Briarenols C–E, New Polyoxygenated Briaranes from the Octocoral Briareum excavatum

Three new polyoxygenated briarane diterpenoids, briarenols C–E (1–3), were isolated from the octocoral Briareum excavatum. The structures of briaranes 1–3 were elucidated by interpretation of spectroscopic data, and the methylenecyclohexane ring in 1 was found to exist in a twisted boat conformation. Briarenol D (2) displayed an inhibitory effect on the release of elastase by human neutrophils with an IC50 value of 4.65 μM. Briarenol E (3) was found to inhibit the protein expression of pro-inflammatory inducible nitric oxide synthase (iNOS) in a murine macrophage-like cell line, RAW 264.7, stimulated with lipopolysaccharides (LPS).