabolites.

The evaluation and structure–activity relationships of 2-benzoylaminobenzoic esters and their analogues as anti-inflammatory and anti-platelet aggregation agents

Forty-seven 2-benzoylaminobenzoic esters were synthesized and evaluated in anti-platelet aggregation, inhibition of superoxide anion generation, and inhibition of neutrophil elastase release assays. Most 2-benzoylamino-4-chlorobenzoic acid derivatives showed selective inhibitory effects on arachidonic acid (AA)-induced platelet aggregation. Among them, compounds 6b and 7b exhibited more potent inhibitory effects (ca. 200-fold) than aspirin. Additionally, compounds 1a and 5a showed strong inhibitory effects on neutrophil superoxide generation with IC(50) values of 0.65 and 0.17 microM, respectively. However, compounds 6d and 6e exhibited dual inhibitory effects on platelet aggregation and neutrophil elastase (NE) release; therefore, these two compounds may be new leads for development as anti-inflammatory and anti-platelet aggregatory agents.

Current developments in anti-platelet therapy

Platelets play a life-saving role in hemostasis and blood clotting at sites of vascular injury and consequently are similarly involved in the pathological counterpart, namely thrombosis. Thus, anti-platelet therapy has become a mainstay in treatment and/or prophylaxis of conditions like myocardial infarction, stroke and other cardiovascular diseases. Acetyl-salicylic acid (ASA, aspirin) is still the most widely used agent and considered as the prototype antiplatelet drug. Since platelet activation occurs via several pathways that are not influenced by ASA, several other compounds have been developed to add to its beneficial effect. Currently four main classes of antiplatelet agents are available for clinical use: acetyl-salicylic acid (ASA), phosphodiesterase (PDE) inhibitors, thienopyridines and the intravenous GPIIb/IIIa antagonists. This article gives a concise review of these four classes of anti-platelet agents, using ASA as the reference standard.

Prevention of platelet glycoprotein IIb/IIIa activation by 3,4-methylenedioxy-beta-nitrostyrene, a novel tyrosine kinase inhibitor

Binding fibrinogen to activated glycoprotein (GP)IIb/IIIa is the final common pathway of platelet aggregation and has become a successful target for antiplatelet therapy. In the present study, we found that a small chemical compound, 3,4-methyl-enedioxy-beta-nitrostyrene (MNS), exhibited potent and broad-spectrum inhibitory effects on human platelet aggregation caused by various stimulators. Moreover, addition of MNS to human platelets that had been aggregated by ADP caused a rapid disaggregation. We demonstrated that the antiaggregatory activity of MNS is due to inhibition of GPIIb/IIIa activation by measuring the binding amount of PAC-1 in platelets. In contrast, MNS is not a direct antagonist of GPIIb/IIIa, because MNS did not affect fibrinogen binding to fixed ADP-stimulated platelets. By investigating how MNS inhibits GPIIb/IIIa activation, we found that MNS potently inhibited the activity of tyrosine kinases (Src and Syk) and prevented protein tyrosine phosphorylation and cytoskeletal association of GPIIb/IIIa and talin, but it had no direct effects on protein kinase C, Ca2+ mobilization, Ca2+-dependent enzymes (myosin light chain kinase and calpain), and arachidonic acid metabolism, and it did not affect the cellular levels of cyclic nucleotides. Therefore, MNS represents a new class of tyrosine kinase inhibitor that potently prevents GPIIb/IIIa activation and platelet aggregation without directly affecting other signaling pathways required for platelet activation. Because MNS inhibits GPIIb/IIIa functions in a manner different from GPIIb/IIIa antagonists, this feature may provide a new strategy for treatment of platelet-dependent thrombosis.

α-Bulnesene, a novel PAF receptor antagonist isolated from Pogostemon cablin

Alpha-bulnesene is a sesquiterpenoid isolated from the water extract of Pogostemon cablin. It showed a potent and concentration-dependent inhibitory effect on platelet-activating factor (PAF) and arachidonic acid (AA) induced rabbit platelet aggregation. In a radioligand binding assay for the PAF receptor, alpha-bulnesene competitively inhibited [(3)H]PAF binding to the PAF receptor with an IC(50) value of 17.62+/-5.68microM. alpha-Bulnesene also dose-dependently inhibited PAF-induced intracellular Ca(2+) increase in fluo-3/AM-loaded platelets (IC(50) values of 19.62+/-1.32microM). Furthermore, alpha-bulnesene inhibited AA-induced thromboxane B(2) (TXB(2)) formation and prostaglandin E(2) (PGE(2)) formation. These results indicate that the inhibitory effect of alpha-bulnesene on platelet aggregation was due to a dual activity; specifically the chemical blocked PAF-induced intracellular signal transduction and interfered with cyclooxygenase activity, which resulted in a decrease in thromboxane formation. This study is the first to demonstrate that alpha-bulnesene is a PAF receptor antagonist as well as an anti-platelet aggregation agent.

2-(2-Br-phenyl)-8-methoxy-benzoxazinone (HPW-RX2), a direct thrombin inhibitor with a suppressive effect on thromboxane formation in platelets

2-(2-Br-phenyl)-8-methoxy-benzoxazinone (HPW-RX2), a newly synthetic benzoxazinone derivative, has previously been shown to inhibit rabbit platelet aggregation caused by thrombin and arachidonic acid. In the present study, the mechanism for the antiplatelet effect of HPW-RX2 was further investigated. In human platelets, HPW-RX2 concentration-dependently inhibited platelet aggregation, ATP release, P-selectin expression, and intracellular calcium mobilization caused by thrombin. In contrast, HPW-RX2 had no significant effect on either SFLLRN- or GYPGKF-induced platelet aggregation, indicating that HPW-RX2 did not interfere with platelet thrombin receptors. Moreover, HPW-RX2 inhibited the amidolytic activity of thrombin and prolonged the fibrinogen clotting time. These results suggest that the inhibitory effect of HPW-RX2 on thrombin-induced platelet aggregation is via direct inhibition of thrombin proteolytic activity. Besides the inhibition on thrombin, HPW-RX2 also prevented platelet aggregation, ATP release, and increase in [Ca2+]i caused by arachidonic acid and low concentration collagen. In a parallel manner, both arachidonic acid-induced thromboxane B2 and prostaglandin D2 formations were decreased in platelets treated with HPW-RX2. This indicates that HPW-RX2 is able to inhibit the arachidonic acid cascade at the cyclooxygenase level. This is the first report of a benzoxazinone derivative possessing both thrombin and cyclooxygenase inhibitory properties. The dual effect of HPW-RX2 might provide extra therapeutic benefits for treatment of arterial thrombosis.

The evaluation of 2,8-disubstituted benzoxazinone derivatives as anti-inflammatory and anti-platelet aggregation agents

A series of 2,8-disubstituted benzoxazinones were synthesized and subjected to anti-platelet aggregation, inhibition of superoxide anion generation, and inhibition of neutrophil elastase release assays. Among them, 2-(2'-substituted-phenyl)-benzoxazinones exhibited significant inhibitory effect to target assays. Additionally, all of them were more potent than aspirin on AA-induced platelet aggregation, and these suggested that 2-(2'-substituted-phenyl)-benzoxazinones also possess aspirin-like activity. On the other hand, the compounds 6 and 16 showed inhibitory effects on neutrophil elastase release and superoxide generation.