Alkaloids are a class of compounds that typically contain nitrogen and have complex, ring structures. They naturally occur in seed-bearing plants and are found in berries, bark, fruit, roots, and leaves. Often, they are bases that have some physiological effect.
Evidence suggests that alkaloids have been used by humanity for thousands of years. The first civilizations to use them were probably the ancient Sumarians and Egyptians. However, it was not until the early nineteenth century that these compounds were reproducibly isolated and analyzed. Advances in analytical separation techniques, such as chromatography and massspectroscopy, led to the elucidation of the chemical structure of alkaloids. The term for these compounds is thought to have originated from the fact that the alkaloid, morphine, had similar properties to basic salts derived from the alkali ashes of plants; thus, it was called a vegetable alkali or alkaloid. Since the first alkaloids were isolated, thousands more have been identified and classified.
Although numerous alkaloids exist, they have similar properties when separated. In general, they are colorless, crystalline solids that are basic, have a ring structure, and have definite melting points. They are also derived from plants and have a bitter taste. However, some exceptions are known. For instance, some alkaloids are not basic and others are brightly colored or liquid. Other alkaloids are produced synthetically. Most alkaloids are also chiral molecules, meaning they have nonsuperimposable mirror images. This results in isomers that have different chemical properties. For example, one isomer may have a physiological function while the other does not.
It is mostly unknown why plants produce alkaloids. Various theories have been proposed to explain their existence. Some suggest that alkaloids are byproducts of normal plant metabolism. It is also thought that alkaloids may provide a means of defense against insects and animals. Alkaloids may also be a reservoir for molecules that plants often use. It is likely that all of these theories are correct to some extent.
Many of the thousands of alkaloids can be classified in certain families.Nicotine is an alkaloid found in the tobacco plant. It is concentrated in this plant's leaves and is derived from pyridine molecules. In addition to being a component of cigars and cigarettes, it is a poison that is used as an insecticide.
The opium poppy contains a variety of alkaloids. Morphine, which gets its name from the Greek god of dreams Morpheus, is a powerful painkiller. It is often given to terminally ill patients. Codeine, similar in structure to morphine, is also obtained from the poppy. It functions much like morphine but is less potent. Heroin is a synthetic derivative of morphine that is highly addictive. The muscle relaxer papavarine is also derived from the opium poppy. The majority of opiates are produced in India.
Some alkaloids are based on chemical structures called indole rings.Strychnine is an example of this type of compound. It is a powerful central nervous system stimulant. Lysergic acid, which is produced by a fungus that grows on rye, is another example. A synthetic variation of this compound called lysergic acid diethylamide is a powerful hallucinogen called LSD. Another class of alkaloids are based on structures called piperidine rings. These include compounds such as cocaine and atropine. Cocaine is a powerful stimulant that can be addictive. Atropine is an important medicine that is used to dilate the pupils of the eye, or act as a smooth muscle relaxer. Other important alkaloids are caffeine, ricinine, and quinine.
To produce commercial quantities of alkaloids, manufacturers begin by drying large quantities of the plants in which they occur. Since most alkaloids are basic, they can then be separated from their biomass sources by extraction with a dilute mineral acid. Using high pressure liquid chromatography, the alkaloids can be purified and crystalized. In this way, large amounts of physiologically active compounds can be obtained.
The physiological effects of alkaloids have made them important compounds in medicine. They have been used as painkillers, stimulants, muscle relaxers, tranquilizers, and anesthetics. The four types of alkaloids that have the most important economic impact include opiates, cocaine, caffeine, and nicotine.
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