Alkaloid
Alkaloid
Alkaloids for pain and pleasure
Alkaloids are chemical compounds, found in plants, that can react with acids to form salts. All alkaloids contain the element nitrogen, usually in complex, multi-ring structures.
Role in the plant
Between 10 and 15% of all plants contain some type of alkaloid. It is unclear why alkaloids are so common, and it is a matter of controversy among scientists. Some believe that plants rid themselves of excess nitrogen through the production of alkaloids, just as humans and other mammals convert excess nitrogen into urea to be passed in the urine. Some modify this theory by suggesting that plants use alkaloids to temporarily store nitrogen for later use, instead of discarding this difficult-to-obtain element altogether.
Perhaps the most likely theory is that the presence of alkaloids discourages insects and animals from eating plants. The poisonous nature of most alkaloids supports this theory, although various alkaloids that are employed in small quantities for specific purposes can be useful to man.
Role in animals
Many alkaloids act by blocking or intensifying the actions of neurotransmitters, chemicals released by nerve cells in response to an electrical impulse called a neural signal. Neurotransmitters diffuse into neighboring cells where they produce an appropriate response, such as an electrical impulse in another nerve cell or contraction in a muscle cell.
Each nerve cell produces only one type of neuro-transmitter; acetylcholine and norepinephrine are the most common. Cells may respond to more than one type of neurotransmitter, however, and the response to each type may be different.
Medical use
A number of alkaloids are used as drugs. Among the oldest and best known of these is quinine, derived from the bark of the tropical Cinchona tree. Indians of South America have long used Cinchona bark to reduce fever, much as willow bark was used in Europe as a source of aspirin. In the 1600s Europeans discovered that the bark could treat malaria—a debilitating and often-fatal parasitic disease.
Quinine was purified as early as 1820, and soon it replaced crude cinchona bark as the standard treatment for malaria. Not until the 1930s was quinine replaced by synthetic analogues that offered fewer side effects and a more reliable supply. Quinine is still used as the principal flavoring agent in tonic water, although in a far less concentrated dose than originally used.
Cinchona bark also produces quinidine, which controls heart rhythm abnormalities such as fibrillation, a series of rapidly quivering beats that do not pump any blood, and heart block, a condition in which electrical currents fail to coordinate the contractions of the upper and lower chambers of the heart.
Vincaleukoblastine and vincristine, two alkaloids derived from the periwinkle plant (Catharanthus roseus ), are used to treat white blood cell cancers. Vincaleukoblastine is especially useful against lymphoma (cancer of the lymph glands), while vincristine is used against the most common form of childhood leukemia.
Atropine is an alkaloid produced by several plants, including the deadly nightshade (Atropa belladonna ), Jimson weed (Datura stramonium ), and henbane (Hyoscyamus niger ). It has a variety of medical uses, as it is able to relax smooth muscle by blocking the action of the neurotransmitter acetylcholine. Atropine is most commonly used to dilate the pupil during eye examinations. Atropine also relieves nasal congestion, serves as an antidote to nerve gas and insecticide poisoning, and is used to resuscitate patients in cardiac arrest.
Pilocarpine, derived from several Brazilian shrubs of the genus Pilocarpus, is another alkaloid used in ophthalmology. This drug stimulates the drainage of excess fluid from the eyeball, relieving the high optical pressure caused by glaucoma. If untreated, glaucoma can lead to blindness.
The introduction of reserpine in the 1950s revolutionized high blood pressure treatment and brought new hope to those suffering from this previously untreatable and life-threatening condition. Derived from tropical trees and shrubs of the genus Rauwolfia, reserpine works by depleting the body’s stores of the neurotransmitter norepinephrine. Among its other functions, norepinephrine contracts the arteries, thereby contributing to high blood pressure. Unfortunately, reserpine also causes drowsiness and sometimes severe depression. Medications without these side effects have been developed in recent decades, and reserpine is now rarely used.
