α-Tocospiro C, a novel cytotoxic α-tocopheroid from Cirsium setosum

alpha-Tocospiro C (1), the first example of nor-alpha-tocopheroid possessing unusual 7,8-dimethyl-1-oxaspiro[ 4.4] non-7-ene-6,9-dione carbon skeleton, was isolated and characterized from Cirsium setosum. Its structure and absolute configuration were determined by extensive spectroscopic methods, especially 2D NMR and ECD data analysis. The biosynthetic pathway was postulated. alpha-Tocospiro C (1) exhibited significant selective cytotoxic activities against human colon cancer (HCT8) cells, with IC50 values of 0.03 mu M. (C) 2014 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.