Cytotoxic oplopane sesquiterpenoids from Arnoglossum atriplicifolium

Abstract

Pale Indian plantain (Arnoglossum atriplicifolium (L.) H. Rob.) is a plant with traditional medicinal usage among the Cherokee Native American tribe for treating cancer. Two oplopane sesquiterpenoids were isolated from an extract of A. atriplicifolium from Western North Carolina. The compounds were isolated by bioassay-guided fractionation using an MCF-7 breast tumour cell line assay. The known compound (1S,6R,7R,8R)-1-acetoxy-6,7-diangeloxy-8,10-epoxy-2-oxo-oplopa-3,14Z,11,12-dien-13-al (1) had an EC₅₀ value of 9.0 μM against MCF-7 cells, while the new compound (1S,3R,6R,7R,8R,11S)-1-acetoxy-6,7-diangeloxy-8,10,11,13-bisepoxyoplopan-2-one (2) had an EC₅₀ value of 96 μM. The compounds were characterised by 1D and 2D NMR spectroscopy and by comparison with literature values in the case for 1. Based on NOESY analysis, a correction of the relative configuration for 1 is presented. The presence of these compounds may help to explain the folk remedy usage of this plant as an anticancer agent.

Keywords:

• Oplopane
• sesquiterpenoid
• Arnoglossum atriplicifolium

Acknowledgements

We thank the Cancer and Viral Vector Core Laboratory, Wake Forest School of Medicine. We thank David Kingston at Virginia Tech for polarimeter access. We thank Syngenta Corporation, Greensboro NC, for equipment donations.

Disclosure statement

The authors confirm that this article content presents no conflict of interest.

Funding

This research was supported in part by a North Carolina Biotechnology Center Biotechnology Research [grant number 2007-BRG-1264] awarded to Bent Creek Institute and UNC-Asheville.