Bis-Iridoids from Pterocephalus hookeri and Evaluation of Their Anti-Inflammatory Activity

Four new secoiridoid-iridoid heterodimers, pterocenoids E-H (1-4), together with a known analog (5), were separated from the whole plants of Pterocephalus hookeri. Their structures were characterized by detailed spectroscopic analyses and NMR comparison with reported data for known analogs. Pterocenoid E (1) represents the first bis-iridoid example incorporating a rare trans-fused monomeric unit, and the C(8) configuration in 5 was corrected to be reversed to the original assignment. Among all the isolates, compound 5 not only showed moderate inhibition against the nitric oxide production (IC₅₀ =36.0±4.3 μM) but also dose-dependently suppressed the secretion of an important pro-inflammatory cytokine TNF-α, in lipopolysaccharide-induced RAW264.7 cells.