An S-mandelic acid imprinted chitosan resin was synthesized by cross-linking chitosan with glutaraldehyde in 2% acetic acid solution. S-Mandelic acid imprinted chitosan resin was used to enantioselectively separate racemic mandelic acid in aqueous medium. When keeping the pH of sample solution (100 mM Tris-H 3 PO 4 ) at 3.5 and adsorption time at 40 min, the enantiomer excess of mandelic acid in supernatant was 78.8%. The adsorption capacities of S-mandelic acid imprinted chitosan resin for S- and R-mandelic acid were determined to be 29.5 and 2.03 mg/g, respectively. While the adsorption capacities of non-imprinted cross-linked chitosan for S- and R-mandelic acid were 2.10 and 2.08 mg/g, respectively. The result suggests that the imprinted caves in S-mandelic acid imprinted chitosan resin are highly matched with S-mandelic acid molecule in space structure and spatial arrangement of action sites. Interestingly, the enantiomer excess value of mandelic acid in supernatant after adsorption of racemic mandelic acid by R-mandelic acid imprinted cross-linked chitosan was 25.4%. The higher enantiomer excess value by S-mandelic acid imprinted chitosan resin suggests that the chiral carbons in chitosan and the imprinted caves in S-mandelic acid imprinted chitosan resin combine to play roles for the enantioselectivity of S-mandelic acid imprinted chitosan resin toward S-mandelic acid. Furthermore, the excellent enantioselectivity of S-mandelic acid imprinted chitosan resin toward S-mandelic acid demonstrates that using chiral chitosan as functional monomer to prepare molecularly imprinted polymers has great potential in enantioseparation of chiral pharmaceuticals.
Yang Zhang,Chen Su,Jinxiu Lei,Lu Chen,Haihong Hu,Su Zeng,Lushan Yu
Mandelic acid (MA) is generally used as a biomarker of the exposure of styrene , which is classified as a class of hazardous environmental pollutants, and also used as an important chiral intermediate in pharmaceutical industry. The previous studies have found the excretion of phenylglyoxylic acid (PGA) in human and rat, a metabolite of MA, was mainly from S- MA rather than R -MA. The metabolic mechanism, however, is not clear. In order to explore the possible metabolic mechanism, the enzyme types involved in the stereoselectivity metabolism of MA were firstly studied, and then human and rat long-chain 2-hydroxy-acid oxidase 2 (HAO2) were recombinantly expressed to study the metabolic profiles of S- MA and its analogues. The results indicated that HAO2 might catalyze the stereoselectivity metabolism of S- MA in rats. Human HAO2 ( h HAO2) and rat HAO2 ( r HAO2) isozymes β 1 and β 2 were successfully cloned and expressed with high purity and good enzyme activities. The enzyme kinetic profiles of these enzymes were different for S- MA and analogues. The order of catalytic efficiency for h HAO2 and r HAO2, however, was reverse. It might be relevance to the difference in active amino acid residues and loop 4 in human and rat L-2-hydroxy acid oxidase isozyme B crystal structures.
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