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Xanthine, also known as 2,6-dioxopurine, belongs to the class of organic compounds known as xanthines. These are purine derivatives with a ketone group conjugated at carbons 2 and 6 of the purine moiety. Xanthine is also classified as an oxopurine. An oxopurine in which the purine ring is substituted by oxo groups at positions 2 and 6 and N-9 is protonated. Xanthine exists in all living species, ranging from bacteria to plants to humans. In plants, several stimulants can be derived from xanthine, including caffeine, theophylline, and theobromine. Derivatives of xanthine (known collectively as xanthines) are a group of alkaloids commonly used for their effects as mild stimulants and as bronchodilators, notably in the treatment of asthma or influenza symptoms. Within humans, xanthine participates in a number of enzymatic reactions. In particular, xanthine can be biosynthesized from guanine; which is mediated by the enzyme guanine deaminase. In addition, xanthine and ribose 1-phosphate can be biosynthesized from xanthosine through the action of the enzyme purine nucleoside phosphorylase. In humans and other primates, xanthine can be converted to uric acid by the action of the xanthine oxidase enzyme. People with rare genetic disorders, specifically xanthinuria and Lesch–Nyhan syndrome, lack sufficient xanthine oxidase and cannot convert xanthine to uric acid. Individuals with xanthinuria have unusually high concentrations of xanthine in their blood and urine, which can lead to health problems such as renal failure and xanthine kidney stones. Individuals with Lesch-Nyhan syndrome have a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). The HGPRT deficiency causes a build-up of uric acid in all body fluids. This results in both high levels of uric acid in the blood and urine, associated with severe gout and kidney problems. Neurological signs include poor muscle control and moderate intellectual disability.

Oxipurinol is a xanthine oxidase inhibitor. Oxipurinol is potentially used for treatment of congestive heart failure. PMID: 15139781.

Xanthosine, also known as xanthine riboside, belongs to the class of organic compounds known as purine nucleosides. Purine nucleosides are compounds comprising a purine base attached to a ribosyl or deoxyribosyl moiety. Xanthosine is a nucleoside derived from xanthine and ribose. Xanthosine exists in all living species, ranging from bacteria to plants to humans. In plants xanthosine is the biosynthetic precursor to 7-methylxanthosine which is produced by the action of the enzyme known as 7-methylxanthosine synthase. 7-Methylxanthosine in turn is the precursor to theobromine (the active alkaloid in chocolate), which in turn is the precursor to caffeine, the active alkaloid in coffee and tea. Within humans, xanthosine participates in a number of enzymatic reactions. In particular, xanthosine can be biosynthesized from xanthylic acid; which is catalyzed by the enzyme cytosolic purine 5'-nucleotidase. In addition, xanthosine can be converted into xanthine and ribose 1-phosphate; which is mediated by the enzyme purine nucleoside phosphorylase. Xanthosine monophosphate (XMP) is an intermediate in purine metabolism, formed from IMP (inosine monophosphate).

3,4-Dihydroxyphenylglycol, also known as DHPG or DOPEG, belongs to the class of organic compounds known as catechols. Catechols are compounds containing a 1,2-benzenediol moiety. 3,4-Dihydroxyphenylglycol is an extremely weak basic (essentially neutral) compound. 3,4-Dihydroxyphenylglycol exists in all living organisms, ranging from bacteria to plants to humans. It is a potent antioxidant (PMID: 30007612). In mammals, 3,4-Dihydroxyphenylglycol is the primary metabolite of norepinephrine and is generated through the action of the enzyme monoamine oxidase (MAO). DHPG is then further metabolized by the enzyme Catechol-O-methyltransferase (COMT) to 3-methoxy-4-hydroxyphenylglycol (MHPG). Within humans, 3,4-dihydroxyphenylglycol participates in a number of enzymatic reactions. In particular, 3,4-dihydroxyphenylglycol can be biosynthesized from 3,4-dihydroxymandelaldehyde; which is mediated by the enzyme alcohol dehydrogenase 1A. In addition, 3,4-dihydroxyphenylglycol and guaiacol can be converted into vanylglycol and pyrocatechol through its interaction with the enzyme catechol O-methyltransferase. Outside of the human body, 3,4-dihydroxyphenylglycol is found, on average, in the highest concentration in olives. High levels of DHPG (up to 368 mg/kg of dry weight) have been found in the pulp of natural black olives. This could make 3,4-dihydroxyphenylglycol a potential biomarker for the consumption of olives and olive oil. 3,4-Dihydroxyphenylglycol has been linked to Menkes disease (PMID: 19234788). DHPG level are lower in Menkes patients (3.57 ± 0.40 nM) than healthy infants 8.91 ± 0.77 nM). Menkes disease (also called “kinky hair disease”) is an X-linked recessive neurodevelopmental disorder caused by defects in a gene that encodes a copper-transporting ATPase (ATP7A). Affected infants typically appear healthy at birth and show normal neurodevelopment for 2-3 months. Subsequently there is loss of milestones (e.g., smiling, visual tracking, head control) and death in late infancy or childhood (PMID: 19234788).

