STRUCTURE 97 



salt. The algae chromoproteins (Section 7) also contain bile pig- 

 ments of type IX; they are either derived from chlorophyll or their 

 synthesis is linked up with that of chlorophyll. Surprises may, how- 



HO" N X' N^C^N'^C-'^N^OH 



Fig. 3. Type IX bile pigments. 



ever, still be in store for us. Thus dipyrrolic compounds which on 

 condensation might yield bile pigments with copro or uro side chains 

 evidently play a role as intermediates in hemoglobin synthesis, and 

 dipyrrolic compounds with the uro type of side chains have been 

 found in the urine of porph\'ria patients and have been condensed 

 in vitro to bile pigments probably of uro type (Waldenstrom, cf. 

 Section 6.5.). 



The correct structure of the bile pigments was recognized com- 

 paratively late (in 1931) and most of the earlier reviews {882,883, 

 1597,1602) are now mainly of historical value, although they contain 

 much interesting detail. In Fischer's book {861) the synthetic work 

 which led to the recognition of the correct structure of bilirubin is 

 fully dealt with, but other bile pigment classes are treated less ade- 

 quately and considerable progress has been made in this field since 

 1938. This later development has been onh' incompletely reviewed 

 (860,1534,1683,2990). A few other reviews (1349,2240,2371) deal 

 with the physiology of bile pigments, which will be discussed in 

 Chapter XI. 



For many years (1911-1926) Fischer had assumed a tetrapyrryl- 

 ethylene structure for bile pigments, while Ktister defended another 

 more complicated formula. The correct tetrapyrrane formula was 

 discovered in 1931 by Fischer and Hess (826) in an interesting manner. 

 An attempt was made to use the Schumm method (2505) for the 

 removal of vinyl groups from hematin in the hope of preparing a 

 deuterobilirubin from bilirubin. No clear-cut results were obtained. 

 (Later, Fischer and Heinecke isolated a vinyl-substituted dipyrrolic 

 body from the resorcinol melt of bilirubin (869).) Fischer now 

 applied the method to mesobilirubin, although the removal of its 

 ethyl groups could hardly be expected. The results are an interesting 

 justification of the value of occasionally carrying out a logically 

 pointless experiment. 



