4-Hydroxycoumarins are a class of vitamin K antagonist (VKA) anticoagulant drug molecules. Chemically, they are derived from coumarin by adding a hydroxy group at the 4 position to obtain 4-hydroxycoumarin, then adding a large aromatic substituent at the 3-position (the ring-carbon between the hydroxyl and the carbonyl). The large 3-position substituent is required for anticoagulant activity.
The primary mechanism of the 4-hydroxycoumarin drugs is the inhibition of vitamin K epoxide reductase. These compounds are not direct antagonists (in the pharmaceutical sense) of vitamin K, but rather act to deplete reduced vitamin K in tissues. For this reason vitamin K antagonizes their effect, and this has led to the loose terminology of "vitamin K antagonist".
Although 4-hydroxycoumarin itself is not an anticoagulant, it is an important fungal metabolite from the precursor coumarin, which is also not an anticoagulant, and its production leads to further fermentative production of the natural anticoagulant dicoumarol. This happens in the presence of naturally occurring formaldehyde, which allows attachment of a second 4-hydroxycoumarin molecule through the linking carbon of the formaldehyde, to the 3-position of the first 4-hydroxycoumarin molecule, giving the semi-dimer the motif of the drug class. Dicoumarol appears in spoiled silage of sweet clover and is considered a natural mycotoxin substance of combined plant and fungal origin. [1] The identification of dicoumarol in 1940 was the precursor to development of the 4-hydroxycoumarin class of drugs.
The synthetic drugs in the 4-hydroxycoumarin class are all noted primarily for their use as anticoagulants, though they can have several additional effects. All affect the normal metabolism of vitamin K in the body by inhibiting the enzyme vitamin K epoxide reductase which recycles vitamin K to active form. As such, these compounds form the most important and widely used subset of vitamin K antagonist drugs, but other such drugs exist which do not have the 4-hydroxycoumarin structure. All the vitamin K antagonist agents diminish the amount of available vitamin K in the body, and thus inhibit the action of vitamin K-dependent enzymes that are critically involved in the production of active forms of certain clotting factors, and certain other metabolic processes involving the binding of calcium ion.
The simplest synthetic molecule in the 4-hydroxycoumarin class is warfarin, in which the aromatic 3-position substituent is a simple phenyl group. So called "super-warfarins" or second-generation anticoagulants in this class, were developed as rodenticides for rodents that have developed warfarin resistance. The second generation agents have even larger lipid-soluble substituents at the 3-position (e.g. brodifacoum), a chemical change that causes their half-lives in the body to be greatly increased (sometimes to months). The rodenticide chemicals are sometimes incorrectly referred to as "coumadins" rather than 4-hydroxycoumarins ("Coumadin" is a brand name for warfarin). They are also referred to as "coumarins," in reference to their derivation, although this term also may be deceptive since coumarin itself, as noted, is not active in clotting, and is used mostly as a perfumery agent.
Pharmaceutical examples of 4-hydroxycoumarin pharmaceuticals include:
Compounds in this class have also been used as pesticides, specifically rodenticides. They act by causing the affected animal to hemorrhage, causing it to seek water, and thus leave dwellings to die outdoors.
The second-generation vitamin K antagonist agents, used only in this fashion as poisons (because their duration of action is too long to be used as pharmaceuticals) include:
Coumarin This molecule does not affect coagulation | 4-Hydroxycoumarin This molecule does not affect coagulation, but is a known carcinogen in diesel fumes and tobacco smoke; in the latter, it probably derives from combustion of the tobacco additive coumarin. | Dicumarol This molecule was the first discovered 4-hydroxycoumarin anticoagulant. It is a dimer type structure connected at the 3 ring position. |
Phenprocoumon (anticoagulant) | Warfarin Most commonly used anticoagulant pharmaceutical | Acenocoumarol (anticoagulant) |
Tecarfarin (experimental anticoagulant) |
Brodifacoum This molecule is a second-generation anticoagulant with a large 3-position substituent which causes it to be retained in fatty tissues for longer times than first-generation compounds and pharmaceuticals. (rodenticide) | Bromadiolone (rodenticide) |
Coumatetralyl (rodenticide) | Difenacoum (rodenticide) |
Flocoumafen (rodenticide) |
Vitamin K is a family of structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation or for controlling binding of calcium in bones and other tissues. The complete synthesis involves final modification of these so-called "Gla proteins" by the enzyme gamma-glutamyl carboxylase that uses vitamin K as a cofactor.
An anticoagulant, commonly known as a blood thinner, is a chemical substance that prevents or reduces the coagulation of blood, prolonging the clotting time. Some occur naturally in blood-eating animals, such as leeches and mosquitoes, which help keep the bite area unclotted long enough for the animal to obtain blood.
