Clavirins, a new type of marine oxylipins with growth-inhibitory activity from the Okinawan soft coral, Clavularia viridis

Coral Lipids

Reef-building corals, recognized as cornerstone species in marine ecosystems, captivate with their unique duality as both symbiotic partners and autotrophic entities. Beyond their ecological prominence, these corals produce a diverse array of secondary metabolites, many of which are poised to revolutionize the domains of pharmacology and medicine. This exhaustive review delves deeply into the multifaceted world of coral-derived lipids, highlighting both ubiquitous and rare forms. Within this spectrum, we navigate through a myriad of fatty acids and their acyl derivatives, encompassing waxes, sterol esters, triacylglycerols, mono-akyl-diacylglycerols, and an array of polar lipids such as betaine lipids, glycolipids, sphingolipids, phospholipids, and phosphonolipids. We offer a comprehensive exploration of the intricate biochemical variety of these lipids, related fatty acids, prostaglandins, and both cyclic and acyclic oxilipins. Additionally, the review provides insights into the chemotaxonomy of these compounds, illuminating the fatty acid synthesis routes inherent in corals. Of particular interest is the symbiotic bond many coral species nurture with dinoflagellates from the Symbiodinium group; their lipid and fatty acid profiles are also detailed in this discourse. This exploration accentuates the vast potential and intricacy of coral lipids and underscores their profound relevance in scientific endeavors.

Prostaglandins in Marine Organisms: A Review

Prostaglandins (PGs) are lipid mediators belonging to the eicosanoid family. PGs were first discovered in mammals where they are key players in a great variety of physiological and pathological processes, for instance muscle and blood vessel tone regulation, inflammation, signaling, hemostasis, reproduction, and sleep-wake regulation. These molecules have successively been discovered in lower organisms, including marine invertebrates in which they play similar roles to those in mammals, being involved in the control of oogenesis and spermatogenesis, ion transport, and defense. Prostaglandins have also been found in some marine macroalgae of the genera Gracilaria and Laminaria and very recently the PGs pathway has been identified for the first time in some species of marine microalgae. In this review we report on the occurrence of prostaglandins in the marine environment and discuss the anti-inflammatory role of these molecules.

Clavukoellians A-F, Highly Rearranged Nardosinane Sesquiterpenoids with Antiangiogenic Activity from Clavularia koellikeri

Six new nardosinane-type sesquiterpenoids, clavukoellians A-F (1-6), together with one new neolemnane-type sesquiterpene, 4- O-deacetylparalemnolin D (7), were isolated from the marine soft coral Clavularia koellikeri. The structures of compounds 1-7 were elucidated by NMR spectroscopy, ECD analysis, and quantum chemical calculation methods. Compounds 1 and 7 demonstrated significant antiangiogenic activities in wound healing assays on HUVECs.

New anti-inflammatory steroids from the Formosan soft coral Clavularia viridis

Four new steroids, stoloniferones R-T (1-3), and (25S)-24-methylenecholestane-3 beta,5 alpha,6 beta-triol-26-acetate (4) were isolated from the methylene chloride solubles of the soft coral Clavularia viridis. The structures of the metabolites were elucidated by extensive spectral analysis and their anti-inflammatory activity was measured in vitro.

New cytotoxic steroids from the soft coral Clavularia viridis

Ten new cytotoxic steroids, stoloniferones H-Q (1-10) were isolated from the methylene chloride solubles of the soft coral Clavularia viridis. The structures of the metabolites were elucidated on the basis of spectroscopic (IR, MS, and 1D and 2D NMR) analysis and their cytotoxicity against selected cancer cells was measured in vitro.

Synthesis and Cytotoxicity of a Novel Iridoid Glucoside Derived from Aucubin

The novel iridoid glycoside 2 was prepared in six steps (15% overall yield) from natural aucubin (1) and fully characterized. Compound 2, which comprises the same conjugated cyclopentenone pharmacophore as known antitumor oxylipins and prostaglandins, displayed significant antiproliferative in vitro activity towards leukemia L1210 cells. The Michael addition of nucleophilic thiols to compound 2 occurred on a different position compared to classical delta7-prostaglandin A1 methyl ester. The resulting adducts 7a and 7b were fully characterized, and their MS fragmentation patterns were elucidated.

Prostaglandins in non-insectan invertebrates: recent insights and unsolved problems

Prostaglandins (PG) are oxygenated derivatives of C20 polyunsaturated fatty acids including arachidonic and eicosapentaenoic acids. In mammals, these compounds have been shown to play key roles in haemostasis, sleep-wake regulation, smooth muscle tone, and vaso-, temperature and immune regulation. In invertebrates, PGs have been reported to perform similar roles and are involved in the control of oogenesis and spermatogenesis, ion transport and defence. Although there is often a detailed understanding of the actions of these compounds in invertebrates such as insects, knowledge of their mechanism of biosynthesis is often lacking. This account provides a critical review of our current knowledge on the structure and modes of biosynthesis of PGs in invertebrates, with particular reference to aquatic invertebrates. It emphasises some of the most recent findings, which suggest that some PGs have been misidentified.

