Direct characterization of drug glucuronide isomers in human urine by HPLC-NMR spectroscopy: Application to the positional isomers of 6,11-dihydro-11-oxodibenz[b,e]oxepin-2-acetic acid glucuronide

In this work, 400 and 600 MHz H-1 HPLC-NMR spectroscopic methods were developed and applied to separate and identify the positional glucuronide isomers and anomers of the model nonsteroidal antiinflammatory drug, 6,11-dihydro-11-oxodibenz[b,e]oxepin-2-acetic acid, in whole human urine, The HPLC methods utilized either an isocratic system, comprising 30% acetonitrile in water at pH 2.5, or a gradient elution system increasing from 30% to 60% acetonitrile, in order to achieve improved separation of the 2-, 3-, and 4-O-acylglucuronide isomers from the faster eluting endogenous urinary metabolites, Directly coupled stop-flow H-1 HPLC-NMR spectroscopic measurements were made at the retention times indicated by the W-monitored chromatographic peaks, The glucuronide isomers were identified from the H-1 NMR spectra on the basis of their chemical shifts and spin-spin coupling patterns. The elution order was 4-O-acyl-, 3-O-acyl-, and finally 2-O-acylglucuronide, with t(R) values of 10.04, 11.68, and 12.64 min, respectively, Although the alpha- and beta-anomers of each of the positional isomers could not be separated in these solvent systems, they could be identified in the individual H-1 NMR spec tra. This work shows for the first time that directly coupled HPLC-NMR spectroscopy can be used directly to isolate and characterize acyl-migrated isomers of drug glucuronides in whole urine, This approach will be of value in the study of glucuronide acyl migration reactions of nonsteroidal antiinflammatory drugs and other xenobiotic ester glucuronides in whole biofluids.