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Citraconic acid, also known as 2-methylmaleate or methylmaleic acid, belongs to the class of organic compounds known as methyl-branched fatty acids. These are fatty acids with an acyl chain that has a methyl branch. Usually, they are saturated and contain only one or more methyl group. However, branches other than methyl may be present. Citraconic acid is a dicarboxylic acid consisting of maleic acid having a methyl substituent at the 2-position. Citraconic acid exists as a white solid. It is the cis-isomer of mesaconic acid and is one of the pyrocitric acids formed upon the heating of citric acid. Citraconic acid has been detected in the urine of both normal and fasting individuals (PMID: 6778884). Citraconic acid is also elevated in the urine of individuals with methylmalonic acidaemia who have suffered ketotic attacks (PMID: 116077). Altered serum levels of citraconic acid have been detected in patients with primary biliary cholangitis (PMID: 28400566).

Itaconic acid is a dicarboxylic acid that is methacrylic acid in which one of the methyl hydrogens is substituted by a carboxylic acid group. It has a role as a fungal metabolite and a human metabolite. It is a dicarboxylic acid and an olefinic compound. It derives from a succinic acid. It is a conjugate acid of an itaconate(2-). This dicarboxylic acid is a white solid that is soluble in water, ethanol, and acetone. Historically, itaconic acid was obtained by the distillation of citric acid, but currently it is produced by fermentation. The name itaconic acid was devised as an anagram of aconitic acid, another derivative of citric acid. Itaconic acid, also known as itaconate, belongs to the class of organic compounds known as branched fatty acids. These are fatty acids containing a branched chain. Itaconic acid is a very hydrophobic molecule, practically insoluble in water, and relatively neutral. Since the 1960s, it is produced industrially by the fermentation of carbohydrates such as glucose or molasses using fungi such as Aspergillus itaconicus or Aspergillus terreus. For A. terreus the itaconate pathway is mostly elucidated. The generally accepted route for itaconate is via glycolysis, tricarboxylic acid cycle, and a decarboxylation of cis-aconitate to itaconate via cis-aconitate-decarboxylase. The smut fungus Ustilago maydis uses an alternative route. Cis-aconitate is converted to the thermodynamically favoured trans-aconitate via aconitate-Δ-isomerase (Adi1). trans-Aconitate is further decarboxylated to itaconate by trans-aconitate-decarboxylase (Tad1). Itaconic acid is also produced in cells of macrophage lineage. It was shown that itaconate is a covalent inhibitor of the enzyme isocitrate lyase in vitro. As such, itaconate may possess antibacterial activities against bacteria expressing isocitrate lyase (such as Salmonella enterica and Mycobacterium tuberculosis). It is also sythesized in the laboratory, where dry distillation of citric acid affords itaconic anhydride, which undergoes hydrolysis to itaconic acid.

Mesaconic acid, also known as 2-methylfumarate or citronic acid, belongs to the class of organic compounds known as methyl-branched fatty acids. These are fatty acids with an acyl chain that has a methyl branch. Usually, they are saturated and contain only one or more methyl group. However, branches other than methyl may be present. Mesaconic acid is a dicarboxylic butenoic acid, with a methyl group in position 2 and the double bound between carbons 2 and 3. Mesaconic acid was first studied for its physical properties in 1874 by Jacobus van ‘t Hoff (https://web.archive.org/web/20051117102410/http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Van%27t-Hoff-1874.html). It is now known to be involved in the biosynthesis of vitamin B12 and it is also a competitor inhibitor of the reduction of fumarate.

Glutaconic acid is related to the fully saturated glutaric acid and belongs to the class of compounds known as dicarboxylic acids and derivatives. These are organic compounds containing exactly two carboxylic acid groups. Glutaconic acid is soluble (in water) and a weakly acidic compound (based on its pKa). Glutaconic acid has been detected in the urine of individuals with inborn errors of metabolism. When present in sufficiently high levels, glutaconic acid can act as an acidogen, a neurotoxin, and a metabotoxin. An acidogen is an acidic compound that induces acidosis, which has multiple adverse effects on many organ systems. A neurotoxin is a compound that is toxic to neural tissues and cells. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of glutaconic acid are associated with glutaric aciduria type I (glutaric acidemia type I, glutaryl-CoA dehydrogenase deficiency, GA1, or GAT1). GA1 is an inherited disorder in which the body is unable to completely break down the amino acids lysine, hydroxylysine, and tryptophan due to a deficiency of mitochondrial glutaryl-CoA dehydrogenase (EC 1.3.99.7, GCDH). Excessive levels of their intermediate breakdown products (e.g. glutaric acid, glutaryl-CoA, 3-hydroxyglutaric acid, glutaconic acid) can accumulate and cause damage to the brain (and also other organs), but particularly the basal ganglia. GA1 is associated with a risk for intracranial and retinal hemorrhage, and non-specific white matter changes. Babies with glutaric acidemia type I are often born with unusually large heads (macrocephaly). Other symptoms include spasticity (increased muscle tone/stiffness) and dystonia (involuntary muscle contractions resulting in abnormal movement or posture), but many affected individuals are asymptomatic. Seizures and coma (encephalopathy) are rare. GA1 also causes secondary carnitine deficiency because 3-hydroxyglutaric acid, like other organic acids, is detoxified by carnitine. Glutaconic acid's neurotoxicity is thought to be partially caused by an excitotoxic mechanism in which glutaconic acid overactivates N-methyl-D-aspartate (NMDA) receptors. Accumulating trans-glutaconic (TG) acids have been proposed to be involved in the development of the striatal degeneration seen in children with glutaric acidemia type I via an excitotoxic mechanism.

