Rugulopteryx-Derived Spatane, Secospatane, Prenylcubebane and Prenylkelsoane Diterpenoids as Inhibitors of Nitric Oxide Production

This study aimed to evaluate the anti-inflammatory potential of the different classes of diterpenoids produced by algae of the genus Rugulopteryx. First, sixteen diterpenoids (1–16), including spatane, secospatane, prenylcubebane, and prenylkelsoane metabolites, were isolated from the extract of the alga Rugulopteryx okamurae collected at the southwestern Spanish coasts. Eight of the isolated diterpenoids are new compounds whose structures were determined by spectroscopic means: the spatanes okaspatols A-D (1–4); the secospatane rugukamural D (8); the prenylcubebanes okacubols A (13) and B (14); and okamurol A (16), which exhibits an unusual diterpenoid skeleton featuring a kelsoane-type tricyclic nucleus. Second, anti-inflammatory assays were performed on microglial cells Bv.2 and macrophage cells RAW 264.7. Compounds 1, 3, 6, 12, and 16 caused significant inhibition of the NO overproduction induced by LPS in Bv.2 cells, and compounds 3, 5, 12, 14, and 16 significantly decreased levels of NO in LPS-stimulated RAW 264.7 cells. The most active compound was okaspatol C (3), which completely suppressed the effects of LPS stimulation, both in Bv.2 and in RAW 264.7 cells.