Add time:09/08/2019         Source:sciencedirect.com

The enantiomeric resolution by fused-silica capillary gas—liquid chromatography (GLC) of non-protein dl-α-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-α-phenylethylamide] and non-chiral (methylphenylcyanopropylvinylpolysiloxane, CP-Sil-19 CB) 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 α-alkyl-α-amino acids in general gave lower resolution coefficients than the enantiomers of protein amino acids, most α-alkyl-α-amino acids could be resolved by using suitable derivatization procedures and, preferbly, isothermal conditions. In addition, a number of dl-α-alkyl-α-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 o of fifteen α-amino acids and eleven α-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.

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