Iridoid and flavone glycosides from Asystasia gangetica subsp. micrantha and Asystasia salicifolia and their antioxidant activities

2012

E05435

Chromatographic separations of the methanolic extract of the aerial parts of Asystasia gangetica subsp. micrantha afforded 5 iridoid glycosides: 6 beta -hydroxyantirrhide (1), angeloside (2), ajugol (3), 6-O- alpha -L-rhamnopyranosyl-catalpol (4), and 6-O- alpha (3"-O-trans-caffeoyl)-L-rhamnopyranosyl-catalpol (5). From the methanolic extract of A. salicifolia, 7 compounds were identified: including compound 5, 6-O- alpha (3"-O-trans-p-coumaroyl)-L-rhamnopyranosyl-catalpol (6), sinuatol (7), luteolin 7-O- beta -D-glucopyranoside (8), luteolin 7-O-rutinoside (9), apigenin 7-O-rutinoside (10) and apigenin 7-O- beta -D-glucuronide (11). Their structures were established by spectroscopic means and comparison of their spectroscopic data with literature values. A. gangetica subsp. micrantha was collected in March 2010 from Khon Kaen University, Khon Kaen Province, whereas A. salicifolia was collected in November 2006 from Nam-Nao National Park, Phetchabun Province, in Thailand. The isolated compounds were evaluated for free radical scavenging activities by using DPPH and ORAC assays. In DPPH assay, iridoid glycosides 5 and flavone glycosides 8 and 9 showed scavenging activity with SC50 value of 20.3, 16.4 and 18.6 micro M, respectively, potent in the same range as the positive control, ascorbic acid, while the remaining compounds were inactive. In the ORAC assay, the unit values of compounds 5-11 ranged from 2.4 to 4.5 folds more potent than the positive control, Trolox. The results provided further confirmation of the typical profile of the secondary metabolites found in this genus. The presence of compound 4 and its acylated derivatives might be useful for further chemotaxonomic studies of the two species.

40:38-42, BIOCHEMICAL SYSTEMATICS AND ECOLOGY

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