THE MECHANISM OF ORGANIC SYNTHESIS 115 



exact steps in this process we are at present ignorant. Knoop's work would 

 point to the ketonic acids as formftig one step, and as interacting with 

 ammonia, with simultaneous reduction, to form amino-acids. 



The pyrrol ring which occurs in proline and in oxyproline may possibly 

 be derived from an open chain amino-acid, and it has in fact been suggested 

 that the proline found in the products of the acid digestion of proteins is 

 derived from ornithine by a process of condensation with the loss of ammonia. 

 Thus: 



CH 2 NH 2 .CH 2 .CH 2 .CH.NH 2 COOH becomes 

 CH 2 .CH 2 .CH 2 .CH.COOH 



NH 



or, as it is generally written : 



CH 2 CH 2 



I I 



CH 2 CH.COOH 



V 



NH 



Its pre-existence in the protein molecule is however practically assured, and 

 it plays an important part in the building up both of chlorophyll and of 

 haematin, the prosthetic group of haemoglobin. 



CH NH 

 Iminazol || 



CH N 



occurs in histidine (which is iminazol alanine), and can be formed fairly 

 readily by the action of certain catalytic agents on a mixture of glucose and 

 ammonia. Thus, if a solution of glucose with ammonia and zinc oxide be 

 exposed to light, methyl iminazol is formed in large quantities. Windaus 

 and Knoop imagined that in this process glyceric aldehyde and formaldehyde 

 are first formed, and that these then interact with ammonia to form methyl 

 iminazol. 



CH 3 



C NH 



II >H 

 CH N 



It is interesting to note that, if we attach to this compound carbamide 

 or urea, we obtain a body belonging to the class of purines. Xanthine, 

 for instance, would have a formula 



NH CO 



I I 



CO C NH 



I H 



NH CH N 



Thus by the action of simple catalytic agencies on sugar and ammonia 

 we can obtain the iminazol nucleus, and by easy transitions pass through 



