Biosynthesis of porphyrins and related macrocycles. Part 52. Synthesis of (11-S)-[11-2H1]porphobilinogen and the (11R)-enantiomer for stereochemical studies on hydroxymethylbilane synthase (porphobilinogen deaminase)

Abstract

A synthetic route is devised for the synthesis of (11S)-[11-²H₁]porphobilinogen 1a and of the (11R)-enantiomer 1b. Their absolute configurations and enantiomeric purity are established by degradation to a derivative of [2-²H₁]glycine of known stereochemistry. Methods are then developed, based on the synthesis of chiral imidate esters, for determination of the configuration of [²H₁]-labelled aminomethylpyrroles by converting them into [²H₁]-labelled amidines followed by analysis using ¹H-NMR. The labelled samples of PBG 1a and 1b serve as substrates for hydroxymethylbilane synthase and the products are trapped as [²H₁]-labelled aminomethylbilanes 7c and 7d. Their configurations are determined by the NMR assay to demonstrate that as PBG 1 is enzymically converted into the aminomethylbilane 7, there is overall retention of configuration at the aminomethyl carbon.