Quinic acid esters and sesquiterpenes from Sonchus arvensis

A phytochemical study on the whole plant of Sonchus arvensis and its antioxidant activity has been carried out. Three quinic acid derivatives (1-3), the rarely naturally occurring (p-hydroxyphenylacetyl) quinic acids, and two eudesmanolides (4 and 5) were newly found. Four known eudesmanolides (6-9) were isolated from the plant for the first time. Their structures were characterized by HRESIMS, IR, UV, 1D NMR, and 2D NIVIR. 1,1-Diphenyl-2-picrylhydrazyl (DPPH center dot)-scavenging activity was evaluated for each of the above 9 compounds (1-9) in comparison to standard antioxidants (caffeic acid and ascorbic acid). However, none proved to have a positive activity. The absence of antioxidant activity could be caused by the absence of ortho or para-diphenolic groups in all detected compounds, that are responsible of the activity against free radicals by an electron transfer reaction. (C) 2008 Elsevier Ltd. All rights reserved.