Stereoselective internal acyl migration of 1beta-O-acyl glucuronides of enantiomeric 2-phenylpropionic acids

Internal acyl migration reactions of 1beta-O-acyl glucuronides of 2-arylpropionic acids (profens) are of interest because of their possible role in covalent binding to serum proteins and consequent allergic reactions. The stereoselective degradation of 1beta-O-acyl glucuronides of enantiomeric 2-phenylpropionic acids (PAs), the basic structures of profens, in phosphate buffer (pH 7.4) at 37 degrees C, has been investigated using HPLC. Apparent first-order degradation of 1beta-O-acyl glucuronide and the sequential appearance of 2-, 3- and 4-O-acyl isomers were observed for each enantiomer. Acyl migration was observed to predominate over hydrolysis as in the other profen glucuronides. All the positional isomers and anomers were characterized using NMR and HPLC-NMR. The overall degradation half-life of (R)- and (S)-PA glucuronides was 1.8 and 3.3 h, respectively. These results suggest that (R)-PA glucuronide could be more susceptible to covalent binding to proteins via acyl migration than the corresponding antipode. The lability of the (R)-diastereomer over the antipode is consistent with previous reports on other profen glucuronides. Thus, the diastereomeric PA glucuronides are considered to be the best model compounds for the computation of structural physicochemical parameters to control the stereoselective internal acyl migration of profen glucuronides because PA has the simplest chemical structure of all the profens.