The Analytical Reduction of Porphyrins to Pyrroles

Abstract

When porphyrins or related pigments are reduced by HI-AcOH, their meso-substituents (R = H or alkyl) appear as a-CH2R groups in the resulting pyrroles. The identification of the pyrroles, as by g.l.p.c., defines and orders the meso-substituents flanking each pair of peripheral substituents in the porphyrin. If one meso-substituent differs from the others, all the substituents about the two adjacent pyrrole nuclei are then ordered.The pyrroles can be reductively alkylated in situ, and symmetry then reduces their number when the aldehyde used (R.CH0) corresponds to a bridge and its meso-substituent. This may simplify the pyrrole mixtures, identify meso-substituents, or make pyrroles distinguishable by g.1.p.c.The critical pyrrole -propionic acids are separable as methyl esters by g.1.p.c. Desoxophylloerythrin and pyrophaeophorbides (the latter first reduced with potassium borohydride) are reduced to cyclopenteno-pyrroles which reveal the isocyclic rings and the 5-substituents. The r.r.t.3 of relevant pyrroles are reported.La reduction des porphyrines et des pigments du mCme genre par HI-AcOH fait que les substituants mtso (R = H OLI alkyle) apparaissent sous forme de groupements CH2R en cc des pyrroles resultants. L'identification des pyrroles par c.p.l.g., par exemple, definit et classe les substituants meso qui se trouvent a cBte de chaque paire de substituants peripheriques dans la porphyrine. Si un des substituants meso differe des autres, tous les substituants autour des deux noyaux pyrroles adjacents sont alors clasds.L'alkylation reductive irz situ des pyrroles peut riduire par symitrie le nombre de pyrroles lorsque l'aldehyde utilise (R.CH0) correspond au pont et au substituant meso de la porphyrine initiale. Ceci peut simplifier le melange des pyrroles, identifier les substituant meso et differentier les pyrroles par c.p.1.g.Les acides critiques pyrrole -propioniques sont separables de leurs esters methyliques par c.p.1.g. La dCsoxophylloerythrine et les pyrophaephorbides (ces dernieres d'abord reduites par le borohydrure de potassium) sont reduites en cyclopenteno-pyrroles, ce qui revele les noyaux isocycliques et les substituants en 5. Les donnees t.r.r, des pyrroles correspondants sont rapportkes.

Bacteriochlorophyll e : structure and stereochemistry of a new type of chlorophyll from Chlorobiaceae

“…This is in full agreement with results of reductive degradation experiments by R. A. Chapman et al (1971). It should be noted that the 13C chemical shift changes of the 1-and 8-methyl group caused by a 5-methyl substituent are very similar to those ( -6.31 and H-2.27 parts/106) caused by a 5bromine (Lincoln, Wray, Brockmann & Trowitzsch 1974).…”

Bacteriochlorophylls c from Chloropseudomonas ethylicum. Composition and NMR studies of the pheophorbides and derivatives

“…Potassium íe/7-butoxide was found to be a more effective cyclization agent. The formation of the isocyclic ring was studied in porphyrins using chloroporphyrin es trimethyl ester (22) and in chlorins using chlorin e¿ trimethyl ester (23). Chloroporphyrin e(, trimethyl ester in refluxing pyridine containing potassium re/7-butoxide was converted in 55% yield to pheoporphyrin as dimethyl ester (24).…”

Lipids of aquatic sediments, recent and ancient

“…A part from the novel method of degradation outlined above, there are other, more classical, methods of obtaining structural information of porphyrins by chemical degradation techniques. The reductive conversion to pyrroles has already been mentioned (Chapman al. 1971) but the products are unstable, so the alternative of oxidative cleavage to the respective maleimides (Ellsworth & Aronoff 1968) is preferred, despite the loss of information about the positions on the macrocycle.…”