Internal acyl migration reactions of 1β-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 1β-O-acyl glucuronides of enantiomeric 2-phenylpropionic acids (PAs), the basic structures of profens, in phosphate buffer (pH 7.4) at 37°C, has been investigated using HPLC. Apparent first-order degradation of 1β-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.
The stereoselective acyl migration of diastereomeric 1β-O-acyl glucuronides of (R)- and (S)-2-phenylpropionic acid [(R)-1PG and (S)-1PG, respectively] in phosphate buffer (pH 7.4) at 310 K was investigated using HPLC. The disappearance of (R)-1PG was faster than that of (S)-1PG according to pseudo first-order kinetics. A kinetic model describing the degradation reactions was constructed. The rate constant for acyl migration from the 1β-O-isomer to the 2-O-acyl isomer (k12) was about one order magnitude larger than that for hydrolysis from 1β-O-acyl isomer to aglycone (k10). The k12 of (R)-1PG (0.377±0.005 h-1) was about two times larger than that of (S)-1PG (0.184±0.003 h-1). The results indicated that the stereoselectivity in the degradation of 1PG was apparently governed by the acyl migration from 1-isomer to 2-isomer. The kinetic parameters for acyl migration from 1-isomer to 2-isomer were estimated from temperature-dependent experiments using the transition state theory. The value of the free energy of activation at 310 K for (R)-1PG (99.67 kJ/mol) was smaller than that of (S)-1PG (101.60 kJ/mol), suggesting that (R)-1PG showed thermodynamically higher reactivity in acyl migration than (S)-1PG.
Glycosylation of 2-phenylpropionic acid and its ethyl ester in suspension cultures of Nicotiana tabacum, Dioscoreophyllum cumminsii and Aconitum japonicum☆
Synthesis of a series of phenylacetic acid 1-β-O-acyl glucosides and comparison of their acyl migration and hydrolysis kinetics with the corresponding acyl glucuronides
作者:Lisa Iddon、Selena E. Richards、Caroline H. Johnson、John R. Harding、Ian D. Wilson、Jeremy K. Nicholson、John C. Lindon、Andrew V. Stachulski
DOI:10.1039/c0ob00820f
日期:——
carboxylate group of the acyl glucuronides plays a part in the mechanism of the internal acylmigration. In addition, such acyl glucosides are known to be endogenous biochemicals in their own right and investigation of their acylmigration propensities is novel. Our previously described selective acylation procedure has proved highly successful for 1-β-O-acyl glucuronide synthesis and when subsequently