Pyrroles and related compounds-XXXVI. Transformations of protoporphyrin-IX into harderoporphyrin, pemptoporphyrin, chlorocruoroporphyrin and their isomers

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Treatment of protoporphyrin-IX dimethyl ester (8b) with 2 equiv of thallium(III) nitrate in methanol followed by chromatography affords good yields of a mixture of mono-acetal-mono-vinyl isomers (11b and 12b) which can be converted into the corresponding (2-hydroxyethyl)-vinyldeuteroporphyrins (13b and 14b) by hydrolysis and reduction with sodium borohydride. After separation by preparative TLC these compounds are transformed into isoharderoporphyrin trimethyl ester (3b) and harderoporphyrin trimethyl ester (2b) by treatment with CBr4/Ph3P (to afford the 2-bromoethyl derivatives), then sodium cyanide in 1-methylpyrrolidone (giving the 2-cyanoethyl compounds), followed by methanolysis. Formal syntheses of pemptoporphyrin dimethyl ester (4b) and its isomer (5b) are achieved by devinylation (resorcinol melt) of the haemins from the pure (2-hydroxyethyl)-vinyl isomers (14b and 13b) respectively, followed by demetallation. Controlled oxidation of protoporphydrin-IX dimethyl ester (8b) with osmium tetroxide gives starting material, mono-glycol-mono-vinyl isomers (23b and 24b), and bis-glycol (25b); this mixture can be separated by column chromatography. Further separation of the mono-glycols through preparative TLC followed by treatment with sodium periodate gives pure samples of chlorocruoroporphyrin dimethyl ester (6b) and its isomer (7b). In the TLC separations of unsymmetrically 2,4-substituted deuteroporphyrins studied, the 2-vinyl substituted isomers proved always to be the more polar (less mobile) componnets of the mixtures of isomers. © 1976.

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