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

Four new triterpenes,25-dehydroxy-25-methoxyargentatin C (1), 20S-hydroxyargentatin C (2), 20S-hydroxyisoargentatinC (3),and 24-epi-argentatin C (4), togetherwith 10 known triterpenes (5-14)were isolated from the aerial parts of Parthenium incanum. The structures of 1-4 were elucidatedby detailed analysis of their spectroscopic data, and the known compounds 5-14 were identified by comparison oftheir spectroscopic data with those reported. Since argentatin C (11) was found to exhibit antinociceptive activity by decreasingthe excitability of rat and macaque dorsal root ganglia (DRG) neurons, 11 and its new analogues 1-4 were evaluated for their ability to decrease the excitability ofrat DRG neurons. Of the argentatin C analogues tested, 25-dehydroxy-25-methoxyargentatinC (1) and 24-epi-argentatin C (4) decreased neuronal excitability in a manner comparableto 11. Preliminary structure-activity relationshipsfor the action potential-reducing effects of argentatin C (11) and its analogues 1-4, and theirpredicted binding sites in pain-relevant voltage-gated sodium andcalcium channels (VGSCs and VGCCs) in DRG neurons are presented.

Automated summary

Four new triterpenes were isolated from Parthenium incanum and their structures were determined. These compounds were found to decrease the excitability of dorsal root ganglia neurons. The binding sites of these compounds in pain-relevant voltage-gated sodium and calcium channels were evaluated, and preliminary structure-activity relationships were established.