Briarenones A‒C, New Briarellin Diterpenoids from the Gorgonian Briareum violaceum

Abstract

Three new eunicellin-derived diterpenoids of briarellin type, briarenones A‒C (1‒3), were isolated from a Formosan gorgonian Briareum violaceum. The chemical structures of the compounds were elucidated on the basis of extensive spectroscopic analyses, including two-dimensional (2D) NMR. The absolute configuration of 1 was further confirmed by a single crystal X-ray diffraction analysis. The in vitro cytotoxic and anti-inflammatory potentialities of the isolated metabolites were tested against the growth of a limited panel of cancer cell lines and against the production of superoxide anions and elastase release in N-formyl-methionyl-leucyl-phenyl-alanine and cytochalasin B (fMLF/CB)-stimulated human neutrophils, respectively.

Keywords: Briareum violaceum; briarellin; briarenones; gorgonian.

Figure 1

Structures of new briarellin diterpenoids (1‒3) isolated from Briareum violaceum and pachyclavulariaenone F (4).

Figure 2

Key ¹H-¹H COSY, HMBC, and NOE correlations for 1.

Figure 3

Oak Ridge Thermal Ellipsoid Plot (ORTEP) diagram of the molecular structure of 1 as determined by X-ray analysis.

Figure 4

Key ¹H-¹H COSY and HMBC correlations for 2 and 3.

Figure 5

Key NOE correlations for 2 and 3.

Figure 6

A partial structure of eunicellin-derived diterpenoids: cladiellisin [27], 3-acetyl cladiellisin [28], pachycladin B [29], and klysimplexins C and E [30].