Cembrane derivatives from the soft corals, Sinularia gaweli and Sinularia flexibilis

Abstract

A new norcembranoidal diterpene, 1-epi-sinulanorcembranolide A (1), and a new cembranoidal diterpene, flexibilin D (2), were isolated from the soft corals, Sinularia gaweli and Sinularia flexibilis, respectively. The structures of new metabolites 1 and 2 were elucidated by spectroscopic methods, and compound 2 was found to significantly inhibit the accumulation of the pro-inflammatory iNOS and COX-2 proteins of the lipopolysaccharide (LPS)-stimulated RAW264.7 macrophage cells. In addition, S. flexibilis yielded a known cembrane, 5-dehydrosinulariolide (3); the structure, including its absolute stereochemistry, was further confirmed by single-crystal X-ray diffraction analysis.

Figure 1

The structures of 1-epi-sinulanorcembranolide A (1), flexibilin D (2), 5-dehydrosinulariolide (3) and sinulanorcembranolide A (4).

Figure 2

¹H–¹H COSY and selected HMBC correlations (protons→quaternary carbons) for 1.

Figure 3

The computer-generated model of 1 using molecular mechanics calculations (MM2) force field calculations and the calculated distances (Å) between selected protons with key NOESY correlations.

Figure 4

¹H–¹H COSY and selected HMBC correlations (protons→quaternary carbons) for cembrane 2.

Figure 5

The computer-generated model of 2 using MM2 force field calculations and the calculated distances (Å) between selected protons with key NOESY correlations.

Figure 6

Molecular plot of 3 with confirmed absolute configuration.

Figure 7

Effects of compound 2 on iNOS and COX-2 protein expression of RAW264.7 macrophage cells by immunoblot analysis. The values are the mean ± SEM (n = 5). Relative intensity of the lipopolysaccharide (LPS)-alone stimulated group was taken as 100%. Under the same experimental condition, CAPE (caffeic acid phenylethyl ester, 10 μM), reduces the levels of the iNOS and COX-2 to 2.8 ± 4.6 and 66.7% ± 9.6%, respectively. * Significantly different from LPS-alone stimulated group (p < 0.05).