Biosynthesis of porphyrins and related macrocycles. Part 16. Proof that the single intramolecular rearrangement leading to natural porphyrins (type-III) occurs at the tetrapyrrole level

Abstract

The unrearranged aminomethylbilane (2) is synthesised by a rational route and is proved to be converted by the enzymes deaminase and cosynthetase, working co-operatively, into uro'gen-III (3). The single rearrangement step established earlier is thus proved to take place at the tetrapyrole level. Synthesis of singly ¹³C-labelled bilane (2) followed by its enzymic conversion into uro'gen-III serves to register each of the pyrrole rings of the product relative to the initial bilane. Finally, methods for synthesis of the bilane are developed in two different doubly ¹³C-labelled forms to allow the following key points to be established largely by ¹³C n.m.r. spectroscopy: (a) as the bilane system is converted into uro'gen-III, intramolecular rearrangement of the terminal ring D occurs, and (b) the lineartetrapyrrole is converted intact into uro'gen-III.

Syntheses of [15-¹³C]-, and [20-¹³C]-uroporphyrin octamethyl ester are described together with improved h.p.l.c. conditions for the separation of isomeric coproporphyrin tetramethyl esters.