Structural and stereochemical investigations into bromotyrosine-derived metabolites from southern Australian marine sponges, Pseudoceratina spp

Potential of Marine Sponge Metabolites against Prions: Bromotyrosine Derivatives, a Family of Interest

The screening of 166 extracts from tropical marine organisms (invertebrates, macroalgae) and 3 cyclolipopeptides from microorganisms against yeast prions highlighted the potential of Verongiida sponges to prevent the propagation of prions. We isolated the known compounds purealidin Q (1), aplysamine-2 (2), pseudoceratinine A (3), aerophobin-2 (4), aplysamine-1 (5), and pseudoceratinine B (6) for the first time from the Wallisian sponge Suberea laboutei. We then tested compounds 1-6 and sixteen other bromotyrosine and bromophenol derivatives previously isolated from Verongiida sponges against yeast prions, demonstrating the potential of 1-3, 5, 6, aplyzanzine C (7), purealidin A (10), psammaplysenes D (11) and F (12), anomoian F (14), and N,N-dimethyldibromotyramine (15). Following biological tests on mammalian cells, we report here the identification of the hitherto unknown ability of the six bromotyrosine derivatives 1, 2, 5, 7, 11, and 14 of marine origin to reduce the spread of the PrPSc prion and the ability of compounds 1 and 2 to reduce endoplasmic reticulum stress. These two biological activities of these bromotyrosine derivatives are, to our knowledge, described here for the first time, offering a new therapeutic perspective for patients suffering from prion diseases that are presently untreatable and consequently fatal.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Demystifying racemic natural products in the homochiral world

Natural products possess structural complexity, diversity and chirality with attractive functions and biological activities that have significantly impacted drug discovery initiatives. Chiral natural products are abundant in nature but rarely occur as racemates. The occurrence of natural products as racemates is very intriguing from a biosynthetic point of view; as enzymes are chiral molecules, enzymatic reactions generating natural products should be stereospecific and lead to single-enantiomer products. Despite several reports in the literature describing racemic mixtures of stereoisomers isolated from natural sources, there has not been a comprehensive review of these intriguing racemic natural products. The discovery of many more natural racemates and their potential enzymatic sources in recent years allows us to describe the distribution and chemical diversity of this 'class of natural products' to enrich discussions on biosynthesis. In this Review, we describe the chemical classes, occurrence and distribution of pairs of enantiomers in nature and provide insights about recent advances in analytical methods used for their characterization. Special emphasis is on the biosynthesis, including plausible enzymatic and non-enzymatic formation of natural racemates, and their pharmacological significance.

Targeted Isolation of Antibiotic Brominated Alkaloids from the Marine Sponge Pseudoceratina durissima Using Virtual Screening and Molecular Networking

Many targeted natural product isolation approaches rely on the use of pre-existing bioactivity information to inform the strategy used for the isolation of new bioactive compounds. Bioactivity information can be available either in the form of prior assay data or via Structure Activity Relationship (SAR) information which can indicate a potential chemotype that exhibits a desired bioactivity. The work described herein utilizes a unique method of targeted isolation using structure-based virtual screening to identify potential antibacterial compounds active against MRSA within the marine sponge order Verongiida. This is coupled with molecular networking-guided, targeted isolation to provide a novel drug discovery procedure. A total of 12 previously reported bromotyrosine-derived alkaloids were isolated from the marine sponge species Pseudoceratina durissima, and the compound, (+)-aeroplysinin-1 (1) displayed activity against the MRSA pathogen (MIC: <32 µg/mL). The compounds (1−3, 6 and 9) were assessed for their central nervous system (CNS) interaction and behavioral toxicity to zebrafish (Danio rerio) larvae, whereby several of the compounds were shown to induce significant hyperactivity. Anthelmintic activity against the parasitic nematode Haemonchus contorutus was also evaluated (2−4, 6−8).

