Ligand-Specific Allosteric Coupling Controls G-Protein-Coupled Receptor Signaling

Allosteric coupling describes a reciprocal process whereby G-protein-coupled receptors (GPCRs) relay ligand-induced conformational changes from the extracellular binding pocket to the intracellular signaling surface. Therefore, GPCR activation is sensitive to both the type of extracellular ligand and intracellular signaling protein. We hypothesized that ligand-specific allosteric coupling may result in preferential (i.e., biased) engagement of downstream effectors. However, the structural basis underlying ligand-dependent control of this essential allosteric mechanism is poorly understood. Here, we show that two sets of extended muscarinic acetylcholine receptor M₁ agonists, which only differ in linker length, progressively constrain receptor signaling. We demonstrate that stepwise shortening of their chemical linker gradually hampers binding pocket closure, resulting in divergent coupling to distinct G-protein families. Our data provide an experimental strategy for the design of ligands with selective G-protein recognition and reveal a potentially general mechanism of ligand-specific allosteric coupling.

Cyclopropane-Containing Fatty Acids from the Marine Bacterium Labrenzia sp. 011 with Antimicrobial and GPR84 Activity

Bacteria of the family Rhodobacteraceae are widespread in marine environments and known to colonize surfaces, such as those of e.g., oysters and shells. The marine bacterium Labrenzia sp. 011 is here investigated and it was found to produce two cyclopropane-containing medium-chain fatty acids (1, 2), which inhibit the growth of a range of bacteria and fungi, most effectively that of a causative agent of Roseovarius oyster disease (ROD), Pseudoroseovarius crassostreae DSM 16950. Additionally, compound 2 acts as a potent partial, β-arrestin-biased agonist at the medium-chain fatty acid-activated orphan G-protein coupled receptor GPR84, which is highly expressed on immune cells. The genome of Labrenzia sp. 011 was sequenced and bioinformatically compared with those of other Labrenzia spp. This analysis revealed several cyclopropane fatty acid synthases (CFAS) conserved in all Labrenzia strains analyzed and a putative gene cluster encoding for two distinct CFASs is proposed as the biosynthetic origin of 1 and 2.

Biosynthetic Studies on Acetosellin and Structure Elucidation of a New Acetosellin Derivative

Natural products from fungi, especially Ascomycota, play a major role in therapy and drug discovery. Fungal strains originating from marine habitats offer a new avenue for finding unusual molecular skeletons. Here, the marine-derived fungus Epicoccum nigrum (strain 749) was found to produce the azaphilonoid compounds acetosellin and 5',6'-dihydroxyacetosellin. The latter is a new natural product. The biosynthesis of these polyketide-type compounds is intriguing, since two polyketide chains are assembled to the final product. Here we performed ¹³C labeling studies on solid cultures to prove this hypothesis for acetosellin biosynthesis.

Combining metabolomic analysis and microarray gene expression analysis in the characterization of the medicinal plant Chelidonium majus L

BACKGROUND AND OBJECTIVE

Even though herbal medicines have played an important role in disease management and health for many centuries, their present frequent use is challenged by the necessity to determine their complex composition and their multitarget mode of action. In the present study, modern methods were investigated towards their potential in the characterization of herbal substances. As a model the herbal substance Chelidonii herba was used, for which several reports on liver toxicities exist. Extracts of Chelidonii herba with different solvents were characterized phytochemically and functionally by experiments with HepG2 liver cells.

METHODS

Chelidonii herba was extracted with four solvents of different polarity (dichloromethane, water, ethanol, and ethanol 50% (V/V); four replicates each). The different extracts were characterized metabolomically by (1)H-NMR fingerprinting analysis and principal component analysis (PCA). The content of alkaloids was additionally determined by RP-HPLC. Functional characterization was achieved by the determination of cell proliferation and by transcriptomics techniques (Whole Genome Gene Expression Microarrays v2, Agilent Technologies) in HepG2 cells after exposure to the different extracts (four experimental replicates each).

