DIFFERENTIATION OF MESO ISOMERS FROM RACEMIC MIXTURES WITH THE COMBINED USE OF CHIRAL SHIFT-REAGENTS AND 2-DIMENSIONAL HETERONUCLEAR CORRELATION NMR-SPECTROSCOPY

In the presence of chiral shift reagents the enantiotopic nuclei of a pair of enantiomers become diastereotopic and have the potential to gi ve resolved NMR signals. Similarly, the enantiotopic nuclei within a m eso isomer become diastereotopic in the presence of a chiral shift rea gent acid may give resolved NMR signals, However, the diastereotopic n uclei of a meso isomer mixed with a chiral shift reagent, unlike those of a racemic mixture, are located in the same molecule. Their intramo lecular character can be established experimentally by detection of sp in-spin splitting between them or to a common third nucleus. Compariso n of the correlation peaks in a two-dimensional, heteronuclear, multip le-quantum correlation (HMQC) spectrum with those of a heteronuclear m ultiple-bond correlation (HMBC) spectrum is an effective means of dete ction of coupling to a third nucleus. Two-dimensional NMR spectroscopy was used to identify the meso form of di-(trans-2-aminocyclohexyl)ami ne.