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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.

An imidazole-4-carboxylic acid compound having a ureido substituent at the 5-position." []

Glyceric acid is a colourless syrupy acid, obtained from oxidation of glycerol. It is a compound that is secreted excessively in the urine by patients suffering from D-glyceric aciduria, an inborn error of metabolism, and D-glycerate anemia. Deficiency of human glycerate kinase leads to D-glycerate acidemia/D-glyceric aciduria. Symptoms of the disease include progressive neurological impairment, hypotonia, seizures, failure to thrive, and metabolic acidosis. At sufficiently high levels, glyceric acid can act as an acidogen and a metabotoxin. An acidogen is an acidic compound that induces acidosis, which has multiple adverse effects on many organ systems. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Glyceric acid is an organic acid. Abnormally high levels of organic acids in the blood (organic acidemia), urine (organic aciduria), the brain, and other tissues lead to general metabolic acidosis. Acidosis typically occurs when arterial pH falls below 7.35. In infants with acidosis, the initial symptoms include poor feeding, vomiting, loss of appetite, weak muscle tone (hypotonia), and lack of energy (lethargy). These can progress to heart abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of untreated glyceric aciduria. Many affected children with organic acidemias experience intellectual disability or delayed development. In adults, acidosis or acidemia is characterized by headaches, confusion, feeling tired, tremors, sleepiness, and seizures. Elevated values may also be due to microbial sources such as yeast (Aspergillus, Penicillium, probably Candida) or due to dietary sources containing glycerol (glycerine). Glyceric acid is isolated from various plants (e.g. brassicas, pulses, and Vicia faba).

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

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

ortho-Hydroxyphenylacetic acid, also known as (o-hydroxyphenyl)acetate or 2-hydroxybenzeneacetic acid, is a member of the class of compounds known as 2(hydroxyphenyl)acetic acids. 2(Hydroxyphenyl)acetic acids are phenylacetic acids that carry a hydroxyl group at the 2-position. ortho-Hydroxyphenylacetic acid is slightly soluble (in water) and a weakly acidic compound (based on its pKa). ortho-Hydroxyphenylacetic acid can be found in a number of food items such as natal plum, lemon verbena, half-highbush blueberry, and parsley, which makes ortho-hydroxyphenylacetic acid a potential biomarker for the consumption of these food products. ortho-Hydroxyphenylacetic acid can be found primarily in blood, feces, and urine. Moreover, ortho-hydroxyphenylacetic acid is found to be associated with phenylketonuria, which is an inborn error of metabolism. ortho-Hydroxyphenylacetic acid is a substrate of the enzyme oxidoreductases (EC 1.14.13.-) in the pathway styrene degradation (KEGG). ortho-Hydroxyphenylacetic acid is also a microbial metabolite.

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.

A benzoate that is the conjugate base of 4-(hydroxyamino)benzoic acid resulting from the deprotonation of the carboxy group; Major species at pH 7.3." []

Xylitol is a five-carbon sugar alcohol that is obtained through the diet. It is not endogenously produced by humans. Xylitol is used as a diabetic sweetener which is roughly as sweet as sucrose with 33% fewer calories. Xylitol is naturally found in many fruits (strawberries, plums, raspberries) and vegetables (e.g. cauliflower). Because of fruit and vegetable consumption the human body naturally processes 15 grams of xylitol per day. Xylitol can be produced industrially starting from primary matters rich in xylan which is hydrolyzed to obtain xylose. It is extracted from hemicelluloses present in the corn raids, the almond hulls or the barks of birch (or of the by-products of wood: shavings hard, paper pulp). Of all polyols, it is the one that has the sweetest flavor (it borders that of saccharose). It gives a strong refreshing impression, making xylitol an ingredient of choice for the sugarless chewing gum industry. In addition to his use in confectionery, it is used in the pharmaceutical industry for certain mouthwashes and toothpastes and in cosmetics (creams, soaps, etc.). Xylitol is produced starting from xylose, the isomaltose, by enzymatic transposition of the saccharose (sugar). Xylitol is not metabolized by cariogenic (cavity-causing) bacteria and gum chewing stimulates the flow of saliva; as a result, chewing xylitol gum may prevent dental caries. Chewing xylitol gum for 4 to 14 days reduces the amount of dental plaque. The reduction in the amount of plaque following xylitol gum chewing within 2 weeks may be a transient phenomenon. Chewing xylitol gum for 6 months reduced mutans streptococci levels in saliva and plaque in adults (PMID:17426399, 15964535). Studies have also shown xylitol chewing gum can help prevent acute otitis media (ear aches and infections) as the act of chewing and swallowing assists with the disposal of earwax and clearing the middle ear, while the presence of xylitol prevents the growth of bacteria in the eustachian tubes. Xylitol is well established as a life-threatening toxin to dogs. The number of reported cases of xylitol toxicosis in dogs has significantly increased since the first reports in 2002. Dogs that have ingested foods containing xylitol (greater than 100 milligrams of xylitol consumed per kilogram of bodyweight) have presented with low blood sugar (hypoglycemia), which can be life-threatening. Xylitol is found to be associated with ribose-5-phosphate isomerase deficiency, which is an inborn error of metabolism.

