A Solid-state NMR Study of Formoterol Fumarate

Abstract

Spectra have been obtained for each of the three formoterol fumarate solvates diethanol, diisopropanol and dibenzyl alcohol and, with the aid of solution-state data and dipolar dephasing experiments, carbon-13 spectral assignments have been made. It was shown that diethanol and diisopropanol solvates are relatively stable to magic-angle spinning but do gradually convert to anhydrate C. The coalescence temperature of the methoxybenzene carbon atoms for diethanol, diisopropanol solvates and anhydrate C were found and an exchange rate for this ring-flip calculated. The formoterol fumarate dihydrate, anhydrate A, anhydrate B and anhydrate C have been prepared and spectra obtained, again with the aid of solution-state data and dipolar dephasing experiments carbon-13 spectral assignments have been made where possible. (^13)C and (^2)H T(_1) measurements suggest that the fumarate ion is mobile in the anhydrate C structure. A (^2)H DPMAS spectrum, however does not indicate isotropic motion for the ion. Water measurements of anhydrate A and anhydrate C indicate them to contain water. It is believed that this water is hydrogen bonded to the NH(_2)+ ion and is difficult to remove by heating. A route for preparing the solvates by bypassing the need to dry the dihydrate has-been found. An ethyl acetate solvate of formoterol fumarate was produced by slurrying anhydrate C with ethyl acetate.