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(±)-erythro-Isoleucine is a flavouring ingredient, dietary supplement, and a nutrient. Branched-chain amino acids (BCAA) are essential amino acids whose carbon structure is marked by a branch point. These three amino acids are critical to human life and are particularly involved in stress, energy and muscle metabolism. BCAA supplementation as therapy, both oral and intravenous, in human health and disease holds great promise. BCAA denotes valine, isoleucine, and leucine which are branched chain essential amino acids. Despite their structural similarities, the branched amino acids have different metabolic routes, with valine going solely to carbohydrates, leucine solely to fats, and isoleucine to both. The different metabolism accounts for different requirements for these essential amino acids in humans: 12 mg/kg, 14 mg/kg, and 16 mg/kg of valine, leucine, and isoleucine respectively. Furthermore, these amino acids have different deficiency symptoms. Valine deficiency is marked by neurological defects in the brain, while isoleucine deficiency is marked by muscle tremors. BCAA are decreased in patients with liver disease such as hepatitis, hepatic coma, cirrhosis, extrahepatic biliary atresia, or portacaval shunt. Aromatic amino acids (AAA)-tyrosine, tryptophan, and phenylalanine (as well as methionine) are increased in these conditions. Valine, in particular, has been established as a useful supplemental therapy to the ailing liver. All the BCAA probably compete with AAA for absorption into the brain. Supplemental BCAA with vitamin B6 and zinc help normalize the BCAA:AAA ratio. The BCAA are not without side effects. Leucine alone, for example, exacerbates pellagra and can cause psychosis in pellagra patients by increasing excretion of niacin in the urine. Leucine may lower brain serotonin and dopamine. The ratio of leucine to other BCAA is greatest in pork, where leucine is 7 to 8 g and the other BCAA together are only 3 to 4 g (http://www.dcnutrition.com).

Isoleucine (Ile) or L-isoleucine is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. L-isolecuine is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Isoleucine is found in all organisms ranging from bacteria to plants to animals. It is classified as a non-polar, uncharged (at physiological pH) aliphatic amino acid. Isoleucine is an essential amino acid in humans, meaning the body cannot synthesize it and that it must be obtained from the diet. In plants and microorganisms, isoleucine is synthesized starting from pyruvate and alpha-ketobutyrate. Isoleucine is classified as a branched chain amino acid (BCAA). BCAAs include three amino acids: isoleucine, leucine and valine. They are alpha amino acids whose carbon structure is marked by a beta branch point. Despite their structural similarities, BCAAs have different metabolic routes, with valine going solely to carbohydrates (glucogenic), leucine solely to fats (ketogenic) and isoleucine being both a glucogenic and a ketogenic amino acid. Isoleucine is catabolized via with alpha-ketoglutarate where upon it is oxidized and split into propionyl-CoA and acetyl-CoA. Propionyl-CoA is converted into succinyl-CoA, a TCA cycle intermediate which can be converted into oxaloacetate for gluconeogenesis (hence glucogenic). The acetyl-CoA can be fed into the TCA cycle by condensing with oxaloacetate to form citrate or used in the synthesis of ketone bodies or fatty acids. The different metabolism of BCAAs accounts for different requirements for these essential amino acids in humans: 12 mg/kg, 14 mg/kg and 16 mg/kg of valine, leucine and isoleucine are required respectively. Furthermore, these amino acids have different deficiency symptoms. Valine deficiency is marked by neurological defects in the brain, while isoleucine deficiency is marked by muscle tremors. BCAAs are decreased in patients with liver disease, such as hepatitis, hepatic coma, cirrhosis, extrahepatic biliary atresia. An inability to break down isoleucine, along with other amino acids, is associated with maple syrup urine disease (MSUD) (PMID: 34125801). Isoleucine, like other BCAAs, is associated with insulin resistance. In particular, higher levels of isoleucine are observed in the blood of diabetic mice, rats, and humans (PMID 25287287). Mice fed an isoleucine deprivation diet for one day have improved insulin sensitivity, and feeding of an isoleucine deprivation diet for one week significantly decreases blood glucose levels (PMID: 24684822).

