Argentatin C Analogues with Potential Antinociceptive Activity and Other Triterpenoid Constituents from the Aerial Parts of .

Four new triterpenes, 25-dehydroxy-25-methoxyargentatin C (), 20-hydroxyargentatin C (), 20-hydroxyisoargentatin C (), and 24--argentatin C (), together with 10 known triterpenes (-) were isolated from the aerial parts of . The structures of - were elucidated by detailed analysis of their spectroscopic data, and the known compounds - were identified by comparison of their spectroscopic data with those reported. Since argentatin C () was found to exhibit antinociceptive activity by decreasing the excitability of rat and macaque dorsal root ganglia (DRG) neurons, and its new analogues - were evaluated for their ability to decrease the excitability of rat DRG neurons. Of the argentatin C analogues tested, 25-dehydroxy-25-methoxyargentatin C () and 24--argentatin C () decreased neuronal excitability in a manner comparable to . Preliminary structure-activity relationships for the action potential-reducing effects of argentatin C () and its analogues -, and their predicted binding sites in pain-relevant voltage-gated sodium and calcium channels (VGSCs and VGCCs) in DRG neurons are presented.