RESULTS

Based on data from (1)H-NMR fingerprints and RP-HPLC analyses the different extracts showed a divergent composition of constituents depending on the solvent used. HepG2 liver cells responded differentially to the four extracts. Microarray analysis revealed a significant regulation of genes and signal cascades related to biotransformation. Also liver-toxic signal cascades were activated. Neither the activated genes nor the proliferation response could be clearly related to the differing alkaloid content of the extracts.

CONCLUSION

Different manufacturing processes lead to different herbal preparations. A systems biology approach combining a metabolomic plant analysis with a functional characterization by gene expression profiling in HepG2 cells is an appropriate strategy to characterize variations in plant extracts. Safety assessments of herbal substances may benefit from such complementary analyses.

Evaluation of selected Sudanese medicinal plants for their in vitro activity against hemoflagellates, selected bacteria, HIV-1-RT and tyrosine kinase inhibitory, and for cytotoxicity

Ethnobotanical investigations led to the selection of 19 plant species, used traditionally in Sudan against malaria and other similar tropical diseases, for further studies. Pamianthe peruviana (Amaryllidaceae) exhibited significant activity against a chloroquine-resistant Plasmodium falciparum strain (K1) and a chloroquine-sensitive strain (NF54) with IC(50) values of 0.6 and 1.1 microg/ml, respectively. Additionally, P. peruviana showed considerable activities against Trypanosoma brucei rhodesiense (IC(50) 1.5 microg/ml) and T. cruzi (IC(50) 11.8 microg/ml). The antiplasmodial activity of the different extracts of Salvadora persica (Salvadoraceae) against P. falciparum NF54 strain were found to be 0.6 microg/ml (stems) and 0.7 microg/ml (leaves). Extracts of different parts of Combretum hartmannianum (Combretaceae) possessed significant activity against the chloroquine-sensitive P. falciparum strain (NF54) with IC(50) values of 0.2 microg/ml (bark), 0.4 microg/ml (stem) and 4.3 microg/ml (leaves). Most interestingly, the extracts of the leaves of C. hartmannianum totally inhibited the enzyme HIV-1 reverse transcriptase (HIV-1 RT) at a concentration of 66 microg/ml. A comparably strong activity against p56(lck) tyrosine kinase was also seen for this extract.

Screening of African medicinal plants for antimicrobial and enzyme inhibitory activity

Seven plant species, belonging to different families, were collected in the eastern part of the Republic of Congo (Kivu) based on ethnopharmacological information. Their dichloromethane and methanolic extracts were tested for biological activity. Five of the seven collected plants exhibited antiplasmodial activity with IC(50) values ranging from 1.1 to 9.8 microg/ml. The methanolic extract of Cissampelos mucronata was the most active one showing activity against chloroquine sensitive (D6) and chloroquine resistant (W2) Plasmodium falciparum strains with IC(50) values of 1.5 and 1.1 microg/ml, respectively. Additionally, this extract significantly inhibited the enzyme tyrosine kinase p56(lck) (TK). The dichloromethane extract of Amorphophallus bequaertii inhibited the growth of Mycobacterium tuberculosis with a MIC of 100 microg/ml and the methanolic extract of Rubus rigidus inhibited the activity of both enzymes HIV1-reverse transcriptase (HIV1-RT) and TK p56(lck).

New 4-methoxybenzoyl derivatives from the ascidian Polycarpa aurata

From the hydrophilic extract of the ascidian Polycarpa aurata three new compounds, N-(4-methoxybenzoyl)-N'-methylguanidine (1), butyl 2-(4-methoxyphenyl)-2-oxoacetate (2), and 2-(4-methoxyphenyl)-N-methyl-2-oxoacetamide (3), together with the known compounds methyl 2-(4-methoxyphenyl)-2-oxoacetate (4) and 4-methoxybenzoic acid were isolated. The structures of all isolates were determined from their spectroscopic data (NMR, MS, IR, UV).

New carbonimidic dichlorides from the Australian sponge Ulosa spongia and their possible taxonomic significance

Five sesquiterpene carbonimide dichlorides (1-5) have been isolated from the dichloromethane extract of the Australian sponge Ulosa spongia. The structures of the two new compounds, ulosins A (1) and B (2), were elucidated by employing spectroscopic techniques (NMR, MS, UV, and IR). The chemotaxonomic significance of our data is discussed.