Application of Networking Approaches to Assess the Chemical Diversity, Biogeography, and Pharmaceutical Potential of Verongiida Natural Products

This study provides a review of all isolated natural products (NPs) reported for sponges within the order Verongiida (1960 to May 2020) and includes a comprehensive compilation of their geographic and physico-chemical parameters. Physico-chemical parameters were used in this study to infer pharmacokinetic properties as well as the potential pharmaceutical potential of NPs from this order of marine sponge. In addition, a network analysis for the NPs produced by the Verongiida sponges was applied to systematically explore the chemical space relationships between taxonomy, secondary metabolite and drug score variables, allowing for the identification of differences and correlations within a dataset. The use of scaffold networks as well as bipartite relationship networks provided a platform to explore chemical diversity as well as the use of chemical similarity networks to link pharmacokinetic properties with structural similarity. This study paves the way for future applications of network analysis procedures in the field of natural products for any order or family.

Bromo-spiroisoxazoline Alkaloids, Including an Isoserine Peptide, from the Caribbean Marine Sponge Aplysina lacunosa

Three new bromotyrosine spiroisoxazoline alkaloids, lacunosins A and B (1 and 2) and desaminopurealin (3), were isolated from a MeOH extract of the marine sponge Aplysina lacunosa that showed modest α-chymotrypsin inhibitory activity. The structures of 1-3 share the spirocyclohexadienyl-isoxazoline ring system found in purealidin-R and several other Verongid sponge secondary metabolites. Compounds 1 and 2 are coupled to a glycine and an isoserine methyl ester, respectively. Alkaloid 3 is linked, contiguously, to an O-1-aminopropyl 3,5-dibromotyrosyl ether and, finally, to histamine through an amide bond. The planar structures of all three compounds were obtained from analysis of MS and 1D and 2D NMR data. The absolute configuration of the SIO unit of 1-3 was assigned by electronic circular dichroism (ECD). The isoserine amino acid residue in 2 was found to be a 1:1 mixture of epimers using a new Marfey's type reagent, derived from Trp-NH2. Allylic O-naphthoylation of the SIO subunit enhances the ECD spectrum of SIOs and improves discrimination of enantiomorphs. A unifying hypothesis is proposed that links the biosynthesis of several of the new compounds with previously reported analogues.

Sponge chemical defenses are a possible mechanism for increasing sponge abundance on reefs in Zanzibar

Coral reefs are experiencing increasing anthropogenic impacts that result in substantial declines of reef-building corals and a change of community structure towards other benthic invertebrates or macroalgae. Reefs around Zanzibar are exposed to untreated sewage and runoff from the main city Stonetown. At many of these sites, sponge cover has increased over the last years. Sponges are one of the top spatial competitors on reefs worldwide. Their success is, in part, dependent on their strong chemical defenses against predators, microbial attacks and other sessile benthic competitors. This is the first study that investigates the bioactive properties of sponge species in the Western Indian Ocean region. Crude extracts of the ten most dominant sponge species were assessed for their chemical defenses against 35 bacterial strains (nine known as marine pathogens) using disc diffusion assays and general cytotoxic activities were assessed with brine shrimp lethality assays. The three chemically most active sponge species were additionally tested for their allelopathic properties against the scleractinian coral competitor Porites sp.. The antimicrobial assays revealed that all tested sponge extracts had strong antimicrobial properties and that the majority (80%) of the tested sponges were equally defended against pathogenic and environmental bacterial strains. Additionally, seven out of ten sponge species exhibited cytotoxic activities in the brine shrimp assay. Moreover, we could also show that the three most bioactive sponge species were able to decrease the photosynthetic performance of the coral symbionts and thus were likely to impair the coral physiology.

