Preparation and evaluation of an ethylenediamine dicarboxyethyl diamido-bridged bis(β-cyclodextrin)-bonded chiral stationary phase for high performance liquid chromatography

Abstract

An ethylenediamine dicarboxyethyl diacetamido-bridged bis(β-cyclodextrin) was firstly synthesized through the reaction of 6-deoxy-6-amino-β-cyclodextrin (NH2-CD) with ethylenediaminetetraacetic dianhydride. Then it was bonded onto the surface of silica gel SBA-15 to obtain an ethylenediamine dicarboxyethyl diacetamido-bridged bis(β-CD)-bonded chiral stationary phase (EBCDP). The structures of the bridged bis(β-CD) and EBCDP were characterized by infrared spectroscopy, mass spectrometry, elemental analysis and thermogravimetric analysis, accordingly. The chiral chromatographic performances of EBCDP were systematically evaluated by separating 28 racemic analytes in the reversed-phase or polar organic mode, including eight flavanones, eight bolckers, five dansyl-amino acids, three DL-amino acids and four other common drugs. As a result, the relatively high enantioselectivity of EBCDP was observed in comparison with a native β-CD-CSP (CDSP). All selected analytes were separated on EBCDP, of which 20 analytes had resolutions up to baseline, 2′-hydroxyflavanone and arotinolol had resolutions up to 4.35 and 2.05 in about 30 min, respectively, whereas CDSP only separated 11 analytes with low resolutions (0.55~1.69). Moreover, EBCDP was able to utilize the complexation of the bridging linker (ethylenediamine dicarboxyethyl diamide group, EDTA-based) to realize direct separations of DL-amino acids with a mobile phase containing copper ion (Cu2+), which was similar to the chiral ligand exchange chromatography. Unlike the native cyclodextrin with small cavity (~242 Å3), the bridged bis(β-CD) combined two β-CD units with a bridging linker, having a well-organized “pseudo-cavity” as an organic whole to encapsulate more analytes, which made EBCDP have broad-spectrum applications in chiral separations.