Glucoside

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A glucoside is a type of glycoside in which the sugar part is glucose. They are common in plants but rare in animals. When the bond holding the sugar to the other part of the molecule is broken (hydrolysis), you get glucose plus the non-sugar part, called the aglycone.

Historically, glucosides were plant products where the non-sugar part was often an aromatic aldehyde or phenol, though there are exceptions. The name has been broadened to include some synthetic ethers and even certain polysaccharides, such as cane sugar, which also act like ethers.

Although glucose is the most common sugar linked in glucosides, some yield other sugars like rhamnose. The non-sugar parts (the aglycones) have been studied a lot; many have been identified, synthesized, or even used to make new glucosides.

The simplest glucosides are alkyl glucosides made by treating glucose solutions with acid. A better method is to dissolve solid glucose in methanol with acid, which gives a mix of alpha- and beta-glucosides.

Classifying glucosides is complex. One chemical approach groups them by their aglycone into four types: alkyl, benzene, styrene, and anthracene derivatives, with another group for cyanogenic glucosides that contain prussic acid. Botanically, related plants often have similar glucosides, so a plant-based classification is also used. This article focuses on the chemical classification and the most important examples.

Key examples and notes:
- Mustard oils: glucosides such as sinigrin (in mustard seeds, black pepper, horseradish) and sinalbin (in white pepper). Hydrolysis can produce glucose, allyl mustard oil, and other products.
- Jalapin and Scammonin: from scammony; hydrolyze to glucose and jalapinolic acid.
- Benzoyl glucosides: occur in various plants; populin is a benzoyl glucoside from poplar; benzoyl glucoside is also found in ferns.
- Arbutin: in bearberry; hydrolyzes to hydroquinone and glucose and acts as a urinary antiseptic and diuretic.
- Salicin: in willow; hydrolyzes to glucose and saligenin, which can be further converted to related compounds; enzymes like ptyalin and emulsin help convert salicin to glucose and saligenin.
- Coniferin: found in conifer wood; hydrolysis yields glucose and coniferyl alcohol; oxidation gives glucovanillin, which can yield vanillin.
- Syringin: found in lilac bark; related to other conifer-derived glucosides.
- Phloridzin: from fruit-tree roots; hydrolyzes to glucose and phloretin.
- Related compounds include naringin and hesperidin, which yield sugars and aglycones upon hydrolysis and are linked to various dyes and medicinal uses.
- Anthraquinone glycosides: many are substituted anthraquinones with uses as purgatives; ruberythric acid yields the dye alizarin.
- Rhubarb: contains chrysophanic acid and emodin, both anthraquinone derivatives; these glycosides are often used for laxatives and dyes.
- Amygdalin: a well-known cyanogenic glucoside in bitter almonds; enzymes or hydrolysis yield glucose, benzaldehyde, and prussic acid (cyanide-containing compounds).
- Saponins: a group of glucosides that form a soapy lather.
- Indican: a glucoside from indigo plants; hydrolyzed to indoxyl and indiglucin.

Overall, glucosides are a diverse family of plant compounds with many roles, including medicinal uses, dyes, and plant defense. Some can release toxic cyanide, while others have beneficial effects or industrial value.