Biosynthesis of porphyrins and related macrocycles. Part VII. Synthesis of specifically labelled [14C1]uroporphyrin-III and of [10,14-13C2]uroporphyrin-III. Conversion of the latter into [10,14-13C2]protoporphyrin-IX; biosynthetic significance of its 13C nuclear magnetic resonance spectrum

Abstract

Uroporphyrin-III (4) has been synthesised by a route which allows [2,11-¹³C₂]porphobilinogen (3) to be elaborated to give [10,14-¹³C₂]uroporphyrin-III (4). This, after reduction to the corresponding porphyrinogen, has been transformed enzymically into [10,14-¹³C₂]protoporphyrin-IX (2). The ¹³C n.m.r. signal from position 10 (β-meso-carbon) of the methyl esters of both porphyrins (2) and (4) appears as a 5.5 Hz doublet. This demonstration of long-range coupling is of decisive importance for related research on the nature of the rearrangement process by which the natural type III porphyrins are biosynthesised.

A new procedure has been developed for pyrromethane formation, based on catalysis by tin(IV) chloride, which appears to be of general value.