seco-Briarellinone and briarellin S, two new eunicellin-based diterpenoids from the Panamanian octocoral Briareum asbestinum

Abstract

Two new eunicellin-based diterpenes, seco-briarellinone (1) and briarellin S (2), and a known seco-asbestinin (3) have been isolated from the methanolic extract of the common octocoral Briareum asbestinum collected in Bocas del Toro, Caribbean of Panama. The structures and relative stereochemistry of the compounds were defined using extensive spectroscopic analysis including 1D, 2D-nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). Compounds 1 and 2 displayed anti-inflammatory properties inhibiting nitric oxide (NO) production induced by lipopolisacharide (LPS) in macrophages with an Inhibitory concentration 50% (IC₅₀) of 4.7 μM and 20.3 μM, respectively. This is the first report of briarellin diterpenes containing a ketone group at C-12.

Figure 1

Structures of compounds 1–4.

Figure 2

Correlation spectroscopy (COSY) or total correlation spectroscopy (TOCSY) and heteronuclear multiple bond correlation (HMBC) correlations of compounds 1 and 2.

Figure 3

NOE correlations of compounds 1 and 2.

Figure 4

Inhibition of nitric oxide (NO) production induced by lipopolisacharides (LPS) in macrophages. (A) Peritoneal macrophages from C57Bl/6 mice were treated with different concentrations of compounds 1–3 (1, 2, 5, 10, or 20 μg/mL) 1 h before the stimulus with LPS (1 μg/mL). After 24 h of stimulus with LPS, supernatants were collected for NO determination. (B) Cell viabilities were assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay after collection of the supernatant. Results represent mean ± S.E.M. and are representative of two different experiments. * P < 0.005 compared with LPS stimulus alone. C, control; Comp, compound.