13C and1H NMR spectroscopy as a tool in the configurational analysis of iridoid glucosides
1981; Elsevier BV; Volume: 20; Issue: 12 Linguagem: Inglês
10.1016/0031-9422(81)85275-2
ISSN1873-3700
AutoresSøren Damtoft, Søren Rosendal, Jensen, Bent Nielsen,
Tópico(s)Analytical Chemistry and Chromatography
ResumoThe13C NMR data of 51 iridoid glucosides or glucoside acetates are tabulated. The collection includes 20 pairs of C-6, C-7 or C-8 epimers. Three parameters in using the data for the configurational assignment of 6-O-substituents are given. The chemical shift for C-9 in a range of substituted compounds is shown to be numerically related to the stereochemistry at C-8. This allows the determination of the configuration at this centre for most types of substitution patterns by calculation of the C-9 shift using increments for each substituent. Such increments are given for 25 substituents in three different solvents. A method for simulation of spectra of unknown iridoid glucosides is presented. By this method, the structures of five novel iridoid glucosides have been elucidated, and that of tecomoside has been revised. The methods used to assign the configurations to C-6 and C-8 epimeric iridoid glucosides by1H NMR spectroscopy are discussed and a table with selected data is presented. It is suggested that the structures in the literature for ajugol and myoporoside should be interchanged. Consequently, Horeau's method has failed in these instances. Finally, the differences in the13C NMR spectra of pairs of C-6 and C-8 epimeric iridoid glucosides have been interpreted as originating from cis/trans-interactions.
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