The Structure of Porphyrin a, Cryptoporphyrin a and Chlorin ag 345 



chromic acid under mild conditions to carboxyl, its reduction by sodium 

 borohydride to hydroxymethyl, and its condensation with acetone-HCI, 

 probably to -CHiCH-CO-CHg. Porphyrin a undergoes all these reactions. 

 Since acetone-hydrochloric acid is used in the isolation of haemin a from 

 heart muscle, and for its crystallization in the Warburg procedure, the last- 

 mentioned reaction is of interest; unless care is used, this reaction partially 

 converts haemin a into its acetone condensate. 



The magnitude of the shift of the absorption bands of porphyrin a in the 

 oxime formation (CHO -^ •CH:NOH) shows that only one carbonyl, i.e. 

 the formyl group is present. The average shift for the four bands is 75 A 

 for porphyrin a, 82 for monoformyl deuteroporphyrin, 77 for chlorocruoro- 

 porphyrin and 79 for cryptoporphyrin a. This shift is about the same for 

 acetyl and formyl groups, and two such groups cause a band shift of about 

 120 A. 



Porphyrin a does not contain a carboxyl group directly on the nucleus. 

 After treatment of the porphyrin with hydriodic acid or after diazoacetic 

 ester addition to the double bond, hydroxylamine gave aetio-type porphyrins 

 (Rimington, Hale, Rawlinson, Lemberg and Falk, 1949); a carboxyl group 

 would not be altered by these reagents and would retain its rhodofying 

 effect on the spectrum. Two carboxylic acid groups can be demonstrated in 

 porphyrin a by manometry (Morell, unpublished) and both are accounted for 

 as propionic acid side chains, as the conversion of porphyrin a into cyto- 

 deuteroporphyrin shows (Warburg and Gewitz, 1953). In the paper chroma- 

 tography in lutidine-water (Nicholas and Rimington, 1949), porphyrin a had 

 an Rp of 0-84, slightly higher than the 0-81 of other dicarboxylic acids. 



The Unsaturated Side Chain Conjugated to the Nucleus and Its Position 

 Relative to the Formyl 



Rimington et al. (1949) believed to have evidence for the presence of two 

 vinyl groups from absorption spectra of the oxime and its presumed diazo- 

 acetic ester adduct. The latter was, however, prepared by diazoacetic ester 

 addition to porphyrin a before oximation. Since the formyl group also reacts 

 with the ester, it is necessary to protect it by oximation first before the 

 diazoacetic ester addition. This experiment was carried out in our laboratory 

 (Parker, 1959) and gave evidence for only one vinyl group (band shift about 

 2 m/<, as for chlorocruoroporphyrin). Warburg and Gewitz (1951) also 

 found that only two atoms of hydrogen (plus one needed for the reduction of 

 the iron from ferric to ferrous) were added on catalytic hydrogenation of 

 haemin a in borate buffer pH 11. 



Porphyrin a differs, however, from chlorocruoroporphyrin, which has a 

 formyl and one vinyl group in two aspects. Firstly, its absorption bands are 

 slightly shifted towards the red (cf. Table 1). It may be noted that it is 

 essential to compare absorption spectra in the same solvent. Chloroform, as 



