126 IV. BILE PIGMENTS 



mesobilane can occur at b and c quite as well as at a and b, the product 

 obtained from mesobilane is probably a mixture of side chain iso- 

 merides. Other side chain isomerides with a different order of side 

 chains have also been synthesized by Siedel {2559). 



By reduction of their "mesobiliviolin" Fischer and Niemann {858; 

 861, p. 709) obtained "mesobiliviolinogen" which they found to differ 

 from mesobilane. Siedel and Moller {2559), however, showed that 

 mesobiliviolin yields mesobilane on reduction. On catalytic hydro- 

 genation, mesobilene-(a) was obtained (reduction of methene group 

 b to methylene) in agreement with Siedel's formula. The transfor- 

 mation to mesobilirubin (mesobiladiene-(a,c) ) by zinc in glacial acetic 

 acid {2552) is, however, not easily explained by this formula; it 

 would require an isomerization with shift of hydrogen from the 

 methylene group at c and pyrrole ring IV to the methene group b 

 and pyrrole ring III. The formula would lead us to expect a spectro- 

 scopic similarity to tripyrrodienes. Similar tripyrrodienes with one 

 a-hydroxyl group and bromide or C02Et in a have indeed been found 

 (Fischer and Reinecke, 871; Siedel, 2553). Its relatively strong 

 basicity is accounted for by the true pyrrolene ring III. It is extracted 

 completely from ether by 0.1 N hydrochloric acid. So far decent 

 crystals of the substance or of its hydrochloride have not yet been 

 obtained, probably because it is a mixture of isomerides {cf. Sect. 2.4.). 



TABLE VI 



Colors and Absorption Spectra of Mesobiliviolin 

 and Its Zinc Complex Salt 



Absorption maximum 

 Compound Solvent Color :^ TmM 



21.3 



Siedel (2550) found the bands at 630 and 573 mn. The position varies somewhat 

 with pH and concentration of ammonia, and also, since the bands are not sym- 

 metrical, with the concentrations of the pigment, if measured spectroscopically; 

 admixture of mesobiliverdin shifts the bands toward the infrared. 



5.2.2. Absorption Spectra and Complex Salts. In Table VI 

 colors and absorption maxima of solutions of mesobiliviolin in various 



