Acyclic tetraprenyltoluquinols from Cystoseira sauvageuana and their possible role as biogenetic precursors of the cyclic cystoseira metabolites

From the brown alga Cystoseira sauvageuana two novel tetraprenyltoluquinols with an acyclic terpenoid side chain have been isolated. Their chemical transformation into compounds containing a cyclopentane ring provides a clue to the biogenesis of the cyclic Cystoseira metabolites.     

Tetraprenyltoluquinols from the brown alga Cystoseira jabukae

The chloroform extract of the brown alga Cystoseira jabukae afforded two new tetraprenyltoluquinols and two tetraprenyltoluquinones. The structures were determined by spectral analysis and chemical correlations. The quinones are possibly artifacts formed by oxidation of the corresponding quinols in the isolation procedure.     

Diterpenes from the brown algae Dictyota dichotoma and Dictyota linearis

Nineteen secondary metabolites of the brown alga Dictyota dichotoma (Huds.) Lam. and fifteen metabolites of the brown alga D. linearis (Ag.) Grev. were isolated and their chemical structures were elucidated on the basis of their NMR and mass spectral data. The diterpenes isopachydictyolal (1) from D. dichotoma and 4alpha-acetyldictyodial (2) from D. linearis are new natural products. The antiviral activity of metabolites isolated in adequate amounts was evaluated in laboratory assays against Herpes simplex virus I (HSV I) and Poliomyelitis Virus I, using Vero cells as hosts.     

Diterpenes from the Far-eastern brown alga Dictyota dichotoma

Two diterpenes, ent-erogorgiaene and (+)-1,5-cyclo-5,8,9,10-tetrahydroerogorgiaene, were isolated from the Russian Far-eastern population of the brown alga Dictyota dichotoma along with three previously known from this alga terpenoids. In addition, pentadecane was the first time isolated as natural product from this species. The structures of all compounds and their stereochemistry were determined using 1D and 2D NMR ((1)H-(1)H COSY, DEPT, HSQC, HMBC and NOESY), mass spectrometry, and optical rotation data.     

Chemical investigation of seven Australasian Cystophora species: New chemistry and taxonomic insights

Chemical investigation of seven species from the brown algal genus Cystophora collected throughout Australia and New Zealand resulted in the isolation of two new compounds, 9,10-farnesylacetone epoxide (1) from Cystophora moniliformis and 1′-(2′,4′,6′-trihydroxyphenyl)-13-hydroxyoctadeca-6Z,9Z,11E,15Z-tetraen-1-one (12) from Cystophora scalaris, and 16 others that have been previously reported. Structures were elucidated using spectrometric methods, particularly 1D and 2D NMR spectroscopy. Taxonomic implications of the chemical findings are discussed including the possibility that 1 may be an intra-specific marker for the Western Australian population of C. moniliformis, and that 12 may be diagnostic for populations of C. scalaris from New Zealand waters.     

Linear diterpenoids from Cystoseira balearica

From the brown alga Cystoseira balearica we have isolated, in addition to previously reported acyclic diterpenoids, two new compounds (eleganonal and iso-eleganonal). Their structures have been elucidated by spectral analysis and chemical correlation.     

Chemical composition of Cystoseira crinita Bory from the Eastern Mediterranean

The chemical composition of the brown alga Cystoseira crinita Bory from the Eastern Mediterranean was investigated. Fourteen sterols have been identified, five of them for the first time in algae. The structure of one new sterol was established. The origin of seven sterols with short side chains was discussed. In the volatile fraction 19 compounds and in the polar fraction 15 compounds were identified. The main lipid classes were isolated and their fatty acid composition was established.     

Tetraprenyltoluquinols from the brown alga Cystoseira stricta

Four novel metabolites of mixed biogenesis have been isolated from the brown alga Cystoseira stricta and their structures determined by chemical and spectral methods.     

Further acetogenins from Tasmanian collections of Caulocystis cephalornithos demonstrating chemical variability

Samples of the brown alga Caulocystis cephalornithos, from five locations in southern and southeastern Tasmania, were investigated for comparison of their acetogenin content. In contrast with previously studied brown algae, including mainland Australian collections of C. cephalornithos, Tasmanian collections of C. cephalornithos were found to contain unusually high levels of tridec-1-ene, a hydrocarbon not previously reported from a marine alga. The novel metabolite (E)-nonadec-3-en-2-one was also isolated. Compounds previously described from this alga were present, together with a suite of homologues not previously observed in this species. The compounds present suggested that the alkyl chain of the orsellinic acid derivatives was present prior to cyclisation. Large variations in relative metabolite content were observed both within and between collection sites.     

