Longifoliols A-C, three unprecedented isopimarane derivatives from Callicarpa longifolia

One unprecedented isopimarane longifoliol A (1) and two unprecedented C₉-spiro-fused seco-7,8-isopimaranes longifoliols B and C (2 and 3) along with a known phenolic glucoside trichocarpin (4) were obtained from the branches and leaves of Callicarpa longifolia. Their structures were elucidated by extensive analysis of their 1D, 2D NMR and HRESIMS data. The relative configuration was established using spectroscopic experiments as well as conformational analysis, DP4+ calculations, and J-coupling constant predictions (via DU8 and pcnJ methods). The absolute configurations of 1-3 were determined by comparing experimental and calculated ECD spectra and specific optical rotation values. Furthermore, the plausible biosynthetic pathways of 1-3 were proposed. Moreover, all isolates were evaluated for their in vitro nitric oxide (NO) inhibitory activity. Compound 4 revealed moderate activity with IC₅₀ = 67.61 ± 3.23 µM while 1 and 3 exhibited weak inhibitory effect on NO production in LPS-stimulated RAW264.7 cells, with IC₅₀ values of 80.01 ± 3.74 and 82.26 ± 3.45 µM, respectively.