Ent-kaurane derivatives from the root cortex of yacon and other three Smallanthus species (Heliantheae, Asteraceae)

The metabolites produced by the secretory canals of the root cortex from four Smallanthus species belonging to the yacon group were identified as ent-kaurane-type diterpenes. The dichloromethane root cortex extracts of the four species were treated with diazomethane and analyzed comparatively by GC–MS using a simple and rapid procedure which is very sensitive and reproducible permitting detection of minor components. In all cases, ent-16-kauren-19-oic acid (kaurenoic acid) methyl ester was the main component, differences being observed only in the minor components. The minor components identified were grandiflorenic acid methyl ester, ent-16-kauren-19-al, 16α,17-epoxy-15α-angeloyloxy-kauran-19-oic acid methyl ester and several O-acyl derivatives at C-15 or C-18 of kaurenoic acid. One of the minor components, 18-isobutyroyloxy-ent-kaur-16-en-19-oic acid is a new kaurenoic acid derivative. Grandiflorenic acid and 15-α-angeloyloxy-16,17-α-epoxy-ent-16-kauren-19-oic acid were present only in Smallanthus sonchifolius and Smallanthus siegesbeckius which showed very similar GC traces. The different GC profile of RC diterpenes from Smallanthus connatus and Smallanthus macroscyphus supports the view that they are different taxa. Some chemotaxonomic aspects of the genus Smallanthus and the subtribe Milleriinae are briefly discussed.

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► This paper deals with the secondary metabolites produced by the secretory canals of the root cortex (RC) of Smallanthus sonchifolius (yacon), Smallanthus macroscyphus, Smallanthus connatus and Smallanthus siegesbeckius.
► A simple and rapid procedure for the isolation of the metabolites contained in the secretory canals is presented.
► The metabolites produced by the secretory canals were analyzed by GC-MS and found to be diterpenes of the ent-kaurane type, ent-16-kauren-19-oic acid (kaurenoic acid) being the main component in the four investigated species.
► The different GC profile of RC diterpenes from S. connatus and S. macroscyphus supports the view that they are different taxa.
► Some chemotaxonomic aspects of the genus Smallanthus and the subtribe Milleriinae are briefly discussed.