62 III. PORPHYRIN CHEMISTRY 



phyrins may be present in insufficiently purified coproporphyrin and deu- 

 teroporphyrin fractions. Some of the "pseudodeuteroporphyrins" of Watson 

 (24.24,2986) may perhaps contain a porphyrin with one vinyl and one hydroxy- 

 ethyl side chain, e.g., that found in the bile after perfusion of rabbit liver 

 with protoporphyrin (2424) ■ An increase of "coproporphyrin" has been 

 found in the excreta after meat diet, and a "deuteroporphyrin" has been 

 observed in the feces of rabbits after lead and sulfonal poisoning (cf. Chapter 

 XII and 829,849). These need further investigation. 



Hematoporphyrin forms a more easily soluble sodium salt than 

 other porphyrins with two propionic acid side chains. Its dimethyl 

 ester melts at 212°. The dimethyl ether dimethyl ester (tetramethyl- 

 hematoporphyrin) can be readily obtained in large crystals, but occurs 

 in several modifications with four different melting points (861, 

 p. 425; 1292). It is not yet clear whether these are due to poly- 

 morphism only, or whether diastereoisomerism plays a role. 



The oxidation of tetramethylhematoporphyrin to a-methoxyethyl- 

 methylmaleimide (Fig. 7), with a yield of two molecules of this sub- 



ru /CH3 



^C=C OCH3 



I I 



co^co 



>^ 



H 



Fig. 7. Q-Methoxyethylmethylmaleimide 



stance from one molecule of the porphyrin (884), was of significance 

 since it finally disproved the earlier formulation of hematoporphyrin 

 with one hydroxyethyl and one hydroxyvinyl side chain and the 

 formulation of hemin with one vinyl and one acetylene side chain. 



3.3.5. Porphyrins with Carbonyl Groups in Side Chains. 



Diacetyldeuteroporphyrin has been mentioned as an intermediate 

 product in the synthesis of hemin. Porphyrins containing acetyl side 

 chains may arise by oxidation of the vinyl group to the acetyl group. 

 Thus the "cryptoporphyrin" of Negelein (2021,2022), later recog- 

 nized as a product of photautoxidation of protoporphyrin in acid 

 solution, may be a monoacetylmonovinyl porphyrin. Such por- 

 phyrins are of particular interest since the spectroscopic properties 

 of their hematin compounds resemble those of Warburg's respiratory 

 enzyme and of the cytochromes a (cf. Chapter VIII). The same holds 

 for porphyrins with formyl (CHO) instead of acetyl side chains. 



