Chemo-Enzymatic Synthesis, Structural and Stereochemical Characterization, and Intrinsic Degradation Kinetics of Diastereomers of 1-β-O-Acyl Glucuronides Derived from Racemic 2-{4-[(2-Methylprop-2-en-1-yl)amino]phenyl}propanoic Acid

Abstract

Alminoprofen, ( RS )-2-{4-[(2-methylprop-2-en-1-yl)amino]phenyl}propanoic acid (ALP) 1 , is a racemic drug categorized as a 2-arylpropanoic acid-class nonsteroidal anti-inflammatory drug. Pharmacokinetic studies of 1 in patients have revealed that the corresponding acyl glucuronide 5 is a major urinary metabolite, but little is known about the structure and stereochemistry of 5 . The present work describes the synthesis of a diastereomeric mixture of 1-β- O -acyl glucuronides (2 RS )- 5 from 1 and methyl 2,3,4-tri- O -acetyl-1-bromo-1-deoxy-α- d -glucopyranuronate 2 using our chemo-enzymatic method that has complete specificity for the β-configuration. The structure of (2 RS )- 5 was characterized by 1 H and 13 C NMR spectroscopy and high-resolution mass spectrometry as well as by complete hydrolysis by β-glucuronidase. The absolute stereochemistry of (2 RS )- 5 was determined by comparison with (2 R )- 5 synthesized alternatively from (2 R )- 1 and 2 . Compound (2 R )- 1 was prepared in two steps starting from chiral ( R )-2-(4-nitrophenyl)propanoic acid (2 R )- 6 . Chiral resolution of (2 RS )- 1 was achieved using a chiral high-performance liquid chromatography column, and its stereochemistry was determined by comparison with (2 R )- 1 . The intrinsic degradation rate constant of (2 R )- 5 was 0.405 ± 0.002 h –1 , which is approximately twice that of (2 S )- 5 (the k value was 0.226 ± 0.002 h –1 ) under physiological conditions (pH 7.40, 37 °C).