A CROSS-POLARIZATION MAGIC-ANGLE-SPINNING C-13 NMR CHARACTERIZATION OF THE STABLE SOLID-STATE FORMS OF CIMETIDINE

Proton decoupled, cross-polarization magic-angle spinning C-13 NMR spe ctra of four polymorphic forms (A, B, C, and D) and a monohydrate form (M1) of the histamine H-2 antagonist cimetidine were obtained, and th e chemical shifts of the various forms were tabulated. A modified pola rization inversion pulse sequence was used to distinguish quaternary, methine, methylene, and methyl carbon resonances and thereby assist sp ectral assignment. It is also shown that the solid-state form of cimet idine in a commercial formulation can be reliably ascertained by NMR, despite the presence in the spectrum ai signals from organic excipient s that are much more intense than those from the compound.