Briavioids E-G, Newly Isolated Briarane-Diterpenoids from a Cultured Octocoral Briareum violaceum

Abstract

The chemical screening of a cultured soft coral, Briareum violaceum, led to the isolation of eight natural, briarane-related diterpenoids, including three unreported metabolites, briavioids E-G (1-3), and five known briaranes, briacavatolides B (4) and C (5), briaexcavatin L (6), briaexcavatolide U (7) and briarenol K (8). The structures of briaranes 1-8 were established using spectroscopic methods. The absolute configuration of briavioid A (9), obtained in a previous study, was reported for the first time in this study by a single-crystal X-ray diffraction analysis using a copper radiation source. The anti-inflammatory activity of briaranes 1 and 2 and briaranes 4-8 was evaluated by screening their inhibitory ability against the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) proteins in lipopolysaccharide (LPS)-induced RAW 264.7 macrophage cells.

Keywords: Briareum violaceum; COX-2; X-ray; anti-inflammation; briarane; briavioid; iNOS.

Figure 1

Structures of briavioids E–G (1–3), briacavatolides B (4) and C (5), briaexcavatin L (6), briaexcavatolide U (7), briarenol K (8) and briavioid A (9).

Figure 2

Key COSY and HMBC correlations of 1.

Figure 3

Stereoview of 1 and calculated distances (Å) between particular protons that have crucial NOESY correlations.

Figure 4

Key COSY and HMBC correlations of 2.

Figure 5

Stereoview of 2 and calculated distances (Å) between particular protons that have crucial NOESY correlations.

Figure 6

Key COSY and HMBC correlations of 3.

Figure 7

Stereoview of 3 and calculated distances (Å) between particular protons that have crucial NOESY correlations.

Figure 8

The ORTEP diagram of briavioid A (9).