Detection of the open-chain forms of d-fructose and L-sorbose in aqueous solution by using 13C-n.m.r. spectroscopy

Observation of the keto tautomer of d-fructose in D2O using 1H NMR spectroscopy

“…15,24 This analysis, combined with further 2D NMR experiments (including homonuclear DQF-COSY and NOESY spectra), allowed the full assignment of all resonances for the keto tautomer. Similarly, other previously unidentified 1 H NMR peaks were assigned to the α-pyranose form on the basis of 2D correlations with the literature values for the 13 C NMR spectrum for this tautomer.…”

“…Similarly, other previously unidentified 1 H NMR peaks were assigned to the α-pyranose form on the basis of 2D correlations with the literature values for the 13 C NMR spectrum for this tautomer. 15,17,20 The identification of the keto and α-pyranose tautomers in D 2 O using 1 H NMR spectroscopy meant that an investigation of the mutarotation reaction and the influences on the tautomeric composition of fructose could be investigated with relative ease.…”

“…12–16 The keto form of fructose has not been previously identified using 1 H NMR spectroscopy in D 2 O. 11,15,17–19 The α-pyranose tautomer has also been difficult to identify using 1 H NMR spectroscopy in aqueous solution, only being observed in experiments measuring the anomeric hydroxyl group conducted on samples equilibrated in water, flash frozen, and then melted into DMSO- d 6 . This relies on the slow tautomeric equilibration in DMSO- d 6 to provide data for the tautomeric composition in water.…”

“…14,15,17,20 However, because of the low isotopic ratio of 13 C as compared to 12 C, these experiments are time consuming. This is particularly the case when trying to resolve components in low concentrations, and so 13 C NMR spectroscopy is not practical for determining changing aqueous tautomeric ratios, for example in the study of the mutarotation reaction.…”

Isolation and Identification of Phase 1 Metabolites of Curcumol in Rats

“…The 8-ketone carbonyl group, formed after decomposition of the hemiketal substructure in curcumol, is easily condensated with the 12-or 13-hydroxy group to form a five-member ring, which is relatively stable in aqueous solution (de Bruyn et al, 1975;Funcke et al, 1979;Dais and Perlin, 1985), and the newly formed hemiketal hydroxy group at C-8 can be further cyclized with the 14-hydroxy group to form another five-member ring.…”