Chemical Investigations of Pacific Marine Organisms

This thesis describes a comparative study of three screening methods for the discovery of new marine natural products (MNP) from South Pacific organisms. Over the course of the study, 13 tunicates, one bryozoan and one red alga collected from the waters of the Kingdom of Tonga and New  Zealand were investigated. Bioassay, ¹H nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) were used to prioritise six organisms for investigation, which resulted in the isolation and characterisation of 16 new and 11 previously reported metabolites.     An NMR–based spectroscopic screening protocol led to the isolation of  the new cyclic polyhalogenated monoterpene costatone C (46), isolated from a NZ red alga identified as Plocamium angustum, which showed moderate antibacterial activity. The absolute configuration of a previously reported and co–isolated bis–normonoterpene (47) was also deduced using Mosher’s method. The NMR screening protocol also  prioritised the Tongan bryozoan Nelliella nelliiformis, from which the nucleosides nellielloside A and B (61 and 62) were isolated and inspired the synthesis of congeners 66–69. All six compounds showed potent kinase inhibitory activity against a subset of disease–relevant kinases, with IC50 values determined to be in the nM range for GSK3A, MAPK14 and RSK2.     An MS screening protocol was also employed utilising molecular networking through the GNPS platform. Of the eight tunicates examined, three were further investigated based on promising constellations in the network, and collectively led to the identification of 13 new compounds. A new aromatic ketone (28) was isolated from the NZ tunicate  Distaplia stylifera, while a comprehensive examination of a NZ Synoicum kuranui sample resulted in two new compounds, rubrolides T and U (110 and 111). The encrusting tunicate Didemnum ternerratum was the most fruitful organism examined in this work, resulting in the isolation of ten new and three previously reported lamellarin sulfates (147–151 and 153–156). The absolute configurations of atropisomers 148–151 were  determined by comparison of experimental and calculated ECD spectra. Compound 151 showed moderate cytotoxicity against HCT–116 cells. This work illustrated the power of molecular networking as a screening tool when applied to the MNP field, particularly for the isolation new derivatives within a previously known family of compounds. It also suggested that the more traditional NMR spectroscopy–based screening protocol is still very useful as a standalone method when no comparative  standards are available. These complementary techniques should be used together to maximise new MNP discovery. </p

Targeted Isolation of Rubrolides from the New Zealand Marine Tunicate Synoicum kuranui

Global natural products social (GNPS) molecular networking is a useful tool to categorize chemical space within samples and streamline the discovery of new natural products. Here, we demonstrate its use in chemically profiling the extract of the marine tunicate Synoicum kuranui, comprised of many previously reported rubrolides, for new chemical entities.Within the rubrolide cluster, two masses that did not correspond to previously reported congeners were detected, and, following MS-guided fractionation, led to the isolation of new methylated rubrolides T (3) and (Z/E)-U (4). Both compounds showed strong growth inhibitory activity against the Gram-positive bacteria Bacillus subtilis, with minimum inhibitory concentration (MIC) values of 0.41 and 0.91 M, respectively

Highly <i>N</i>‑Methylated Peptides from the Antarctic Sponge <i>Inflatella coelosphaeroides</i> Are Active against <i>Plasmodium falciparum</i>

Malaria, caused by the parasite Plasmodium falciparum, continues to threaten much of the world’s population, and there is a pressing need for expanding treatment options. Natural products have been a vital source of such drugs, and here we report seven new highly N-methylated linear peptides, friomaramide B (2) and shagamides A–F (3–8) from the marine sponge Inflatella coelosphaeroides, collected in Antarctic waters, which demonstrate activity against three strains of blood-stage P. falciparum. The planar structures of these metabolites were solved by interpreting NMR data, as well as HRESIMS/MS fragmentation patterns, while Marfey’s analysis was used to establish the configurations of the amino acids. Reisolation of the previously reported compound friomaramide A (1) allowed us to revise its structure. The panel of isolated compounds allowed establishing structure/activity relationships and provided information for future structure optimization for this class of P. falciparum inhibitory metabolites

