Separation of enantiomers on HPLC chiral stationary phases based on human plasma α1-acid glycoprotein:: Effect of sugar moiety on chiral recognition ability

HPLC chiral stationary phases based on human plasma alpha(1)-acid glycoprotein (AGP) and partially deglycosylated AGP (pd-AGP) were prepared to investigate the effects of sugar moiety of AGP on chiral discrimination of various solutes. Removal of a sugar moiety of AGP by treatment with N-glycosidase was confirmed by high-performance capillary electrophoresis, reversed-phase HPLC and matrix-assisted laser desorption-time of flight (MALDI-TOF) mass spectrometry. The average molecular weights of AGP and pd-AGP were estimated to be ca. 33,000 and 30,600, respectively, by MALDI-TOF mass spectrometry. Next, AGP and pd-AGP were bound to aminopropyl-silica gels activated with N,N '-disuccinimidylcarbonate. The retentivity and enantioselectivity of the neutral, acidic and basic solutes tested on the pd-AGP column were significantly or not significantly larger in most solutes than those on the AGP column. This is ascribable to that by cleavage of a sugar chain(s) by N-glycosidase, pd-AGP could become more hydrophobic than AGP, and/or that a solute could be easily accessible to the specific and/or non-specific binding sites of pd-AGP. It is interesting that warfarin enantiomers are not resolved on the pd-AGP column, but resolved on the AGP column. A sugar chain(s) of AGP cleaved by N-glycosidase might be involved in the enantioselective binding of warfarin enantiomers.