SYNTHESIS OF THE PORPHYRIN NUCLEUS 639 



equally probable. We have seen in Chapter III that acetic acid side 

 chains in jS-position of pyrroles are easily decarboxylated. On heating 

 with baryta first a dicarboxylic acid, then a pyrrolemonocarboxylic 

 acid and finally hemopyrrole (III) were obtained. 



CO2H 



I 

 CO2H CHo 



CH2 CH. 

 succinylacetic acid I I a-ketoglutaric acid 



CH2 CO 



I I 



CO ,C02H 

 HO2CCH2 N' 



Fig. 4. Possible synthesis of Dakin and West acid. 



A number of possibilities can be suggested for the synthesis of a 

 compound of the structure of formula II in the animal body. It 

 could, for example, be formed by a condensation of a-ketoglutaric 

 acid, succinylacetic acid, and ammonia (Fig. 4). 



CO2H 



I 

 CO2H CH, 



I I 



CH2 CH2 



a-ketoglutaric acid | | a-ketoglutaric acid 



CH-— -CO 



CO CO2H 



/ -x / 



HO2C N 



H3 



Figure 6 



The porphyrin precursor need not necessarily have an acetic 

 group in the a-position, but might have, for example, a carboxyl or 

 formyl group. A compound of this type may be readily formed by 

 condensation of two molecules of a-ketoglutaric acid with ammonia 

 (Fig. 5). The significance to be attached to this substituent in the 

 a-position will become apparent below. 