(R)-mandelic Acid, also known as (R)-2-Hydroxy-2-phenylacetic acid or (-)-(R)-Mandelate, is classified as a benzene or a Benzene derivative. Benzenes are aromatic compounds containing one monocyclic ring system consisting of benzene. (R)-mandelic Acid is considered to be soluble (in water) and acidic

Eriodictyol, also known as 3',4',5,7-tetrahydroxyflavanone or 2,3-dihydroluteolin, belongs to the class of organic compounds known as flavanones. Flavanones are compounds containing a flavan-3-one moiety, with a structure characterized by a 2-phenyl-3,4-dihydro-2H-1-benzopyran bearing a ketone at the carbon C3. Thus, eriodictyol is considered to be a flavonoid lipid molecule. Outside of the human body, eriodictyol has been detected, but not quantified in, several different foods, such as common oregano, common thymes, parsley, sweet basils, and tarragons. This could make eriodictyol a potential biomarker for the consumption of these foods. Eriodictyol is a compound isolated from Eriodictyon californicum and can be used in medicine as an expectorant. BioTransformer predicts that eriodictiol is a product of luteolin metabolism via a flavonoid-c-ring-reduction reaction catalyzed by an unspecified-gut microbiota enzyme (PMID: 30612223).

3-Cresotinic acid is a salicylic acid derivative compound with marked fibrinolytic activity in human plasma by activating its fibrinolytic system. (PMID 6040385).

Homoveratric acid is the main metabolite of 3,4-dimethoxyphenylethylamine (DMPEA) in urine. It has been suggested that DMPEA and other amines are in higher concentrations in drug-free schizophrenics than in normal subjects. DMPEA is a the di-methylated metabolite of L-DOPA, the major treatment for Parkinson's disease (PD). (PMID 7059639, 14311254, 588645, 10834300).

p-Anisic acid, also known as 4-anisate or draconic acid, belongs to the class of organic compounds known as p-methoxybenzoic acids and derivatives. These are benzoic acids in which the hydrogen atom at position 4 of the benzene ring is replaced by a methoxy group. p-Anisic acid is a drug. p-Anisic acid exists in all eukaryotes, ranging from yeast to humans. p-Anisic acid is a faint, sweet, and cadaverous tasting compound. Outside of the human body, p-anisic acid has been detected, but not quantified in several different foods, such as anises, cocoa beans, fennels, and german camomiles. This could make p-anisic acid a potential biomarker for the consumption of these foods. It is a white crystalline solid which is insoluble in water, highly soluble in alcohols and soluble in ether, and ethyl acetate. p-Anisic acid has antiseptic properties. It is also used as an intermediate in the preparation of more complex organic compounds. It is generally obtained by the oxidation of anethole or p-methoxyacetophenone. The term "anisic acid" often refers to this form specifically. p-Anisic acid is found naturally in anise.

Xanthoxylin is found in fats and oils. Xanthoxylin is obtained from Zanthoxylum piperitum (Japanese pepper tree) and Sapium sebiferum (Chinese tallowtree

Dihydroferulic acid, also known as 3-(4-hydroxy-3-methoxyphenyl)propionic acid or dihydroconiferylate, is classified as a member of the phenylpropanoic acids. Phenylpropanoic acids are compounds with a structure containing a benzene ring conjugated to a propanoic acid. Dihydroferulic acid is considered to be slightly soluble (in water) and acidic. Dihydroferulic acid is a phenolic acid metabolite and was found to be significantly elevated in serum after whole grain consumption which makes this compound a potential serum biomarker of whole grain intake (PMID: 25646321).

used in parkinson's disease metabolite of carbidopa Dollery, Colin Therapeutic Drugs, 2nd Ed. 1999 p. C52

4-Hydroxy-3-methylbenzoic acid, also known as 4,3-cresotic acid or 4-hydroxy-m-toluic acid, belongs to the class of organic compounds known as hydroxybenzoic acid derivatives. Hydroxybenzoic acid derivatives are compounds containing a hydroxybenzoic acid (or a derivative), which is a benzene ring bearing a carboxyl and hydroxyl groups.

gamma-Tocopherol, also known as 7,8-dimethyltocol, belongs to the class of organic compounds known as tocopherols. These are vitamin E derivatives containing a saturated trimethyltridecyl chain attached to the carbon C6 atom of a benzopyran ring system. They differ from tocotrienols which contain an unsaturated trimethyltrideca-3,7,11-trien-1-yl chain. It is estimated that 50% of gamma-tocopherol is metabolized into gamma-CEHC and excreted into the urine. gamma-Tocopherol is the predominant form of vitamin E in plant seeds and derived products (e.g. nuts and vegetable oils). Unlike alpha-tocopherol, gamma-tocopherol inhibits cyclooxygenase activity and, therefore, exhibit anti-inflammatory properties (PMID: 11722951).

