Alkylresorcinols, also known as resorcinolic lipids, are

phenolic lipid Phenolic lipids are a class of natural products composed of long aliphatic chains and phenolic rings. Phenolic lipids occur in plants, fungi and bacteria. Types * Alkylcatechols * Alkylphenols (nonylphenol, cardanol) * Alkylresorcinols * Anac ...

s composed of long

aliphatic In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, ...

chains and

resorcinol Resorcinol (or resorcin) is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1,3-isomer (or '' meta''-isomer). Resorcinol crystallizes from benzene as colorless needles that are readily soluble i ...

-type phenolic rings.

Natural sources of alkylresorcinols

Alkylresorcinols are relatively rare in nature, with the main known sources being wheat, rye, barley, triticale (cereal grasses), quinoa, the fruit of ''

Ginkgo biloba ''Ginkgo biloba'', commonly known as ginkgo or gingko ( ), also known as the maidenhair tree, is a species of tree native to China. It is the last living species in the order Ginkgoales, which first appeared over 290 million years ago. Fossil ...

Bilobol Bilobol is an alkylresorcinol, a type of phenolic lipids composed of long aliphatic chains and phenolic rings. Chemically, it is similar in structure to urushiol, the irritant found in poison ivy; it is a strong skin irritant itself. Natura ...

, a mollusc and some species of bacteria. DB-2073

DB-2073 DB-2073 is an alkylresorcinol antibiotic isolated from the broth culture of ''Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The memb ...

is an antibiotic isolated from the broth culture of ''

Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able t ...

'' sp. They are also the main constituents of the outer shell of the cyst of ''

Azotobacter ''Azotobacter'' is a genus of usually motile, oval or spherical bacteria that form thick-walled cysts (and also has hard crust) and may produce large quantities of capsular slime. They are aerobic, free-living soil microbes that play an impo ...

''.

Occurrence in cereals

Alkylresorcinols are present in high amounts in the

bran Bran, also known as miller's bran, is the hard outer layers of cereal grain. It consists of the combined aleurone and pericarp. Corn (maize) bran also includes the pedicel (tip cap). Along with germ, it is an integral part of whole grains, ...

layer (e.g. pericarp, testa and aleurone layers) of

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

and rye (0.1-0.3 % of dry weight). 5-Alkylresorcinols can also be found in

rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...

, though not in the edible parts of the rice plant. They are only present in very low amounts in the endosperm (the part of cereal grain that is used to make white flour), which means that alkylresorcinols can be used as 'biomarkers' for people who eat foods containing wholegrain wheat and rye, rather than cereal products based on white flour. Alkylresorcinols were thought to have anti-nutritive properties (e.g. decreasing growth of pigs and chickens fed rye), but this theory has been discredited, and a number of animal studies have demonstrated that they have no obvious negative effect on animals or humans.

Biomarkers of a whole grain diet

Increasing evidence from human intervention trials suggests that they are the most promising biomarker of

whole grain A whole grain is a grain of any cereal and pseudocereal that contains the endosperm, germ, and bran, in contrast to refined grains, which retain only the endosperm. As part of a general healthy diet, consumption of whole grains is associated ...

wheat and rye intake. Alkylresorcinol metabolites,

3,5-dihydroxybenzoic acid 3,5-Dihydroxybenzoic acid (α-resorcylic acid) is a dihydroxybenzoic acid. It is a colorless solid. Preparation and occurrence It is prepared by disulfonation of benzoic acid followed by hydrolysis of the disulfonate. It is a metabolite of alky ...

(DHBA) and 3,5-dihydroxyphenylpropionoic acid (DHPPA) were first identified in urine and can be quantified in urine and plasma, and may be an alternative, equivalent biomarker of whole grain wheat intake. The average intake of alkylresorcinols in the UK is around 11 mg/person/day, and in Sweden is around 20 mg/person/day. This varies widely depending on whether people normally consume wholegrain/wholemeal/brown bread, which is high in alkylresorcinols (300-1000 μg/g), or white wheat bread, which has very low concentrations of alkylresorcinols (<50 μg/g).

Possible biological activities

In vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology ...

studies have shown that alkylresorcinols may prevent cells turning

cancerous Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

, but that they do not have any effect on cells that are already cancerous. Alkylresorcinols also increase gamma-

tocopherol Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated phenols), many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rat ...

levels in rats when fed in high amounts (0.2% of total diet and above). The alkylresorcinols in ''

Grevillea banksii ''Grevillea banksii'', commonly known as Banks' grevillea, Byfield waratah, red flowered silky oak and dwarf silky oak, and in Hawaii as kāhili flower, is a species of flowering plant in the family Proteaceae and is endemic to Queensland. It is ...

'' and Grevillea 'Robyn Gordon' are responsible for

contact dermatitis Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes are ...

Trivial names of some resorcinolic lipids

* olivetol * persoonol * grevillol * ardisinol I * ardisinol II *

adipostatin A Adipostatin A is an alkylresorcinol, a type of phenolic lipids composed of long aliphatic chains and phenolic rings. Chemically, it is similar in structure to urushiol, the irritant found in poison ivy. Adipostatin A can be found in ''Gingko ...

* adipostatin B *

bilobol Bilobol is an alkylresorcinol, a type of phenolic lipids composed of long aliphatic chains and phenolic rings. Chemically, it is similar in structure to urushiol, the irritant found in poison ivy; it is a strong skin irritant itself. Natura ...

hexylresorcinol Hexylresorcinol is an organic compound with local anaesthetic, antiseptic, and anthelmintic properties. It is available for use topically on small skin infections, or as an ingredient in throat lozenges. It is marketed as S.T.37 by Numark Labora ...

* hydrobilobol *

cardol Adipostatin A is an alkylresorcinol, a type of phenolic lipids composed of long aliphatic chains and phenolic rings. Chemically, it is similar in structure to urushiol, the irritant found in poison ivy. Adipostatin A can be found in ''Gingko ...

* rucinol * irisresorcinol * panosialin * stemphol * R- leprosol * α- leprosol * merulinic acid * xenognosin

Derivatives

Sorgoleone is a hydrophobic root exudate of '' Sorghum bicolor''.

References

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