Variable-Temperature 1H-NMR Studies on Two C-Glycosylflavones

Julia H Frank,William F Reynolds,Russel S Ramsewak,Yomica L Powder-George

doi:10.3390/molecules17077914

Julia H Frank, William F Reynolds + Show 2 more

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https://doi.org/10.3390/molecules17077914

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Journal: Molecules	Publication Date: Jul 2, 2012
Citations: 31	License type: CC BY 4.0

Affiliation: University of Toronto, University of the West Indies

Abstract

Two known C-glycosylflavones, swertisin and embinoidin, were isolated from the leaves of Anthurium aripoense, and characterized by room temperature 1D and 2D NMR experiments. At this temperature, the 1H- and 13C-NMR spectra of these C-glycosylflavones revealed doubling of signals, which suggested the presence of two rotamers in solution. Variable-temperature (VT) 1H-NMR studies supported this hypothesis. The T-ROESY data, in addition to the theoretical (MM2) calculations utilizing the Chem3D Pro software, confirmed the hypothesis that the two rotamers interchange via rotation about the C-glycosidic bond.

Highlights

Anthurium is a genus of evergreen, climbing or epiphytic herbs which belongs to the Araceae [1], and has reported folkloric uses, which include hallucinogens, insecticides, oral contraceptives, rheumatoid arthritis treatments and skin care agents [2,3,4]
The structures of swertisin (1) and embinoidin (2) were confirmed and spectra assigned by a combination of 1H-1H COSY [11], HSQC [12] and HMBC [13] spectra
The structure of embinoidin (2) is shown in Figure 4, with carbons and the 5-OH proton giving rise to doubled signals marked with asterisks

Summary

Introduction

Anthurium is a genus of evergreen, climbing or epiphytic herbs which belongs to the Araceae [1], and has reported folkloric uses, which include hallucinogens, insecticides, oral contraceptives, rheumatoid arthritis treatments and skin care agents [2,3,4]. A survey of the literature revealed that there has been no phytochemical investigation of this species. The chemical constituents of this plant were investigated. Two known C-glycosylflavones, swertisin and embinoidin [7], were isolated from the leaves of Anthurium aripoense. Both compounds showed duplication of signals in the 1H- and 13C-NMR spectra at room temperature. For the purpose of this study, steric hindrance proved to be the dominating effect. In this investigation, the structure of the two compounds was confirmed with the aid of 2D NMR experiments while the origin of signal doubling was investigated using variable-temperature (VT).

Results and Discussion

General

Spectral Data

Conclusions