This article is largely based on an article in the out-of-copyright Encyclopædia Britannica Eleventh Edition, which was produced in 1911.(February 2023) |
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.
The name was originally given to plant products of this nature, in which the other part of the molecule was, in the greater number of cases, an aromatic aldehydic or phenolic compound (exceptions are Jinigrin and Jalapin or Scammonin). It has now been extended to include synthetic ethers, such as those obtained by acting on alcoholic glucose solutions with hydrochloric acid, and also the polysaccharoses, e.g. cane sugar, which appear to be ethers also. Although glucose is the most common sugar present in glucosides, many are known which yield rhamnose or iso-dulcite; these may be termed pentosides. Much attention has been given to the non-sugar parts (aglyca) of the molecules; the constitutions of many have been determined, and the compounds synthesized; and in some cases the preparation of the synthetic glucoside effected. [1]
The simplest glucosides are the alkyl ethers which have been obtained by reacting hydrochloric acid on alcoholic glucose solutions. A better method of preparation is to dissolve solid anhydrous glucose in methanol containing hydrochloric acid. A mixture of alpha- and beta-methylglucoside results. [1]
The classification of glucosides is a matter of some intricacy. One method based on the chemical constitution of the non-glucose part of the molecules has been proposed that posits four groups: (I) alkyl derivatives, (2) benzene derivatives, (3) styrolene derivatives, and (4) anthracene derivatives. A group may also be constructed to include the cyanogenic glucosides, i.e. those containing prussic acid. Alternate classifications follow a botanical classification, which has several advantages; in particular, plants of allied genera contain similar compounds. In this article the chemical classification will be followed, and only the more important compounds will be discussed herein. [1]
These are generally mustard oils, which are characterized by a burning taste; their principal occurrence is in mustard and Tropaeolum seeds. Sinigrin, or the potassium salt of inyronic acid not only occurs in mustard seed, [2] but also in black pepper and in horseradish root. Hydrolysis with barium hydroxide, or decomposition by the ferment myrosin, gives glucose, allyl mustard oil and potassium hydroxide. Sinalbin occurs in white pepper; it decomposes to the mustard oil, glucose and sinapin, a compound of choline and sinapic acid. Jalapin or Scammonin occurs in scammony; it hydrolyses to glucose and jalapinolic acid. [1]
These are generally oxy and oxyaldehydic compounds. [1]
The benzoyl derivative cellotropin has been used for tuberculosis. Populin, which occurs in the leaves and bark of Populus tremula, is benzoyl salicin. [1] Benzoyl-beta-D-glucoside is a compound found in the fern Pteris ensiformis .
There are a number of glucosides found in natural phenols and polyphenols, as, for example, in the flavonoids chemical family. Arbutin, which occurs in bearberry along with methyl arbutin, hydrolyses to hydroquinone and glucose. Pharmacologically it acts as a urinary antiseptic and diuretic; Salicin, also termed Saligenin and glucose occurs in the willow. The enzymes ptyalin and emulsin convert it into glucose and saligenin, ortho-oxybenzylalcohol. Oxidation gives the aldehyde helicin. [1]
This group contains a benzene and also an ethylene group, being derived from styrene. Coniferin (C16H22O8) occurs in the cambium of conifer wood. Emulsin converts it into glucose and coniferyl alcohol. Oxidation of coniferin gives glucovanillin, which yields upon treatment with emulsin glucose and vanillin. Syringin, which occurs in the bark of Syringa vulgaris , is a methoxyconiferin. Phloridzin occurs in the root-bark of various fruit trees; it hydrolyses to glucose and phloretin, which is the phloroglucin ester of paraoxyhydratropic acid. It is related to the pentosides naringin (C27H32O14), which hydrolyzes to rhamnose and naringenin, the phloroglucin ester of p-coumaric acid, and hesperidin, which hydrolyzes to rhamnose and hesperetin, the phloroglucin ester of isoferulic acid (C10H10O4). [3]
This section needs to be updated.(September 2018) |
These are generally substituted anthraquinones; many have medicinal applications, being used as purgatives, while one, ruberythric acid, yields the valuable dyestuff madder, the base of which is alizarin. Chrysophanic acid, a dioxymethylanthraquinone, occurs in rhubarb, which also contains emodin, a trioxymethylanthraquinone; this substance occurs in combination with rhamnose in Frangula bark. [6]
Arguably the most important cyanogenic glucoside is amygdalin, which occurs in bitter almonds. The enzyme maltase decomposes it into glucose and mandelic nitrile glucoside; the latter is broken down by emulsin into glucose, benzaldehyde and prussic acid. Emulsin also decomposes amygdalin directly into these compounds without the intermediate formation of mandelic nitrile glucoside. [6]
Several other glucosides of this nature have been isolated. The saponins are a group of substances characterized by forming a lather with water; they occur in soap-bark. Mention may also be made of indican, the glucoside of the indigo plant; this is hydrolysed by the indigo ferment, indimulsiri, to indoxyl and indiglucin. [6]
Amygdalin is a naturally occurring chemical compound found in many plants, most notably in the seeds (kernels) of apricots, bitter almonds, apples, peaches, cherries and plums, and in the roots of manioc.
Benzoic acid is a white solid organic compound with the formula C6H5COOH, whose structure consists of a benzene ring with a carboxyl substituent. The benzoyl group is often abbreviated "Bz", thus benzoic acid is also denoted as BzOH, since the benzoyl group has the formula –C6H5CO. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, which was for a long time its only source.
Hydrolysis is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
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.
