100 



IV. BILE PIGMENTS 



The pyrromethene-a-aldehyde is now condensed with the other 

 pyrromethene in reaction 8 to a bilatriene. Finally the urethan 

 groups are transformed into vinyl groups (9) as described in the 

 figure. 



The transformation of hematin and hemoglobin into bile pigments 

 will be described in Chapter X. Theoretically, four different iso- 



TABLE I 



Synthesis of Bile Pigments 



1931-1934 

 Synthesis of 

 intermediates 



Preparation of a-hydroxypyrromethenes 

 from a-bromopyrromethenes by reaction 

 with acetates or sodium methoxide. 



1932-1934 Preparation of a-hydroxy pyrroles from 



Synthesis of pyrroles with hydrogen peroxide in pyr- 



intermediates idine. 



1931 Synthesis of a mixture of mesobilirubin 



isomerides from a-OH,a'-H — substi- 

 tuted pyrromethenes with formaldehyde. 



Fischer and co-workers, 

 Siedel, 798,815,255^. 



Fischer and co-workers , 



Fischer and Hess, 



merides may thus arise from protoporphyrin IX by removal of one 

 of the four methene groups, a, /3, y, or 8, and its replacement by 

 hydroxyl groups (Fig. 7), while no less than 52 isomeric bilirubins 

 are possible. Only one of these bile pigment isomerides, IXa, has 

 been isolated so far either from natural bile pigments or from the 

 in vitro transformation of hematin and hemoglobin into bile pigments. 

 Evidently the methene group a between the two pyrroles bearing no 

 acid side chains is removed preferentially. 



1.4. Stereochemistry 



Bile pigments are conventionally written as linear tetrapyrrolic 

 chains (cf. biliverdin in Fig. 6 and the formulas in Tables II and III). 