Alkaloids for pain and pleasure
Many medically useful alkaloids act by way of the peripheral nervous system; others work directly on the brain. Prominent among the latter are the pain relievers morphine and codeine, derived from the opium poppy (Papaver somniferum ). Morphine is the stronger of the two, but codeine is often prescribed for moderate pain and is also an effective cough suppressant; for years it was a standard component of cough syrups. Now, however, it has been replaced for the most part by drugs that do not have the potential side effects of codeine.
Both morphine and codeine are addictive drugs that can produce a state of relaxed, dreamy euphoria— an exaggerated state of good feeling that drug addicts call a “high.” The equivalent street drug is heroin, derived from morphine by a simple chemical modification. Heroin addicts typically believe that their drug is stronger and produces a more pronounced “high” than morphine; however, since heroin is rapidly converted to morphine once it enters the body, most medical scientists consider the two drugs essentially equivalent.
The effects of cocaine are almost the opposite of those of morphine; cocaine’s legal classification as a narcotic—a drug that produces stupor—is misleading from a medical standpoint. This product of the coca plant, native to the Andes Mountains in South America, produces a state of euphoric hyperarousal. The user feels excited, elated, and intensely aware of his or her surroundings, with an impression of enhanced physical strength and mental ability. These feelings are accompanied by physical signs of arousal, including elevated heart rate and blood pressure. The increased heart rate caused by a high dose may lead to fibrillation and death.
A cocaine high, unlike those from most abused drugs, lasts less than half an hour—often much less. Once an individual becomes addicted, he or she needs large amounts of the expensive drug. Users’ enhanced aggressiveness and physical self-confidence further increase cocaine’s social dangers. Cocaine usage over time can result in paranoid schizophrenia, a type of mental disorder characterized by unfounded suspicion and fantasies of persecution. When this psychological condition is combined with continued cocaine use, the addict may become violent. Cocaine is also a local anesthetic and was used medically for that purpose in the early part of the century. Procaine and xylocaine, synthetic local anesthetics introduced during the mid-1900s, have replaced it.
Another addictive drug is nicotine, usually obtained by either smoking or chewing leaves of the tobacco plant, Nicotiana tabacum. Ground-up leaves, known as snuff, may be placed in the nose or cheek, allowing the nicotine to diffuse through the mucous membranes into the bloodstream.
With the possible exception of alcohol, nicotine is the world’s most widely used addictive drug. Its attractiveness undoubtedly results from the drug’s paradoxical combination of calming and stimulating properties—it can produce either relaxation or arousal, depending on the user’s state. Its physical effects, however, are primarily stimulatory. By increasing the heart rate and blood pressure while constricting the arteries—including those in the heart—nicotine significantly increases the risk of a heart attack.
Some alkaloid stimulants are not addictive, however. These include caffeine and the related compounds theophylline and theobromine. Caffeine is found in coffee, made from beans of Coffea arabica ; in tea, from leaves of Camellia sinensis ; in cocoa and chocolate, from seeds of Theobroma cacao ; and in cola drinks, which contain flavorings derived from nuts of Cola plants. In northern Argentina and southern Brazil, leaves of Ilex paraguariensis (a type of holly) are used to make mate´, a drink more popular there than either coffee or tea.
In addition to caffeine, tea also contains small amounts of theophylline, while theobromine is the major stimulant in cocoa. Large amounts of coffee, tea, cocoa, or cola drinks (more than 6-12 cups of coffee a day, for example), can produce nervousness, shakiness (muscle tremors), and insomnia, and may increase the risk of heart attack. Adverse effects from smaller amounts of these beverages have been claimed but never clearly demonstrated.
Black pepper falls into an entirely different category of the pain/pleasure grouping. This spice derives its burning flavor primarily from the alkaloids piper-ine, piperidine, and chavicine.
Addiction
Addiction was originally defined by the appearance of physical symptoms—such as sweating, sniffling, and trembling—when a drug was withdrawn from an addicted person or animal. It was also thought that addiction is accompanied by adaptation, in which more and more of the drug is required to produce the same effect.
