THE CHEMICAL CONSTITUTION OF THE UNITS 121 



NH 2 NH a 



NH = C NH CH 2 CH a CH 2 CH COOH + H 2 O = 



NH 2 NH 2 



NH. 2 C = O + NH 2 CH 2 CH 2 CH 2 CH COOH 



Schulze and Winterstein, in 1 899, showed that arginine could be 

 obtained by synthesis from cyanamide and ornithine : 



NH 2 

 HjN CH 2 CHa CH 2 CH COOH + CN NH 2 = 



NH 2 NH 2 



NH = C NH CH 2 CH 2 CH 2 CH COOH 



This synthesis proved that arginine contained a guanidine group. 



The presence of a guanidine group in arginine is also proved by the 

 formation of guanidinebutyric acid and of guanidine and succinic acid 

 by oxidation with permanganate, which probably takes place according 

 to the following equations (Kutscher) : 



NH 2 NH 2 



NH = C-NH-CH 2 CH 2 CH 2 CH COOH + O 2 = C0 2 + NH 3 + 

 NH 2 



NH = C NH CH 2 CH 2 CH 2 COOH 



NH 2 NH 2 



NH = C NH CH 2 CH 2 CH 2 -COOH + O 2 = NH = C NH,,+ 

 HOOC CH 2 CH 2 COOH 



Neither the synthesis of arginine by Schulze and Winterstein nor 

 the oxidation experiments of Kutscher prove to which of the amino 

 groups of ornithine the guanido group is attached ; the S-position was 

 assumed to be the more probable. 



This constitution of arginine was only established by Sorensen, in 

 1910, who prepared the two isomers. He found that ornithuric acid 

 (dibenzoylornithine) gave S-monobenzoylornithine, when hydrolysed 

 with concentrated hydrochloric acid, and a-monobenzoylornithine, 

 when hydrolysed with baryta water. By the addition of cyanamide 

 to these two compounds he obtained S-monobenzoylamino-a-guanido- 

 valerianic acid and a-monobenzoylamino-8-guanidovalerianic acid. 

 The benzoyl group was then removed by boiling with hydrochloric 

 acid : 



