36 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



baryta water under pressure, it was found to also undergo a rearrange- 

 ment, and the product seemed identical with that obtained by synthesis: 



CH 3 v CH 3 \ CH 3 v /NH 2 CH.v xNH 2 



>CH.CH 2 OH-* >CH.CHO-> >CH . CH/ _> )CH . CH/ 



C 2 H/ C 2 H/ C 2 H/ X CN C 2 H/ X COOH 



d-amylalcohol d-valeraldehyde d-valeroaminonitrile d-isoleucine 



+ 

 Allo-isoleucine 



Further proof that isoleucine has trys constitution was given by 

 Bouveault and Locquin in 1906. They synthesised it from sec. butyl- 

 acetoacetic ester, which they prepared from sec. butyliodide and sodium- 

 acetoacetic ester : 



CH 3 CH, 



CO CH, CO CH 3 



I I I I 



HCNa + I C CH 2 .CH 3 = NaI + HC CH CH 2 CH 3 



COOC 2 H 5 H COOC 2 H 5 



This compound, when treated with nitrosyl sulphate was decomposed 

 into a-oximino-sec-butylacetic acid, which, on reduction with zinc dust 

 and hydrochloric acid in alcohol, gave a 60 per cent, yield of dl- 

 isoleucine : 



CH 3 



| C = NOH 



CO 



| /CH 3 ,C 



H C C\ -> H C C\ 



X C 2 H 6 



iNn 2 

 H c _ 



1 



\ 



C 2 H 5 

 COOC 2 H 5 COOH COOH 



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, i.e., according to the follow- 

 ing scheme : 



C 2 H 5 . CHI . CH 3 + CHNa(COOC 2 H 5 ) 2 -> C 2 H 5 . CH(CH 3 ) . CH(COOC 2 H 5 ) 2 

 -> C 2 H 5 . CH(CH 3 ) . CH(COOH) 2 -> C 2 H 5 . CH(CH 3 ) . CBr(COOH) 2 



-> C 2 H 5 . CH(CH 3 ) . CHBr . COOH -> C 2 H 5 . CH(CH 3 ) . CH(NH 2 ) . COOH 



The same synthesis has also been carried out by Brasch and 

 Friedmann. 