Inhibition of heme detoxification processes underlies the antimalarial activity of terpene isonitrile compounds from marine sponges

A series of terpene isonitriles, isolated from marine sponges, have previously been shown to exhibit antimalarial activities. Molecular modeling studies employing 3D-QSAR with receptor modeling methodologies performed with these isonitriles showed that the modeled molecules could be used to generate a pharmacophore hypothesis consistent with the experimentally derived biological activities. It was also shown that one of the modeled compounds, diisocyanoadociane (4), as well as axisonitrile-3 (2), both of which have potent antimalarial activity, interacts with heme (FP) by forming a coordination complex with the FP iron. Furthermore, these compounds were shown to inhibit sequestration of FP into beta-hematin and to prevent both the peroxidative and glutathione-mediated destruction of FP under conditions designed to mimic the environment within the malaria parasite. By contrast, two of the modeled diterpene isonitriles, 7-isocyanoamphilecta-11(20),15-diene (12) and 7-isocyano-15-isothiocyanatoamphilecta-11(20)-ene (13), that displayed little antimalarial activity also showed little inhibitory activity in these FP detoxification assays. These studies suggest that the active isonitrile compounds, like the quinoline antimalarials, exert their antiplasmodial activity by preventing FP detoxification. Molecular dynamics simulations performed with diisocyanoadociane (4) and axisonitrile-3 (2) allowed their different binding to FP to be distinguished.

3-Acetoxyspathulenol, a new aromadendrane-type natural product from the soft Coral Parerythropodium fulvum

From the lipophilic extract of the soft coral Parerythropodium fulvum a new sesquiterpene with an aromadendrane-type carbon skeleton, 3-acetoxyspathulenol (1), was isolated, and the known compounds spathulenol (2) and tridensenone (3) were identified. The structure of the new compound was determined by interpretation of its spectroscopic data, including 1D and 2D (1)H and (13)C NMR (COSY, HMQC, HMBC) and MS.

Ascosalipyrrolidinone A, an antimicrobial alkaloid, from the obligate marine fungus Ascochyta salicorniae

From the green alga Ulva sp., the endophytic and obligate marine fungus Ascochyta salicorniae was isolated. A. salicorniae was mass cultivated and found to produce the unprecedented and structurally unusual tetramic acid containing metabolites ascosalipyrrolidinones A (1) and B (2). Additionally, the new natural product ascosalipyrone (3) and the known metabolites 4 and 5 were obtained. Ascosalipyrrolidinone A (1) has antiplasmodial activity toward Plasmodium falciparum strains K1 and NF 54, as well as showing antimicrobial activity and inhibiting tyrosine kinase p56lck.

Pelorol from the tropical marine sponge Dactylospongia elegans

From the dichloromethane solubles of the tropical marine sponge Dactylospongia elegans, a new aromatic substituted sesquiterpene, pelorol (1), and the known sesquiterpene, ilimaquinone (2), were isolated. The structures of 1 and 2 were deduced from their spectroscopic data. The biological activities of compounds 1 and 2 were assessed in a variety of bioassays, and both compounds were found to have weak antitrypanosomal and antiplasmodial effects.

New natural product isolation and comparison of the secondary metabolite content of three distinct samples of the sea hare Aplysia dactylomela from tenerife

Three distinct samples of the sea hare Aplysia dactylomela from two different locations around Tenerife (Spain) were investigated for their secondary metabolite content. The investigation resulted in the isolation of five new natural products (1, 2, 5-7), a number of compounds known from red algae of the genera Laurencia (4, 8-14) and Plocamium (17-19), and three known sea-hare metabolites (3, 15, 16). This is the first report of monoterpenes (17-19) from A. dactylomela. All structures were determined mainly by spectroscopic methods (1D and 2D NMR, MS, IR). Compounds 11, 14, 15, and 17 demonstrated significant cytotoxicity toward three cancer cell lines (HM02, HEP G2, and MCF 7; IC(50) for 11, 7.0 to <1.0 microg/mL; 14, <1.0 microg/mL; 15, 17 to <1.0 microg/mL; 17, 1.0 to 1.5 microg/mL). Compounds 3, 8, 9, 11, 15, 18, and 19 exhibited activity in a brine shrimp bioassay in the range of 100% lethality within 24 h to 40% after 48 h. Metabolites 11, 14, 15, and 19 showed moderate antimicrobial activities (2-25 mm total/growth inhibition of several organisms), with 19 also being strongly algicidal (MIC 7-11 microg/filter disk).

