The regiochemistry and stereochemistry of the biosynthesis of vitamin B6 from triose units

13C and 2H NMR spectroscopy has been employed to probe the biosynthesis of vitamin B6 in Escherichia coli. The 13C NMR spectrum of a sample of pyridoxol derived biosynthetically from D-[1,2,3,4,5,6-13C6]glucose shows that the bonds, C(2)-C(3) and C(4)-C(5), of the pyridine nucleus are the only two carbon-carbon bonds of pyridoxol which are generated de novo in the course of its biosynthesis from glucose. It follows that the pyridoxol skeleton is generated from two intact triose units and a triose-derived two-carbon unit, all of which are supplied by glucose. From the 2H NMR spectra of samples of pyridoxol derived from (R)-[1,1-2H2]glycerol and (S)-[1,1-2H2]glycerol, respectively, it can be deduced that the rehydroxymethyl group of glycerol enters C-2′, C-4′, and C-5′ of the pyridoxol skeleton. It follows that each of the three fragments is derived from glycerol in stereo-specific fashion. These results answer questions concerning the regiochemistry and the stereochemistry of pyridoxol biosynthesis.