Biosynthesis of vitamin B12: the structure of factor IV, the oxidized form of precorrin-4

Abstract
13 C Labelling and NMR experiments establish the structure of factor IV, the oxidized form of the tetramethylated intermediate on the biosynthetic pathway to precorrin-6x 2 in Pseudomonas denitrificans, thus demonstrating that the contraction of the macrocycle leads to an acetyl derivative at C-1.