Anti-Influenza Triterpene Saponins from the Bark of Burkea africana.

Christina E Mair,Michaela Schmidtke,Judith M Rollinger,Ulrike Grienke,Ernst Urban,Martin Zehl,Anke Wilhelm

doi:10.1021/acs.jnatprod.7b00774

Abstract

In an in vitro cytopathic effect inhibition assay with the H3N2 influenza virus A/Hong Kong/68 (HK/68), the bark extract of Burkea africana was found to be a promising antiviral lead with an IC50 value of 5.5 μg/mL without noteworthy cytotoxicity in Madin Darby canine kidney cells. After several chromatographic steps, triterpene saponins of the lupane and oleanane types were identified as the bioactive principles. In total, eight new triterpene saponins (1–8) with four so far undescribed aglycone structures were isolated and characterized via HRESIMS, GC-MS, and 1D and 2D NMR spectroscopy. Their anti-influenza virus activity on 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 between 0.05 and 0.27 μM. This is the first time triterpene saponins have been reported as constituents of the investigated plant material.

Highlights

Burkea af ricana Hook. is known under various names such as “wild syringa”, “seringa tree”, and “Rhodesian ash” in English or “mpulu” (Tsonga), “monato” (Tswana), “mufhulu” (Venda), and “wildesering” in Afrikaans
In an in vitro cytopathic effect inhibition assay with the H3N2 influenza virus A/Hong Kong/68 (HK/68), the bark extract of Burkea af ricana was found to be a promising antiviral lead with an IC50 value of 5.5 μg/mL without noteworthy cytotoxicity in Madin Darby canine kidney cells
Triterpene saponins are distributed widely as plant secondary metabolites with great structural diversity, which is reflected in the variety of reported biological and pharmacological properties, such as antidiabetic, antifungal, cytotoxic, hepatoprotective, anticancer, chemopreventive, antiallergic, immunomodulatory, immunostimulatory, molluscicidal, hemolytic, and anti-inflammatory activities.[8−11] antiviral activities against, for example, human respiratory syncytial virus (HRSV), human immunodeficiency virus (HIV), herpes simplex type 1 and 2 viruses (HSV), human rhinovirus (RV), tobacco mosaic virus (TMV), or hepatitis B virus (HBV) have been described.[12−17] So far, there are only a few reports on the anti-influenza virus activity of triterpene saponins.[18]

Summary

Introduction

Burkea af ricana Hook. is known under various names such as “wild syringa”, “seringa tree”, and “Rhodesian ash” in English or “mpulu” (Tsonga), “monato” (Tswana), “mufhulu” (Venda), and “wildesering” in Afrikaans. The findings from the HRESIMS analysis were confirmed by the NMR data, which displayed six additional carbons to the otherwise analogous resonances for the sapogenin alphitolic acid with the Xyl and Glc unit analogous to 1.

Results

Conclusion