So long as the focus was on opium-derived drugs such as morphine and heroin, this definition was appropriate. Beginning in the 1960s, however, scientists realized that it did not define the properties that render cocaine and other drugs so dangerous. Cocaine does not produce adaptation, and its withdrawal does not result in physical symptoms that can be seen in laboratory animals. Cocaine withdrawal does, however, produce an intense depression that disappears when the drug is again available. Similarly, nicotine withdrawal produces psychological symptoms such as restlessness, anxiety, irritability, difficulty in concentrating, and a craving for the drug. Today these psychological withdrawal symptoms are recognized as valid indicators of addiction.
Poisonous alkaloids
Nearly all of the alkaloids mentioned so far are poisonous in large amounts. Some alkaloids, however, are almost solely known as poisons. One of these is strychnine, derived from the small Hawaiian tree Strychnos nux-vomica. Symptoms of strychnine poisoning begin with feelings of restlessness and anxiety, proceeding to muscle twitching and exaggerated reflexes. In severe poisoning, even a loud sound can cause severe muscle spasms throughout the entire body. These spasms may make breathing impossible and result in death.
In the early part of the twentieth century, strychnine was widely used as a rat poison. In recent decades, however, slower-acting poisons have been used for rodent control; since rats can remember which foods have made them sick, one that receives a nonfatal dose of a fast-acting poison such as strychnine will never again take that type of poisonous bait.
A number of other plants also derive their lethal properties from alkaloids of one type or another. Among these are the poison hemlock (Conium maculatum ) and plants of the genus Aconitum, commonly called monkshood—known by devotees of werewolf stories as wolfsbane. Other examples include shrubs of the genus Calycanthus, known as Carolina allspice, spicebush, and sweet betty, among other names; vines of the genus Solandra, such as the chalice vine, cup-of-gold, silver cup, and trumpet plant; trees or shrubs of the genus Taxus, such as yews; plants of the lily-like genus Veratrum, including false hellebore; and the golden chain or bean tree (Laburnum anagyroides ).
Although vines and nonwoody plants of the genus Solanum pose a real danger only to children, they represent an extremely varied group. Poisonous members of this genus range from the common potato to the nightshade (not the same as the deadly nightshade that produces atropine). The group also includes the Jerusalem cherry, the false Jerusalem cherry, the love apple, the Carolina horse nettle, the bittersweet, the nipplefruit, the star-potato vine, and the apple of Sodom.
Poisoning by ordinary potatoes usually results from eating uncooked sprouts or sun-greened skin. These parts should be cut away and discarded. For other plants in the group, it is the immature fruit that is most likely to be poisonous. In contrast to the nervous-system effects of most alkaloids, the alkaloids found in the genus Solanum produce mainly fever and diarrhea.
See also Antipsychotic drugs; Nux vomica tree; Poisons and toxins.
Resources
BOOKS
Lampe, Kenneth F., and Mary Ann McCann. AMA Handbook of Poisonous & Injurious Plants. Chicago: Chicago Review Press, 1985.
Pelletier, S. W. Alkaloids: Chemical and Biological Perspectives. New York: John Wiley & Sons, 1983.
OTHER
“Alkaloids” Virginia Commonwealth University <http://www.people.vcu.edu/~asneden/alkaloids.htm> (accessed October 13, 2006).
W. A. Thomasson
Alkaloid
Alkaloid
Alkaloids are chemical compounds found in plants that can react with acids to form salts. All alkaloids contain the element nitrogen , usually in complex, multi-ring structures.
Role in the plant
Between 10% and 15% of all plants contain some type of alkaloid. It is unclear why alkaloids are so common, and it is a matter of controversy among scientists. Some believe that plants rid themselves of excess nitrogen through the production of alkaloids just as humans and other mammals convert excess nitrogen into urea to be passed in the urine. Some modify this theory by suggesting that plants use alkaloids to temporarily store nitrogen for later use, instead of discarding altogether this difficult-to-obtain element.
