l-Amino Acids as Chiral Selectors for the Enantioseparation of (±)-Bupropion by Ligand Exchange Thin-Layer Chromatography Using Cu(II) Complex via Four Different Approaches

The present paper deals with direct enantioresolution of (±)-bupropion using thin-layer chromatography and different Cu(II)-l-amino acid complexes as chiral ligand exchange reagent (LER). Cu(II) acetate and four l-amino acids (viz., l-proline, l-histidine, l-phenylalanine, and l-tryptophan) were used for the preparation of LER. Four different approaches were adopted for impregnating/loading the plate with the LER. In the present work, plate impregnation was achieved (a) by mixing LER with silica gel slurry, (b) by developing plain plates with solutions of the Cu complexes, (c) using a solution of Cu(II) acetate as mobile phase additive for the thin-layer chromatography (TLC) plates impregnated with one of the l-amino acids, and (d) by using the LER as mobile phase additive. Spots were located using iodine vapor. The results obtained with all the approaches have been compared in terms of resolution. Effect of concentration of Cu(II) acetate and chiral selector has also been studied.