ISSN:
0749-1581
Keywords:
1H NMR 13C NMR Aspidosperma-eburnea diastereoisomers
;
Revised configuration
;
NOE difference
;
‘Hidden’ exchange partner
;
Conformational analysis Thermodynamic parameters
;
Molecular mechanics
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Full 1H and 13C assignments are reported for two aspidosperma - eburnea type diastereoisomers. Homonuclear NOE difference measurements revealed that the previously reported configurational assignment of these compounds is in error. More interestingly, rotation about the bond connecting the two indole units is hindered in both molecules and gives a strongly biased two-site chemical exchange system. At room temperature the exchange rates are slow on the chemical shift time-scale with regard to certain 1H signals. In addition, the exchange rates are such that the signals due to the minor component are broadened to the extent that they escape detection in a conventional 1H spectrum, whereas only a very small amount of broadening is observed on the main signals. The presence of this ‘hidden’ exchange partner can give rise to peculiar effects in the NOE difference spectra. Such spurious effects can be the source of misinterpretation if the existence of the ‘silent partner’ goes unnoticed. Thermodynamic parameters are evaluated based on earlier work addressing the problem of the ‘hidden’ exchange partner.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260310816
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