Chiral capillary electrophoresis: facts and fiction on the reproducibility of resolution with randomly substituted cyclodextrins.
Comparative enantioseparation of the enantiomers of 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate was performed with cyclodextrin (CD)-modified capillary electrophoresis (CE). Two single isomers, beta-CD, heptakis(2,3,6-tri-O-methyl)-beta-CD (TM-beta-CD), and heptakis(2,6-di-O-methyl)-beta-CD (DM-beta-CD) of 98% purity as well as heptakis(2,3-di-O-acetyl)-beta-CD were used and compared in terms of resolution power to randomly methylated and corresponding acetylated beta-CDs, which were synthesized in our laboratory. The methylated ones were characterized by means of matrix-assisted laser desorption/ionization-time of flight-(MALDI-TOF) mass spectrometry. By testing defined mixtures of single isomers and comparing their resolution power to randomly substituted CDs of similar degree of substitution we could show, that a simple characterization by the average molecular degree of substitution (DS) is not sufficient. In order to get reproducible results, a clearly defined substitution pattern is necessary, which is not given using randomly substituted CDs. Taken together, a validation of a chiral separation with "undefined" CD derivatives is almost impossible.
Schmitt
Ulrich
U
Institute of Pharmacy and Food Chemistry, University of Würzburg, Würzburg, Germany.
Ertan
Mevlut
M
Holzgrabe
Ulrike
U
D003505:Cyclodextrins / Q000138:chemical synthesis / Q000737:chemistry*; D019075:Electrophoresis, Capillary / Q000379:methods*; D008745:Methylation; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry / Q000302:isolation & purification; D010755:Organophosphates / Q000737:chemistry / Q000302:isolation & purification; D015203:Reproducibility of Results; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013237:Stereoisomerism
D003505:Cyclodextrins; D009281:Naphthalenes; D010755:Organophosphates; C107195:1,1'-binaphthyl-2,2'-diyl hydrogen phosphate