PREDICTABLE CHROMATOGRAPHIC SEPARATIONS OF ENANTIOMERS - ARYL ALLENICACIDS AND THEIR DERIVATIVES

Designed to distinguish between the enantiomers of compounds having ce rtain rather common structural features, the chiral selector used in c hiral stationary phase (CSP) 1 columns is broadly applicable. The vali dity of the chiral recognition mechanism used to design the selector i s supported by NMR and chromatographic studies and one can honestly cl aim to have a relatively good understanding of when and how this selec tor will differentiate between enantiomers. Consequently, one can ofte n confidently predict not only that this column will separate the enan tiomers of a given compound but also specify the relation between abso lute configuration and elution order. A recent paper describing the us e of a chiral allenic acid to aid in assigning absolute configurations by exciton-coupled circular dichroic measurements focused our attenti on on these allenes. A priori, these aromatic allenic acids appeared t o contain structural features which would allow enantioseparation on C SP 1. Accordingly, a series of chiral allenic acids and their ester an d amide derivatives were prepared for chromatographic study. Indeed, t he enantiomers of the acids and esters are readily resolved, eluting i n the expected order. The amides resolve more poorly for reasons that are clearly defined. Relevant data and mechanistic explanations are pr esented to convey an understanding of how CSP 1 differentiates between enantiomers.