Separation of the stereoisomers of a homologeous series of bis-amides on chiral stationary phases

Summary

A homologeous series of stereoisomericbis-amides derived from racemic N-(3,5-dinitrobenzoyl)leuchine and various α,ω-diamines has been chromatographed on chiral stationary phases (CSP) derived from N-(2-naphthyl)alanine. Plots of α, the separation factor for enantiomers, versus N, the number of methylene groups in the α,ω-diamines, are convex in shape and show a maximum in α when N=B. This maximum is attributed to optimal “bridging” between adjacent binding sites on the CSP. “Bridging” is simultaneous interaction of the two ends of thebis-derivative with sites on the CSP. Separation factors for thebis-analytes are approximately the square of those of correspondingmono-amides.