p-Hydroxyphenylacetic acid, also known as 4-hydroxybenzeneacetate, is classified as a member of the 1-hydroxy-2-unsubstituted benzenoids. 1-Hydroxy-2-unsubstituted benzenoids are phenols that are unsubstituted at the 2-position. p-Hydroxyphenylacetic acid is considered to be slightly soluble (in water) and acidic.  p-Hydroxyphenylacetic acid can be synthesized from acetic acid. It is also a parent compound for other transformation products, including but not limited to, methyl 2-(4-hydroxyphenyl)acetate, ixerochinolide, and lactucopicrin 15-oxalate.  p-Hydroxyphenylacetic acid can be found in numerous foods such as olives, cocoa beans, oats, and mushrooms. p-Hydroxyphenylacetic acid can be found throughout all human tissues and in all biofluids. Within a cell, p-hydroxyphenylacetic acid is primarily located in the cytoplasm and in the extracellular space. p-Hydroxyphenylacetic acid is also a microbial metabolite produced by Acinetobacter, Clostridium, Klebsiella, Pseudomonas, and Proteus. Higher levels of this metabolite are associated with an overgrowth of small intestinal bacteria from Clostridia species including C. difficile, C. stricklandii, C. lituseburense, C. subterminale, C. putrefaciens, and C. propionicum (PMID: 476929, 12173102). p-Hydroxyphenylacetic acid is detected after the consumption of whole grain.

Vanillin, also known as vanillaldehyde or lioxin, belongs to the class of organic compounds known as methoxyphenols. Methoxyphenols are compounds containing a methoxy group attached to the benzene ring of a phenol moiety. It is used by the food industry as well as ethylvanillin. Vanillin exists in all living species, ranging from bacteria to humans. Vanillin is a sweet, chocolate, and creamy tasting compound. Vanillin is found, on average, in the highest concentration within a few different foods, such as corns, ryes, and sherries and in a lower concentration in beers, rums, and oats. Vanillin has also been detected, but not quantified, in several different foods, such as gooseberries, other bread, brazil nuts, shea tree, and ohelo berries. This could make vanillin a potential biomarker for the consumption of these foods. Vanillin is a potentially toxic compound. Synthetic vanillin, instead of natural Vanillin extract, is sometimes used as a flavouring agent in foods, beverages, and pharmaceuticals. Vanillin is the primary component of the extract of the Vanillin bean. Because of the scarcity and expense of natural Vanillin extract, there has long been interest in the synthetic preparation of its predominant component. Artificial Vanillin flavoring is a solution of pure vanillin, usually of synthetic origin. Today, artificial vanillin is made from either guaiacol or from lignin, a constituent of wood which is a byproduct of the paper industry. The first commercial synthesis of vanillin began with the more readily available natural compound eugenol.

Methylparaben, also known as methyl 4-hydroxybenzoate or p-carbomethoxyphenol, belongs to the class of organic compounds known as p-hydroxybenzoic acid alkyl esters. These are aromatic compounds containing a benzoic acid, which is esterified with an alkyl group and para-substituted with a hydroxyl group. Methylparaben is an antimicrobial agent, preservative, and flavouring agent. methylparaben has been detected, but not quantified, in a few different foods, such as alcoholic beverages, saffrons, and fruits (particularly blueberries). It is also a constituent of cloudberry, yellow passion fruit, white wine, botrytized wine, and Bourbon vanilla. Methylparaben is the most frequently used antimicrobial preservative in cosmetics.

Pinoresinol is a lignan, produced by by radical β-β' coupling of two |FRAME: CONIFERYL-ALCOHOL| molecules. It is produced by plants as a defense molecule, and is a component of |FRAME: Lignins lignin|. Pinoresinol is known to be liberated from lignin during the degradation of dead plant material by white rot fungi and to be degraded by bacteria |CITS: [29222099]|. Pinoresinol is contained in cereals, particularly in whole-grain rye products, in olive oil,and in various members of the |FRAME: TAX-3318| family, from the |FRAME: TAX-3328|, |FRAME: TAX-3337| and |FRAME: TAX-3319| genera.

A member of the class of hydroquinones that is 2,3-dimethylbenzene-1,4-diol substituted by a phytyl group at position 6." []

3-Methoxy-4,5-methylenedioxybenzoic acid is found in green vegetables. 3-Methoxy-4,5-methylenedioxybenzoic acid is isolated from seeds of Apium graveolen

z2-Tocopherol is found in cereals and cereal products. z2-Tocopherol is a constituent of rice

Geigy vol.3 p.127

4,2',4'-Trihydroxy-3-methoxydihydrochalcone

2,6-Diaminopurine riboside is a purine nucleoside. See also: 2-Aminoadenosine (annotation moved to).