34 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



isovaleraldehyde, hydrogen cyanide and ammonia, was found to be 

 identical with it, and further, both compounds gave d-leucine, when 

 acted upon by the mould Penicillium glaucum, and the same leucic 

 acid, when treated with nitrous acid. Leucine is therefore a-aminoiso- 

 butylacetic acid, 



CH 3 x 



\CH . CH 2 . CH(NH 2 )COOH. 



CHj 



Among the syntheses of a-amino acids carried out by E. Erlenmeyer 



jun., by his method, that of leucine was described in 1901 by Erlen- 

 meyer and Kunlin. It was prepared from a-benzoylamido-/3-isopro- 



pylacrylic acid, 



CH 5 x 



\CH-CH == C COOH 



prr / I 



NH CO C 6 H 5 



which resulted when isobutylaldehyde and hippuric acid were condensed 

 together in the presence of acetic anhydride and the condensation 

 product, 



CH 3 v /N^ 



en CH= c/ ^c . CH, 



was treated with alkali. 



By heating a-benzoylamido-/3-isopropylacrylic acid in sealed tubes 

 at 150-170 C., with excess of ammonia, hydrolysis occurred with the 

 formation of leucine, isovalerianic acid and benzoic acid : 



CH 3 \ CH 3 \ 



\CH CH 2 CH COOH j)CH . CH 2 . COOH 



CH/ ^ CH/ 



Leucine Isovalerianic acid 



Bouveault and Locquin have also synthesised leucine by the re- 

 duction of a-oximinoisobutylacetic acid, which was prepared in a 

 similar way to the isomeric compound from which they obtained iso- 

 leucine. 



The most convenient method of preparing leucine by synthesis is 

 that given by Fischer and Schmitz in 1906 by the action of ammonia 

 upon the corresponding halogen derivative of isocaproic acid, which 

 they prepared by brominating the alkylmalonic ester and heating 

 whereby it was converted into the bromo-fatty acid. The several 

 reactions are represented by the following scheme : 



COOC 2 H B COOC 2 H 5 COOC 2 H 8 



I Na | (CH,) 2 .CH.CH 2 Br I Br 



CH 2 -- > CHNa -- > CH . CH 2 . CH . (CH S ) 2 -- > 



COOC 2 H 5 COOC 2 H 5 COOC a H 5 



