Phytochemical investigation and cytotoxic characterization of bioactive constituents from Conyza dioscoridis

A follow-up chemical investigation to methanol extract of Conyza dioscoridis (Family Asteraceae) led to the isolation of seven known compounds (1-7). The isolated compounds identified as 2-(3,4-dihydroxyphenyl)ethyl-2-O-[6-deoxy-α-L-mannopyranosyl-4-(3,4-dihydroxyphen-yl)-2-propenoate]-β-D-glucopyranoside (1), rutin (2), isoquercitin (3), E-caffeic acid (4), gallic acid (5), quercitin (6), β-sitosterol-β-D-glucoside (7). The methanol and chloroform extracts of the plant showed cytotoxic activity against brine shrimp in a preliminary assay and inhibitory activity against colon carcinoma cells (HCT-116) with LC₅₀ values; 20, 32 µg/mL and IC₅₀ values; 25, 35.3 µg/mL respectively. Brine shrimp lethality test was conducted on the seven isolated compounds at six different concentrations 400, 200, 100, 20, 10 and 5 µg/mL. Compounds 1, 2, 3, 5, 6 and 7 showed significant cytotoxicity with LC₅₀ values; 9, 10, 11, 22, 8 and 19 µg/mL respectively; while compounds 1, 2, 3 and 6 exhibited inhibitory activity against colon carcinoma cells with IC₅₀ values; 25, 30, 34.2 and 10 µg/mL respectively. These results indicate that Conyza dioscoridis has biochemical activity as potential pharmaceuticals. The chemical structures of active constituents were unambiguously determined by analysis of ¹H NMR, ¹³CNMR, ESI-MS, as well as by comparison with literature data and physical methods.