Five novel tetraprenylhydroquinols from the brown alga Cystoseira algeriensis

Five novel metabolises of mixed biogenesis have been isolated from the brown alga Cystoseira algeriensis. They are tetraprenylhydroquinols and their structures have been determined by spectral analysis and chemical correlations.     

Lipids from the brown alga Cystoseira barbata

Two new diunsaturated lipids, related to palmitic acid, were isolated from the brown alga Cystoseira barbata, one of which is toxic to mice during P388 lymphocytic leukemia tests.     

Antiplasmodial halogenated monoterpenes from the marine red alga Plocamium cornutum

In our continuing search for antimalarial leads from South African marine organisms we have examined the antiplasmodial organic extracts of the endemic marine red alga Plocamium cornutum (Turner) Harvey. Two new and three known halogenated monoterpenes were isolated and their structures determined by standard spectroscopic techniques. The 3,7-dimethyl-3,4-dichloro-octa-1,5,7-triene skeleton is common to all five compounds. Interestingly, compounds bearing the 7-dichloromethyl substituent showed significantly higher antiplasmodial activity toward a chloroquine sensitive strain of Plasmodium falciparum.     

Meroditerpenoids from the southern Australian marine brown alga Sargassum fallax

Chemical investigation of the southern Australian marine brown alga Sargassum fallax resulted in the isolation of three meroditerpenoids fallahydroquinone, fallaquinone and fallachromenoic acid together with the previously reported compounds sargaquinone [isolated and identified in a mixture with sargaquinoic acid], sargahydroquinoic acid, sargaquinoic acid and sargachromenol. As a result of this study the complete 2D NMR characterisation for sargaquinoic acid and sargahydroquinoic acid can now be reported for the first time. All structures were elucidated by detailed spectrometric analysis. Sargaquinoic acid and sargahydroquinoic acid displayed moderate antitumour activity.     

Natural Products among Brown Algae: The Case of Cystoseira schiffneri Hamel (Sargassaceae,Phaeophyceae)

A chemotaxonomic study on the marine brown alga Cystoseira schiffneri collected from the Tunisian marine coast allowed us to identify kjellmanianone ( 1 ) and a new isololiolide derivative named schiffnerilolide ( 2 ). The structure elucidation and the assignment of relative configurations of the isolated natural products were based on advanced mass spectrometric and nuclear magnetic resonance techniques. This outcome suggested a close phylogenetic relationship of C. schiffneri with brown algae belonging to genus Sargassum C. Agardh . Molecular characterization using the nuclear small subunit rRNA (SSU rRNA) gene (18S) sequence as genetic marker was made. Pigment analysis showed a significant seasonal change of carotenoids, in particular of fucoxanthin and fucoxanthinol. Also galactolipids, the main constituents of the thylakoid membranes, showed remarkable seasonal changes.     

Methoxybifurcarenone: an antifungal and antibacterial meroditerpenoid from the brown alga Cystoseira tamariscifolia.

A meroditerpenoid metabolite has been isolated from the brown alga Cystoseira tamariscifolia and characterized as methoxybifurcarenone, by spectral analysis. Methoxybifurcarenone possesses antifungal activity against three tomato pathogenic fungi: Botrytis cinerea, Fusarium oxysporum sp. mycopersici and Verticillium alboatrum and antibacterial activity against Agrobacterium tumefaciens and Escherichia coli.     

Polar acyclic diterpenoids from Bifurcaria bifurcata (Fucales, Phaeophyta)

From the lipophilic extract of the brown alga Bifurcaria bifurcata collected off the Atlantic coast of Southern Brittany (Quiberon, France), five polar linear diterpenoids have been isolated. These metabolites have been identified as hydroxylated derivatives of 13-oxo- and 13-hydroxygeranylgeraniol. Their structures were characterized on the basis of chemical and spectral evidence including two-dimensional NMR experiments and mass spectrometric techniques. The absolute configuration of the 13-position has been determined, for the 13-hydroxygeranylgeraniol derivatives, to be R by means of a modified Mosher's method and therefore that of 13-hydroxygeranylgeraniol (eleganediol) has been revised. Along with these compounds, three related known geranylgeraniol derivatives were also identified, and these data were used for chemotaxonomical purposes.     

