276 NITROGEN BASES 



action on the circulation, and causes contraction of the uterus. 

 Its close relationship to tyrosine, from which it can be ob- 

 tained by loss of carbon dioxide, is of interest. 



H0<f ^>CH 2 CHNH 2 COOH - HO<^ ^>CH 2 CH 2 NH 2 +CO 2 

 Tyrosine Hydroxyphenylethylamine 



Hordenine, HO<^ ^>CH 2 CH 2 N(CH 3 ) 2 , is the dimethyl 

 derivative of the previous compound, and occurs in barley. 



The fact that all nitrogenous bases form crystalline deriva- 

 tives with such substances as platinic or auric chlorides, or with 

 picric or picrolonic acids is frequently made use of for isolating 

 or identifying small quantities of these substances (see choline, 

 lecithine, p. 49) ; since the derivatives produced can, as a 

 rule, be identified by their crystalline form and melting point, 

 they provide a certain method of recognizing substances which 

 do not give any characteristic colour reactions. 



An additional advantage of the method lies in the fact 

 that the reagents employed (auric or platinic chloride, etc.) 

 being substances of,high molecular weight produce crystalline 

 derivatives whose weight is very considerably greater than 

 that of the substance which is being isolated, and thus ponder- 

 able quantities of substance may be obtained from compara- 

 tively small amounts of material. 



PURINE BASES. 







Under this heading are included such substances as caffeine, 

 theobromine, xanthine, guanine, etc., which are called purine 

 bases because they are all derivatives of the same substance, 

 purine, whose formula is given below : 



i N = 6 CH 



2 CH 5 C 7 NH 



8CH 



/ 



3 N 4 C 9 N 



Purine 