L-Norleucine, also known as L-aminohexanoate or caprine, belongs to the class of organic compounds known as l-alpha-amino acids. These are alpha amino acids which have the L-configuration of the alpha-carbon atom. Thus, L-norleucine is considered to be a fatty acid lipid molecule. An unnatural amino acid that is used experimentally to study protein structure and function. L-Norleucine is a very hydrophobic molecule, practically insoluble in water, and relatively neutral. L-Norleucine exists in all eukaryotes, ranging from yeast to humans. Outside of the human body, L-Norleucine has been detected, but not quantified in cow milk. This could make L-norleucine a potential biomarker for the consumption of these foods. It binds reversibly to the kringle domain of plasminogen and blocks the binding of plasminogen to fibrin and its activation to plasmin.

2-Amino-4-methylpentanoic acid

Leucine (Leu) or L-leucine is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. L-leucine is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Leucine is found in all organisms ranging from bacteria to plants to animals. It is classified as a non-polar, uncharged (at physiological pH) aliphatic amino acid. Leucine is essential in humans, meaning the body cannot synthesize it, and it must be obtained from the diet. Human dietary sources are foods that contain protein, such as meats, dairy products, soy products, beans and legumes. L-Leucine is a branched chain amino acid (BCAA). The BCAAs consist of leucine, valine and isoleucine (and occasionally threonine). BCAAs are essential amino acids whose carbon structure is marked by a branch point at the beta-carbon position. BCAAs are critical to human life and are particularly involved in stress, energy and muscle metabolism. BCAA supplementation as therapy, both oral and intravenous, in human health and disease holds great promise. BCAAs have different metabolic routes, with valine going solely to carbohydrates (glucogenic), leucine solely to fats (ketogenic) and isoleucine being both a glucogenic and a ketogenic amino acid. The different metabolism accounts for different requirements for these essential amino acids in humans: 12 mg/kg, 14 mg/kg and 16 mg/kg of valine, leucine and isoleucine respectively. The primary metabolic end products of leucine metabolism are acetyl-CoA and acetoacetate; consequently, it is one of the two exclusively ketogenic amino acids, with lysine being the other. Leucine is the most important ketogenic amino acid in humans. The vast majority of l-leucine metabolism is initially catalyzed by the branched-chain amino acid aminotransferase enzyme, producing alpha-ketoisocaproate (alpha-KIC). alpha-KIC is metabolized by the mitochondrial enzyme branched-chain alpha-ketoacid dehydrogenase, which converts it to isovaleryl-CoA. Isovaleryl-CoA is subsequently metabolized by the enzyme isovaleryl-CoA dehydrogenase and converted to beta-methylcrotonyl-CoA (MC-CoA), which is used in the synthesis of acetyl-CoA and other compounds. During biotin deficiency, HMB can be synthesized from MC-CoA via enoyl-CoA hydratase and an unknown thioesterase enzyme, which convert MC-CoA into HMB-CoA and HMB-CoA into HMB respectively. Leucine has the capacity to directly stimulate myofibrillar muscle protein synthesis (PMID 15051860). This effect of leucine arises results from its role as an activator of the mechanistic target of rapamycin (mTOR) (PMID 23551944) a serine-threonine protein kinase that regulates protein biosynthesis and cell growth. The activation of mTOR by leucine is mediated through Rag GTPases. Leucine, like other BCAAs, is associated with insulin resistance. In particular, higher levels of leucine are observed in the blood of diabetic mice, rats, and humans (PMID 25287287). BCAAs such as leucine have different deficiency symptoms. Valine deficiency is marked by neurological defects in the brain, while isoleucine deficiency is marked by muscle tremors. Persistently low leucine levels can result in decreased appetite, poor feeding, lethargy, poor growth, weight loss, skin rashes, hair loss, and desquamation. Many types of inborn errors of BCAA metabolism exist and these are marked by various abnormalities. The most common form is maple syrup urine disease, marked by a characteristic urinary odor. Other abnormalities are associated with a wide range of symptoms, such as mental retardation, ataxia, hypoglycemia, spinal muscle atrophy, rash, vomiting and excessive muscle movement. Most forms of BCAA metabolism errors are corrected by dietary restriction of BCAAs and at least one form is correctable by supplementation with 10 mg of biotin daily. - BCAAs are useful because they are metabolized primarily by muscle. Stress states - e.g surgery, trauma, cirrhosis, infections, fever and starvation--require proportionately more BCAAs than other amino acids and probably proportionately more leucine than either valine or isoleucine. BCAAs and other amino acids are frequently fed intravenously (TPN) to malnourished surgical patients and in some cases of severe trauma. BCAAs, particularly leucine, stimulate protein synthesis, increase reutilization of amino acids in many organs and reduce protein breakdown. Furthermore, leucine can be an important source of calories, and is superior as fuel to the ubiquitous intravenous glucose (dextrose). - Leucine also stimulates insulin release, which in turn stimulates protein synthesis and inhibits protein breakdown. These effects are particularly useful in athletic training. Huntington's chorea and anorexic disorders both are characterized by low serum BCAAs. These diseases, as well as forms of Parkinson's, may respond to BCAA therapy.