Perhaps the most likely theory is that the presence of alkaloids discourages insects and animals from eating plants. The poisonous nature of most alkaloids supports this theory, although various alkaloids that are employed in small quantities for specific purposes can be useful to man.
Role in animals
Many alkaloids act by blocking or intensifying the actions of neurotransmitters, chemicals released by nerve cells in response to an electrical impulse called a neural signal. Neurotransmitters diffuse into neighboring cells where they produce an appropriate response, such as an electrical impulse, in another nerve cell or contraction in a muscle cell.
Each nerve cell produces only one type of neurotransmitter ; acetylcholine and norepinephrine are the most common. Cells may respond to more than one type of neurotransmitter, however, and the response to each type may be different.
Medical use
A number of alkaloids are used as drugs. Among the oldest and best known of these is quinine , derived from the bark of the tropical cinchona tree . Indians of South America have long used cinchona bark to reduce fever, much as willow bark was used in Europe as a source of aspirin. In the 1600s Europeans discovered that the bark could actually cure malaria—one of the most debilitating and fatal diseases of tropical and subtropical regions.
Quinine was purified as early as 1823, and soon it replaced crude cinchona bark as the standard treatment for malaria . Not until the 1930s was quinine replaced by synthetic analogues that offered fewer side effects and a more reliable supply. Quinine is still used as the principal flavoring agent in tonic water—a beverage named for its ability to prevent malarial symptoms.
Cinchona bark also produces quinidine. It is used primarily to control abnormalities of heart rhythm such as fibrillation, a series of rapidly quivering beats that do not pump any blood , and heart block, a condition in which electrical currents fail to coordinate the contractions of the upper and lower chambers of the heart.
Vincaleukoblastine and vincristine, two alkaloids derived from the periwinkle plant (Catharanthus roseus), are used effectively for the treatment of white-blood-cell cancers. Vincaleukoblastine is especially useful against lymphoma (cancer of the lymph glands ), while vincristine is used against the most common form of childhood leukemia .
Atropine is an alkaloid produced by several plants, including deadly nightshade (Atropa belladonna), Jimson weed (Datura stramonium), and henbane (Hyoscyamus niger). It has a variety of medical uses, as it is able to relax smooth muscle by blocking action of the neurotransmitter acetylcholine. Atropine is most commonly used to dilate the pupil during eye examinations. Atropine also relieves nasal congestion and serves as an antidote to nerve gas and insecticide poisoning.
Pilocarpine, derived from several Brazilian shrubs of the genus Pilocarpus, is another alkaloid used in ophthalmology, the medical specialty that treats the eye. This drug stimulates the drainage of excess fluid from the eyeball, relieving the high pressure in the eye caused by glaucoma. If untreated, glaucoma can lead to blindness.
Introduction of reserpine in the 1950s revolutionized high blood pressure treatment and brought new hope to those suffering from this previously untreatable and life-threatening condition. Derived from tropical trees and shrubs of the genus Aauwolfia, reserpine works by depleting the body's stores of the neurotransmitter norepinephrine. Among its other functions, norepinephrine contracts the arteries and thereby contributes to high blood pressure.
Unfortunately, reserpine also causes drowsiness and sometimes severe depression . Medications without these side effects have been developed in recent decades, and reserpine is rarely used.
Alkaloids for pain and pleasure
Many medically useful alkaloids act by way of the peripheral nervous system ; others work directly on the brain . Prominent among the latter are the pain relievers morphine and codeine , derived from the opium poppy (Papaver somniferum). Morphine is the stronger of the two, but codeine is often prescribed for moderate pain. Codeine is also an effective cough suppressant; for years it was a standard component of cough syrups. Now, however, it has been replaced for the most part by drugs that do not have the psychological side effects of codeine.
