Biosynthesis of porphyrins and related macrocycles. Part 47. Synthesis and chemistry of 2H-pyrroles (pyrrolenines) related to the proposed spiro-intermediate for porphyrin biosynthesis

It is proposed that the biosynthesis of uroporphyrinogen III 3, the parent precursor of the natural porphyrins, chlorins and corrins, involves a pyrrolenine 2 as a key intermediate, yet methods for the synthesis of such systems are not available. Novel routes for the synthesis of pyrrolenines by desulfurisation of unsaturated thiolactams have now been devised and the chemistry of such compounds has been explored. Enzymic experiments are carried out using a model pyrrolenine indicating that deletion of one of the pyrrole rings of the putative intermediate 2 leads to loss of tight binding.