New eudesmane‐type sesquiterpenoids and other volatile constituents from the roots of <i>Gynura bicolor</i> DC.

Abstract

Abstract 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, α ‐humulene, and germacrenes A, B, and C. ( E )‐ β ‐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 α ‐ol (4), intermedeol (5), alismol (6), alismoxide (7), (2 E ,6 E )‐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 © 2010 John Wiley &amp; Sons, Ltd.