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The overlooked rotational isomerism of C-glycosyl flavonoids

Authors
  • Zhou, Guohong1
  • Yan, Renliang1
  • Wang, Xiaogen1
  • Li, Shaolin1
  • Lin, Jin1
  • Liu, Jia1
  • Zhao, Zhendong1
  • 1 Guangdong Food and Drug Vocational College, No. 321 Longdong North Street, Tianhe District, Guangzhou, 510520, China , Guangzhou (China)
Type
Published Article
Journal
Phytochemistry Reviews
Publisher
Springer-Verlag
Publication Date
Mar 09, 2019
Volume
18
Issue
2
Pages
443–461
Identifiers
DOI: 10.1007/s11101-019-09601-7
Source
Springer Nature
Keywords
License
Yellow

Abstract

C-glycosyl flavonoids are important secondary plant metabolites with a wide range of biological activities. Rotational isomerism, arising from restricted bond rotation, has been observed on a portion of C-glycosyl flavonoids. NMR technique contributes most to the observation and research of this phenomenon. Signal duplication in NMR spectra may be the key characteristic of C-glycosyl flavonoids existing as rotamers. Bulky steric hindrance from the substituents at position 7 and sugar moieties are responsible for the restricted bond rotation. There are other influence factors including temperature, solvents, H-bonds and π-stacking, but these are of lesser importance. Difference exists between 8-C-glycosyl flavonoids and their 6-C-glycosyl isomers despite sharing the same flavonoid aglycone and sugar moiety. 8-C-glycosyl flavonoids are more likely to suffer from restricted rotation. The energy barriers between rotamers of C-glycosyl flavonoids seem not high enough for atropisomerism to be realized and the isolation of rotamers should be difficult.

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