Anti-inflammatory diterpenoids from the Brazilian alga Dictyota menstrualis

The chemical investigation of the brown alga Dictyota menstrualis provided three previously unreported prenylated guaiane diterpenes derivatives named as dictyols K, M and N (1 - 3), along with five structurally known diterpenoids (4 - 8). The structures of the new compounds, including their relative stereochemistry, were established by nuclear magnetic resonance (NMR) and high resolution mass spectrometry (HAMS) data analysis. In addition, their structures were improved by quantum mechanical calculations. Anti-inflammatory, antimicrobial and cytotoxic assays were performed with the isolated compounds, however, only the anti-inflammatory activity was particularly prominent. The cell viability effects of 1 - 8 on murine macrophage cell line (RAW 264.7) showed IC50 values ranging from 1.12 to 2.53 mu M, and the inhibitory activity against the nitric oxide production over the lipopolysaccharide-stimulated RAW 264.7 cell was observed for all compounds with IC50 values ranging to 0.12 - 0.23 mu M.