Isolation and structure elucidation of natural products of three soft corals and a sponge from the coast of Madagascar

We investigated the three soft corals Sarcophyton stellatum, Capnella fungiformis and Lobophytum crassum and the sponge Pseudoceratina arabica, which have been collected at the coast of Madagascar. In addition to previously known marine natural products, S. stellatum provided the new (+)-enantiomer of the cembranoid (1E,3E,11E)-7,8-epoxycembra-1,3,11,15-tetraene (2). Capnella fungiformis afforded three new natural products, ethyl 5-[(1E,5Z)-2,6-dimethylocta-1,5,7-trienyl]furan-3-carboxylate (6), ethyl 5-[(1E,5E)-2,6-dimethylocta-1,5,7-trienyl]furan-3-carboxylate (7) and the diepoxyguaiane sesquiterpene oxyfungiformin (9a). The extracts of all three soft corals exhibited moderate activities against the malarial parasite Plasmodium falciparum. Extracts of the sponge Pseudoceratina arabica proved to be very active against a series of Gram-positive and Gram-negative bacteria.

Cytotoxic Anomoian B and Aplyzanzine B, New Bromotyrosine Alkaloids from Indonesian Sponges

Two new bromotyrosine derivatives, anomoian B (1) and aplyzanzine B (2), were isolated, respectively, from the organic extracts of a Verongida sponge belonging to the Hexadella genus and from a two-sponge association (Jaspis sp. and Bubaris sp.), both collected off the coast of Indonesia. The planar structure of 1 and 2 was determined by 1D and 2D NMR experiments and by high-resolution mass spectrometry, while their absolute stereochemistry was assigned by comparison with optical rotation values of known bromotyrosines and by chemical degradation. Both compounds showed moderate antiproliferative activity against a panel of different cancer cell lines. Their cytotoxic activity is facilitated through the induction of apoptosis, which is mediated neither by the generation of reactive oxygen species nor by the inhibition of histone deacetylases in these cell lines.

Muscarine, imidazole, oxazole and thiazole alkaloids

Covering: July 2012 to June 2015. Previous review: Nat. Prod. Rep., 2013, 30, 869-915The structurally diverse imidazole-, oxazole-, and thiazole-containing secondary metabolites are widely distributed in terrestrial and marine environments, and exhibit extensive pharmacological activities. In this review the latest progress involving the isolation, biological activities, and chemical and biogenetic synthesis studies on these natural products has been summarized.

Enantiodivergence in the Biosynthesis of Bromotyrosine Alkaloids from Sponges?

The isolation of bromotyrosine alkaloids, some of which are enantiomers of previously isolated compounds, has highlighted a possible enantiodivergence in their biosynthesis. Two new (1, 2) and six known bromotyrosine alkaloids (4-9), and the enantiomer (10) of a known compound, have been isolated from a Western Australian marine sponge, Pseudoceratina cf. verrucosa. The compounds inhibited the growth of multidrug-resistant and methicillin-resistant Staphylococcus aureus with comparable activity to vancomycin. In addition, one possible artifact of extraction (3) containing an ethoxy group was isolated. From analysis of the known bromotyrosine alkaloids, a biogenesis is proposed that explains the formation of antipodal natural products within this family of sponges.

Biological Activity of Recently Discovered Halogenated Marine Natural Products

This review presents the biological activity-antibacterial, antifungal, anti-parasitic, antiviral, antitumor, antiinflammatory, antioxidant, and enzymatic activity-of halogenated marine natural products discovered in the past five years. Newly discovered examples that do not report biological activity are not included.

New antimicrobial bromotyrosine analogues from the sponge Pseudoceratina purpurea and its predator Tylodina corticalis

Bioassay-guided fractionation of extracts from temperate Australian collections of the marine sponge Pseudoceratina purpurea resulted in the isolation and characterisation of two new and six known bromotyrosine-derived alkaloids with antibiotic activity. Surprisingly, a single specimen of the mollusc Tylodina corticalis, which was collected while feeding on P. purpurea, contained only a few of the compounds found in the sponge suggesting selective accumulation and chemical modification of sponge metabolites.

Marine natural products

This review covers the literature published in 2012 for marine natural products, with 1035 citations (673 for the period January to December 2012) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1241 for 2012), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.