Ketoleucine is an abnormal metabolite that arises from the incomplete breakdown of branched-chain amino acids. Ketoleucine is both a neurotoxin and a metabotoxin. A neurotoxin causes damage to nerve cells and nerve tissues. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of ketoleucine are associated with maple syrup urine disease (MSUD). MSUD is a metabolic disorder caused by a deficiency of the branched-chain alpha-keto acid dehydrogenase complex (BCKDC), leading to a buildup of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic by-products (ketoacids) in the blood and urine. The symptoms of MSUD often show in infancy and lead to severe brain damage if untreated. MSUD may also present later depending on the severity of the disease. If left untreated in older individuals, during times of metabolic crisis, symptoms of the condition include uncharacteristically inappropriate, extreme, or erratic behaviour and moods, hallucinations, anorexia, weight loss, anemia, diarrhea, vomiting, dehydration, lethargy, oscillating hypertonia and hypotonia, ataxia, seizures, hypoglycemia, ketoacidosis, opisthotonus, pancreatitis, rapid neurological decline, and coma. In maple syrup urine disease, the brain concentration of branched-chain ketoacids can increase 10- to 20-fold. This leads to a depletion of glutamate and a consequent reduction in the concentration of brain glutamine, aspartate, alanine, and other amino acids. The result is a compromise of energy metabolism because of a failure of the malate-aspartate shuttle and a diminished rate of protein synthesis (PMID: 15930465).

A 2-oxo monocarboxylic acid that is valeric acid carrying oxo- and methyl substituents at C-2 and C-3, respectively. An alpha-keto acid analogue and metabolite of isoleucine in man, animals and bacteria. Used as a clinical marker for maple syrup urine disease (MSUD)." []

2oxo-3R-methyl-pentanoic acid

2-Ketohexanoic acid is a potent insulin secretagogue (PMID 7045091). 2-Ketohexanoic acid directly inhibits the ATP-sensitive K+ channel (KATP channel) in pancreatic beta-cells (stimulated in isolated mouse islets), but it is unknown whether direct KATP channel inhibition contributes to insulin release by 2-ketohexanoic acid and related alpha-keto acid anions, which are generally believed to act via beta-cell metabolism (PMID 16014804).

3-Methyl-2-oxovaleric acid (CAS: 1460-34-0) is an abnormal metabolite that arises from the incomplete breakdown of branched-chain amino acids. 3-Methyl-2-oxovaleric acid is a neurotoxin, an acidogen, and a metabotoxin. A neurotoxin causes damage to nerve cells and nerve tissues. 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. Chronically high levels of 3-methyl-2-oxovaleric acid are associated with maple syrup urine disease. MSUD is a metabolic disorder caused by a deficiency of the branched-chain alpha-keto acid dehydrogenase complex (BCKDC), leading to a buildup of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic by-products (ketoacids) in the blood and urine. The symptoms of MSUD often show in infancy and lead to severe brain damage if untreated. MSUD may also present later depending on the severity of the disease. If left untreated in older individuals, during times of metabolic crisis, symptoms of the condition include uncharacteristically inappropriate, extreme, or erratic behaviour and moods, hallucinations, anorexia, weight loss, anemia, diarrhea, vomiting, dehydration, lethargy, oscillating hypertonia and hypotonia, ataxia, seizures, hypoglycemia, ketoacidosis, opisthotonus, pancreatitis, rapid neurological decline, and coma. In maple syrup urine disease, the brain concentration of branched-chain ketoacids can increase 10- to 20-fold. This leads to a depletion of glutamate and a consequent reduction in the concentration of brain glutamine, aspartate, alanine, and other amino acids. The result is a compromise of energy metabolism because of a failure of the malate-aspartate shuttle and a diminished rate of protein synthesis (PMID: 15930465). 3-Methyl-2-oxovaleric acid is a keto-acid, which is a subclass of organic acids. 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, liver, and kidney abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of untreated MSUD. Many affected children with organic acidemias experience intellectual disability or delayed development.

