BILATRIENES. VERDINS 113 



ments. With bilirubin or biliverdiii itself the vinyl side chains 

 undergo alterations. By the addition of groups to double bonds two 

 optically active carbon atoms are formed so that diastereoisomerides 

 may arise. Finally' further oxidations ("biliviolins type 11" to "bili- 

 violins type III") and isomerizations ("biliviolins type 11" tochrysins) 

 further complicate the picture (Lemberg and Lockwood, 1711). 



3. BILATRIENES. VERDINS 



3.1. Structure 



Even before their synthesis, the structure of these compounds was 

 clear from their properties and their relation to bilirubins (803,1676): 



H H H H 



The deep color is in agreement with the conjugation of double bonds 

 through the whole length of the molecule, and the nonhydroxylated 

 pyrrolene nucleus (III) with the existence of stable hydrochlorides. 

 Biliverdin contains two hydrogen atoms less than bilirubin to which 

 it is related as pyrromethene is to a dipyrrylmethane. 



The dehydrogenation of rubins can be carried out with ferric 

 chloride (803,1676), nitric acid (1680), benzoquinone (820,1612,2152), 

 lead dioxide (820), hydrogen peroxide (1703), or by autoxidation 

 (1680), although not all of these (e.g., nitric acid and autoxidation) 

 are suitable for oxidation of bilirubin, since they attack its vinyl 

 groups. This also holds for hydrogen peroxide (1852), unless special 

 precautions (1703) are taken. The two hydrogen atoms removed by 

 these procedures can easily be added again by zinc dust or by enzymic 

 reduction (690,803,1715), with reconversion into bilirubin. 



The hydrochlorides or hydrobromides of biliverdins give double 

 salts with ferric chloride and ferric bromide, which are not complex 

 salts of biliverdins, but salts of the complex acids H(FeCl4) and 

 H(FeBr4) or "double salts" of biliverdin hydrochloride with ferric 

 chloride. The name "ferrobilins" applied to them by the Fischer 

 school has misled some authors to assume that they are biliverdin 

 complexes related to the verdohematin compounds (Chapter X). 



A series of "verdins" exist in the porpliyrin series which are isomerization 

 products of s\'nthetic rliodins (.S'67, pp. 547. 55i). They have a resonance 

 structure similar to that of l)iliverdin (Fig. 11). Tlie porphyrin ring is closed. 