L-alloisoleucine is a branched chain amino acid and is a stereo-isomer of L-isoleucine. It is a common constituent of human plasma (albeit at low levels). L-alloisoleucine is produced as a byproduct of isoleucine transamination. L-Isoleucine is one of the four common amino acids (the 3 others being threonine, hydroxyproline, and hydroxylysine) that have two asymmetric carbon atoms which produce four structural possibilities for the same chemical composition. L-alloisoleucine differs from L-isoleucine by having having different stereochemistry around its beta carbon. Plasma L-alloisoleucine, which is derived from L-isoleucine in vivo, can be used for the diagnosis of maple syrup urine disease (MSUD), a genetic disorder. Indeed, plasma L-alloisoleucine levels above 5 umol/L is the most specific and most sensitive diagnostic marker for all forms of MSUD (PMID: 10508118). In MSUD the degradation of the essential branched-chain L-amino acids leucine, valine, and isoleucine and their derived 2-oxoacids is impaired because of an inherited deficiency in branched-chain 2-oxoacid dehydrogenase complex (EC 1.2.4.4) activity. The accumulation of branched-chain compounds in blood and other body fluids can exert neurotoxic effects.

Piperidine (Azinane after the Hantzsch Widman nomenclature) is an organic compound with the molecular formula (CH2)5NH. This heterocyclic amine consists of a six-membered ring containing five methylene units and one nitrogen atom. It is a colorless fuming liquid with an odor described as ammoniacal, pepper-like; the name comes from the genus name Piper, which is the Latin word for pepper. Piperidine is found in barley, black pepper (Piper nigrum). Piperidine has been found to be a microbial metabolite. Piperidine is a flavouring agent and it is also widely used as a building block and chemical reagent in the synthesis of organic compounds, including pharmaceuticals. Piperidine is a widely used secondary amine. It is used to convert ketones to enamines. Enamines derived from piperidine can be used in the Stork enamine alkylation reaction. Piperidine is used as a solvent and as a base. The same is true for certain derivatives: N-formylpiperidine is a polar aprotic solvent with better hydrocarbon solubility than other amide solvents, and 2,2,6,6-tetramethylpiperidine is highly sterically hindered base, useful because of its low nucleophilicity and high solubility in organic solvents.

The D-enantiomer of isoleucine." []

A 2-methylpyrrolidine that has (R)-configuration." []

A 2-methylpyrrolidine that has (R)-configuration." []

1-Methylpyrrolidine is a natural product found in Arisarum vulgare and Solanum lycopersicum with data available.

