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Phytochemistry is the study of phytochemicals, which are chemicals derived from plants. Phytochemists strive to describe the structures of the large number of secondary metabolites found in plants, the functions of these compounds in human and plant biology, and the biosynthesis of these compounds. Plants synthesize phytochemicals for many reasons, including to protect themselves against insect attacks and plant diseases. The compounds found in plants are of many kinds, but most can be grouped into four major biosynthetic classes: alkaloids, phenylpropanoids, polyketides, and terpenoids.
Phytochemistry can be considered a subfield of botany or chemistry. Activities can be led in botanical gardens or in the wild with the aid of ethnobotany. Phytochemical studies directed toward human (i.e. drug discovery) use may fall under the discipline of pharmacognosy, whereas phytochemical studies focused on the ecological functions and evolution of phytochemicals likely fall under the discipline of chemical ecology. Phytochemistry also has relevance to the field of plant physiology.
Techniques commonly used in the field of phytochemistry are extraction, isolation, and structural elucidation (MS,1D and 2D NMR) of natural products, as well as various chromatography techniques (MPLC, HPLC, and LC-MS).
Many plants produce chemical compounds for defence against herbivores. The major classes of pharmacologically active phytochemicals are described below, with examples of medicinal plants that contain them. [1] Human settlements are often surrounded by weeds containing phytochemicals, such as nettle, dandelion and chickweed. [2] [3]
Many phytochemicals, including curcumin, epigallocatechin gallate, genistein, and resveratrol are pan-assay interference compounds and are not useful in drug discovery. [4] [5]
Alkaloids are bitter-tasting chemicals, widespread in nature, and often toxic. There are several classes with different modes of action as drugs, both recreational and pharmaceutical. Medicines of different classes include atropine, scopolamine, and hyoscyamine (all from nightshade), [6] the traditional medicine berberine (from plants such as Berberis and Mahonia ), caffeine ( Coffea ), cocaine ( Coca ), ephedrine ( Ephedra ), morphine (opium poppy), nicotine (tobacco), reserpine ( Rauvolfia serpentina ), quinidine and quinine ( Cinchona ), vincamine ( Vinca minor ), and vincristine ( Catharanthus roseus ). [7]
Anthraquinone glycosides are found in senna, [9] rhubarb, and Aloe . [10]
The cardiac glycosides are phytochemicals from plants including foxglove and lily of the valley. They include digoxin and digitoxin which act as diuretics. [11]
Polyphenols of several classes are widespread in plants, including anthocyanins, phytoestrogens, and tannins. [13] Polyphenols are secondary metabolites produced by almost every part of plants, including fruits, flowers, leaves and bark. [13]
Terpenes and terpenoids of many kinds are found in resinous plants such as the conifers. They are aromatic and serve to repel herbivores. Their scent makes them useful in essential oils, whether for perfumes such as rose and lavender, or for aromatherapy. [14] [15] Some have had medicinal uses: thymol is an antiseptic and was once used as a vermifuge (anti-worm medicine). [16] [17]
Contrary to bacteria and fungi, most plant metabolic pathways are not grouped into biosynthetic gene clusters, but instead are scattered as individual genes. Some exceptions have been discovered: steroidal glycoalkaloids in Solanum , polyketides in Pooideae, benzoxazinoids in Zea mays , triterpenes in Avena sativa , Cucurbitaceae, Arabidopsis , and momilactone diterpenes in Oryza sativa . [18]
Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar structure may also be termed alkaloids. In addition to carbon, hydrogen and nitrogen, alkaloids may also contain oxygen or sulfur. Rarer still, they may contain elements such as phosphorus, chlorine, and bromine.
Cardiac glycosides are a class of organic compounds that increase the output force of the heart and decrease its rate of contractions by inhibiting the cellular sodium-potassium ATPase pump. Their beneficial medical uses include treatments for congestive heart failure and cardiac arrhythmias; however, their relative toxicity prevents them from being widely used. Most commonly found as secondary metabolites in several plants such as foxglove plants and milkweed plants, these compounds nevertheless have a diverse range of biochemical effects regarding cardiac cell function and have also been suggested for use in cancer treatment.
Digitalis is a genus of about 20 species of herbaceous perennial plants, shrubs, and biennials, commonly called foxgloves.
The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes", terpenoids contain additional functional groups, usually containing oxygen. When combined with the hydrocarbon terpenes, terpenoids comprise about 80,000 compounds. They are the largest class of plant secondary metabolites, representing about 60% of known natural products. Many terpenoids have substantial pharmacological bioactivity and are therefore of interest to medicinal chemists.
Secondary metabolites, also called specialised metabolites, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, archaea, fungi, animals, or plants, which are not directly involved in the normal growth, development, or reproduction of the organism. Instead, they generally mediate ecological interactions, which may produce a selective advantage for the organism by increasing its survivability or fecundity. Specific secondary metabolites are often restricted to a narrow set of species within a phylogenetic group. Secondary metabolites often play an important role in plant defense against herbivory and other interspecies defenses. Humans use secondary metabolites as medicines, flavourings, pigments, and recreational drugs.
A glucoside is a glycoside that is chemically derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes.
