Biosynthesis of porphyrins and related macrocycles. Part 44. Synthetic and stereochemical studies on the proposed spiro intermediate for biosynthesis of the natural porphyrins

Abstract

A route is devised for synthesis of both enantiomers of the spiro lactam 4. The enzyme uroporphyrinogen III synthase (cosynthetase), which converts hydroxymethylbilane 1 into uroporphyrinogen III 3, is competitively inhibited more than twenty times more strongly by one enantiomer of 4 than by the other. This finding adds further strong support to the view that cosynthetase acts by generating the spiro pyrrolenine 2 as an intermediate.