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New Highly in Vitro Antioxidative 3,8″-Linked Biflav(an)ones and Flavanone-C-glycosides from Garcinia buchananii Stem Bark

Stark, Timo D., Germann, Daniel, Balemba, Onesmo B., Wakamatsu, Junichiro, Hofmann, Thomas
Journal of agricultural and food chemistry 2013 v.61 no.51 pp. 12572-12581
Garcinia buchananii, antioxidants, bark, hydrogen peroxide, oxygen radical absorbance capacity, polyphenols, spectroscopy, trees
Very recently, we described highly antioxidative polyphenols isolated from the stem bark extract of the Garcinia buchananii tree. In this study, we describe additional antioxidants from Garcinia buchananii bark extract using hydrogen peroxide scavenging, oxygen radical absorbance capacity (ORAC), and trolox equivalent antioxidant capacity (TEAC) assays. UPLC-HR-ESI-TOF-MSᵉ analysis, 1- and 2D-NMR, and circular dichroism (CD) spectroscopy led to the unequivocal identification of the antioxidative molecules as a series of five 3,8″-linked biflav(an)ones and two flavanone-C-glycosides. (2S,3R)-Taxifolin-6-C-β-d-glucopyranoside (2), (2R,3S,2″S,3″S)-manniflavanone (3), (2R,3S)-buchananiflavonol (4), and (2S,3R,2″R,3″R)-GB-1 (6) are new compounds, and (2S,3S)-taxifolin-6-C-β-d-glucopyranoside (1) was described so far only in one other plant. The structure of (2R,3S,2″R,3″R)-GB-1 (5) and (2R,3S,2″S)-GB2a (7) were confirmed. The H₂O₂ scavenging, TEAC, and the ORAC assays demonstrated that these natural products have an extraordinarily high antioxidative power, especially (2R,3S,2″S,3″S)-manniflavanone (3) with an EC₅₀ value of 3.0 μM, 4.00 mmol TE/mmol, and 10.30 μmol TE/ μmol.