Assessment of antimycobacterial activity of a series of mainly marine derived natural products

A series of mainly marine derived natural products were tested for their activities against Mycobacterium tuberculosis and M. avium. Of the thirty-nine compounds tested fifteen demonstrated minimum inhibition concentrations (MICs) of 32 micrograms/ml or less, and eleven had MICs of 16 micrograms/ml or less. The most active compound found in this study was the sponge derived metabolite axisonitrile-3 (MIC 2 micrograms/ml).

Plocamium hamatum and its monoterpenes: chemical and biological investigations of the tropical marine red alga

The polyhalogenated monoterpene content of six samples of the tropical marine red alga Plocamium hamatum, collected from the southern, central and northern regions of The Great Barrier Reef, Australia, was assessed. In all but two of the samples, the polyhalogenated monoterpene content was shown to differ markedly. In total, eleven previously reported compounds were isolated and characterised (1-11). Compound 2 was obtained for the first time as a pure natural product. For compound 4 a single crystal X-ray crystallographic analysis was undertaken which established its absolute configuration as (1S,2S,4R,5R,1'E)-2-bromo-1- bromomethyl-1,4-dichloro-5-(2'-chloroethenyl)-5-methylcyclohexa ne. Complete and unambiguous 1H and 13C NMR data are reported for 2 and 4. For 6-8, some prior 13C NMR assignments are revised. The biological activities of compounds 2-8 and 11 were assessed and indicated 4 to have potent antialgal activity towards Chlorella fusca in an agar diffusion bioassay, as well as being moderately antitubercular and cytotoxic. Compound 6 demonstrated moderate cytotoxicity.

HIV reverse transcriptase inhibitors of natural origin

Inhibitors of HIV reverse transcriptase (RT) are important drugs for the treatment of acquired immuno-deficiency syndrome (AIDS). One approach to identify novel inhibitors of HIV-1-RT is the screening of natural compounds. Many natural products have been shown to be active as RT inhibitors. These compounds belong to a wide range of different structural classes, e.g., coumarins, flavonoids, tannins, alkaloids, lignans, terpenes, naphtho- and anthraquinones, and polysaccharides. The life forms from which the bioactive compounds were isolated are as equally diverse and comprise terrestrial and marine plants, micro-organisms, and marine animals. From the most extensive screening effort, carried out by the NCl, calanolide A, isolated from the terrestrial plant Calophyllum lanigerum (Guttiferae), has been discovered as the most interesting natural RT inhibitor. The promise of this natural product probably relates to a novel mechanism of action. The current review describes natural products from various sources that are able to inhibit HIV-RT.

A new tyrosine kinase inhibitor from the marine brown alga Stypopodium zonale

From the lipophilic extract of the marine brown alga Stypopodium zonale (Dictyotaceae) the new terpenoid compound stypoquinonic acid (1) together with the known compounds taondiol (2) and atomaric acid (3) were isolated. The structures of all isolates were determined from their spectroscopic data, including 1- and 2-dimensional NMR methods. The new compound, 1, and atomaric acid (3), showed inhibition of tyrosine kinase (p56lck).

Hierridin B and 2,4-dimethoxy-6-heptadecyl-phenol, secondary metabolites from the cyanobacterium Phormidium ectocarpi with antiplasmodial activity

Bioassay guided fractionation of the lipophilic extract of the marine cyanobacterium Phormidium ectocarpi yielded a new natural product hierridin B and the previously described compound 2,4-dimethoxy-6-heptadecyl-phenol. Both structures were secured by extensive spectroscopic analysis (1D and 2D NMR, MS, GC-MS, IR). The isolate (mixture) showed antiplasmodial activity towards Plasmodium falciparum.

