Phytochemistry

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

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).

Phytochemicals

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.<ref name="Angio">Template:Cite encyclopedia</ref> Human settlements are often surrounded by weeds containing phytochemicals, such as nettle, dandelion and chickweed.<ref name="meskin-2002-p123">Template:Cite book</ref><ref>Template:Cite book</ref>

Many phytochemicals, including curcumin, epigallocatechin gallate, genistein, and resveratrol are pan-assay interference compounds and are not useful in drug discovery.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Alkaloids

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),<ref name="EMEA">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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).<ref name="Gremigni">Template:Cite journal</ref>

• Opium poppy.jpg

  The opium poppy Papaver somniferum is the source of the alkaloids morphine and codeine.

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• Koeh-018.jpg

  Deadly nightshade, Atropa belladonna, yields tropane alkaloids including atropine, scopolamine and hyoscyamine.<ref name="EMEA"/>

• DMT.svg

  N,N-Dimethyltryptamine (DMT) a powerful psychedelic compound which is present in several plant species found across the globe, commonly found in Mimosa and Acacia species but has also been discovered in grasses such as Philaris Aquatica.

Glycosides

Anthraquinone glycosides are found in senna,<ref name=Hietala>Template:Cite journal</ref> rhubarb, and Aloe.<ref>Template:Cite book</ref>

The cardiac glycosides are phytochemicals from plants including foxglove and lily of the valley. They include digoxin and digitoxin which act as diuretics.<ref name=USDAingredients>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

• Senna alexandrina Mill.-Cassia angustifolia L. (Senna Plant).jpg

  Senna alexandrina, containing anthraquinone glycosides, has been used as a laxative for millennia.<ref name=Hietala/>

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• Digoxin.svg

  Digoxin is used to treat atrial fibrillation, atrial flutter and sometimes heart failure.<ref name=USDAingredients/>

Polyphenols

Polyphenols of several classes are widespread in plants, including anthocyanins, phytoestrogens, and tannins.<ref name="lpi">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Polyphenols are secondary metabolites produced by almost every part of plants, including fruits, flowers, leaves and bark.<ref name=lpi/>

• Angelica sylvestris 3.jpg

  Angelica, containing phytoestrogens

• Phytoestrogens2.png

  Polyphenols include phytoestrogens (top and middle)

• Figure 1 Chemical structures of the three main types of anthocyanins.jpg

  Anthocyanins are a class of polyphenol that contributes to the color of many plants.

• Tannic acid.svg

  Tannic acids are one example of many complex polyphenolic structures produced by plants.

Terpenes

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.<ref name="tchen">Template:Cite journal</ref><ref name="Singsaas">Template:Cite journal</ref> Some have had medicinal uses: thymol is an antiseptic and was once used as a vermifuge (anti-worm medicine).<ref name=PubChemThymol/><ref name=":1">Template:Cite journal</ref>

• Thymian.jpg

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• Thymol2.svg

  Thymol is one of many terpenes found in plants.<ref name=PubChemThymol/>

• Isoprene Structural Formulae V.1.svg

  Terpenes are polymer of isoprene

Genetics

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.<ref name="Lacchini-Goossens-2020">Template:Cite journal</ref>

References

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