Isoleucine Ehrlich

DL-Isoleucine is synthesized in about 56% over-all yield by the method of Hamlin and Hartung (366). o-Oximino- -methyl-w-valeric acid (A) is prepared in 70% yield from ethyl sec.-bulyl acetoacetate, butyl nitrite and sulfuric acid. DL-Isoleucine is prepared in 80% yield by the reduction of (A) with hydrogen, palladium chloride and ethanol. This method is essentially the same as that originated by Bouveault and Locquin (117, 118, 525). By the comparable procedure of Feofilaktov (264, 265) the phenylhydrazone of methyl ethyl pyruvic acid, prepared from sec.-butyl acetoacetate and phenyldiazonium chloride (aniline and NaN02) in 68% yield, is reduced by means of rinc and alcoholic HCl to nearly the theoretical yield of a mixture of DL-isoleucine and DL-allo-isoleucine. Ehrlich (235) synthesized a mixture of isoleucine and allo-isoleucine from 2-methyl-n-butyraldehyde by the Strecker reaction. 

Locquin has since obtained d-isoleucine from this racemic compound which was identical with Ehrlich s natural product, and this therefore has the above constitution. 

By the same series of reactions which Fischer and Schmitz employed in the preparation of leucine, F. Ehrlich synthesised isoleucine in 1908 from malonic ester and secondary butyliodide, /., according to the following scheme —... 

Fusel Oil and Succinic Acid, etc.—It has been shown that this group of by-products derives not from the sugar but from other materials present in the fermenting liquor. F. Ehrlich in many researches (1904-1910) has shown that the higher alcohols and aldehydes, which when mixed we call fusel oil, are formed by the deammination of amino acids resulting from the hydrolysis of proteins. Thus isoamyl alcohol, which is the chief constituent of fusel oil, is closely related to leucine, amino-isohexoic acid, and active amyl alcohol is similarly related to isoleucine, a-amino-/ -... 

L-Isoleucine from sugarbeet molasses, a little later from protein hydroly-zates by Felix Ehrlich. Structure estabhshed by synthesis L. Bouveault and R. Loquin, 1906. 

FIGURE 12.1 The Ehrlich pathway exemplified for the conversion of the branched-chain amino acids L-valine, L-isoleucine, and L-leucine to the corresponding alcohols isobntanol, 2-methyl-1-bntanol, and 3-methyl-1-butanol. Adh, alcohol dehydrogenase KE)C, 2-ketoacid decarboxylase TA, transaminase. 

Synthesis. Dn-Isoleucine is synthesized in about 27% over-all yield by the method of Marvel (554). Diethyl sec.-butylmalonate (A) is prepared in 83% yield from diethyl malonate, sodium, absolute ethanol and sec.-butyl bromide (b.p. 91.3°C.) essentially by the method of Romburgb (673). a-Bromo- S-methylvaleric acid (B) is pr ared in about 67% yield by the alkaline hydrolysis of (A), isolation of sec.-butylmalonic acid ((j), and bromination and decarboxylation of (C). DL-Isoleucine (D), prepared by amination of (B), is recrystallized from 30% ethanol. It has been suggested (39, 485) that the product should be repeated recrystallized from 80% ethanol to free it from allo-isoleucine. It has been found in the writers laboratory that recrystallization from 20% ethanol is an effective purification procedure. The described s thesis is essentially that originated by Brasch and Friedman (125) and Ehrlich (237) and employed by Abd halden and Zeisset (39). 

Isolation, L-Isoleucine was isolated from de-sugared molasses by Ehrlich (233) who separated the less soluble copper salt of L-leucine from the more soluble copper salt of L-isoleucine by fractional crystallization from methanol. This procedure has been employed for the isolation of isoleucine from lupine seed (873), silkworm egg cases (790), brain (7,720), flbrin (91), mold (881), and other proteins but there is no practicable procedure for the isolation of analytically pure L-isoleucine. According to Locquin (524) the speciflc rotation of pure resolved L-isoleucine in 20% HCl is = -1-40.6°. Approximately the same value, =s 4-... 

Isoleucine was first isolated from fibrin by Ehrlich in 1904. It is an essential amino acid. Meat and ceral proteins contain 4—5% isoleucine egg and milk proteins, 6-7%. 

The relative positions of the substituents on the two adjacent asymmetric carbon atoms are not known and these formulas are therefore quite arbitrary in that respect. Ehrlich synthesized a mixture of L-iso-leucine and n-alloisoleucine from (-l-)a-methylbutyric aldehyde by Strecker s method. From this and also another mixture which was produced by inversion of the configuration of the a-carbon atom, n-alloiso-leucine was obtained by removal of the L-isoleucine with yeast, which only attacks the latter isomeride. A synthesis and resolution of iso-leucine was carried out by Locquin (1907), while Abderhalden and Zeisset (1931a) prepared and resolved alloisoleucine these authors also described... 

---