Studies on the Biosynthesis of Corrinoids and Porphyrinoids. I : The Labeling of Oxygen of Vitamin B₁₂

Abstract

Recently the amide-oxygen has been suggested to participate in the formation of the corrin ring of vitamin B₁₂. To confirm this hypothesis, ¹⁷O-labeled aminolevulinic acid (ALA) was prepared and administered to Propionibacterium shermanii. The isolated vitamin B₁₂ showed only broad ¹⁷O signals in the oxygen-17 nuclear magnetic resonance (¹⁷O-NMR) spectrum. However, distinct isotope-shifted peaks were observed in the ¹³C-NMR spectrum of vitamin B₁₂ isolated after incorporation of [1-¹³C : 1, 4-¹⁸O₂]ALA. Of these shifted peaks, one peak (C₂₇) showed very low intensity. This indicates that dilution of ¹⁸O occurred at the acetyl chain of the A ring of vitamin B₁₂. This result supports the assumption that the lactone formation of the A ring promotes the ring contraction, as proposed by Eschenmoser.