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Aglucoside is aglycoside that is chemically derived fromglucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside ishydrolysed by purely chemical means, or decomposed byfermentation orenzymes.
The name was originally given to plant products of this nature, in which the other part of themolecule was, in the greater number of cases, an aromatic aldehydic orphenolic compound (exceptions areJinigrin andJalapin orScammonin). It has now been extended to include syntheticethers, such as those obtained by acting onalcoholic glucose solutions withhydrochloric 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 yieldrhamnose or iso-dulcite; these may be termed pentosides. Much attention has been given to the non-sugar parts (aglycone) 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 reactinghydrochloric acid on alcoholic glucose solutions. A better method of preparation is to dissolve solid anhydrous glucose inmethanol 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: (1)alkyl derivatives, (2)benzene derivatives, (3) styrolene derivatives, and (4)anthracene derivatives. A group may also be constructed to include thecyanogenic glucosides, i.e. those containingprussic acid. Alternate classifications follow a botanical classification, which has several advantages; in particular, plants of alliedgenera contain similar compounds. This article follows the chemical classification and discusses only the more important compounds.[1]
These are generally mustard oils, which are characterized by a burning taste; their principal occurrence is inmustard andTropaeolum seeds.Sinigrin, or thepotassiumsalt ofinyronic acid not only occurs in mustard seed,[2] but also inblack pepper and inhorseradish root. Hydrolysis withbarium hydroxide, or decomposition by the fermentmyrosin, gives glucose, allyl mustard oil andpotassium hydroxide.Sinalbin occurs in white pepper; it decomposes to the mustard oil, glucose andsinapin, a compound ofcholine andsinapic acid.Jalapin orScammonin occurs inscammony; it hydrolyses to glucose andjalapinolic acid.[1]
These are generally oxy and oxyaldehydic compounds.[1]
The benzoyl derivativecellotropin has been used fortuberculosis.Populin, which occurs in the leaves and bark ofPopulus tremula, is benzoyl salicin.[1]Benzoyl-beta-D-glucoside is a compound found in the fernPteris ensiformis.
There are a number of glucosides found innatural phenols andpolyphenols, as, for example, in theflavonoids chemical family.Arbutin, which occurs inbearberry along withmethyl arbutin, hydrolyses tohydroquinone andglucose. Pharmacologically it acts as a urinaryantiseptic anddiuretic;Salicin, also termedSaligenin and glucose occurs in thewillow. The enzymesptyalin andemulsin convert it into glucose and saligenin, ortho-oxybenzylalcohol. Oxidation gives the aldehydehelicin.[1]
This group contains a benzene and also anethylene group, being derived fromstyrene.Coniferin (C16H22O8) occurs in thecambium ofconifer wood.Emulsin converts it into glucose andconiferyl alcohol.Oxidation of coniferin givesglucovanillin, which yields upon treatment with emulsin glucose andvanillin.Syringin, which occurs in the bark ofSyringa vulgaris, is amethoxyconiferin.Phloridzin occurs in the root-bark of variousfruit trees; it hydrolyses to glucose and phloretin, which is the phloroglucinester ofparaoxyhydratropic acid. It is related to thepentosidesnaringin (C27H32O14), which hydrolyzes torhamnose andnaringenin, thephloroglucin ester ofp-coumaric acid, andhesperidin, which hydrolyzes to rhamnose andhesperetin, the phloroglucin ester ofisoferulic acid (C10H10O4).[3]
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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 containsemodin, atrioxymethylanthraquinone; this substance occurs in combination with rhamnose inFrangula bark.[5] A recent study suggests, that purified anthraquinone glycosides from rhubarb could be a potential therapeutic avenue to treat type 2 diabetes mellitus by modulating the gut microbiota and reducing systematic inflammation.[6]
Arguably the most importantcyanogenic glucoside isamygdalin, which occurs in bitter almonds. The enzymemaltase decomposes it intoglucose andmandelic nitrile glucoside; the latter is broken down byemulsin into glucose,benzaldehyde andprussic acid. Emulsin also decomposesamygdalin directly into these compounds without the intermediate formation of mandelic nitrile glucoside.[5]
Several other glucosides of this nature have been isolated. Thesaponins are a group of substances characterized by forming a lather with water; they occur in soap-bark. Mention may also be made ofindican, the glucoside of theindigo plant; this is hydrolysed by theindigo ferment,indimulsiri, toindoxyl and indiglucin.[5]
This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Glucoside".Encyclopædia Britannica. Vol. 12 (11th ed.). Cambridge University Press. pp. 142–143.