Antiaggregants

Inhibitors of aggregations of blood thrombocytes possess practical importance, and to a large degree are regulated by the thromboxane—prostacyclin system. Thromboxane A2 enhances aggregation, while prostacycline (prostaglandin I2) inhibits aggregation of blood thrombocytes. Prostaglandin E2, collagen of vascular walls, thrombin, adenosindiphos-phate, serotonin, and catecholamines are also aggregation stimulants. Prostaglandin E1, adenosine monophosphate, adenosine, methylanthines, antagonists of serotonin, heparin, and others are also aggregant inhibitors. Nonsteroid anti-inflammatory, fever-reducing analgesics such as aspirin, indomethacin, ibuprofen, and others, which block cyclooxyge-nase and prevent transformation of arachidonic acid to thromboxane A2, have gained practical importance in medicine as aggregant inhibitors of blood thrombocytes. Other aggregant inhibitors of blood thrombocytes, such as the coronary vasodilating drugs dipyridamole and ticlopidine, control activation of thrombocytes.

Aspirin (3.2.2): Synthesis and properties of this drug are described in Chapter 3.

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Aspirin is a cyclooxygenase inhibitor that is expressed in the inhibition of synthesis of thromboxane A2 and prostacyclin (prostaglandin I2), which are functional antagonists. Synthesis of thromboxane A2 is suppressed to a large degree when using aspirin in small doses. Using aspirin reduces the risk of myocardial infarction, and increases the survival of patients with myocardial infarction. It lowers the risk of stroke in cases of damaged brain blood circulation.

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Sulfinpyrazone (3.2.8): Synthesis of this drug is described in Chapter 3.

Sulfinpyrazone is used in medicine as a nonsteroid anti-inflammatory, fever-reducing analgesic; however, it is believed, that it inhibits cyclooxygenase of thrombocytes. In addition, it is also possible that its action is also linked with the action on membrane of thrombocytes and reduced quantities of secreted adenosine diphosphate and serotonin, which facilitate thrombocyte aggregation. Unlike aspirin, it has no effect on those who do not have irregular aggregation systems.

Indomethacin (3.2.51): Synthesis and properties of indomethacin are described in Chapter 3.

Indomethacin, like aspirin, reversibly inhibits cyclooxygenase action by blocking formation of thromboxane A2.

Dipiridamol (19.4.13): Synthesis of this drug is described in Chapter 19.

Dipiridamol is known as a coronary vasodilating agent, although it also possesses specific antiaggregant activity. It is used for preventing thrombo-formation after cardiac valve replacement in combination with warfarin. The mechanism of dipiridamol's antiaggregant action is not completely clear, and its efficacy is questionable.

Ticlopidine: Ticlopidine, 5-(o-chlorobenzyl)-4,5,6,7-tetrahydrothieno[3,2-c]pyridine (24.2.1), is synthesized in many different ways [33-39]. The first way consists of N-alky-lation of 4,5,6,7-tetrahydrothieno[3,2-c]pyridine with 2-chlorobenzylchloride.

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