Bbstract.Apparent separation factors of 1.1 or higher on Chirasil Val I11 can be obtained for Na-acyl N-alkyl aminoacid amides allowing the use of short capillary gas chromatographic columns. A clean derivatization protocol without racemization is described, proceding through the NCA derivatives that are prepared from "in situ" silylated amino acids with trimethylsilyl cyanide.A panoply of suitable derivatives of amino acids and protocols exists that enable the enantiomeric separations by GC using chiral solid phases (11, and accurate methods of determinations of the enantiomeric content of peptide hydrolysates are well documented ( 2 ) . We report here that acylated U-amino acid amides ( 3 ) show pronounced enantioselectivity ( 4 ) on commercial chiral capillary columns (Tables 1 and 2 ) .This allows the use of relatively short columns, compensating for the long retention times. Most common amino acids can be evaluated except Asp, Asn, Glu, Gln, His, Trp and Lys. Conversions of Thr, Ser and Tyr need more drastic circumstances but proceed without difficulties provided that the intermediates remain not silylated prior to acylation (see experimental part). Stereomutation up to 5% is noticed for phenylglycine (Phg ) . A slight modification of the method is also convenient for cyclic imino acids, especially Pro, for which a-values as high as 1.15 can be obtained.We have looked to a variety of Nu-acyl amino acid N-alkylamides and found that among the acyl groupings [pivaloyl (Piv) , pentafluoropropionyl (Pfp), trifluoroacetyl (Tfa), pentafluorobenzoyl, formyl ...I the N-Piv and N-Pfp show the highest separation factors, but N-Tfa derivatives remain interesting candidates because of their shorter retention times. The isopropylamides or trifluoroethylamides (5) show the best performances (Tables 1 and 2 ) for the common amino acids, while the present method is mostly unsuitable for enantiomeric quantification of Na-Me amino acids.Several protocols for the derivatizations were tested out, but most fail to give clean chromatograms or racemization-free samples. The most trivial methods, e.g. those proceding via the stage of amino acid chlorides or esters prepared in a separate step ( 6 1 , were in general not satisfactory. Clean procedures with almost quantitative conversions were found when proceding via N-carboxyanhydride (NCA) derivatives.-4 5 -
