Anti-inflammatory diterpenoids from the brown alga Dictyota coriacea.

A new xenicane diterpene named 4α-acetoxyisodictyohemiacetal (1) was isolated from the brown alga Dictyota coriacea, along with 11 known diterpenoids. The structure of 1 was established by spectroscopic analyses, and its absolute configuration was determined by comparing the experimental and theoretical electronic circular dichroism spectra. Two dictyodiacetal diastereomers (5 and 6) were isolated, and the full NMR assignments were performed. The anti-inflammatory activities of the isolated compounds were evaluated using the lipopolysaccharide-stimulated mouse macrophage cell line, RAW264. The hemiacetal-containing xenicanes and dictyol-type diterpene inhibited not only the production of nitric oxide but also the expression of inducible nitric oxide synthase, interleukin-6, and cyclooxygenase-2 mRNA in RAW264 cells. This study demonstrated that diterpenes from D. coriacea may be useful as natural anti-inflammatory agents.