CHAPTER III. 



BETAINES. 



THE betaines are amino-acids in which the nitrogen atom is completely 

 methylated. In addition to trimethyl-glycine, which has been known 

 for a long time and occurs both in plants and in animals, fully methyl- 

 ated derivatives of proline, oxyproline, histidine, and tryptophane have 

 so far been obtained from plants, and corresponding derivatives of y- 

 amino-butyric and of y-amino-hydroxy-butyric acid from animals. 

 Except in the case of trigonelline, which occurs in many plants but is 

 not related to any known decomposition product of protein, the betaine 

 grouping does not occur in the typical vegetable alkaloids ; the two 

 cases of its alleged occurrence, in damascenine and in chrysanthemine, 

 have lately been disproved (respectively by Ewins [1912] and 

 Yoshimura and Trier [1912, section on stachydrine]). 



The betaines therefore form a fairly natural group comprising 

 feeble bases of simple constitution ; the a-betaines are devoid of marked 

 physiological activity, but the two y-betaines (being presumably stronger 

 bases) have a distinct action. A comprehensive study of the chemical 

 behaviour of betaines has been made by Willstatter [1902, l] whose 

 nomenclature is here employed. He points out that a-betaines and 

 the isomeric esters of dimethyl-amino-acids are interconvertible : 

 /CH 3 /CH, 



COOCH 3 COO CH 3 



In the case of the betaines of $-and-y-amino-acids the above change 

 only proceeds from left to right, but not in the reverse direction. From 

 the methyl ester of /3-dimethyl-amino-propionic acid -propio-betaine 

 is thus obtainable ; when y-dimethyl-amino-butyrate is heated, the y- 

 butyro-betaine which no doubt first results, is unstable and yields 

 trimethylamine and y-butyro-lactone. Further details concerning the 

 interconversion in the case of trimethyl-glycine are given in the next 

 section. 



The a-betaines differ greatly in the ease with which they split off 



39 



