The conformation of 6-methoxyerythromycin A in water determined by proton NMR spectroscopy

The proton NMR spectrum of an aqueous solution of 6-methoxyerythromycin A (2) has been assigned and nuclear Overhauser effects have been obtained from a series of NOESY spectra. Carbon-13 antisymetric spin-lattice relaxation times have been measured for the methylene and methine carbons. The NMR data show that 2 is present exclusively in the keto form and has a conformation very similar to that reported for erythromycin A (1) in the solid and solution phases.