Phytochemicals are chemical compounds produced by plants, generally to help them resist fungi, bacteria and plant virus infections, and also consumption by insects and other animals. The name comes from Greek φυτόν (phyton) 'plant'. Some phytochemicals have been used as poisons and others as traditional medicine.
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme hydrolysis, which causes the sugar part to be broken off, making the chemical available for use. Many such plant glycosides are used as medications. Several species of Heliconius butterfly are capable of incorporating these plant compounds as a form of chemical defense against predators. In animals and humans, poisons are often bound to sugar molecules as part of their elimination from the body.
Saponins are bitter-tasting usually toxic plant-derived secondary metabolites, being organic chemicals, that have a foamy quality when agitated in water and a high molecular weight. They are present in a wide range of plant species throughout the bark, leaves, stems, roots and flowers but found particularly in soapwort, a flowering plant, the soapbark tree, common corn-cockle, baby's breath and soybeans. They are used in soaps, medicines, fire extinguishers, as dietary supplements, for synthesis of steroids, and in carbonated beverages. Saponins are both water and fat soluble, which gives them their useful soap properties. Some examples of these chemicals are glycyrrhizin and quillaia, a bark extract used in beverages.
Pharmacognosy is the study of crude drugs obtained from medicinal plants, animals, fungi, and other natural sources. The American Society of Pharmacognosy defines pharmacognosy as "the study of the physical, chemical, biochemical, and biological properties of drugs, drug substances, or potential drugs or drug substances of natural origin as well as the search for new drugs from natural sources".
Medicinal plants, also called medicinal herbs, have been discovered and used in traditional medicine practices since prehistoric times. Plants synthesize hundreds of chemical compounds for various functions, including defense and protection against insects, fungi, diseases, and herbivorous mammals.
Isoflavones are substituted derivatives of isoflavone, a type of naturally occurring isoflavonoids, many of which act as phytoestrogens in mammals. Isoflavones occur in many plant species, but are especially high in soybeans.
Oil of clove, also known as clove oil or eugenol, is an essential oil extracted from the clove plant, Syzygium aromaticum. Clove oil is commonly used in aromatherapy and for flavoring food, tea, and toothpaste. In alternative medicine, it may be used as a topical medication to relieve toothache. There is insufficient medical evidence to support its use as an analgesic for treating pain.
Iridoids are a type of monoterpenoids in the general form of cyclopentanopyran, found in a wide variety of plants and some animals. They are biosynthetically derived from 8-oxogeranial. Iridoids are typically found in plants as glycosides, most often bound to glucose.
Senna glycoside, also known as sennoside or senna, is a medication used to treat constipation and empty the large intestine before surgery. The medication is taken by mouth or via the rectum. It typically begins working in around 30 minutes when given by rectum and within twelve hours when given by mouth. It is a weaker laxative than bisacodyl and castor oil.
Tropane alkaloids are a class of bicyclic [3.2.1] alkaloids and secondary metabolites that contain a tropane ring in their chemical structure. Tropane alkaloids occur naturally in many members of the plant family Solanaceae. Certain tropane alkaloids such as cocaine and scopolamine are notorious for their psychoactive effects, related usage and cultural associations. Particular tropane alkaloids such as these have pharmacological properties and can act as anticholinergics or stimulants.
Secondary metabolism produces a large number of specialized compounds that do not aid in the growth and development of plants but are required for the plant to survive in its environment. Secondary metabolism is connected to primary metabolism by using building blocks and biosynthetic enzymes derived from primary metabolism. Primary metabolism governs all basic physiological processes that allow a plant to grow and set seeds, by translating the genetic code into proteins, carbohydrates, and amino acids. Specialized compounds from secondary metabolism are essential for communicating with other organisms in mutualistic or antagonistic interactions. They further assist in coping with abiotic stress such as increased UV-radiation. The broad functional spectrum of specialized metabolism is still not fully understood. In any case, a good balance between products of primary and secondary metabolism is best for a plant’s optimal growth and development as well as for its effective coping with often changing environmental conditions. Well known specialized compounds include alkaloids, polyphenols including flavonoids, and terpenoids. Humans use many of these compounds for culinary, medicinal and nutraceutical purposes.
Littorine is a tropane alkaloid found in a variety of plants including Datura and Atropa belladonna. It is closely related in chemical structure to atropine, hyoscyamine, and scopolamine, which all share a common biosynthetic pathway.
Psychoactive plants are plants, or preparations thereof, that upon ingestion induce psychotropic effects. As stated in a reference work:
Psychoactive plants are plants that people ingest in the form of simple or complex preparations in order to affect the mind or alter the state of consciousness.
Cannabicitran (CBTC) is a phytocannabinoid first isolated in 1974 as a trace component of Cannabis sativa. Structurally related compounds can be found in some other plants. It is not psychoactive, but was found to reduce intraocular pressure in tests on rabbits, which may reflect agonist activity at the NAGly receptor that is known to be a target of many structurally related cannabinoids.
The man credited with the introduction of digitalis into the practice of medicine was William Withering.
THYMOL is a phenol obtained from thyme oil or other volatile oils used as a stabilizer in pharmaceutical preparations, and as an antiseptic (antibacterial or antifungal) agent. It was formerly used as a vermifuge.