Lonimacranaldes A–C, three iridoids with novel skeletons from Lonicera macranthoides

Abstract

Lonimacranaldes A and B (1 and 2), along with one biogenetically related intermediate, lonimacranalde C (3), were isolated from the flower buds of Lonicera macranthoides. Characterized by an iridoid structure and an additional C-6 unit with an aldehyde group, compounds 1 and 2 are the first examples of hybrid iridoids possessing an unexpected 6/5/6 fused tricyclic ring system, while compound 3 serves as an important precursor for their generation. The structures of lonimacranaldes A–C (1–3) were revealed by extensive spectroscopic and X-ray diffraction analyses. A plausible biogenetic pathway for them was proposed. Compound 3 showed anti-inflammatory activities by inhibiting the production of IL-6 on LPS-induced RAW 264.7 cells with an IC₅₀ value of 6.33 μM.