Warfarin is an anticoagulant used as a medication under several brand names including Coumadin. While the drug is described as a "blood thinner", it does not reduce viscosity but rather inhibits coagulation. Accordingly, it is commonly used to prevent blood clots in the circulatory system such as deep vein thrombosis and pulmonary embolism, and to protect against stroke in people who have atrial fibrillation, valvular heart disease, or artificial heart valves. Less commonly, it is used following ST-segment elevation myocardial infarction (STEMI) and orthopedic surgery. It is usually taken by mouth, but may also be administered intravenously.
Coumarin or 2H-chromen-2-one is an aromatic organic chemical compound with formula C9H6O2. Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by an unsaturated lactone ring −(CH)=(CH)−(C=O)−O−, forming a second six-membered heterocycle that shares two carbons with the benzene ring. It belongs to the benzopyrone chemical class and considered as a lactone.
Warfarin-induced skin necrosis is a condition in which skin and subcutaneous tissue necrosis occurs due to acquired protein C deficiency following treatment with anti-vitamin K anticoagulants.
Coumatetralyl is an anticoagulant of the 4-hydroxycoumarin vitamin K antagonist type used as a rodenticide.
Phenprocoumon is a long-acting blood thinner drug to be taken by mouth, and a coumarin derivative. It acts as a vitamin K antagonist and inhibits blood clotting (coagulation) by blocking synthesis of coagulation factors II, VII, IX and X. It is used for the prophylaxis and treatment of thromboembolic disorders such as heart attacks and pulmonary (lung) embolism. The most common adverse effect is bleeding. The drug interacts with a large number of other medications, including aspirin and St John's Wort. It is the standard coumarin used in Germany, Austria, and other European countries.
Dicoumarol (INN) or dicumarol (USAN) is a naturally occurring anticoagulant drug that depletes stores of vitamin K. It is also used in biochemical experiments as an inhibitor of reductases.
Brodifacoum is a highly lethal 4-hydroxycoumarin vitamin K antagonist anticoagulant poison. In recent years, it has become one of the world's most widely used pesticides. It is typically used as a rodenticide, but is also used to control larger pests such as possums.
Tioclomarol is an anticoagulant of the 4-hydroxycoumarin vitamin K antagonist type. It is a second generation drug, used as a rodenticide that is effective for the control of rodents that are resistant to this class of drugs.
Diphenadione is a vitamin K antagonist that has anticoagulant effects and is used as a rodenticide against rats, mice, voles, ground squirrels and other rodents. The chemical compound is an anti-coagulant with active half-life longer than warfarin and other synthetic 1,3-indandione anticoagulants.
Bromadiolone is a potent anticoagulant rodenticide. It is a second-generation 4-hydroxycoumarin derivative and vitamin K antagonist, often called a "super-warfarin" for its added potency and tendency to accumulate in the liver of the poisoned organism. When first introduced to the UK market in 1980, it was effective against rodent populations that had become resistant to first generation anticoagulants.
In enzymology, a vitamin-K-epoxide reductase (warfarin-sensitive) is an enzyme that catalyzes the chemical reaction
The human gene VKORC1 encodes for the enzyme, Vitamin K epOxide Reductase Complex (VKORC) subunit 1. This enzymatic protein complex is responsible for reducing vitamin K 2,3-epoxide to its active form, which is important for effective clotting (coagulation). In humans, mutations in this gene can be associated with deficiencies in vitamin-K-dependent clotting factors.
Vitamin K antagonists (VKA) are a group of substances that reduce blood clotting by reducing the action of vitamin K. The term "vitamin K antagonist" is technically a misnomer, as the drugs do not directly antagonize the action of vitamin K in the pharmacological sense, but rather the recycling of vitamin K. Vitamin K antagonists (VKAs) have been the mainstay of anticoagulation therapy for more than 50 years.
Chlorophacinone is a first-generation anticoagulant rodenticide. The mechanism of action results in internal bleeding due to non-functional clotting factors. It was used as a toxin to control rodent populations. It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.
4-Hydroxycoumarin is a coumarin derivative with a hydroxy group at the 4-position.
d-CON is a brand of rodent control products, which is distributed and owned in the United States by the UK-based consumer goods company Reckitt.
Four drugs from the class of direct Xa inhibitors are marketed worldwide. Rivaroxaban (Xarelto) was the first approved FXa inhibitor to become commercially available in Europe and Canada in 2008. The second one was apixaban (Eliquis), approved in Europe in 2011 and in the United States in 2012. The third one edoxaban was approved in Japan in 2011 and in Europe and the US in 2015. Betrixaban (Bevyxxa) was approved in the US in 2017.
Coumarin derivatives are derivatives of coumarin and are considered phenylpropanoids. Among the most important derivatives are the 4-hydroxycoumarins, which exhibit anticoagulant properties, a characteristic not present for coumarin itself.