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A combination of NMR analysis and molecular mechanics calculations has succeeded in the determination of the stereostructure of flexible briarane diterpenoids. The molecular mechanics calculations ...

The alcyonacean soft coral Sinularia flexibilis Quoy and Gaimard produces a number of bioactive complementary (secondary) metabolites. The ability of three of these diterpenes — flexibilide, sinulariolide and dihydroflexibilide — to elicit differential discriminatory feeding behavior in Gambusia affinis was assessed in a feeding deterrence study. Terpene-impregnated fish flakes were offered to fish trained to feed on such food, and their responses (acceptance, rejection, avoidance, or no response) were assessed as indicative of feeding deterrence. Food treated with sinulariolide (a compound previously determined to be non-bioactive) was generally accepted at a 1% concentration. It was avoided and rejected, however, at a concentration of 10%, a concentration level generally restricted to polyp-rich branchlets. This indicated negative olfactory and palatability cues, respectively. Flexibilide-treated flakes were accepted to some extent by the fish at the 1% concentration, but strongly avoided at the 10% concentration, indicating effective feeding deterrence via olfaction. Dihydroflexibilide-impregnated flakes were strongly rejected even at low concentrations (1%) after tasting, indicating a negative palatibility cue. They were strongly avoided or rejected at higher concentrations (10%), indicating a negative olfactory cue as well. This response at higher concentrations indicates that sinulariolide and flexibilide become effective at concentrations between 1% and 10%. Such concentrations may be found in the polypary (polyp-bearing portion) of the soft coral colonies. Dihydroflexibilide elicited the strongest negative palatability response from these test fish. The feeding deterrence characteristics of the compounds determined here represent the potentials of individual compounds to elicit differential feeding responses in organisms like Gambusia which are capable of discriminating between different but closely related complementary (secondary) metabolites.

Two new halogenated briarane diterpenes, (-)-2-deacetyljunceellin (1) and (-)-3-deacetyljunceellin (2). and five known diterpenoids, junceellin, praelolide, junceellolide A. B. and D were isolated from the Papuan gorgonian coral Junceela fragilis. The structures of the new metabolites were determined by extensive 2D NMR experiments and by chemical conversion. The absolute configuration of 2 was determined through the 1 H NMR study of the corresponding ester with a newly developed chiral auxiliary 3a.

A new cembranolide diterpene, 7-epidenticulatolide, was isolated from a soft coral, Lobophytum denticulatum. The structute was deduced spectroscopically and determined by X-ray crystallography.

The structure and relative stereochemistry of three new eunicellin-based diterpenoids (2), (3) and (4) from a Cladiella sp. of soft coral have been determined by spectral evidence and confirmed by chemical interconversion.

New brominated fatty acids (3, 5-8, 10) and new sterol esters (14-16) have been isolated from an unidentified marine sponge collected in Papua New Guinea. Their structures were determined on the basis of their spectroscopic data. A major component of the marine sponge (1) was tested for activities against Arutemia salina and some fungi.

Two new halogenated briarane diterpenes, (-)-2-deacetyljunceellin (1) and (-)-3-deacetyljunceellin (2). and five known diterpenoids, junceellin, praelolide, junceellolide A. B. and D were isolated from the Papuan gorgonian coral Junceela fragilis. The structures of the new metabolites were determined by extensive 2D NMR experiments and by chemical conversion. The absolute configuration of 2 was determined through the 1 H NMR study of the corresponding ester with a newly developed chiral auxiliary 3a.

Two new fatty acid methyl esters having an enone ether group were isolated from the root bark of Hibiscus rosa-sinensis along with three known cyclopropenoids. The new compounds, methyl ( E )-11-methoxy-9-oxo-10-nonadecenoate and ( E )-10-methoxy-8-oxo-9-octadecenoate, were chemically correlated to the corresponding cyclopropenoids. propenoids.

A new cembranolide diterpene, 7-epidenticulatolide, was isolated from a soft coral, Lobophytum denticulatum. The structute was deduced spectroscopically and determined by X-ray crystallography.

The soft coral Sinularia flexibilis is rarely overgrown by bacteria and algae. Various studies have shown that it contains diterpenes that protect it from competitors and predators. However, of the many diterpenoids isolated from S. flexibilis, only sinulariolide has been studied for antibiotic properties. Samples of soft corals were collected from Orpheus Island and freeze-dried for chemical extraction and isolation of pure diterpenes. Antimicrobial activity of the diterpenes was determined using the disc assay method with antibiotics as controls and the minimum inhibitory concentrations of the diterpenes were determined using the Tube Dilution Technique. Two out of the five diterpenes tested (sinulariolide and flexibilide), showed marked antimicrobial activity and inhibited growth of Gram-positive bacteria. Flexibilide was effective even at concentrations as low as 5 ppm, whereas sinulariolide was effective at concentrations of 10 ppm. These compounds show potential as antibiotics.