4-Acetylbutyrate belongs to the class of organic compounds known as medium-chain fatty acids. These are fatty acids with an aliphatic tail that contains between 4 and 12 carbon atoms.

Flavouring compound [Flavornet]

An enoate ester that is the monomethacryloyl derivative of ethylene glycol." []

2-Methylbut-2-enedioic acid is a natural product found in Phaseolus vulgaris and Fragaria with data available.

3-oxo-4-methyl-pentanoic acid

(R)-3-hydroxy-3-methyl-2-oxopentanoic acid

2-Methyl-3-ketovaleric acid is a metabolite of beta-leucine in the beta-keto pathway of leucine metabolism. 2-Methyl-3-ketovaleric acid is a known pathological metabolite and associated with propionic acidemia, especially during periods of ketoacidosis; a severe deficiency of propionyl-CoA carboxylase in cultured fibroblasts has been detected in some neonatal cases. (PMID 7389125, 6820422, 7119896, 7430116, 3356699). 2-Methyl-3-ketovaleric acid induces a strong activity of inosine-5'-monophosphate dehydrogenase (IMPDH; the rate-limiting enzyme in GTP synthesis), mimicking glucose. (PMID: 11145582).

Ammelide is a dihydroxy-1,3,5-triazine and a monoamino-1,3,5-triazine.

3-(Methylthio)-1-propanol, also known as methionol or 3-(methylsulfanyl)-1-propanol, belongs to the class of organic compounds known as dialkylthioethers. These are organosulfur compounds containing a thioether group that is substituted by two alkyl groups. An alkyl sulfide that is propan-1-ol substituted by a methylsulfanyl group at position 3. 3-(Methylthio)-1-propanol is a sweet, onion, and potato tasting compound. 3-(Methylthio)-1-propanol has been detected, but not quantified, in several different foods, such as beans, lemon grass, mollusks, limes, and orange bell peppers. This could make 3-(methylthio)-1-propanol a potential biomarker for the consumption of these foods.

Adipate semialdehyde is the intermediate metabolite in the formation of caproic acid. Adipate semialdehyde is converted from .alpha.-ketopimelate catalyzed by the decarboxylase enzyme, and the aminotransferase enzyme catalyzes the conversion of adipate semialdehyde to amino caproic acid.

Mevalonolactone

2-dehydropantoic acid, also known as ketopantoate, belongs to short-chain keto acids and derivatives class of compounds. Those are keto acids with an alkyl chain the contains less than 6 carbon atoms. 2-dehydropantoic acid is soluble (in water) and a weakly acidic compound (based on its pKa). 2-dehydropantoic acid can be found in a number of food items such as radish (variety), red algae, cherimoya, and avocado, which makes 2-dehydropantoic acid a potential biomarker for the consumption of these food products. 2-dehydropantoic acid exists in E.coli (prokaryote) and yeast (eukaryote).

3-Mercapto-2-butanol is a flavouring ingredient.

Pyrrole-2-carboxylic acid was synthesized over a century ago, but its history as a compound of biological origin is rather recent. It was first identified as a degradation product of sialic acids, then as a derivative of the oxidation of the D-hydroxyproline isomers by mammalian D-amino acid oxidase. The latter relationship results from the lability of the direct oxidation product, A'-pyrroline-4-hydroxy-2-carboxylic acid, which loses water spontaneously to form the pyrrole. A similar reaction is catalyzed by the more specific allohydroxy-D-proline oxidase of Pseudomonas. In whole animal observations, pyrrole-2-carboxylate (PCA) ' was identified in rat or human urine after administration of the D-isomers of hydroxyproline, a finding ascribable to the action of D-amino acid oxidase. (PMID:4430715). Urinary excretion of N-(pyrrole-2-carboxyl) glycine has been reported in a 5-year-old affected with type II hyperprolinemia; The child has mild developmental delay, recurrent seizures of the grand mal type and EEG alterations. The urinary excretion of the conjugate is stressed, since it appears that only one previous report in the literature described this compound in the urine of two patients affected by this disturbance (PMID 2383933).

Gamma-delta-Dioxovaleric acid (DOVA) is the final oxidation product of 5-aminolevulinic acid, a precursor of porphyrin in the biosynthesis of heme. It can accumulate in liver, brain, and other organs under pathological conditions such as acute intermittent porphyria.

A nucleobase analogue that is uracil in which the oxo group at C-2 is replaced by a thioxo group." []