DERIVATIZATION OF DL-AMINO ACIDS BY URETHANE-PROTECTED ALPHA-AMINO-ACID N-CARBOXYANHYDRIDES FOR SEPARATION BY LC

Using a robotic autosampler, free DL-amino acids were derivatized with highly reactive, urethane-protected, L-alpha-amino acid N-carboxyanhydrides (NCAs) with structures: Boc-Phe-NCA, Boc-Asn(Trt)-NCA, Fmoc-Lys(Boc)-NCA, Fmoc-Met-NCA, Fmoc-Ala-NCA, Z-Ala-NCA, Z-Val-NCA and Z-Leu-NCA (Boc = tert-butyloxycarbonyl, Trt = trityl, Fmoc = 9-(fluor-enyl-methyl)oxycarbonyl, Z = benzyloxycarbonyl). Using sodium berate buffer and acetonitrile solvent, derivatization was complete in 3.5 min at room temperature. By selection of an appropriate reagent, the resulting diastereomeric, N-protected dipeptides were separated on an octylsilica stationary phase using mixtures of sodium acetate buffer and acetonitrile as eluents.