INTERMOLECULAR 1H-1H TWO-DIMENSIONAL NUCLEAR OVERHAUSER ENHANCEMENTS IN THE CHARACTERIZATION OF A RATIONALLY DESIGNED CHIRAL RECOGNITION SYSTEM

Chiral stationary phases (CSPs) for liquid chromatography derived from N-(acyl)proline-3,5-dimethylanilides separate the enantiomers of N-(3,5-dinitrobenzoyl)-α-amino esters and amides with high levels of selectivity. These CSPs have been used to assemble a large body of chromatographic data which indirectly supports the validity of the mechanistic rationale originally used in the design of these CSPs. We herein report 1H and 13C chemical shift data obtained when the (S)-enantiomer of chiral solvating agent (CSA) 3, a soluble analogue of the selector used in CSP (S)-1, acts on each of the enantiomers of the dimethylamide of N-(3,5-dinitrobenzoyl)leucine, 2. The changes in chemical shift in the mixture of (S)-2 and (S)-3 support the existence of those interactions thought to be essential to chiral recognition in this system. In addition, significant intermolecular NOESY enhancements are observed in this mixture. These NOE data are consistent with the structure expected for the more stable diastereomeric ad...