2-Oxo-4E-hexenoic acid

D-Arabitol is a polyol. Polyols are sugar alcohols linked to the pentose phosphate pathway (PPP). They are classified on the basis of the number of carbon atoms. Polyols occur in body fluids. A patient with leukoencephalopathy and peripheral neuropathy has been identified as suffering from ribose-5-phosphate isomerase (RPI) deficiency, a defect in the PPP. In this disorder, highly elevated concentrations of the C5 polyols such as D-arabitol are found in body fluids. In addition, transaldolase deficiency, another defect in the PPP, has been diagnosed in a patient with mainly liver problems among others. This patient had increased concentrations of polyols, mainly D-arabitol. So far, the pathophysiological role of polyols is relatively unknown. It is thought that D-arabitol is a metabolic end-product in humans. The strong brain-CSF-plasma gradient of polyols in the patient with RPI deficiency suggested a primary metabolic disorder. The mechanisms of brain and neuronal damage in RPI deficiency remain to be elucidated. A neurotoxic effect due to the accumulation of the polyols may play a role. D-Arabitol is a product of the enzyme D-arabinitol 4-dehydrogenase (EC 1.1.1.11) in the pentose and glucuronate interconversion pathway (PMID: 16435225, J Inherit Metab Dis. 2005;28(6):1181-3). D-Arabitol has also been found to be a fungal metabolite, urinary D-Arabinitol is a marker for invasive candidiasis or infection by Candida fungal species (PMID: 15183861; PMID: 10647119). It can also a metabolite in Debaryomyces, Pichia and Zygosaccharomyces (PMID: 25809659).

L-Arabitol, also known as L-arabinitol or L-lyxitol, is a member of the class of compounds known as sugar alcohols. Sugar alcohols are hydrogenated forms of carbohydrate in which the carbonyl group (aldehyde or ketone reducing sugar) has been reduced to a primary or secondary hydroxyl group. L-Arabitol is soluble in water. L-Arabitol can be found in a number of food items such as sweet potato, deerberry, moth bean, and European chestnut, which makes L-arabitol a potential biomarker for the consumption of these food products. L-Arabitol can be found in most biofluids, including urine, cerebrospinal fluid (CSF), saliva, and blood. L-Arabitol exists in all living species, ranging from bacteria to humans. Moreover, L-arabitol is found to be associated with Alzheimer's disease and ribose-5-phosphate isomerase deficiency, which is an inborn error of metabolism. L-Arabitol can be formed by the reduction of either arabinose or lyxose. L-Arabitol has been reported in pentosuric acidemia (PMID:13525419). L-Arabinosinuia has been described in a patient, presented at the age of 16 months with delayed motor development and facial dysmorphism (PMID:12359133) Congenital liver cirrhosis has been recently described in a patient with highly elevated plasma and urine levels of arabitol due to transaldolase deficiency (Inherit Metab Dis 23(Suppl. 1):172, 2000).

Ribitol is a pentose alcohol formed by the reduction of ribose. It occurs naturally in plants as well as in the cell walls of some Gram-positive bacteria. Ribitol forms part of the chemical structure of riboflavin and flavin mononucleotide (FMN). It is also a metabolic end product formed by the reduction of ribose in human fibroblasts and erythrocytes. In this regard ribitol is found in all organisms from bacteria to plants to humans. Ribitol is a normal constituent of human urine (PMID: 2736321). Elevated levels of ribitol in the serum or urine can be found in patients with transaldolase deficiency (PMID: 11283793). Transaldolase is an important enzyme in the pentose phosphate pathway (PPP). Elevated levels of ribitol in the serum or urine can be found in patients with Ribose-5-phosphate isomerase deficiency (PMID: 14988808). Ribose-5-phosphate isomerase is an important enzyme in the pentose phosphate pathway (PPP). Export of ribitol across the cell membrane indicates that can be cleared from the body without metabolic conversion (PMID 15234337). Ribitol is normally absent in Breast milk (PMID 16456418).

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.

The conjugate base of 3-amino-4-hydroxybenzoic acid; major species at pH 7.3." []

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.

Thiodiacetic acid belongs to the family of Thiodiacetic Acid Derivatives. These are compounds containing a thiodiacetic acid group (or esters/salts thereof) which is made up of two 2-sulfanylacetic (OC(=O)CS) acid moieties sharing their sulfur atom.

Dihydrophloroglucinol is a phloroglucinol. It is a conjugate acid of a dihydrophloroglucinol(1-).

3-Hydroxyphenylacetic acid is a rutin metabolite and an antioxidant. It has a protective biological activity in human. It is a substrate of enzyme 4-hydroxyphenylacetate 3-monooxygenase [EC 1.14.13.3] in the pathway tyrosine metabolism (KEGG, PMID 155437). 3-Hydroxyphenylacetic acid is found to be associated with phenylketonuria, which is an inborn error of metabolism. It is also a marker of gut Clostridium species. Higher levels are associated with higher levels of Clostridia (PMID: 27123458). 3-Hydroxyphenylacetic acid can also be found in Klebsiella (PMID: 1851804).

C11354

Thiomalic acid is a C4-dicarboxylic acid. It is functionally related to a succinic acid. It is a conjugate acid of a thiomalate(1-).

7-Methylhypoxanthine is a methyl derivative of xanthine, found occasionally in human urine.

1-Methylhypoxanthine is a methylated hypoxanthine. Hypoxanthine is a naturally occurring purine derivative and a reaction intermediate in the metabolism of adenosine and in the formation of nucleic acids by the salvage pathway.

2,5-furandimethanol is a furan carrying two hydroxymethyl substituents at the 2- and 5-positions. It is a member of furans and a diol. 2,5-Furandimethanol is a natural product found in Wallemia sebi with data available.

This compound belongs to the family of Phenol Esters. These are aromatic compounds containing a benzene ring substituted by an hydroxyl group and an ester group.