Assignment of 15N-NMR resonances of vitamin B12 analogues by 2D-[15N, 1H] long-range correlation: Fully [15N]-labelled Co-β-cyano-5-hydroxybenzimidazoylcobamide (factor III) and derivatives

The ¹⁵N-NMR spectra of vitamin B₁₂ analogues obtained in fully ¹⁵N-labelled form have been measured by direct and inverse (¹⁵N, ¹H) correlated spectroscopy. All resonances, except those of the NH₂ groups, have been assigned to individual N-atoms. The influences on δ (N) are analyzed and discussed which are caused by changing the α-face ligand from CN to H₂O or CH₃ and by switching the β-face ligand from the base-on to the base-off state. An implication of the correct resonance assignment on biosynthetic pathways is demonstrated.