Five new sulfur-containing polybrominated bisindole (1∼5) were isolated from the red alga, Laurencia brongniartii, in addition to six related compounds (6∼11), which have been previously found in the Okinawan alga. The structures of these new bisindole metabolites were elucidated on the basis of spectroscopic studies, as well as X-Ray crystallographic analysis of 1.

Air oxidation of cyclopropane fatty acid methyl esters, methyl sterculate and malvalate, resulted in the cleavage of cyclopropene ring, respectively, to afford a pair of conjugated enones containing a terminal methylene group.

The essential oil of Chrysanthemum japonense has been analyzed to isolate a new monoterpenoid named nojigiku alcohol together with its acetate, the structure of which has been elucidated as (5R)-2,2-dimethyl-3-methylenebicyclo[2.2.1]heptan-5-ol. In addition, fifteen monoterpenoids including (+)-α-pinene, (+)-camphene, β-pinene, sabinene, 1,8-cineole, p-cymene, filifolone, (+)-chrysanthenone, (+)-camphor, (+)-borneol, (−)-cis-and (+)-trans-chrysanthenyl acetate, cis- and trans-carveyl acetate, (+)-bornyl acetate and nine sesquiterpenoids including α-copaene, β-elemene, β-caryophyllene, germacrene-D, γ-cadinene, calamenene, β-caryophyllene oxide, T-muurolol and α-cadinol were identified in the essential oil.

Denticulatolide, an ichthyotoxic cembranoid diterpene bearing acetoxy, α-methylene γ-lactone, and cyclic peroxide functions, has been isolated from the soft coral Lobophytum denticulatum. The structure (1) has been determined by spectral and chemical evidence and X-ray crystallographic method.

A novel reaction of ketone enolate with dimethylformamide (DMF) to give 1,5-diketone has been found. It is a dimerization of ketone enolates accompanying the incorporation of one-methyl one from DMF.

The most stable conformation of denticulatolide (1), an ichthyotoxic cembranolide, obtained as a major metabolite of the soft coral, Lobophytum denticulatum, was given by molecular mechanics calculations and it was confirmed by 1H NMR measurement. The geometry of 14-membered carbocycle of 1 was found to be different from that of derivative (2) especially around the juncture part of γ-lactone. The molecular mechanics calculation successfully reproduced the conformational changes between 1 and 2.

Three labdane type diterpene glycosides ( 1 , 2 and 3 ) with 6-deoxy-L-idose have been isolated from Aster spathulifolius Maxim. and their structures have been determined on the basis of chemical and spectral data.

The structures of lobohedleolide (1) and (7Z)-lobohedleolide (2), two new cembranolides containing the α,β-unsaturated carboxylic acid system isolated from the Japanese soft coral Lobophytum hedleyi Whitelegge, were elucidated from spectral and chemical evidence, and the absolute configuration of (1) was determined by X-ray analysis of its p-bromophenacyl ester (9). Lobohedleolide (1) showed growth inhibition of the in vitro Hella cells.

Three new sesquiterpenoids were isolated from the liverwort Marsupella emarginata subsp. tubulosa. The structures and absolute configurations of the compounds have been shown to be (−)-marsupellone(1), (+)-marsupellol(2) and (+)-acetoxymarsupellone(3), containing an ent-longipinane skeleton, on the basis of chemical and spectral evidence.

The mass spectral fragmentation behaviour of some labda-7,14-dien-13(R)-ol monoglycosides has been studied. Mass spectra of O-isopropylidine derivatives of the glycosides have been determined to distinguish the isomeric sugar moieties containing rhamnopyranose, fucopyranose and 6-deoxyidopyranose, respectively. The main fragment ions of the sugar moieties were investigated with the aid of deuterium labelling and high resolution mass measurement.

The chemical constituents of the volatile oils from Chrysanthemum indicum, C. yoshinaganthum and C. cuneifolium, three botanically related tetraploid species, are described. By spectroscopic methods, 42 compounds were identified, including 22 monoterpenoids, 17 sesquiterpenoids and 3 acetylenic compounds. The sesquiterpenoids estafiatin (C. yoshinaganthum) and valeranone (C. indicum) have been found for the first time in Chrysanthemum species.

Two simple γ-lactonic cembranolides were isolated from the soft coral Sinularia mayi Luttschw. and structurally elucidated on the basis of spectral and chemical evidence.

A new eunicellin-based diterpene has been isolated from a Cladiella sp. (Octocorallia, Alcyonacea). The structure and relative stereochemistry of the metabolite (1) was determined on the basis of spectroscopic and chemical evidence, and confirmed by a single-crystal X-ray structure determination.

Two new cembranoid diterpenes, cembrenene (1) and mayol (2), have been isolated from Sinularia mayi Lűttschw, along with the first reported cembrene (3) from marine organism. The structures were determined from spectral data and chemical transformations.

The structures and absolute configurations of three cembranoids, 10-oxo-, 10-hydroxy-, and 10-methoxycembrenes, isolated from the soft coral Sarcophyta elegans, are reported.