New xenicane diterpenes isolated from the acetone extract of the soft coral Xenia florida

Transient Receptor Potential Melastatin 7 (TRPM7) Ion Channel Inhibitors: Preliminary SAR and Conformational Studies of Xenicane Diterpenoids from the Hawaiian Soft Coral Sarcothelia edmondsoni

Waixenicin A, a xenicane diterpene from the octocoral Sarcothelia edmondsoni, is a selective, potent inhibitor of the TRPM7 ion channel. To study the structure-activity relationship (SAR) of waixenicin A, we isolated and assayed related diterpenes from S. edmondsoni. In addition to known waixenicins A (1) and B (2), we purified six xenicane diterpenes, 7S,8S-epoxywaixenicins A (3) and B (4), 12-deacetylwaixenicin A (5), waixenicin E (6), waixenicin F (7), and 20-acetoxyxeniafaraunol B (8). We elucidated the structures of 3-8 by NMR and MS analyses. Compounds 1, 2, 3, 4, and 6 inhibited TRPM7 activity in a cell-based assay, while 5, 7, and 8 were inactive. A preliminary SAR emerged showing that alterations to the nine-membered ring of 1 did not reduce activity, while the 12-acetoxy group, in combination with the dihydropyran, appears to be necessary for TRPM7 inhibition. The bioactive compounds are proposed to be latent electrophiles by formation of a conjugated oxocarbenium ion intermediate. Whole-cell patch-clamp experiments demonstrated that waixenicin A inhibition is irreversible, consistent with a covalent inhibitor, and showed nanomolar potency for waixenicin B (2). Conformational analysis (DFT) of 1, 3, 7, and 8 revealed insights into the conformation of waixenicin A and congeners and provided information regarding the stabilization of the proposed pharmacophore.

Terpenoids from Marine Soft Coral of the Genus Xenia in 1977 to 2019

Members of the marine soft coral genus Xenia are rich in a diversity of diterpenes. A total of 199 terpenes consisting of 14 sesquiterpenes, 180 diterpenes, and 5 steroids have been reported to date. Xenicane diterpenes were reported to be the most common chemical skeleton biosynthesized by members of this genus. Most of the literature reported the chemical diversity of Xenia collected from the coral reefs in the South China Sea and the coastal waters of Taiwan. Although there was a brief review on the terpenoids of Xenia in 2015, the present review is a comprehensive overview of the structural diversity of secondary metabolites isolated from soft coral genus Xenia and their potent biological activity as reported between 1977 to 2019.

New secondary metabolite with cytotoxicity from spawning soft coral Asterospicularia laurae in Taiwan

We have conducted a long-term research on the Taiwanese soft coral Asterospicularia laurae, which resulted in many xenicane-type diterpenoids such as asterolaurins A-M from A. laurae coral tissues during the non-spawning period were isolated. Here, we report a new xenicane diterpenoid, asterolaurin N (1), along with three known xenicane-type monocarbocyclic diterpenes [13-epi-9-desacetylxenicin (2), xeniolide-B 9-acetate (3) and asterolaurin I (4)] from A. laurae during the spawning period. The structures of the new secondary metabolite were established with an extensive spectroscopic analysis. The 1D and 2D nuclear magnetic resonance (NMR) data of the compounds were discussed. We discovered that the C-15 of 1 contains two methyl groups on a carbon bearing an acetyl group, which has not been reported previously. In addition, Compounds 1, 3, and 4 showed selective cytotoxic activity against Molt 4, while 2 exhibited significant cytotoxicity against Molt 4, K562, Sup-T1 and U937 cell lines.

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

This review describes strategies for the chemical synthesis of xenicane diterpenoids and structurally related metabolites. Selected members from the four different subclasses of the Xenia diterpenoid family, the xenicins, xeniolides, xeniaphyllanes and xeniaethers, are presented. The synthetic strategies are discussed with an emphasis on the individual key reactions for the construction of the uncommon nine-membered carbocycle which is the characteristic structural feature of these natural products. Additionally, the putative biosynthetic pathway of xenicanes is illustrated.

Asterolaurins A-F, xenicane diterpenoids from the Taiwanese soft coral Asterospicularia laurae

Six new xenicane-type diterpenoids, designated as asterolaurins A-F (1-6), have been isolated from the organic extract of the soft coral Asterospicularia laurae, collected in southern Taiwan. Compounds 1-4 possess a xenicin skeleton with a 2-oxabicyclo[7.4.0]tridecane ring system, while 5 and 6 are xeniolide A-type compounds. The structures of the new secondary metabolites, including their configurations, were established on the basis of an extensive spectroscopic analysis, including 1D and 2D NMR (1H-1H COSY, HMQC, HMBC, and NOESY), and by comparison of their NMR data with those of the related compounds. The structure of asterolaurin A (1) was confirmed by X-ray diffraction analysis, and its absolute configuration was determined using the modified Mosher's method. Asterolaurin A (1) exhibited moderate cytotoxicity against HepG2 cells with an IC50 of 8.9 microM, while asterolaurin D (4) showed potent inhibition of elastase release and superoxide anion generation in vitro.

Induction of apoptosis by diterpenes from the soft coral Xenia elongata

Four new diterpenes ( 1- 4) were isolated from the soft coral Xenia elongata using a novel cell-based screen for apoptosis-inducing, potential anticancer compounds. The molecular structures of the diterpenes were determined using a combination of NMR and mass spectrometry. The bioactivities were confirmed using a specific apoptosis induction assay based on genetically engineered mammalian lines with differential, defined capacities for apoptosis. The diterpenes induce apoptosis in micromolar concentrations. This is the first report of apoptosis induction by marine diterpenes in xenicane skeletons.

Four diterpenoid inhibitors of Cdc25B phosphatase from a marine anemone

Three new diterpenoids and one known diterpenoid have been isolated from a sea anemone of the order Actiniara, and the structures of the new compounds, actiniarins A-C (1-3) were established on the basis of extensive 1D and 2D NMR spectroscopic data interpretation. Compound 1 has a six-membered ring hemiacetal ring, and the equilibrium of this ring is discussed. All the isolates were evaluated for their inhibition of Cdc25B and for cytotoxicity against the A2780 ovarian cancer cell line.

Xenibellols A and B, New Diterpenoids from the Formosan Soft CoralXeniaumbellata

Xenibellols A (1) and B (2), possessing an unprecedented diterpenoid skeleton, were isolated from the soft coral Xenia umbellata. The structures of xenibellols A and B were established by extensive analysis of spectroscopic data.