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Complete NMR assignments of bioactive rotameric (3 → 8) biflavonoids from the bark of Garcinia hombroniana
Author(s) -
Jamila Nargis,
Khairuddean Melati,
Khan Sadiq Noor,
Khan Naeem
Publication year - 2014
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.4071
Subject(s) - chemistry , biflavonoids , garcinia , clusiaceae , two dimensional nuclear magnetic resonance spectroscopy , stereochemistry , proton nmr , circular dichroism , antimicrobial , bark (sound) , nuclear magnetic resonance spectroscopy , organic chemistry , traditional medicine , medicine , physics , acoustics
The genus Garcinia is reported to possess antimicrobial, anti‐inflammatory, anticancer, hepatoprotective and anti‐HIV activities. Garcinia hombroniana in Malaysia is used to treat itching and as a protective medicine after child birth. This study was aimed to isolate the chemical constituents from the bark of G . hombroniana and explore their possible pharmacological potential. Ethyl acetate extract afforded one new (1) and six (2–7) known 3 → 8 rotameric biflavonoids. Their structures were elucidated by UV, IR and NMR (1D and 2D) spectroscopy together with electron ionization/ESI mass spectrometric techniques and were identified as (2 R , 3 S ) volkensiflavone‐7‐ O ‐rhamnopyranoside (1), volkensiflavone (2), 4″‐ O ‐methyl‐volkensiflavone (3), volkensiflavone‐7‐ O ‐glucopyranoside (4), morelloflavone (5), 3″‐ O ‐methyl‐morelloflavone (6) and morelloflavone‐7‐ O ‐glucopyranoside (7). The absolute configuration of compound 1 was assigned by circular dichroism spectroscopy as 2 R , 3 S . The coexistence of conformers of isolated biflavonoids in solution at 25 °C in different solvents was confirmed by variable temperature NMR studies. At room temperature (25 °C), compounds 1–7 exhibited duplicate NMR signals, while at elevated temperature (90 °C), a single set of signals was obtained. Compound 5 showed significant in vitro antioxidant activities against 1,1‐diphenyl‐2‐picrylhydrazyl and 2,2′‐azino‐bis‐3‐ethyl benzthiazoline‐6‐sulfonic acid radicals. The antibacterial studies showed that compounds 5 and 6 are the most active against Staphylococcus aureus , Bacillus subtilis and Escherichia coli . Compounds 3 and 6 also showed moderate antituberculosis activity against H 38 Rv . Based on the research findings, G . hombroniana could be concluded as a rich source of flavanone–flavone (3 → 8) biflavonoids that exhibit rotameric behaviour at room temperature and display significant antioxidant and antibacterial activities. Copyright © 2014 John Wiley & Sons, Ltd.