Carbon-13 magnetic resonance spectroscopy of drugs III: penicillins.

The natural abundance 13C-NMR spectra of a series of penicillins (penicillin V methyl ester, penicillin V, penicillin G, methicillin, oxacillin, cloxacillin, and dicloxacillin) were studied. The chemical shifts were assigned using the pulse Fourier transform technique with the aid of long-range carbon-13 hydrogen coupling. The previous assignments of pencillin V methyl ester were revised.