Hypoglycaemic activity of an HMG-containing flavonoid glucoside, chamaemeloside, from Chamaemelum nobile

The 3-hydroxy-3-methylglutaric acid (HMG) containing flavonoid glucoside chamaemeloside, has been determined to have in vivo hypoglycaemic activity comparable to that of free HMG. An improved isolation scheme for obtaining chamaemeloside from Chamaemelum nobile is presented.

Antiplasmodial and cytotoxic metabolites from the Maltese sponge Agelas oroides

From a Maltese sample of the marine sponge Agelas oroides, five compounds: oroidin (1), 2-cyano-4,5-dibromopyrrole (2), 4,5-dibromopyrrole-2-carboxylic acid (3), 4,5-dibromopyrrole-2-carboxylic acid methyl ester (4), and 4 alpha-methyl-5 alpha-cholest-8-en-3 beta-ol (5) have been isolated. For compounds 1-5, completely assigned 1H- and 13C-NMR data are reported for the first time. For 2 a single crystal X-ray crystallographic analysis proved its structure unambiguously. The X-ray analysis of 2 indicated it to crystallise in an unexpected polar space group. Biological activity assessment of all isolates indicate 5 to have moderate antiplasmodial activity, as well as being cytotoxic, and 2 to be moderately cytotoxic towards several cancer cell lines.

Three new diterpenes from the marine soft coral Lobophytum crassum

Three new terpenoid metabolites (1-3) were isolated from the CH2Cl2 extract of the soft coral Lobophytum crassum together with the eudesmane derivative 4 and the known cembrane (2S,7S,8S)-sarcophytoxide (5). Compound 1 is a new cembrane-based diterpene with an C7-C8-epoxide and a methyl ester functionality at C-16. (3E,5Z)- (2) and (3Z,5E)-2-methyl-6-(4a'-methyl-8'-methylene-trans-perhydr onaphthalen-2'-yl)hepta-3,5-dien-2-ol (3) represent two new carbon-carbon double bond isomers of 4, which has the 3E,5E-configuration. The structures of 1-5 were established by interpretation of their spectroscopic data, mainly 1D and 2D NMR and MS. Biological activity evaluation of compounds 1 and 5 and the crude extracts was carried out using agar diffusion assays toward microbial targets and ELISA assays for investigating the inhibition of HIV-1 reverse transcriptase and p56lck tyrosine kinase.

An unprecedented compound from the dichloromethane solubles of the tropical marine sponge Agelas oroides

Further investigation into the natural product chemistry of the tropical marine sponge Agelas oroides has yielded the new compound 2,4,6,6-tetramethyl-3(6 H)-pyridone (1), and 2,2,6,6-tetramethyl-4-piperidone (2). Both compounds are volatile. The structures of 1 and 2 were determined from the interpretation of their 1D and 2D NMR, UV, IR, and mass spectral data.

Mueggelone, a novel inhibitor of fish development from the fresh water cyanobacterium Aphanizomenon flos-aquae

A novel C18 lipid, containing a 10-membered lactone, mueggelone (1), was isolated from a field-collected sample of Aphanizomenon flos-aquae, together with the known compound lupenyl acetate (3). Both structures were secured using extensive spectroscopic analysis (1D and 2D NMR, MS, IR). Biological activity assessment of both compounds indicated them to have significant inhibitory effects on fish embryo larval development.

Laurencia rigida: chemical investigations of its antifouling dichloromethane extract

From the CH2Cl2 extract of the temperate marine red alga, Laurencia rigida, which has antifouling properties, eight sesquiterpenes (1-8) were isolated. Of these, four (3-acetoxy-E-gamma-bisabolene (1), (-)-10 alpha-bromo-9 beta-hydroxy-alpha-chamigrene (2), rigidol (3), and (+)-(10S)-10-bromo-beta-chamigrene (4)), were shown to be new natural products. For the known compound deschloroelatol (5), reassignment of the 1H- and 13C-NMR data was found to be necessary on the basis of extensive NMR measurements. For elatol (6), complete 1H- and 13C-NMR data are also reported. The antimicrobial and antialgal activities of all isolates were assessed.

Sesquiterpene content of the antibacterial dichloromethane extract of the marine red alga Laurencia obtusa

For a sample of Laurencia obtusa, collected from the Caribbean island of Dominica, allolaurinterol was isolated for the first time and found to be responsible for the biological activity of the dichloromethane extract. For allolaurinterol, complete and assigned 1H- and 13C-NMR data are given, together with an assessment of its antibacterial, antifungal, and antialgal activities.

