THE CHEMICAL CONSTITUTION OF THE UNITS 145 



NH 3 

 1-a-bromisovaleryl-d- valine ~~ > 1-valyl-d-valine 



^ trans-valine anhydride l 



glycine NH 3 



d-o-bromisovalerylchloride > d-a-bromisovalerylglycine > d-valylglycine 



hydrolysis 

 > d-valine 



The protection of the carboxyl group has again prevented the 

 inversion ; the experiments on the interconversion of valine ester and 

 bromisovalerianic ester were not successful. 



The changes of the bromisovaleric acid and of valine into the oxy- 

 acid were also different from those observed with the other acids : 



AgaO 



d-a-bromisovaleric acid > d-o-oxyisovaleric acid 



and 

 KOH 



AgaO 

 d-a-bromisovalerylglycine ~ > d-o-oxyisovalerylglycine 



HN0 2 ' *.!**?. 



1-valine > d-o-oxyisovaleric acid. 



Here nitrous acid acts abnormally, but silver oxide acts normally. 

 The change, 



NH 3 

 d-bromisovaleric acid > 1-valine, 



is also abnormal. 



The difference between valine and the other amino acids may be 

 due to the effect of the isopropyl group. In valine, 



(CH 3 ) 2 . CH . CH(NH 2 ) . COOH, 

 it is attached directly to the asymmetric carbon atom ; in leucine, 



(CH 3 ) 2 . CH . CH 2 . CH(NH 2 ) . COOH, 



a methylene group is present between it and the CH(NH 2 ) group 

 which contains the asymmetric carbon atom. 



If phosphorus pentachloride ammonia and potash act normally 

 since the products have the same configuration, it may be concluded 

 that the "Walden inversion" is limited to the reactions between 

 nitrosyl bromide and the amino group and between silver oxide and 

 halogen fatty acid, and that it is dependent upon the presence of the 

 carboxyl group. 



In order to ascertain if the Walden inversion, caused by the action of 

 nitrosyl bromide and silver oxide, were due to the attachment of the 

 carboxyl group to the asymmetric carbon atom, Fischer > and Scheibler 



1 See Part II. for these compounds. 

 PT. I. 10 



