RESOLUTION OF ACYLATED DIPEPTIDE STEREOISOMERS BY CAPILLARY ELECTROPHORESIS USING SULFOBUTYLETHER DERIVATIZED BETA-CYCLODEXTRIN

The separation of enantiomerically and diastereomerically related ster eoisomers of acylated Asp-Phe dipeptides was explored using capillary electrophoresis (CE). This series of dipeptides included the alpha-L,L parent compound and the three other potential Asp containing stereois omers (alpha-D,D, alpha-L,D, and alpha-D,L), as well the four possible isoAsp containing stereoisomers (beta-L,L, beta-D,D, beta-L,D and bet a-DL,). The separation of these substances was explored using both neu tral and charged cyclodextrins as the stereoisomer selector added to t he running electrolyte. The major experimental parameters investigated included pH, the cyclodextrin type, and the cyclodextrin concentratio n. Due to differences in the pK(a) values of the carboxylic acid group s, adjustment of the separation buffer to between pH 3.0 and 4.0 provi ded for sufficient electrophoretic mobility differences to result in e xcellent separations of the diastereomerically related peptides in thi s pH region. The resolution of the enantiomerically related peptide st ereoisomers was accomplished using low concentrations (1 mM) of the an ionic cyclodextrin derivative, sulfobutylether-beta-cyclodextrin (SBE- beta-CD). This negatively charged cyclodextrin was found to be superio r for the resolution of the enantiomerically related peptides as compa red to native beta-cyclodextrin or the neutral derivatives, dimethyl b eta-cyclodextrin and hydroxypropyl beta-cyclodextrin. An alternative a pproach using anionic or neutral surfactants in conjunction with the S BE-beta-CDs was also explored and found to be successful but problemat ic.