| Summary: | Enantiomeric mixtures of alanine, serine, threonine, valine, methionine, leucine and norleucine were resolved in ligand exchange reversed phase HPLC (reproducibly), by using L-proline, L-hydroxyproline or N,N-dimethyl-L-phenylalanine (2 mmol L-1) and Cu(CH3COO)2 (1 mmol L-1) in water or in water/methanol. The latter mobile phase greatly decreased the retention time of the more hydrophobic alpha-amino acids, preserving enantioseparation. pH must be high enough to allow the presence of free <FONT FACE=Symbol>fraction three-quarters</FONT>NH2 groups in order to make the complexation with Cu(II) easier. The more restricted conformation of L-proline and L-hydroxyproline led to lower enantioseparations. The ligand exchange formation of pseudo-homochiral and pseudo-heterochiral complexes, thermodynamically and kinetically controlled, plays a fundamental role for the desired enantiomeric chromatographic separation. This simple and inexpensive methodology can be used routinely by any laboratory involved in alpha-amino acid synthesis.
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