Structural determination of 5′-OH α-ribofuranoside modified cobalamins via 13C and DEPT NMR

A protocol for the rapid NMR characterization of cobalamin (vitamin B-12) analogues with 5'-hydroxy-alpha-ribofuranoside modification is reported. The structure of cyanocobalamin in DMSO-d(6) has been assigned using COSY, NOESY, HSQC, and HMBC NMR methods. The robust precision of C-13 NMR assignments in DMSO-d(6) allows for the rapid structural determination of 5'-hydroxy-alpha-ribofuranosyl cyanocobalamin derivatives with solely 1-D C-13 and DEPT NMR spectra and only 10 mg of derivatized cobalamin. Using this method, the C-13 NMR resonances of four cobalamin analogues were determined with the most significant variance of C-13 chemical shifts occurring in the alpha-ribofuranoside ring. In DMSO-d(6), cobalamin concentrations greater than 30 mM can be achieved for an improved signal-to-noise ratio.