Iridoids from Pedicularis verticillata and Their Anti-Complementary Activity

Three new iridoids named as pediverticilatasin A - C (1 - 3, resp.), together with five known iridoids (4 - 8, resp.) were isolated from the whole plants of Pedicularis verticillata. The structures of three new compounds were identified as (1S,7R)-1-ethoxy-1,5,6,7-tetrahydro-7-hydroxy-7-methylcyclopenta[c]pyran-4(3H)-one (1), (1S,4aS,7R,7aS)-1-ethoxy-1,4a,5,6,7,7a-hexahydro-7-hydroxy-7-methylcyclopenta[c]pyran-4-carboxylic acid (2), (1S,4aS,7R,7aS)-1-ethoxy-1,4a,5,6,7,7a-hexahydro-7-hydroxy-7-methylcyclopenta[c]pyran-4-carbaldehyde (3). Their structures were elucidated on the basis of spectroscopic methods and compared with the NMR spectra data in the literature. All compounds were evaluated for their anti-complementary activity on the classical pathway of the complement system in vitro. Among which, compounds 1, 3, and 6 exhibited anti-complementary effects with CH₅₀ values ranging from 0.43 to 1.72 mm, which are plausible candidates for developing potent anti-complementary agents.