New eudesmane-type sesquiterpenoids and other volatile constituents from the roots of Gynura bicolor DC.

Diethyl ether extracts from fresh, field-grown plant roots and the thin roots of the cultured plantlet were analysed by gas chromatography (GC) and GC-mass spectrometry (GC-MS), and their constituents were compared. Of the components identified, major components of the field-grown plant roots were revealed to be sesquiterpene hydrocarbons such as (E)-caryophyllene, alpha-humulene, and germacrenes A, B, and C. (E)-beta-Farnesene and germacrene C were predominant in the roots of the cultured plantlet. Three new sesquiterpenoids, gynuradienol (1), hydroperoxy-gynuradiene (2), and gynurenol (3) were isolated from the field-grown plant roots and their chemical structures were elucidated by nuclear magnetic resonance (NMR) spectra together with five known sesquiterpenoids, eudesm-11-en-4 alpha-ol (4), intermedeol (5), alismol (6), alismoxide (7), (2E,6E)-3-isopropyl-6-methyl-10-oxoundeca-2,6-dienal (8), and a polyacetylenic compound, 1-tridecene-3,5,7,9,11-pentayne (9). Furthermore, characteristic green, moldy, and earthy aromas of the field-grown plant roots, which were remarkably different from those of the thin roots of the cultured plantlet, were revealed to be contributed by four methoxypyrazines, 2-methoxy-3-isopropylpyrazine (10), 2-methoxy-3-sec-butylpyrazine (11), 2-methoxy-3-isopropyl-5-methylpyrazine (12), and 2-methoxy-3-sec-butyl-5-methoxypyrazine (14) using a combination of GC-MS and GC-olfactometry (GC-O). Copyright (C) 2010 John Wiley & Sons, Ltd.