5179. Isoleucine

Nomenclature

CAS number: 73-32-5
l-Isoleucine; Ile; I; 2-amino-3-methylvaleric acid; α-amino-β-methylvaleric acid; (2S,3S)-2-amino-3-methylpentanoic acid.
C6H13NO2; mol wt 131.17.
C 54.94%, H 9.99%, N 10.68%, O 24.39%.

Description and references

An essential amino acid for human development. Isoln from beet-sugar mother liquors: F. Ehrlich, Ber. 37, 1809 (1904). Structure and identification of isomers: idem, Ber. 40, 2538 (1907); J. P. Greenstein et al., J. Biol. Chem. 204, 307 (1953). Early chemistry and biochemistry: Amino Acids and Proteins, D. M. Greenberg, Ed. (Charles C. Thomas, Springfield, IL, 1951) 950 pp., passim; J. P. Greenstein, M. Winitz, Chemistry of the Amino Acids vol 1-3 (John Wiley and Sons, Inc., New York, 1961) pp. 2043-2074, passim. TLC determ in serum from patients with maple sugar urine disease (MSDU): R. J. Allen et al., Clin. Chem. 18, 413 (1972). Metabolism of Ile and isomers in MSDU: U. Wendel et al., Pediatr. Res. 25, 11 (1989); and clinical consequences: T. Mogos et al., Rev. Roum. Med. Interne 32, 57 (1994). Review of biosynthesis: M. Iaccarino et al., Curr. Top. Cell. Regul. 14, 29-73 (1978).

Chemical structure

Properties

Waxy, shiny, rhombic leaflets from alc. Bitter taste. Sublimes 168-170°. Dec 284°. [α]D20 +40.61° (c = 4.6 in 6.1N HCl); +11.09° (c = 3.3 in 0.33N NaOH). [M]D +53.5° (5N HCl); +64.2° (glacial acetic acid). pK1 2.36; pK2 9.68. Soly at 23.7°: 33.85 g/kg water. Sparingly sol in hot alc (0.13% w/w at 80°), hot acetic acid. Insol in ether.

Derivative

dl-Form.

Nomenclature

(±)-erythro-2-Amino-3-methylpentanoic acid.

Properties

Glistening rhombic or monoclinic plates from dil alc. Dec 292°. pK1 2.32; pK2 9.76. Soly in water (g/l): 18.3 at 0°; 22.3 at 25°; 30.3 at 50°; 46.1 at 75°; 78.0 at 100°.

Derivative

l-allo-Form.

Nomenclature

α-Ile; l(+)-alloisoleucine; (+)-threo-2-amino-3-methylpentanoic acid .

Properties

Waxy leaflets. Sweet taste. Dec 280°. [α]D20 +14.0° (c = 2); +38.1° (c = 2 in 6N HCl). [M]D +53.1° (5N HCl); +55.7° (glacial acetic acid). pK1 2.27; pK2 9.62. One part dissolves in 34.2 parts water at 20°; 0.82 part dissolves in 100 parts 80% alcohol at 20°; 1.97 parts dissolve in 100 parts 80% alcohol; 0.19 part dissolves in 100 parts abs alcohol at 90°.