TY - JOUR
T1 - A new NMR approach for structure determination of thermally unstable biflavanones and application to phytochemicals from Garcinia buchananii
AU - Stark, Timo D.
AU - Lösch, Sofie
AU - Salger, Mathias
AU - Balemba, Onesmo B.
AU - Wakamatsu, Junichiro
AU - Frank, Oliver
AU - Hofmann, Thomas
N1 - Publisher Copyright:
© 2015 John Wiley & Sons, Ltd.
PY - 2015/10/1
Y1 - 2015/10/1
N2 - Previous activity-guided phytochemical studies on Garcinia buchananii stem bark, which is traditionally used in Africa to treat various gastrointestinal and metabolic illnesses, revealed xanthones, polyisoprenylated benzophenones, flavanone-C-glycosides, biflavonoids, and/or biflavanones as bioactive key molecules. Unequivocal structure elucidation of biflavonoids and biflavanones by means of NMR spectroscopy is often complicated by the hindered rotation of the monomers around the C-C axis (atropisomerism), resulting in a high spectral complexity. In order to facilitate an unrestricted rotation, NMR spectra are usually recorded at elevated temperatures, commonly over 80°C, which effects in a single set of resonance signals. However, under these conditions, one of the target compounds of this investigation, (2R,3S,2″R,3″R)-manniflavanone (1), undergoes degradation. Therefore, we demonstrated in the present study that the 1,1-ADEQUATE could be successfully used as a powerful alternative approach to confirm the C-C connectivities in 1, avoiding detrimental conditions. However, a moderate increase in temperature up to 50 °C was sufficient to deliver sharp signals in the proton NMR experiment of (2R,3S,2″R,3″R)-isomanniflavanone (2) and (2″R,3″R)-preussianone (3). In addition, two new compounds could be isolated, namely (2R,3S,2″R,3″R)-GB-2 7″-O-β-d-glucopyranoside (4) and (2R,3S,2″R,3″R)-manniflavanone-7″-O-β-d-glucopyranoside (5), and whose structures were elucidated by spectroscopic analysis including 1D and 2D NMR and mass spectrometry methods. The absolute configurations were determined by a combination of NMR and electronic circular dichroism (ECD) spectroscopy. The aforementioned compounds exhibited high anti-oxidative capacity in the H2O2 scavenging, hydrophilic Trolox equivalent antioxidant capacity (H-TEAC) and hydrophilic oxygen radical absorbance capacity (H-ORAC) assays.
AB - Previous activity-guided phytochemical studies on Garcinia buchananii stem bark, which is traditionally used in Africa to treat various gastrointestinal and metabolic illnesses, revealed xanthones, polyisoprenylated benzophenones, flavanone-C-glycosides, biflavonoids, and/or biflavanones as bioactive key molecules. Unequivocal structure elucidation of biflavonoids and biflavanones by means of NMR spectroscopy is often complicated by the hindered rotation of the monomers around the C-C axis (atropisomerism), resulting in a high spectral complexity. In order to facilitate an unrestricted rotation, NMR spectra are usually recorded at elevated temperatures, commonly over 80°C, which effects in a single set of resonance signals. However, under these conditions, one of the target compounds of this investigation, (2R,3S,2″R,3″R)-manniflavanone (1), undergoes degradation. Therefore, we demonstrated in the present study that the 1,1-ADEQUATE could be successfully used as a powerful alternative approach to confirm the C-C connectivities in 1, avoiding detrimental conditions. However, a moderate increase in temperature up to 50 °C was sufficient to deliver sharp signals in the proton NMR experiment of (2R,3S,2″R,3″R)-isomanniflavanone (2) and (2″R,3″R)-preussianone (3). In addition, two new compounds could be isolated, namely (2R,3S,2″R,3″R)-GB-2 7″-O-β-d-glucopyranoside (4) and (2R,3S,2″R,3″R)-manniflavanone-7″-O-β-d-glucopyranoside (5), and whose structures were elucidated by spectroscopic analysis including 1D and 2D NMR and mass spectrometry methods. The absolute configurations were determined by a combination of NMR and electronic circular dichroism (ECD) spectroscopy. The aforementioned compounds exhibited high anti-oxidative capacity in the H2O2 scavenging, hydrophilic Trolox equivalent antioxidant capacity (H-TEAC) and hydrophilic oxygen radical absorbance capacity (H-ORAC) assays.
KW - 1,1-ADEQUATE
KW - C
KW - GB2 7″-O-β- d -glucopyranoside
KW - H
KW - NMR
KW - biflavanone glucosides
KW - biflavanones
KW - manniflavanone
KW - manniflavanone-7″-O-β- d -glucopyranoside
KW - variable temperature NMR
UR - http://www.scopus.com/inward/record.url?scp=84941936802&partnerID=8YFLogxK
U2 - 10.1002/mrc.4269
DO - 10.1002/mrc.4269
M3 - Article
C2 - 26195084
AN - SCOPUS:84941936802
SN - 0749-1581
VL - 53
SP - 813
EP - 820
JO - Magnetic Resonance in Chemistry
JF - Magnetic Resonance in Chemistry
IS - 10
ER -