Determination of alpha-alkyl-alpha-amino acids and alpha-amino alcohols by chiral-phase capillary gas chromatography and reverse-phase high-performance liquid chromatography.
The enantiomeric resolution by fused-silica capillary gas-liquid chromatography (GLC) of non-protein DL-alpha-alkyl-alpha-amino acids of the structure H2NCR1R2COOH (R1 = alkyl, R2 = alkyl, alkaryl) was investigated by using chiral [L-valine-tert.-butylamide, linked to a statistical polymer of dimethylsiloxane and (2-carboxypropyl)methylsiloxane, Chirasil-L-Val, and XE-60-S-Val-S-alpha-phenylethylamide] and non-chiral (methylphenylcyanopropylvinylpolysiloxane, CP-Sil-19 stationary phases. To evaluate the resolution coefficients, N-acylamino acid n-propyl esters (acyl = acetyl, propionyl, trifluoroacetyl, pentafluoropropionyl, heptafluorobutyryl) and diastereomeric esters with S(-)-2-methyl-1-butanol, S(+)-2-butanol and S(+)-2-octanol were used. Although alpha-alkyl-alpha-amino acids in general gave lower resolution coefficients than the enantiomers of protein amino acids, most alpha-alkyl-alpha-amino acids could be resolved by using suitable derivatization procedures and, preferably, isothermal conditions. In addition, a number of DL-alpha-alkyl-alpha-amino acids could be separated by ligand-exchange chromatography (L-hydroxyproline/Cu2+) by both thin-layer chromatography (Chiralplate) and high-performance liquid chromatography (HPLC) (Nucleosil Chiral-1). Further, a standard mixture composed of fifteen alpha-amino acids and eleven alpha-amino alcohols could be completely separated by C18 HPLC after derivatization with o-phthaldialdehyde-2-mercaptoethanol (OPA-2-ME). The time and temperature dependences of the relative fluorescence of the adducts were investigated kinetically.
D000596:Amino Acids / Q000032:analysis*; D000605:Amino Alcohols / Q000032:analysis*; D002849:Chromatography, Gas; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D002855:Chromatography, Thin Layer; D007202:Indicators and Reagents
D000596:Amino Acids; D000605:Amino Alcohols; D007202:Indicators and Reagents