Both morphine and codeine are addictive drugs that produce a state of relaxed, dreamy euphoria—an exaggerated state of "feeling good," referred to by drug addicts as a "high." The equivalent street drug is heroin, derived from morphine by a simple chemical modification. Heroin addicts typically believe that their drug is stronger and produces a more pronounced "high" than morphine; however, since heroin is rapidly converted to morphine once it enters the body, most medical scientists consider the two drugs completely equivalent.
The effects of cocaine are almost the opposite of those of morphine; cocaine's legal classification as a narcotic—a drug that produces stupor—is misleading from a medical standpoint. This product of the coca plant, native to the Andes Mountains in South America, produces a state of euphoric hyperarousal. The user feels excited, elated, and intensely aware of his or her surroundings, with an impression of enhanced physical strength and mental ability. These feelings are accompanied by the physical signs of arousal: elevated heart rate and blood pressure. The increased heart rate caused by a high dose may lead to fibrillation and death.
A cocaine "high," unlike the "highs" from most abused drugs, lasts less than half an hour—often much less. Once an individual becomes addicted, he or she needs large amounts of the expensive drug. Users' enhanced aggressiveness and physical self-confidence further increase cocaine's social dangers. Cocaine usage over time can result in paranoid schizophrenia , a type of insanity characterized by unfounded suspicion and fantasies of persecution; when this psychological condition is combined with continued cocaine use, the addict may perform violent acts against the supposed plotters.
Cocaine is also a local anesthetic, and was used medically for that purpose in the early part of the century. Procaine and xylocaine, synthetic local anesthetics introduced during the mid-1900s, have replaced cocaine as a medical drug.
Another pleasurable yet addictive drug is nicotine , usually obtained by either smoking or chewing leaves of the tobacco plant, Nicotiana tabacum. Ground-up leaves, known as snuff, may be placed in the nose or cheek, allowing the nicotine to diffuse through the linings of the cavities into the bloodstream.
With the possible exception of alcohol , nicotine is the world's most widely used addictive drug. Its attractiveness undoubtedly results from the drug's paradoxical combination of calming and stimulating properties—it can produce either relaxation or arousal, depending on the user's state. Its physical effects, however, are primarily stimulatory. By increasing the heart rate and blood pressure while constricting the arteries—including those in the heart—nicotine significantly increases the risk of a heart attack.
Some alkaloid stimulants are not addictive, however. These include caffeine and the related compounds theophylline and theobromine. Caffeine is found in coffee, made from beans of Coffea arabica; in tea, from leaves of Camellia sinensis; in cocoa and chocolate, from seeds of Theobroma cacao; and in cola drinks, which contain flavorings derived from nuts of Cola plants. In northern Argentina and southern Brazil, leaves of Ilex paraguariensis (a type of holly) are used to make maté, a drink more popular there than either coffee or tea.
In addition to caffeine, tea also contains small amounts of theophylline, while theobromine is the major stimulant in cocoa. Large amounts of coffee, tea, cocoa, or cola drinks (more than 6-12 cups of coffee a day, for example), can produce nervousness, shakiness (muscle tremors), and insomnia , and may increase the risk of heart attack. Adverse effects from smaller amounts of these beverages have been claimed but never clearly demonstrated.
Black pepper falls into an entirely different category of the pain/pleasure grouping. This spice derives its burning flavor primarily from the alkaloids piperine, piperidine, and chavicine.
Addiction
Addiction was originally defined by the appearance of physical symptoms—such as sweating, sniffling, and trembling—when a drug was withdrawn from an addicted person or animal . It was also thought that addiction was accompanied by adaptation , in which more and more of the drug is required to produce the same effect.
So long as the focus was on opium-derived drugs such as morphine and heroin, this definition was appropriate. Beginning in the 1960s, however, scientists realized that it did not define the properties that render cocaine and other drugs so dangerous. Cocaine does not produce adaptation, and its withdrawal does not result in physical symptoms that can be seen in laboratory animals. Cocaine withdrawal does, however, produce an intense depression that disappears when the drug is again available. Similarly, nicotine withdrawal produces psychological symptoms such as restlessness, anxiety , irritability, difficulty in concentrating, and a craving for the drug. Today these psychological withdrawal symptoms are recognized as valid indicators of addiction.
