allothreonine

trivial name for α-amino-β-hydroxybutyric acid; (2R*,3R*)-2-amino-3-hydroxybutanoic acid; CH₃−CH(OH)− CH(NH₂)−COOH; an α-amino acid with two chiral centres. Because molecules of allothreonine possess a second chiral centre, at C-3, in addition to the chiral centre at C-2 common to all α-amino acids other than glycine, the enantiomers l-allothreonine (symbol: aThr), (2S,3S)-2-amino-3-hydroxybutanoic acid, and d-allothreonine (symbol: d-aThr), (2R,3R)-2-amino-3-hydroxybutanoic acid, are diastereoisomeric with those of threonine, (2R*,3R*)-2-amino-3-hydroxybutanoic acid. [Note: the enantiomers of allothreonine may also be named semi-systematically as derivatives of erythrose: l_s-allothreonine in amino-acid nomenclature is synonymous with 2-amino-2,4-dideoxy-l_g-erythronic acid in carbohydrate nomenclature, and d_s-allothreonine with 2-amino-2,4-dideoxy-d_g-erythronic acid (the subscript letters d or g being added to the configurational prefixes where there might be uncertainty regarding the reference centre of chirality; see d/l convention).]l-Allothreonine does not occur in peptide linkage in proteins; however, one residue per molecule is present in the peptide antibiotic telomycin. Residues of d-allothreonine have been found in the glycolipid and peptidolipid of actinomycetes, and in mycobacteria.

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