114 IV. BILE PIGMENTS 



but tlie conjugation of its double l)onds is interrupted by enolization of a 

 rhodin carbonyl group l)ound to one of the methene groups. 



Fig. 11. Verdins (with closed ring system). 



3.2. Individual Bilatrienes* 



3.2.1. Bilatriene, Biliverdin. Biliverdin (C33H34O6N4) was iso- 

 lated from icteric urine and investigated by Scherer as early as 1845 

 (34.38). It is remarkable that his effort to purify the substance came 

 nearer to success than those of many later workers. Stadeler gave a 

 formula with 10, Maly and Kiister with 8, and Kiister, later, with 7, 

 oxygen atoms. Pure bilatriene was first isolated by Lemberg and 

 Barcroft from dog placenta and called uteroverdin (1691,1692). It 

 was then obtained by dehydrogenation of bilirubin (1676). Oocyan, 

 the green-blue pigment from bird egg shells, for which at first a 

 tripyrrene structure was tentatively assumed (1674), was also found 

 to be identical with biliverdin (1676,1680). The close relationship 

 of oocyan with uteroverdin had been recognized early by Thudichum 

 (2802). 



The occurrence of biliverdin in nature is discussed in Chapter XI. 



Biliverdin can be obtained by autoxidation of bilirubin in alkaline 

 solution, but the yield is poor (1680), the "biliverdin" thus formed 

 being a mixture of bilatrienes with altered side chains. The green 

 color produced from bilirubin by oxidants in the Fouchet and Huppert 

 tests and as the first step in the Gmelin reaction is also due to bila- 

 trienes. Biliverdin is prepared by dehydrogenatioD of bilirubin 

 (1676) or by coupled oxidation of hemoglobin and ascorbic acid (1712). 

 It is moderately soluble in ether with greenish-blue color and extracted 



* Only the naturally occurring hile pigments of type IXa are discussed. 



