Studies in the Thymelaeaceae, V. 2'-Hydroxyflavone from Daphnopsis sellowiana: Isolation and Synthesis

Abstract

From the leaves of Daphnopsis sellowiana (Thymelaeceae), 2'-hydroxyflavone [1], a rare natural product, has been isolated and characterized through its spectroscopic properties. Confirmation of the structure was achieved through total synthesis, which also afforded adequate material for complete 13C-nmr analysis.

A predictive tool for assessing 13C NMR chemical shifts of flavonoids

“…Ł Correspondence to: Raymond E. March, Department of Chemistry, Trent University, 1600 West Bank Drive, Peterborough, ON K9J 7B8, Canada. E-mail: rmarch@trentu.ca A range of flavonoids have been extracted from plants and subsequently characterized by 13 C and 1 H nuclear magnetic resonance (NMR) spectroscopy. 13 -18 NMR spectroscopy has also been combined with fast atom bombardment/tandem mass spectrometry (FAB/MS/MS); 19 with high-performance liquid chromatography (HPLC)-MS for the structural characterization of flavonoids and flavonoid-O-glycosides; 20,21 with HPLC-UV (ultra-violet absorbance)-SPE (solid phase extraction)-MS for the identification of flavonoids taxifolin, aromadendrin, eriodictyol, naringenin, and apigenin present in Greek Oregano; 22 HPLC-MS for the identification of quercitin and quercetin glycosides in Hypericum perforatum L.; 20 HPLC-MS for the identification of quercetin glycosides in apple peel; 21 and with HPLC-UV-MS for the on-line structural investigation of isoflavones and isoflavanones.…”

“…13 -18 NMR spectroscopy has also been combined with fast atom bombardment/tandem mass spectrometry (FAB/MS/MS); 19 with high-performance liquid chromatography (HPLC)-MS for the structural characterization of flavonoids and flavonoid-O-glycosides; 20,21 with HPLC-UV (ultra-violet absorbance)-SPE (solid phase extraction)-MS for the identification of flavonoids taxifolin, aromadendrin, eriodictyol, naringenin, and apigenin present in Greek Oregano; 22 HPLC-MS for the identification of quercitin and quercetin glycosides in Hypericum perforatum L.; 20 HPLC-MS for the identification of quercetin glycosides in apple peel; 21 and with HPLC-UV-MS for the on-line structural investigation of isoflavones and isoflavanones. 23 In addition, 13 C NMR spectra have been obtained for a number of glycosylated flavonoids, 16,24,25 and both 13 C and 1 H NMR spectra have been reported for acylated derivatives of apigenin-7-O-glucoside. 26 In NMR spectroscopy, the magnetic field experienced at the nucleus of an atom is less than that of the applied magnetic field because electrons around the nucleus shield it from the applied field; the difference between the applied magnetic field and the field at the nucleus is termed the nuclear shielding.…”

“…For two bonded or adjacent carbon atoms, the chemical shifts will reflect the environment of both atoms and is indicative of the order (and thus the strength) of the connecting bond. The environment of a 13 C nucleus can also be affected in an inductive, through-space (field effect), or resonance-based manner by substituents that are bonded to its carbon framework (skeleton). These effects, which become apparent when 13 C substituent chemical shift (SCS) analyses are performed, 27 cause the associated chemical shifts to vary in a systematic and predictable manner.…”

“…Recently a method has been described for the estimation of 13 C-chemical shifts of carbon atoms in ions that also relies upon systematic variation of chemical shifts in response to differential hydroxyl substitution; such chemical shifts are described as pseudo-NMR chemical shifts. 28 The method involves computation of atomic charges for each carbon atom in neutral, protonated, and deprotonated molecules and relating atomic charges for molecules with experimental 13 C chemical shifts for carbon atoms.…”

“…28 The method involves computation of atomic charges for each carbon atom in neutral, protonated, and deprotonated molecules and relating atomic charges for molecules with experimental 13 C chemical shifts for carbon atoms. The relationship between atomic charges and experimental 13 C chemical shifts, together with computed atomic charges for carbon atoms in protonated and deprotonated molecules was applied to obtain pseudo-NMR 13 C chemical shifts for carbon atoms in protonated and deprotonated molecules.…”