Halogenated phlorethols and fucophlorethols from the brown alga Cystophora retroflexa.

From an ethyl acetate fraction of the brown alga Cystophora retroflexa several halogenated phlorotannins were isolated. Most of the compounds are derivatives of diphlorethol penta-acetate and triphlorethol-A hepta-acetate. The majority turned out to be chlorinated and/or brominated. Only one iodinated substance, 2-iodophloroglucinol triacetate, was isolated. The structure of this derivative and the following compounds have been characterized previously: 2([D])-bromodiphlorethol penta-acetate, 3([A1])-bromodiphlorethol penta-acetate, 4([D])-bromo-diphlorethol penta-acetate, 4([D])-chlorodiphlorethol penta-acetate, 3([A1])-chlorotriphlorethol-A hepta-acetate, 4([D])-bromotriphlorethol-A hepta-acetate and 4([D])-chlorobisfucopentaphlorethol-A nonadeca-acetate. Ten halogenated phlorethols and two chlorinated fucophlorethols are described for the first time and characterized as their acetates: 2([B])-bromotriphlorethol-A hepta-acetate, 2([D])-bromotriphlorethol-A hepta-acetate, 2([B]), 2([D])-dibromotriphlorethol-A hepta-acetate, 3([A1]), 5([A1])-dichlorotriphlorethol-A hepta-acetate, 3([A1]), 4([D])-dichlorotriphlorethol-A hepta-acetate, 3([A1])-chloro-4([D])-bromotriphlorethol-A hepta-acetate. 2([B]), 4([D])-dichlorotriphlorethol-A hepta-acetate, 2([D]), 3([A1])-dibromotriphlorethol-A hepta-acetate, 3([A1])-bromo-2([D])-chlorotriphlorethol-A hepta-acetate, 2([D])-bromotetraphlorethol-C nona-acetate, 4([D])-chlorofucotriphlorethol-B dodeca-acetate and 4([D])-chlorobisfucotetraphlorethol-A heptadeca-acetate.     

Trihydroxylated linear diterpenes from the brown alga Bifurcaria bifurcata

Two novel polar diterpenes were isolated from the brown alga Bifurcaria bifurcata collected off the Atlantic coast of Morocco, and their structures established by spectral methods. Both compounds are trihydroxylated acyclic diterpenes derived from 12-hydroxygeranylgeraniol. They were tested in vitro for their cytotoxicity and proved to be active against the NSCLC-N6 cell line. Their absolute configuration at the C-12 position has been determined with a modified Mosher's method [J. Am. Chem. Soc. 113 (1991) 4092] and that of the 12-hydroxygeranylgeraniol (bifurcadiol) has been revised.     

Prenylated flavanones and flavanonols as chemical markers in Glycosmis species (Rutaceae)

Fifteen prenylated or geranylated flavanones and flavanonols were isolated from the leaf extracts of different Glycosmis species collected in Thailand and Malaysia. All structures were elucidated by spectroscopic methods, especially 1D and 2D NMR. Six compounds were described for the first time and two were only known so far as synthetic products. The chemotaxonomic significance of flavanoid accumulation within the genus Glycosmis is highlighted.     

New steroidal alkaloids from the bulbs of Fritillaria puqiensis

Six new steroidal alkaloids, namely puqienines C-E (1-3), puqiedine (4), 3alpha-puqiedin-7-ol (5), and puqietinedione (6), along with two known steroidal alkaloids puqiedinone (7) and peimisine (8), were isolated from the bulbs of Fritillaria puqiensis G.D. Yu et G.Y. Chen (Liliaceae). Their structures were elucidated on the basis of spectroscopic analysis, including 1D and 2D NMR experiments. Among these alkaloids, 1-3 had a veratramine-type skeleton, 4, 5, 7 a cevanine-type skeleton, 6 a secosolanidine-type skeleton, and 8 a jervine-type skeleton. The existence of multiple types of steroidal skeletons, especially of relatively large amount of veratramine-type alkaloids in one species is rare in the genus Fritillaria, and the results might be of chemotaxonomic significance for this species.