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Drugs and drug metabolites containing a carboxylic-acid moiety can undergo in vivo conjugation to form 1-β-O-glucuronides (1-β-O-AGs). In addition to hydrolysis, these conjugates can undergo spontaneous acyl migration, and anomerisation reactions, resulting in a range of positional isomers. Facile transacylation has been suggested as a mechanism contributing to the toxicity of acyl glucuronides, with the kinetics of these processes thought to be a factor. Previous ¹H NMR spectroscopic and HPLC-MS studies have been conducted to monitor the hydrolysis, transacylation, and anomerisation behaviours of the 1-β-O-AGs of three nonsteroidal anti-inflammatory drugs (ibufenac, R-ibuprofen, S-ibuprofen) and a dimethyl-analogue (termed here as “bibuprofen”). These studies have determined the relative contributions of hydrolysis and acyl migration in both buffered aqueous solution, and human plasma. Here, a …