on the occasion of his 60th birthduy Many biologically active substances are now tested in their enantiomerically pure form. Chiral stationary phases (CSPs) can ensure not only reliable enantiomer analysis but also ready availability of the two enantiomers of a racemic active substance at a very early point in biological screening. Extensive use requires a range of CSPs which permit preparative separation at reasonable cost. Until now only a few types of CSPs could be considered : cellulose triacetate, cellulose tribenzoate," -31 and more recently cellulose urethanes,I4] N-(3,5-dinitrobenzoyl)amino acid phases,['l and polyamide phases from optically active N-(meth)acryloyl monomers.[6-81 The present report concerns new, highly selective polyamide phases prepared from the optically active amino acid amides 1 a-c and 2a-c for chromatographic separation of enantiomers. lo-c 20-c a, R=CH,: b. R=CHzCHICH,Iz; C.R=ISI-CHICH,IC~H,
Since good separation results had been obtained with poly(meth)acrylamides, it was expected that new adsorbents of this type would extend the possibilities of direct enantiomer separation without prior derivatization. Besides the development of analytically useful HPLC lo] these monomers should also make the synthesis of cross-linked bead polymers for preparative separations possible.[6 - Poly(N-acryloyl-(a-phenylalanine ethyl ester)"] shows a good enantioselective separation of some racemates.l6. ''I But more broadly applicable CSPs, distinguished by higher enantioselectivities particularly for the more polar, biologically active racemates, are also desirable.
It seemed necessary to us first of all to strongly restrict the conformative mobility of the monomer molecule by the incorporation of an additional amide group and a bulky residue. This reduces the number of energetically equivalent conformers which possibly have opposite effects on enantioselectivity. Secondly, the use of a rigid, bulky, and also chiral residue should enable a further increase in enantioselectivity through double stereodifferentiation.
Our new CSPs contain an amino acid structural unit which permits rational synthesis and fulfills the requirements mentioned. The increased rigidity in the immediate surroundings of the stereogenic center of the amino acid is ensured by a peptide bond. As the rigid bulky and additionally chiral group we chose optically active menthylamine, used in