Prostaglandins in invertebrates can be categorised into two main types; the classical forms, such as PGE2 and PGD2 that are found in mammals, and novel forms including clavulones, bromo- and iodo-vulones and various PGA2 and PGE2 esters. A significant number of reports of PG identification in invertebrates have relied upon methods such as enzyme immunoassay that do not have the necessary specificity to ensure the validity of the identification. For example, in the barnacle Balanus amphitrite, although there are PG-like compounds that bind to antibodies raised against PGE2, mass spectrometric analysis failed to confirm the presence of this and other classical PGs. Therefore, care should be taken in drawing conclusions about what PGs are formed in invertebrates without employing appropriate analytical methods. Finally, the recent publication of the Ciona genome should facilitate studies on the nature and mode of biosynthesis of PGs in this advanced deuterostomate invertebrate.

New prostanoids with cytotoxic activity from Taiwanese octocoral Clavularia viridis

Bioassay-directed fractionation of the CH(2)Cl(2)-MeOH extract of Clavularia viridis collected in Taiwan has afforded seven new prostanoids, designated as 4-deacetoxyl-12-O-deacetylclavulone I (1), 4-deacetoxyl-12-O-deacetylclavulone II (2), bromovulone II (4), iodovulone II (5), 4-deacetoxyl-12-O-deacetylclavulone III (6), bromovulone III (7), and iodovulone III (8), in addition to seven known prostanoids (clavulones I, II, III, 7-acetoxy-7,8-dihydroiodovulone, chlorovulones II, III, and 4-deacetoxylclavulone II (3, claviridenone E)). The structures of compounds 1-8 were determined on the basis of 1D and 2D NMR techniques including COSY, HSQC, and HMBC experiments. Pharmacological study revealed that bromovulone III (7) and chlorovulone II exhibited the most promising cytotoxicity against human prostate (PC-3) and colon (HT29) cancer cells.

Isolation and structures of new halogenated prostanoids from the Okinawan soft coral Clavularia viridis

Fifteen new halogenated prostanoids 9-23 were isolated as minor constituents from the Okinawan soft coral Clavularia viridis. Compounds 9-11 were new members of iodovulone, and compounds 12-18 were 12-O-acetyliodovulones, 12-O-acetylbromovulones, and 12-O-acetylchlorovulones. Compounds 19-23 were 10,11-epoxy congeners of iodovulone, bromovulone, and chlorovulone. The structures of these compounds were determined on the basis of spectroscopic analysis and chemical conversion.

Isolation of three marine prostanoids, possible biosynthetic intermediates for clavulones, from the Okinawan soft coral Clavularia viridis

Three marine prostanoids, 1, 2, and 3, were isolated from the extract of the Okinawan soft coral Clavularia viridis. The structures of these compounds were assigned based on the results of spectroscopic analysis. Compound 1 was shown to be preclavulone-A methyl ester, and this is the first isolation of the ester of preclavulone-A as a natural product. Preclavulone-A is proposed to be the key intermediate in the biosynthesis of marine prostanoids exemplified by clavulones in C. viridis. The new prostanoid 3 was suggested to be a biosynthetic intermediate from preclavulone-A to clavulones, and a possible biogenetic pathway via 3 is proposed.

New marine diterpenoids from the Okinawan soft coral Clavularia koellikeri

Chemical investigation of the Okinawan soft coral Clavularia koellikeri resulted in the isolation of two new cembrane diterpenoids (1 and 2) and one new dollabelane diterpenoid, 3. Their structures were determined on the basis of the results of spectroscopic analysis. Compounds 1 and 3 were examined for in vitro growth-inhibition effects toward tumor cells.

Enantioselective synthesis of 12-amino alkylidenecyclopentenone prostaglandins

An enantioselective synthesis of new 12-amino alkylidenecyclopentenone prostaglandins is reported. The key step of the synthesis involved a [3.3] sigmatropic rearrangement of an asymmetric allylic cyanate to elaborate an asymmetric 5-amino-1,6-diene which was further transformed into cyclopentenone by successive ring-closing metathesis reaction catalyzed by the Grubbs reagent and one-pot oxidation. A palladium-catalyzed cross-coupling reaction on a 5-iodo-1,5-diene allowed the synthesis of prostanoids with variable Rw side chains. These new compounds exhibit high cytotoxic activities.

Tricycloclavulone and clavubicyclone, novel prostanoid-related marine oxylipins, isolated from the Okinawan soft coral Clavularia viridis

Two novel prostanoid-related marine oxylipins, tricycloclavulone (1) and clavubicyclone (2), were isolated from the Okinawan soft coral Clavularia viridis. The structures of 1, having a tricyclo[5.3.0.0(1,4)]decane ring system, and 2, having a bicyclo[3.2.1]octane ring system, were elucidated on the basis of spectroscopic analysis. Clavubicyclone showed a moderate growth inhibition activity against tumor cells in vitro.

New marine cembrane-type diterpenoids from the Okinawan soft coral Clavularia koellikeri

Seven new marine diterpenoids having a cembrane skeleton were isolated from the Okinawan soft coral Clavularia koellikeri. Their structures were determined based on the results of spectroscopic analysis and chemical conversions. Compound 1 showed cytotoxic activity against human colorectal adenocarcinoma cells (DLD-1, IC(50) 4.2 g/mL) and strong growth inhibition against human T lymphocytic leukemia cells (MOLT-4, IC(50) 0.9 g/mL).