PORPHYRINS WITH MORE THAN FOUR COOH GROUPS 



67 



acid (pH 3.5). On decarboxylation Waldenstrom obtained copropor- 

 phyrin III. The octamethyl ester of uroporphyrin III melts at about 

 255-260°. Spectroscopically there is no difference between uropor- 

 phyrins I and III, but the fluorescence minimum of uroporphyrin III 

 lies at pH 3.1 to 3.2, while that of uroporphyrin I is at pH 2.9 to 3.0 

 (2910). In this respect uroporphyrin III differs from uroporphyrin I 

 in the same manner as coproporphyrin III from coproporphyrin I 

 (cf. 861, p. 596). Recently experiments of Watson and collaborators 

 (1056,3002, cf. also 2193) have thrown some doubt on the existence 

 of uroporphyrin III as an entity. 



(I) 



(HI) 



Fig. 11. Uroporphyrins I and III. 



Their results are, however, confusing. In their first paper they report 

 fractionation by chromatographic analysis of esters corresponding in their 

 behavior to uroporphyrin III ester. One fraction had the melting point of 

 uroporphyrin I ("284°), and a second, a melting point of '■208°. The latter, 

 which according to analytical results was the ester of a heptacarboxylic 

 rather than of an octacarboxylic acid, yielded coproporphyrin III on decar- 

 boxylation. Sometimes they were able to isolate this ester and sometimes 

 they obtained only the ester of uroporphyrin I from the feces of their por- 

 phyria patients. In their second paper, however, they describe a Waldenstrom 

 ester which could not be fractionated by chromatography but which on 

 decarboxylation yielded even more coproporphyrin I and less coproporphyrin 

 III than their fractionable esters. They assume that both kinds of Walden- 

 strom ester were mixtures of uroporphyrin I with a heptacarboxylic ester 

 of type III, and that in the nonfractionable preparation the amount of the 

 latter was so small that it migrated on the column together with viropor- 

 phyrin I ester. This assumption is not convincing. 



It should be pointed out. however, that Waldenstrom's own observations 

 contain a contradiction. Waldenstrom (2911) found that uroporphyrin III 

 is not present as such in the urine, but arises by action of acid on a dipyrrolic 

 colorless precursor (porphobilinogen). While the former is certainly often 

 not correct (a uroporphyrin occurs in acute porphyria in the body as such; 

 cf. Watson and co-workers, 10 'jd. 3002, and Prunty, 2103), there can be no 



