Isolation and identification of phase II enzyme-inducing agents from nonpolar extracts of green onion (Allium spp.)

The objective of the study was to isolate and identify potential cancer preventive constituents from green onion based on the ability to induce quinone reductase (QR, a representative phase II enzyme) in murine hepatoma cells (Hepa 1c1c7). Crude nonpolar solvent extracts were prepared from freeze-dried green onion by sequential refluxing with hexane and then ethyl acetate, followed by liquid-liquid extraction. Active fractions were subjected to the Hepa 1c1c7 bioassay-guided steps of flash chromatography, thin layer chromatography (TLC), and high-pressure preparative liquid chromatography (HPLC) to afford pure isolates capable of inducing QR. Multiple fractions were active in inducing QR. Five pure compounds were isolated from active fractions and identified using spectroscopic methods; these were p-hydroxyphenethyl trans-ferulate (1), 5,6-dimethyl-2-pyridinecarboxylic acid (2), ferulic acid (3), 1-(6-hydroxy-3]pyridyl)-propan-1-one (4), and N-trans-feruloyl 3-O-methyldopamine (5). p-Hydroxyphenethyl trans-ferulate (1) doubled QR specific activity in Hepa 1c1c7 cells at a level of 2.1 microg/mL (6.6 microM).