Synthetic and biosynthetic studies of porphyrins. Part 7. The action of coproporphyrinogen oxidase on coproporphyrinogen-IV: syntheses of protoporphyrin-XIII, mesoporphyrin XIII, and related tricarboxylic porphyrins

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Abstract
Coproporphyrinogen-IV (2a) is converted by an enzyme system from chicken blood into a tricarboxylic porphyrinogen (2b) and protoporphyrinogen-XIII (2c). The corresponding porphyrins were isolated as their methyl esters (3b) and (3c) and their structures were deduced by mass and n.m.r. spectrometry (including the use of shift reagents). Confirmation of these conclusions was obtained by total synthesis of the new porphyrins by the MacDonald and ac-biladiene routes. The vinyl groups were introduced either via acetoxyethyl side-chains derived from precursor pyrroles, or by reduction and dehydration of acetyl groups inserted into the porphyrins during the final stages of the syntheses. Mesoporphyrin-XIII dimethyl ester (3m) and the ethyl analogue (3n) of the vinyl tripropionate porphyrin (3b) were also synthesized by the MacDonald route.