Structure Identification of an Acaricidal Active Ingredient From Green Walnuts Husks (Juglans regia)

Most plants could produce bioactive substances including alkaloids, flavonoids, terpenes and relative materials, which are poisonous or have antifeedant effect to herbivorous animals, including some insects. Some well-known pesticides originated from plant bioactive substances have been successfully identified and used, for example, the azadirachtin from neem, nicotine from tobacco, rotenone and deguelin from derris, and pyrethrin from pyrethrum. It´s necessary to extract, separate and identify single compounds from plants with biological activity in order to use them directly on crop protection, or to use them as model to synthesize new pesticides without pollution. The green walnut husks contain many kinds of bioactive compounds. By now more than 16 kinds of important components have been found, including tannin, walnuts quinone (juglune), nuts Glycoside (juglanin), alpha-hydride quinone walnuts (alpha-Hydrojuglone) and beta-hydride quinone walnuts (beta-Hydrojuglone), naphthalene Qian (naphthazarin), gallic acid, walnuts drunk alkaloids (C₁₀H₈O₃), 1, 4-naphthoquinone and some pigments. We have found that the petroleum-ether extracts of walnut have strong acaricidal activity, but the major compounds of the extracts and the structures of the compounds are unclear. Here we isolated one bioactive fraction G₇ from the green walnut husks which have better acaricidal activity and identified the structure of the compound. The fraction was found to be a signal compound by two-dimensional thin-layer chromatography and High Performance Liquid Chromatography (HPLC), and the HPLC analysis also showed the absorbance peak at 222 nm wavelength of G₇ was the same as that of methyl palmitate reported by Moshitzky and the molecular weight of G₇ was identified by mass spectrometry, and the result showed the G₇ have the same M_W as methyl palmitate. Furthermore the molecular structure was analyzed- with the nuclear magnetic resonance spectroscopy and the infrared spectrum. It was found that G₇ had the same molecular formula as methyl palmitate C₁₇H₃₄O₂. Then, G₇ was compared with methyl palmitate through thin-layer chromatography and HPLC, and it was found that G₇ had the same Rt value 0.6 on TLC and the same absorbance peak at 222 nm wavelength in HPLC as methyl palmitate. So the G₇ fraction was confirmed to be the methyl palmitate.