Antimalarial activity: the search for marine-derived natural products with selective antimalarial activity

In this short review, an approach to the isolation of potential antimalarial agents and lead compounds is outlined. A discussion of organism collection, followed by a description of biological testing and isolation methodologies, is also given. For two organisms, details of their secondary metabolite chemistry are reported. From one of these, Laurencia papillosa, the two aromatic compounds p-hydroxybenzaldehyde (1) and p-methoxybenzyl alcohol (2) were isolated. From the other, the tropical marine sponge Cymbastela hooperi, 15 diterpenes (3-17), which contain isonitrile, isothiocyanate, and isocyanate functionalities, are reported. Together with the diterpenes, three sesquiterpene hydrocarbons, 18-20, and the thiol, 21, were obtained. All structures were established by spectroscopic methods, particularly 1H-1H and 1H-13C shift-correlated 2D NMR spectroscopy and accurate mass measurement (HREIMS). The majority of isolates demonstrate significant and selective in vitro antimalarial activity. For compounds 4-17 a brief description of their possible structure-activity relationships is provided.

Marine natural products research: current directions and future potential

Natural products research is increasingly turning to marine animals, plants, and microbes as source organisms. Several marine natural products are currently in preclinical and clinical evaluation, others show promising biological activities in in vitro and in vivo assays. Investigations of biological and chemical ecological phenomena in the marine world will contribute to a better understanding of marine habitats, and also provide a more founded basis regarding the search for pharmaceutically useful marine natural products.

Studies on the glycolipid content of the cyanobacterium Fischerella ambigua

A series of monogalactosyl diacylglycerols was isolated from lipophilic extracts of Fischerella ambigua. These glycolipids were identified on the basis of chemical and spectroscopic analyses.

Biological activities of cyanobacteria: evaluation of extracts and pure compounds

A total of 80 lipophilic and hydrophilic extracts obtained from 20 samples of cultured freshwater and terrestrial cyanobacteria were investigated for their biological activities. Of all the extracts, 26% exhibited a significant lethal effect against brine shrimp. Out of 54 extracts tested for antimicrobial activity, 78% showed antibacterial and 45% antifungal activities. Of 30 extracts tested for cytotoxicity against KB cells, none was found to be active. Bioassay-guided fractionation of the lipophilic extracts of Fischerella ambigua led to the isolation of three compounds; ambigols A (1) and B (2), and tjipanazole D (3). Compounds 1 and 2 exhibited antibacterial, antifungal, cytotoxic, molluscicidal, and anti-inflammatory, and antiviral activities. Tjipanazole D (3) showed moderate antibacterial properties.

Biological activities of selected marine natural products

Sixty-nine natural products derived from Phaeophyta (brown algae), Rhodophyta (red algae), Porifera (sponges), Cnidaria (soft corals), and Mollusca (nudibranchs) were investigated for their cytotoxic, antimalarial, and antimicrobial effects. Fifty-six were found to mediate a positive response in one or more of these test systems.

Four New Hydroazulenoid Diterpenes from the Tropical Marine Brown Alga Dictyota volubilis

The marine brown alga, DICTYOTA VOLUBILIS, was found to contain four unusually substituted hydroazulenoid diterpenes ( 1 - 4) as well as the known compounds dictyol G acetate ( 5) and dilophol. The structures of all isolates were secured by detailed analysis of their spectroscopic data; IR, MS, and NMR.

Antimalarial activity of sesquiterpenes from the marine sponge Acanthella klethra

Five sesquiterpenoids containing isonitrile or isothiocyanate groups were isolated from the sponge Acanthella klethra. Compounds 1 and 2 were identified as axisonitrile 3 and the corresponding isothiocyanate derivative, respectively. Compounds 3-5 were found to be eudesmane sesquiterpenes. None of these compounds was cytotoxic toward cultured KB-3 cells, but varying degrees of activity were observed with cultured Plasmodium falciparum. Compound 1 demonstrated greatest promise as an antimalarial agent.