Juncenolides F and G, Two New Briarane Diterpenoids from Taiwanese Gorgonian Junceella juncea

Abstract

Briaranes are diterpenoid g-lactones of highly substituted bicyclic six-and ten-membered rings that are extensively produced by marine octocorals including gorgonians.1,2) The majority of these compounds are endowed with biological activities that ranges from cytotoxic [3][4][5] to anti-inflammatory, 6,7) immunomodulatory, 8) antiviral, 9) and insecticidal 10,11) actions. In continuation of our interest in the chemistry and potential medicinal importance of briaranes, [12][13][14] we investigated the gorgonian octocoral Junceella juncea collected in Taiwan. Several juncins, 15,16) gemmacolides, 16) junceelolides 13) and juncenolides 12,14) have been reported from this species. The current study resulted in the isolation of the two novel briarane-type diterpenoidal compounds, juncenolides F (1) and G (2) from the acetone extract of Junceella juncea. The structures were defined on the basis of spectral studies, especially 1D and 2D NMR.The HR-ESI-MS of 1 revealed a quasi-molecular ion peak at m/z 693 [MϩNa] ϩ consistent with the molecular formula C 33 H 47 O 12 Cl and ten degrees of unsaturation. The IR spectrum displayed absorption bands diagnostic of hydroxyl, 5-membered lactone and ester groups. Both 1 H-and 13 C-NMR spectral data (Table 1 15,16) Besides the previous four ester carbonyls, the carbon signal at d 174.5 was assigned to a 5-membered lactone ring together with the oxygenated methine at d 81.2 (C-7). The two proton singlets at d 5.81 and 5.52 along with the CH 2 signal at d 121.2 were ascribed to an exocyclic methylene group. The 1 H-NMR spectrum contained two mutually coupled signals at d 2.82, 2.35 (each 1H, d, Jϭ4.0 Hz) together with the corresponding d C 50.5 (t) and d C 57.4 (s) that were appropriate for an exocyclic epoxide. The two remaining degrees of unsaturation required a bicyclic carbon skeleton which fits a briarane diterpene. ϩ were strong evidence of the presence of a chlorine atom in 1.7) Consequently, the CH signal at d 51.7 was confidently assigned to a chlorinated carbon (C-6) that was correlated to d (Fig. 1). On the other hand, the HMBC displayed correlations between H-10/C-8, C-20; H-7/C-5; H- * To whom correspondence should be addressed. Chemical investigation of the gorgonian coral Junceella juncea collected in Taiwan has resulted in the isolation of the two novel briarane-type diterpenoid compounds, juncenolides F (1) and G (2). The structures were determined on the basis of spectral studies, especially 1D and 2D NMR.

Frajunolides L–O, Four New 8-Hydroxybriarane Diterpenoids from the Gorgonian Junceella fragilis

“…The assay of O 2 •− generation was based on the SOD-inhibitable reduction of ferricytochrome c . Degranulation of azurophilic granules was determined by elastase release as described previously [16]. The elastase release experiments were performed using MeO-Suc-Ala-Ala-Pro-Val- p -nitroanilide as the elastase substrate.…”

“…The gorgonian of the genus Junceella grown in the tropical and subtropical waters of Indo-West Pacific regions are well known as a source of highly oxidized briarane-type diterpenoids with a γ-lactone moiety [6–9]. In continuation of our study on the chemistry and biological activities of briarane diterpenoids [10–16], we investigated the Taiwanese gorgonian J. fragilis . A chemical investigation of the acetone extract has yielded four new 8-hydroxybriarane diterpenoids, designated as frajunolides L–O ( 1 – 4 ).…”

Natural Product Chemistry of Gorgonian Corals of Genus Junceella—Part II

“…Sixteen new briaranes, juncenolides E–K ( 66 – 72 ) [43,44,45], juncin N ( 73 ) [46], and junceols A–H ( 74 – 81 ) [20,47] (Table 7), and two known briaranes, junceellolides B and C, were isolated from the gorgonian J. juncea , collected off the waters of Taiwan. Juncenolide G ( 68 ) is the first naturally-occurring briarane found to have an ether linkage between C-5/C-8 [44], and juncin N ( 73 ) is the first briarane derivative found to contain a carboxylic group [46].…”

“…Juncenolide G ( 68 ) is the first naturally-occurring briarane found to have an ether linkage between C-5/C-8 [44], and juncin N ( 73 ) is the first briarane derivative found to contain a carboxylic group [46]. …”

Four New Briarane Diterpenoids from Taiwanese Gorgonian Junceella fragilis

“…Many of the briarane diterpenoids have been reported to exhibit interesting biological activities, such as cytotoxic [4,5,6], anti-inflammatory [7,8], antiviral [8], insecticidal [9] and immunomodulatory [10] activities. Our previous chemical investigation of the genus Junceella has resulted in the isolation of over 20 briaranes, including frajunolides A–O and juncenolides A–O [11,12,13,14,15,16,17,18]. As part of our continuing search for bioactive natural products, the chemical constituents from other chromatographic fractions of J. fragilis were investigated.…”