Partial syntheses of the isomerically pure magnesium(II) protoporphyrin IX monomethyl esters, and their identification

Abstract

Treatment of 2,4-diacetyldeuteroporphyrin IX with oxalyl dichloride and t-butyl alcohol gives mainly the two isomeric mono-t-butyl esters, 10 and 11, which can be separated by thick-layer chromatography on silica gel. These monoesters can be individually transformed, via a sequence of steps, into the corresponding isomerically pure protoporphyrin IX monomethyl esters, 5 and 6, one being the magnesium (II)-free derivative of a key intermediate in the biosynthetic pathway to chlorophylls and bacteriochlorophylls. The isomerically pure monomethyl esters 5 and 6 were magnesiated and the resulting magnesium(II) protoporphyrin IX monomethyl esters 2 and 4, respectively, were challenged with a suspension of isolated developing chloroplasts in the presence and absence of added S-adenosylmethionine. The isomerically pure isomer which was converted into magnesium(II) 2,4-divinylpheoporphyrin a₅3 in the absence of the SAM cofactor was identified as the physiologically significant 6-methyl ester 2.