Poisonous alkaloids
Nearly all of the alkaloids mentioned so far are poisonous in large amounts. Some alkaloids, however, are almost solely known as poisons. One of these is strychnine, derived from the small Hawaiian tree Strychnos nux-vomica. Symptoms of strychnine poisoning begin with feelings of restlessness and anxiety, proceeding to muscle twitching and exaggerated reflexes. In severe poisoning, a loud sound can cause severe muscle spasms throughout the entire body. These spasms may make breathing impossible and result in death.
In the early part of the twentieth century, strychnine was widely used as a rat poison. In recent decades, however, slower-acting poisons have been used for rodent control; since rats can remember which foods have made them sick, one that receives a non-fatal dose of a fast-acting poison such as strychnine will never again take that type of poisonous bait.
A number of other plants also derive their lethal properties from alkaloids of one type or another. Among these are poison hemlock (Conium maculatum) and plants of the genus Aconitum, commonly called monkshood—known by devotees of werewolf stories as wolfsbane. Other examples include shrubs of the genus Calycanthus, known as Carolina allspice, spicebush, and sweet betty, among other names; vines of the genus Solandra, such as the chalice vine, cup-of-gold, silver cup, and trumpet plant; trees or shrubs of the genus Taxus, such as yews; plants of the lily-like genus Veratrum, including false hellebore; and the golden chain or bean tree (Laburnum anagyroides).
Although vines and non-woody plants of the genus Solanum pose a real danger only to children, they represent an extremely varied group. Poisonous members of this genus range from the common potato to the nightshade (not the same as the deadly nightshade that produces atropine). The group also includes the Jerusalem cherry, the false Jerusalem cherry, the love apple, the Carolina horse nettle, the bittersweet, the nipplefruit, the star-potato vine, and the apple of Sodom.
Poisoning by ordinary potatoes usually results from eating uncooked sprouts or sun-greened skin. These parts should be cut away and discarded. For other plants in the group, it is the immature fruit that is most likely to be poisonous. In contrast to the nervous-system effects of most alkaloids, the alkaloids found in the genus Solanum produce mainly fever and diarrhea.
See also Antipsychotic drugs; Nux vomica tree; Poisons and toxins.
Resources
books
Lampe, Kenneth F., and Mary Ann McCann. AMA Handbook of Poisonous & Injurious Plants. Chicago: Chicago Review Press, 1985.
Pelletier, S. W. Alkaloids: Chemical and Biological Perspectives. New York: John Wiley & Sons, 1983.
W. A. Thomasson
Alkaloids
Alkaloids
Alkaloids are natural, organic substances that are predominantly found in plants and normally contain at least one nitrogen atom in their chemical structure. Their basic (alkaline) nature has led to the term alkaloids. Since the identification of the first alkaloid, morphine, from the opium poppy (Papaver somniferum ) in 1806, more than ten thousand alkaloids have been isolated from plants. Alkaloids are the active components of numerous medicinal plants or plant-derived drugs and poisons, and their structural diversity and different physiological activities are unmatched by any other group of natural products.
Although alkaloids have been detected in some animals (e.g., in the toxic secretions of fire ants, ladybugs, and toads), their major occurrence is in the flowering plants. Alkaloids are relatively stable compounds that accumulate as end products of different biosynthetic pathways, mostly starting from common amino acids such as lysine, ornithine, tyrosine, tryptophan, and others. Their classification is usually based on the formed heterocyclic ring system (e.g., piperidine in coniine, pyridine in nicotine, and quinoline in quinine). Some structures are relatively simple, whereas others are quite complex.
Alkaloids can occur in all parts of the plant but frequently, depending on the plant species, they accumulate only in particular organs (e.g., in barks, roots, leaves, and fruits), whereas at the same time other organs are alkaloid-free. In potato plants, the edible tubers are devoid of alkaloids, whereas the green parts contain the poisonous solanine. The organ in which alkaloids accumulate is not always the site of their synthesis. In tobacco, nicotine is produced in the roots and translocated to the leaves where it accumulates.
