Monoterpene Dimers from Lisianthius seemannii

A new acylated dimeric secoiridoid glycoside, seemannoside A (2), has been isolated from the aerial parts of Lisianthius seemannii (GRISEB) O. KUNTZE (Gentianaceae). The structure was established by spectroscopic analysis (UV, MS, 1H‐ and 13C‐NMR, and 2D‐NMR experiments) and chemical reactions as (E‐4′‐O‐p‐coumaroyl)lisianthioside. The structure of the (Z)‐isomer (seemannoside B, 3), also present in the plant, was confirmed by LC/UV/1H‐NMR analysis. The active principle, 6, responsible for the antifungal activity of the apolar extract against Cladosporium cucumerinum, has been isolated. Its structure has been established by NMR spectroscopy and X‐ray crystallographic analysis as a rare type of aglycone monoterpene dimer.