Chiral Separation Of N-Fmoc Amino Acids By Capillary Electrophoresis

For solid-phase synthetic peptide, the racemic phenomenon must to be controlled.Beside keeping react process, we also selected the enough optically pure rawmaterial—N-Fmoc group protected amino acids. So the optical detection of thesematerials was very important. In this paper, we chirally separated five typical N-Fmoc amino acids:Fmoc-Asp(otBu)-OH, Fmoc-Val-OH, Fmoc-Lys-(Boc)-OH, Fmoc-Tyr-(tBu)-OHand Fmoc-Trp-(Boc)-OH by three separation model, because of the solibility of theN-Fmoc amino acids in water. Through the research, we get the following conclusion:1 The enantioseparation of N-Fmoc amino acids by CZE The Fmoc-Asp(otBu)-OH and Fmoc-Val-OH was resoluted with DM-β-CD aschiral selector by capillary zone electrophoresis (CZE). The Rs of the two N-Fmocamino acids were 2.54 and 1.62, respectively. The composition of the backgroundelectrolyte was 20 mM chiral selector-- DM-β-CD in a 40 mM phosphate-Tris buffer(pH5.0) and the enantioseparations were performed at 25oC, at 20 kV and UVdetection wavelength at 214 nm.This method was sample, quick and selective. For two enantiomer, the hydrophobic group – N-Fmoc come into the CD'scavum, then formed the host-guest complex. The enantiomeric selectivity of thecomplex is based on the hydrogen bond of amino acid's carboxyl group or side groupand the CD's second hydroxyl group.2 The enantioseparation of N-Fmoc amino acids by MEKC The Fmoc-Lys-(Boc)-OH was enantioseparated with γ-CD as chiral selector andsodium dodecyl sufate (SDS) as micellar phase by micellar electrokineticchromatography(MEKC). The Rs of the N-Fmoc amino acid was1.2. Electrophoreticconditions employed was: 60 mM chiral selector--γ-CD and 100 mM SDS in a40 mM phosphate buffer (pH8.3), the enantioseparations temperature at 35oC,detection voltage at 18 kV and UV detection wavelength at 214 nm.This method wassample, quick and selective. iABSTRACT3 the enantioseparation of N-Fmoc amino acids by NACE The Fmoc-Tyr-(tBu)-OH and Fmoc-Trp-(Boc)-OH was chirally separated withquinine as chiral selector by non-aqueous capillary electrophoresis (NACE). The Rsof the two N-Fmoc amino acids were 1.64 and 1.23 respectively. The composition ofthe background electrolyte was 12.5 mM tetrabutyl amino hydroxyl-acetyl acidbuffer(pH6.5), and 10 mM chiral selector in an ethanol–methanol (60:40, v/v) mixtureand the enantioseparations were performed at 20oC, in the reversed polarity mode at-25 kV and UV detection wavelength at 254 nm.This method was sample, quick andselective. The quinine was cation and move to cathode, but the N-Fmoc amino acids wereanion and move to anode at pH6.5. Because the movement was reverse, thecounter-current ion-pair chromatrography was formed. In this enantioseparation, theion-pair of the quinine and the N-Fmoc amino acids was not important. Based on theH-bond and hydrophobic interaction, the enantiomers were resoluted.