The functions of alkaloids in plants are mostly unknown, and their importance in plant metabolism has been much debated. A single plant species may contain over one hundred different alkaloids, and the concentration can vary from a small fraction to as much as 10 percent of the dry weight. Breeding for plants devoid of alkaloids has also demonstrated that alkaloids are apparently not vital. Why does a plant invest so much nitrogen and energy in synthesizing such a large number and quantity of compounds? Most alkaloids are very toxic and, therefore, have the potential to function in the chemical defense arsenal of plants against attack by herbivores and micro-organisms. For example, the nicotine present in tobacco leaves inhibits the growth of tobacco hornworm larvae; the purified compound is also applied as an effective insecticide in greenhouses. In addition, alkaloids have been suggested to serve as a storage form of nitrogen or as protectants against damage by ultraviolet light.
Alkaloids have traditionally been of great interest to humans because of their pronounced physiological and medicinal properties. From the beginning of civilization, alkaloid-containing plant extracts have been used in all cultures as potions, medicines, and poisons. Greek philosopher Socrates died in 399 B.C.E. by consumption of coniine-containing hemlock (Conium maculatum ), and Egyptian queen Cleopatra (69-30 B.C.E.) used atropine-containing plant extracts (such as belladonna ) to dilate her pupils. In modern times, the stimulants caffeine in coffee, tea, and cacao and nicotine in cigarettes are consumed worldwide. Alkaloids with hallucinogenic , narcotic, or analgesic properties have found medical application as pure compounds (e.g., morphine, atropine, and quinine) or served as model compounds for modern synthetic drugs, while several are abused as illegal drugs (e.g., cocaine). Other alkaloids are too toxic for any therapeutic use (e.g., coniine and strychnine), but plant constituents are still screened for new, biologically active compounds. An example is the discovery of taxol, which has cytostatic properties and is applied as an anticancer drug.
see also Cacao; Coca; Coffee; Defenses, Chemical; Medicinal Plants; Opium Poppy; Poisonous Plants; Potato; Tobacco.
Erich Kombrink
Bibliography
Harborne, Jeffrey B., and Herbert Baxter, eds. Phytochemical Dictionary: A Handbook of Bioactive Compounds from Plants. Bristol: Taylor & Francis, 1995.
Kutchan, Toni M. "Alkaloid Biosynthesis: The Basis for Metabolic Engineering of Medicinal Plants." Plant Cell 7 (1995): 1095-1070.
Mann, John, R. Stephen Davidson, John B. Hobbs, Derek V. Banthrope, and Jeffrey B. Harborne. Natural Products: Their Chemistry and Biological Significance. Essex: Longman Group, 1994.
Wink, Michael, ed. Biochemistry of Plant Secondary Metabolism. Sheffield, UK, and Boca Raton, FL: Sheffield Academic Press and CRC Press, 1999.
Alkaloids
ALKALOIDS
This is the general term for any number of complex organic bases that are found in nature in seed-bearing plants. These substances are usually colorless but bitter to the taste. Alkaloids often contain nitrogen and oxygen and possess important physiological properties.
Examples of alkaloids include not only quinine, atropine, and strychnine but also Caffeine, Nicotine, Morphine, Codeine, and Cocaine. Therefore, many drugs that are used by humans for both medical and nonmedical purposes are produced in nature in the form of alkaloids. Naturally occurring receptors for many alkaloids have also been identified in humans and other animals, suggesting an evolutionary role for the alkaloids in physiological processes.
Nick E. Goeders
alkaloids
alkaloid
alkaloid
alkaloid
al·ka·loid / ˈalkəˌloid/ • n. Chem. any of a class of nitrogenous organic compounds of plant origin that have pronounced physiological actions on humans. They include many drugs (morphine, quinine) and poisons (atropine, strychnine).