Quercitron is a yellow natural dye obtained from the bark of the Eastern Black Oak, a forest tree indigenous in North America. It was formerly called Dutch pink, English pink, or Italian pink.
Mucic acid, C6H10O8 or HOOC-(CHOH)4-COOH (galactaric acid or meso-galactaric acid) is an aldaric acid obtained by nitric acid oxidation of galactose or galactose-containing compounds such as lactose, dulcite, quercite, and most varieties of gum.
Quercetin is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, seeds, and grains; capers, red onions, and kale are common foods containing appreciable amounts of it. It has a bitter flavor and is used as an ingredient in dietary supplements, beverages, and foods.
Phloroglucinol is an organic compound with the formula C6H3(OH)3. It is a colorless solid. It is used in the synthesis of pharmaceuticals and explosives. Phloroglucinol is one of three isomeric benzenetriols. The other two isomers are hydroxyquinol (1,2,4-benzenetriol) and pyrogallol (1,2,3-benzenetriol). Phloroglucinol, and its benzenetriol isomers, are still defined as "phenols" according to the IUPAC official nomenclature rules of chemical compounds. Many such monophenolics are often termed polyphenols.
Glucosinolates are natural components of many pungent plants such as mustard, cabbage, and horseradish. The pungency of those plants is due to mustard oils produced from glucosinolates when the plant material is chewed, cut, or otherwise damaged. These natural chemicals most likely contribute to plant defence against pests and diseases, and impart a characteristic bitter flavor property to cruciferous vegetables.
Sinigrin or allyl glucosinolate is a glucosinolate that belongs to the family of glucosides found in some plants of the family Brassicaceae such as Brussels sprouts, broccoli, and the seeds of black mustard. Whenever sinigrin-containing plant tissue is crushed or otherwise damaged, the enzyme myrosinase degrades sinigrin to a mustard oil, which is responsible for the pungent taste of mustard and horseradish. Seeds of white mustard, Sinapis alba, give a less pungent mustard because this species contains a different glucosinolate, sinalbin.
Mandelic acid is an aromatic alpha hydroxy acid with the molecular formula C6H5CH(OH)CO2H. It is a white crystalline solid that is soluble in water and polar organic solvents. It is a useful precursor to various drugs. The molecule is chiral. The racemic mixture is known as paramandelic acid.
β-arbutin, also known by its International Nomenclature of Cosmetic Ingredients (INCI) name, arbutin, is a glycosylated derivative of hydroquinone. β-Arbutin is naturally present in the leaves and bark of a variety of plants, notably the bearberry plant, Arctostaphylos uva-ursi. Utilized as a biosynthetic active ingredient in topical treatments for skin lightening, β-arbutin is aimed at addressing hyperpigmentation issues. Its mechanism of action involves inhibiting the activity of tyrosinase, an essential enzyme for melanin synthesis in the human skin, thereby leading to a reduction in hyperpigmentation. It is important to distinguish β-arbutin from its structurally similar stereoisomer, α-arbutin, which exhibits similar effects in clinical applications.
Salicin is an alcoholic β-glucoside. Salicin is produced in willow (Salix) bark. It is a biosynthetic precursor to salicylaldehyde.
Oleuropein is a glycosylated seco-iridoid, a type of phenolic bitter compound found in green olive skin, flesh, seeds, and leaves. The term oleuropein is derived from the botanical name of the olive tree, Olea europaea.
Phenolic compounds—natural phenol and polyphenols—occur naturally in wine. These include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. These compounds include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the color and mouthfeel of the wine. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
Genistin is an isoflavone found in a number of dietary plants like soy and kudzu. It was first isolated in 1931 from the 90% methanol extract of a soybean meal, when it was found that hydrolysis with hydrochloric acid produced 1 mole each of genistein and glucose. Chemically it is the 7-O-beta-D-glucoside form of genistein and is the predominant form of the isoflavone naturally occurring in plants. In fact, studies in the 1970s revealed that 99% of the isoflavonoid compounds in soy are present as their glucosides. The glucosides are converted by digestive enzymes in the digestive system to exert their biological effects. Genistin is also converted to a more familiar genistein, thus, the biological activities including antiatherosclerotic, estrogenic and anticancer effects are analogous.
Caftaric acid is a non-flavonoid phenolic compound.
Benzoyl-CoA is the thioester derived from benzoic acid and coenzyme A. The term benzoyl-CoA also include diverse conjugates of coenzyme A and aromatic carboxylic acids. Benzoate, vanillin, anthranilic acid, 4-ethylphenol, p-cresol, phenol, aniline, terephthalic acid, [3-hydroxybenzoic acid, and phenylalanine are all metabolized to benzoyl-CoA. Additionally, cinnamic acid, p-coumaric acid, ferulic acid, toluene, caffeic acid, benzyl alcohol, and mandelic acid are suspected to be processed similarly.
Echinacoside is a natural phenol. It is a caffeic acid glycoside from the phenylpropanoid class. It is constituted from a trisaccharide consisting of two glucose and one rhamnose moieties glycosidically linked to one caffeic acid and one dihydroxyphenylethanol (hydroxytyrosol) residue at the centrally situated rhamnose. This water-soluble glycoside is a distinctive secondary metabolite of Echinacea angustifolia and Echinacea pallida but only occurs in trace amounts in Echinacea purpurea. It is also isolated from Cistanche spp.
Glucotropaeolin or benzyl glucosinolate is a glucosinolate found in cruciferous vegetables, particularly garden cress. Upon enzymatic activity, it is transformed into benzyl isothiocyanate, which contributes to the characteristic flavor of these brassicas.