Kinetics of intramolecular acyl migration of 1beta-O-acyl glucuronides of (R)- and (S)-2-phenylpropionic acids.
The stereoselective acyl migration of diastereomeric 1beta-O-acyl glucuronides of (R)- and (S)-2-phenylpropionic acid [(R)-1PG and (S)-IPG, respectively] in phosphate buffer (pH 7.4) at 310K 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 1beta-O-isomer to the 2-O-acyl isomer (k12) was about one order magnitude larger than that for hydrolysis from 1beta-O-acyl isomer to aglycone (k10). The k12 of (R)-IPG (0.377 +/- 0.005 h(-1)) was about two times larger than that of (S)-IPG (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)-IPG (101.60kJ/mol), suggesting that (R)-IPG showed thermodynamically higher reactivity in acyl migration than (S)-1PG.
Hasegawa
H
H
School of Pharmacy, Tokyo University of Pharmacy and Life Science, Hachioji, Japan. hasegawa@ps.toyaku.ac.jp
Akira
K
K
Shinohara
Y
Y
Kasuya
Y
Y
Hashimoto
T
T
D000215:Acylation; D002138:Calibration; D002851:Chromatography, High Pressure Liquid; D020719:Glucuronides / Q000737:chemistry*; D007700:Kinetics; D010666:Phenylpropionates / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D013696:Temperature
D020719:Glucuronides; D010666:Phenylpropionates