Hydroarylation of olefins catalysed by a dimeric ytterbium(II) alkyl

International audienceAlthough the nucleophilic alkylation of aromatics has recently been achieved with a variety of potent main group reagents, all of this reactivity is limited to a stoichiometric regime. We now report that the ytterbium(II) hydride, [(BDIYbH)-Yb-Dipp](2) (BDIDipp=CH[C(CH3)NDipp](2), Dipp = 2,6-diisopropylphenyl), reacts with ethene and propene to provide the ytterbium(II) n-alkyls, [(BDIYbR)-Yb-Dipp](2) (R=Et or Pr), both of which alkylate benzene at room temperature. Density functional theory (DFT) calculations indicate that this latter process operates through the nucleophilic (S(N)2) displacement of hydride, while the resultant regeneration of [(BDIYbH)-Yb-Dipp](2) facilitates further reaction with ethene or propene and enables the direct catalytic (anti-Markovnikov) hydroarylation of both alkenes with a benzene C-H bond. Nucleophilic alkylation of aromatics with main group reagents was achieved, but it is limited to a stoichiometric regime. Here, the authors report that the ytterbium(II) hydride reacts with ethene and propene to afford ytterbium(II) n-alkyls, both of which can facilitate the catalytic alkylation of benzene at room temperature via an S(N)2 mechanism

Neosuberitenone, a New Sesterterpenoid Carbon Skeleton; New Suberitenones; and Bioactivity against Respiratory Syncytial Virus, from the Antarctic Sponge <i>Suberites</i> sp.

Respiratory syncytial virus (RSV) is a highly contagious human pathogen that poses a significant threat to children under the age of two, and there is a current need for new small molecule treatments. The Antarctic sponge Suberites sp. is a known source of sesterterpenes, and following an NMR-guided fractionation procedure, it was found to produce several previously unreported metabolites. Neosuberitenone (1), with a new carbon scaffold herein termed the ‘neosuberitane’ backbone, six suberitenone derivatives (2–7), an ansellane-type terpenoid (8), and a highly degraded sesterterpene (9), as well as previously reported suberitenones A (10) and B (11), were characterized. The structures of all of the isolated metabolites including absolute configurations are proposed on the basis of NMR, HRESIMS, optical rotation, and XRD data. The biological activities of the metabolites were evaluated in a range of infectious disease assays. Suberitenones A, B, and F (3) were found to be active against RSV, though, along with other Suberites sp. metabolites, they were inactive in bacterial and fungal screens. None of the metabolites were cytotoxic for J774 macrophages or A549 adenocarcinoma cells. The selectivity of suberitenones A, B, and F for RSV among other infectious agents is noteworthy

Costatone C—A new halogenated monoterpene from the New Zealand red alga plocamium angustum

© 2019 by the authors Red algae of the genus Plocamium have been a rich source of halogenated monoterpenes. Herein, a new cyclic monoterpene, costatone C (7), was isolated from the extract of P. angustum collected in New Zealand, along with the previously reported (1E,5Z)-1,6-dichloro-2-methylhepta-1,5-dien-3-ol (8). Elucidation of the planar structure of 7 was achieved through conventional NMR and (−)-HR-APCI-MS techniques, and the absolute configuration by comparison of experimental and DFT-calculated ECD spectra. The absolute configuration of 8 was determined using Mosher’s method. Compound 7 showed mild antibacterial activity against Staphylococcus aureus and S. epidermidis. The state of Plocamium taxonomy and its implications upon natural product distributions, especially across samples from specimens collected in different countries, is also discussed

Metagenomic Exploration of the Marine Sponge Mycale hentscheli Uncovers Multiple Polyketide-Producing Bacterial Symbionts

