ii CHANGES DURING METABOLISM 107 



homologous with benzole acid became converted into benzoic acid if 

 the side -chain contained more than two carbon atoms, or if the| 

 stability of the side-chain was weakened by the replacement of one 

 H atom by OH, or the replacement of 2H by O, as in benzoyL- 

 carboxylic acid ; but Schotten 1 showed that mandelic aciq. 

 C H 5 . CH(CH)COOH remained unaltered, and explained the peculiaj 

 position occupied by phenyl-alanin and tyrosin amongst all aromatic 1 - 

 substances, inasmuch as these two acids are oxidised almost com- 

 pletely in the body, as due to the side-chain of the benzene-nucleus 

 possessing a 3-C chain, the central C of which contains the NH 2 

 group. Bunge has explained the non- oxidation of phenyl- acetic, 

 C 6 H 5 CH 2 .COOH, and mandelic acid, C 6 H 5 . CH(OH)COOH, by 

 assuming that the non-oxidisable radicals C 6 H 5 and COOH protect 

 the CH 2 and CH(OH) groups. This view cannot, however, be accepted, 

 for Pohl 2 has shown malonic acid, COOH CH 2 COOH, in which 

 CH 2 stands between two carboxyl-groups, to disappear in the body 

 to the extent of over 90 per cent, and diphenyl-methane C 6 H 5 

 CH 2 C 6 H 5 is oxidised into C 6 H 5 CH 2 C 6 H 4 OH. 



Knoop 3 has also studied the changes which the aromatic fatty 

 acids undergo in the body. Such radicals as CH 3 , CH 2 OH, CHO, 

 and CH 2 NH 2 attached to benzene, C 6 H 6 , are as a rule oxidised to 

 CO . OH, and the benzoic acid, C 6 H 5 CO . OH, formed in this way 

 then links on to glycocoll, CH 9 (NH 9 ) CO . OH, to form hippuric acid, 

 C 6 H 6 .CO NH.CH 2 COOH. 



Tyrosin, phenylalanin, and a-amino-cinnamic acid, C 6 H 5 . CH 2 . CH 

 (NH 2 ) . COOH, are completely oxidised, while phenyl-propionic acid 

 and cinnamic acid, C 6 H 5 . CH : CH . COOH are changed into benzoic 

 acid. The carbon -chain remains unaltered in phenylacetic acid, 

 C 6 H 5 CH 2 . COOH, and also in its substitution products : mandelic 

 acid, C 6 H 5 . CH(OH)COOH, and phenyl-amino-acetic acid, C 6 H 5 .CH 

 (NH 2 )COOH, only that in the latter the amino-group, NH 2 , is replaced 

 by OH. 



Phenyl-propionic acid on being converted into benzoic acid cannot 

 pass through the stage of phenyl-acetic acid, as otherwise the latter 

 compound ought to appear in the urine. It follows, therefore, 

 according to Knoop, that the oxidation of phenyl-propionic acid can 

 only occur in the /?- and not in the a-position. 



Administered in gelatine capsules to dogs, 2 grammes of 

 Phenyl-propionic acid was converted into hippuric acid, 



1 Schotten, Zeitschr. f. physiol. Cliem. 8. 68 (1883-4). 



2 Pohl, Arch.f. experim. Pathol. 37. 413 (1896). 



3 Franz Knoop, Hofmeist&r's Beitrage, Q. 150 (1904). 



