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

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

doi:10.3390/molecules17077914

Cited by 33 publications

(17 citation statements)

References 9 publications

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“…We used the Eyring equation to derive the free energy of activation, DG # ,f or the interconversion of the two conformers ( Table 4). [32] These values, 16.55 kcal mol À1 for C 2 D 2 Cl 4 and 16.6 kcal mol À1 for [D 7 ]DMF,a re comparable with those reported for conformational inversion of calix [4]arenes. [33] These results indicatet hat, in contrast to the significant solvente ffect on the conformational ratio, the activation energy barrier is quite insensitive to solvent polarity.S imilar tendencies were reported for rotamers of acyclic tertiary carbamates.…”

Section: Conformational Analysissupporting

confidence: 82%

Synthetic Evolution of the Multifarene Cavity from Planar Predecessors

Solel

Reany

et al. 2018

Chemistry A European J

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The stepwise evolution of curved multifarene structures from planar precursors is demonstrated, highlighting three architectural design elements: 1) employment of various aromatic units, 2) changing the hybridization of the linking atoms from sp to sp , and 3) rigidification of the system by the introduction of five-membered rings. Similar design elements have been employed to transform graphene sheets into curved carbon structures. Specifically, the stepwise synthetic evolution of multifarene[2+2], which has a curved, quite rigid structure, begins with a planar, tetraimine precursor, conversion to pairs of vicinal diamines, and the transformation of these pairs to cyclic thiourea groups. This process was probed by NMR spectroscopy and X-ray crystallography. Since varying the carbonylation conditions resulted in carbamates or thiocarbamates rather than the urea or thiourea isomers, the isomeric interconversion was studied both experimentally and by DFT computations. The carbamate versus urea preference was found to reflect either kinetic or thermodynamic control, respectively.

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Section: Conformational Analysissupporting

confidence: 82%

Synthetic Evolution of the Multifarene Cavity from Planar Predecessors

Solel

Reany

et al. 2018

Chemistry A European J

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“…Among such compounds that have been detected in various plant families [4], coincidence of our NMR data ( Table 2 and 3) with those published [5,6] resulted in identification of these compounds as isoorientin (1), swertiajaponin (2), isovitexin (3), and swertisin (4) ( Figure 2). Doubled 1 H and 13 C NMR signals, derived from rotamers of flavone 6-C-glycoside containing a 7-Omethyl group [5][6][7], were detected also in our swertiajaponin (2) and swertisin (4) preparations. Chemical shifts and coupling constants are in ppm and Hz, respectively.…”

supporting

confidence: 51%

Flavone C-Glucosides Responsible for Yellow Pigmentation Induced by Low Temperature in Bracts of Zantedeschia aethiopica

Nakayama

Koshioka

Kondo

et al. 2015

Natural Product Communications

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We aimed to identify the main compounds responsible for low temperature-induced yellow pigmentation of the bracts of Zantedeschia aethiopica 'Wedding March'. On the basis of the area ratios estimated from absorbance at 400 nm in HPLC analyses, we identified two flavonoids, isoorientin and swertiajaponin, as such compounds. We also identified two additional flavonoids, isovitexin and swertisin, which do not contribute considerably to the yellow pigmentation. Flavonoids of Zantedeschia bracts seem to belong to the class of flavone C-glycosides.

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“…Each rotamer of compounds 8 – 10 shows a different Δ G ‡ for the pirouetting of the macrocycle ring around the thread (see Table ). The values of Δ G ‡ can be determined from the Eyring equation by using coalescence temperature ( T c ) data , , . For further information on the calculations of the kinetic parameters, see the Supporting Information.…”

Section: Resultsmentioning

confidence: 99%

Conformer Distribution in Rotaxanes Containing Nonsymmetric Threads: A Systematic Approach

et al. 2018

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Rotaxanes are designated as molecular machines due their different movements. Systematic studies regarding the different conformations adopted by these systems and the factors that lead to the distribution of the conformations, in both solution and the solid state, have not been widely explored, especially for rotaxanes with nonsymmetric stoppers. Therefore, in this study we have investigated three novel [2]rotaxanes containing threads derived from nonsymmetric succinamides [R1R2NC(O)‐CH2CH2‐C(O)NR2R1, with R1/R2 = Bu/Bn, Bu/2‐furylmethyl, and 5‐methylisoxazol‐3‐yl/2‐furylmethyl]. The proportions of rotamers were investigated for threads and rotaxanes by solution and solid‐state NMR spectroscopy as well as by single‐crystal and powder X‐ray diffraction. In solution, the threads present different proportions of conformer, with the E,Z conformation prevailing, whereas only one conformer is observed in the solid state. For the rotaxanes, only one conformer prevails in the single crystal, whereas the solution and solid (bulk) states present more than one rotamer. These proportions are modified when the threads are incorporated into the macrocycle during rotaxane formation. The intramolecular interactions in each rotamer were investigated by QTAIM and variable‐temperature 1H NMR experiments. The changes in conformational population between the threads and respective rotaxanes can be explained by a set of different intramolecular interactions, with trifurcated hydrogen bonds responsible for most of the stabilization energy.

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

Cited by 33 publications

References 9 publications

Synthetic Evolution of the Multifarene Cavity from Planar Predecessors

Synthetic Evolution of the Multifarene Cavity from Planar Predecessors

Flavone C-Glucosides Responsible for Yellow Pigmentation Induced by Low Temperature in Bracts of Zantedeschia aethiopica

Conformer Distribution in Rotaxanes Containing Nonsymmetric Threads: A Systematic Approach

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