Mycale hentscheli is a marine sponge that is rich in bioactive small molecules. Here, we use direct metagenomic sequencing to elucidate highly complete and contiguous genomes for the major symbiotic bacteria of this sponge. We identify complete biosynthetic pathways for the three potent cytotoxic polyketides which have previously been isolated from M. hentscheli. Remarkably, and in contrast to previous studies of marine sponges, we attribute each of these metabolites to a different producing microbe. We also find that the microbiome of M. hentscheli is stably maintained among individuals, even over long periods of time. Collectively, our data suggest a cooperative mode of defensive symbiosis in which multiple symbiotic bacterial species cooperatively contribute to the defensive chemical arsenal of the holobiont.Marine sponges have been a prolific source of unique bioactive compounds that are presumed to act as a deterrent to predation. Many of these compounds have potential therapeutic applications; however, the lack of efficient and sustainable synthetic routes frequently limits clinical development. Here, we describe a metagenomic investigation of Mycale hentscheli, a chemically gifted marine sponge that possesses multiple distinct chemotypes. We applied shotgun metagenomic sequencing, hybrid assembly of short- and long-read data, and metagenomic binning to obtain a comprehensive picture of the microbiome of five specimens, spanning three chemotypes. Our data revealed multiple producing species, each having relatively modest secondary metabolomes, that contribute collectively to the chemical arsenal of the holobiont. We assembled complete genomes for multiple new genera, including two species that produce the cytotoxic polyketides pateamine and mycalamide, as well as a third high-abundance symbiont harboring a proteusin-type biosynthetic pathway that appears to encode a new polytheonamide-like compound. We also identified an additional 188 biosynthetic gene clusters, including a pathway for biosynthesis of peloruside. These results suggest that multiple species cooperatively contribute to defensive symbiosis in M. hentscheli and reveal that the taxonomic diversity of secondary-metabolite-producing sponge symbionts is larger and richer than previously recognized

Hydroarylation of olefins catalysed by a dimeric ytterbium(II) alkyl

Although the nucleophilic alkylation of aromatics has recently been achieved with a variety of potent main group reagents, all of this reactivity is limited to a stoichiometric regime. We now report that the ytterbium(II) hydride, [BDI YbH] (BDI = CH[C(CH )NDipp] , Dipp = 2,6-diisopropylphenyl), reacts with ethene and propene to provide the ytterbium(II) n-alkyls, [BDI YbR] (R = Et or Pr), both of which alkylate benzene at room temperature. Density functional theory (DFT) calculations indicate that this latter process operates through the nucleophilic (S 2) displacement of hydride, while the resultant regeneration of [BDI YbH] facilitates further reaction with ethene or propene and enables the direct catalytic (anti-Markovnikov) hydroarylation of both alkenes with a benzene C-H bond. Dipp Dipp Dipp Dipp 2 3 2 2 N

Metagenomic exploration of the marine sponge mycale hentscheli uncovers multiple polyketide-producing bacterial symbionts

© 2020 Storey et al. Marine sponges have been a prolific source of unique bioactive compounds that are presumed to act as a deterrent to predation. Many of these compounds have potential therapeutic applications; however, the lack of efficient and sustainable synthetic routes frequently limits clinical development. Here, we describe a metag-enomic investigation of Mycale hentscheli, a chemically gifted marine sponge that pos-sesses multiple distinct chemotypes. We applied shotgun metagenomic sequencing, hybrid assembly of short-and long-read data, and metagenomic binning to obtain a comprehensive picture of the microbiome of five specimens, spanning three chemo-types. Our data revealed multiple producing species, each having relatively modest secondary metabolomes, that contribute collectively to the chemical arsenal of the holo-biont. We assembled complete genomes for multiple new genera, including two species that produce the cytotoxic polyketides pateamine and mycalamide, as well as a third high-abundance symbiont harboring a proteusin-type biosynthetic pathway that appears to encode a new polytheonamide-like compound. We also identified an additional 188 biosynthetic gene clusters, including a pathway for biosynthesis of peloruside. These re-sults suggest that multiple species cooperatively contribute to defensive symbiosis in M. hentscheli and reveal that the taxonomic diversity of secondary-metabolite-producing sponge symbionts is larger and richer than previously recognized. IMPORTANCE Mycale hentscheli is a marine sponge that is rich in bioactive small mol-ecules. Here, we use direct metagenomic sequencing to elucidate highly complete and contiguous genomes for the major symbiotic bacteria of this sponge. We identify complete biosynthetic pathways for the three potent cytotoxic polyketides which have previously been isolated from M. hentscheli. Remarkably, and in contrast to previous studies of marine sponges, we attribute each of these metabolites to a different producing mi-crobe. We also find that the microbiome of M. hentscheli is stably maintained among in-dividuals, even over long periods of time. Collectively, our data suggest a cooperative mode of defensive symbiosis in which multiple symbiotic bacterial species cooperatively contribute to the defensive chemical arsenal of the holobiont