In an in vitro screening for anti-viral natural products, the bark extract of the wild syringa tree (Burkea africana Hook.) was found to be a promising candidate. In a cytopathic effect (CPE) inhibition assay using Madin Darby canine kidney (MDCK) cells, this extract exhibited an IC50 value of 5.5 µg/mL against the H3N2 influenza virus A/Hong Kong/68 (HK/68) [1]. Moreover, it was not toxic to MDCK cells.
Therefore, the wild syringa tree bark extract was selected for a bio-guided phytochemical work-up using various chromatographic techniques including flash CC, supercritical fluid chromatography (SFC), and UPLC.
In sum, eight new triterpene saponins (1-8) of the lupane and oleanane types with four so far undescribed aglycone structures were isolated and characterized via HRESIMS, 1D and 2D NMR spectroscopy. The absolute configuration of the sugar moieties was determined via GC-MS experiments after hydrolysis. This is the first report of triterpene saponins as constituents of the wild syringa tree.
The anti-influenza virus activity of the isolates on the H3N2 strain HK/68 and the 2009 pandemic H1N1 strain A/Jena/8178/09, revealed the most potent effects by compounds 7 and 8 with IC50 values in the nanomolar range between 50 and 270 nM [2].
[1] Grienke U, Mair CE, Kirchmair J, Schmidtke M, Rollinger JM. Planta Med 2018; doi 10.1055/a-0590-5153
[2] Mair CE, Grienke U, Wilhelm A, Urban E, Zehl M, Schmidtke M, Rollinger JM. J Nat Prod 2018; 81: 515-523
This work was supported by the Austrian Science Fund (FWF: P24587) and the European Social Fund (ESF & TMWAT Project 2011 FGR 0137).