An N-alkyl glycine that is glycine in which the amino group is replaced by a diethylnitrilo group." []

N-Acetylcadaverine is the acetylated form of the polyamine cadaverine. Cadaverine is produced by the breakdown of amino acids in living and dead organisms and is toxic in large doses. Cadaverine is largely responsible for the foul odor of putrefying flesh, but also contributes to the odor of such processes as bad breath and bacterial vaginosis. Cadaverine is also found in semen. Polyamines (and their acetylated forms) are known to be closely related with cell growth, cell proliferation, and synthesis of proteins and nucleic acids. Their concentrations are adjusted either by regulating the activity levels of the biosynthetic and catabolic reactions or by controlling the net direction of polyamine acetylation-deacetylation. In Alzheimer's disease (AD), the neurotoxic amyloid β-peptide is known to up-regulate polyamine metabolism by increasing ornithine decarboxylase activity and polyamine uptake by initiating free radical damage. Because of these findings, polyamines have been considered to play an important role in response to neurodegenerative conditions. Altered levels of polyamines have been found in tissue, hair and body fluids of patients with neuromuscular diseases and neurodegenerative conditions. (PMID: 17723614). N-Acetylcadaverine has been found to be a metabolite of several bacteria species (https://www.sciencedirect.com/science/article/pii/S209580991730423X).

An organic cation obtained by protonation of the imino group of (R)-2-methylpyrrolidine. It is the major microspecies at pH 7.3" []

Isoleucyl-Isoleucine is a dipeptied compoosed of two isoleucine residues. It is an incomplete breakdown product of protein digestion or protein catabolism. Some dipeptides are known to have physiological or cell-signaling effects although most are simply short-lived intermediates on their way to specific amino acid degradation pathways following further proteolysis. This dipeptide has not yet been identified in human tissues or biofluids and so it is classified as an 'Expected' metabolite.

Leucylleucine is a dipeptide composed of two leucine residues. It is an incomplete breakdown product of protein digestion or protein catabolism. Some dipeptides are known to have physiological or cell-signalling effects although most are simply short-lived intermediates on their way to specific amino acid degradation pathways following further proteolysis.

A glycine derivative that is glycine with a tertiary butyl group at position 2." []

Glycylleucine is a dipeptide composed of glycine and leucine. It is an incomplete breakdown product of protein digestion or protein catabolism. Some dipeptides are known to have physiological or cell-signaling effects although most are simply short-lived intermediates on their way to specific amino acid degradation pathways following further proteolysis. It appears to be a common substrate for glycyl-leucine dipeptidase.

Isoleucyl-Valine is a dipeptide composed of isoleucine and valine. It is an incomplete breakdown product of protein digestion or protein catabolism. Some dipeptides are known to have physiological or cell-signaling effects although most are simply short-lived intermediates on their way to specific amino acid degradation pathways following further proteolysis. This dipeptide has not yet been identified in human tissues or biofluids and so it is classified as an 'Expected' metabolite.

Leucyl-Valine is a dipeptide composed of leucine and valine. It is an incomplete breakdown product of protein digestion or protein catabolism. Some dipeptides are known to have physiological or cell-signaling effects although most are simply short-lived intermediates on their way to specific amino acid degradation pathways following further proteolysis. This dipeptide has not yet been identified in human tissues or biofluids and so it is classified as an 'Expected' metabolite.

The conjugate acid of piperidine; major species at pH 7.3." []

A member of the class of pyrrolidines that is pyrrolidine which is substituted by a methyl group at position 2." []

An N-acylpiperidine that is piperidine in which the hydrogen attached to the nitrogen is replaced by an acetyl group." []

ε-Caprolactone, also known simply as caprolactone, is a compound belonging to the family of compounds known as lactones. Lactones are cyclic esters of hydroxyl carboxylic acids, wherein the functional group has become part of a ring structure with carbon atoms. Caprolactone consists of a seven membered ring derived from the cyclization of caproic acid. As a monomer it used in the production of highly specialized plastics and polymers. Caprolactone is produced by the Baeyer-Villiger oxidation of cyclohexanone with peracetic acid, and was used previously (until economically inviable) as a precursor in the production of caprolactam. Several other caprolactone isomers are known. These isomers include α-, β-, γ-, and δ-caprolactones. All are chiral. (R)-γ-caprolactone is a component of floral scents and of the aromas of some fruits and vegetables (Journal of Agricultural and Food Chemistry. 37: 413–418), while δ-caprolactone is found in heated milk fat (Journal of Dairy Science. 48 (5): 615–616).