750 MHz HPLC−NMR Spectroscopic Studies on the Separation and Characterization of the Positional Isomers of the Glucuronides of 6,11-Dihydro-11- oxodibenz[b,e]oxepin-2-acetic Acid

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Abstract
Ester glucuronides (beta-1-O-acyl-D-glucopyranuronates) of many drugs can undergo a series of acyl migration reactions, resulting in positional isomers and anomers which can react with serum proteins with possible toxicological consequences. We have investigated the acyl migration of the ester glucuronides of the model drug 6,-11-dihydro-11-oxodibenz[b,e]oxepin-2-acetic acid in pH 7.4 buffer using directly coupled 750 MHz stopped-flow HPLC-NMR spectroscopy. Using a reversed phase isocratic HPLC method with 21% acetonitrile and 79% D2O in the mobile phase, it was possible to separate and hence identify the individual positional isomers of the model drug glucuronide by 750 MHz HPLC-NMR. The order of elution of the isomers from the C18 column was 4alpha-, 4beta-, aglycon, 1beta-, 3beta-, 3alpha-, 2alpha-, 2beta- (alpha- and beta- referring to the anomerization state at C1 on the glucuronide ring and the numbers referring to the carbon number on the glucuronide ring to which the drug moiety has migrated). It is shown that directly coupled ultra-high-field HPLC-NMR spectroscopy offers a unique analytical advantage for obtaining structural information of interconverting compounds in equilibrium mixtures, and this method will be of value in the study of reactive drug glucuronides of toxicological importance.