Biosynthesis of vitamin B12: analysis of the 1H and 13C n.m.r. spectra of heptamethyl dicyanocobyrinate (cobester)

Abstract

Heptamethyl dicyanocobyrinate(1), a key substance for biosynthetic researches on vitamin B₁₂, has been studied by ¹H and ¹³C n.m.r. All the resonances in the ¹H spectrum (apart from those for OMe groups) have been rigorously assigned using partially relaxed spectra and n.O.e. difference and decoupling difference techniques. The assigned ¹H resonances have been correlated with the ¹³C spectrum to allow signal assignments for all the proton bearing carbons. The remaining signals, apart from the carbonyl groups, were assigned either by long-range proton decoupling or by specific labelling of cobester with ²H to cause isotopic shifts of the ¹³C signals across two to five bonds. The full set of assignments for ¹H and ¹³C n.m.r. spectra form the basis for future biosynthetic studied on vitamin B₁₂.