Unprecedented Stylissazoles A-C from Stylissa carteri: Another Dimension for Marine Pyrrole-2-aminoimidazole Metabolite Diversity

Stonikacidin A, an Antimicrobial 4-Bromopyrrole Alkaloid Containing L-Idonic Acid Core from the Northwestern Pacific Marine Sponge Lissodendoryx papillosa

Stonikacidin A (1), the first representative of a new class of 4-bromopyrrole alkaloids containing an aldonic acid core, was isolated from the marine sponge Lissodendoryx papillosa. The compound is named in honor of Prof. Valentin A. Stonik, who is one of the outstanding investigators in the field of marine natural chemistry. The structure of 1 was determined using NMR, MS analysis, and chemical correlations. The L-idonic acid core was established by the comparison of GC, NMR, MS, and optical rotation data of methyl-pentaacetyl-aldonates obtained from the hydrolysis products of 1 and standard hexoses. The L-form of the idonic acid residue in 1 was confirmed by GC analysis of pentaacetate of (S)-2-butyl ester of the hydrolysis product from 1 and compared with corresponding derivatives of L- and D-idonic acids. The biosynthetic pathway for stonikacidin A (1) was proposed. The alkaloid 1 inhibited the growth of Staphylococcus aureus and Escherichia coli test strains, as well as affected the formation of S. aureus and E. coli biofilms. Compound 1 inhibited the activity of sortase A. Molecular docking data showed that stonikacidin A (1) can bind with sortase A due to the interactions between its bromine atoms and some amino acid residues of the enzyme.

Dimeric pyrrole-imidazole alkaloids: sources, structures, bioactivities and biosynthesis

Pyrrole-imidazole alkaloids (PIAs) constitute a highly diverse and densely functionalized subclass of marine natural products. Among them, the uncommon dimeric PIAs with ornate molecular architectures, attractive biological properties and interesting biosynthetic origin have spurred a considerable interest of chemists and biologists. The present review comprehensively summarized 84 dimeric PIAs discovered during the period from 1981 to September 2022, covering their source organisms, chemical structures, biological activities as well as biosynthesis. For a better understanding, these structurally intricate PIA dimers are firstly classified and presented according to their carbon skeleton features as well as biosynthesis pathways. Furthermore, relevant summaries focusing on the source organisms and the associated bioactivities of these compounds belonging to different chemical classes are also provided, which will help elucidate the fascinating chemistry and biology of these unusual PIA dimers.

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.

Marine Pyrrole Alkaloids

Nitrogen heterocycles are essential parts of the chemical machinery of life and often reveal intriguing structures. They are not only widespread in terrestrial habitats but can also frequently be found as natural products in the marine environment. This review highlights the important class of marine pyrrole alkaloids, well-known for their diverse biological activities. A broad overview of the marine pyrrole alkaloids with a focus on their isolation, biological activities, chemical synthesis, and derivatization covering the decade from 2010 to 2020 is provided. With relevant structural subclasses categorized, this review shall provide a clear and timely synopsis of this area.

Structural and Bioactive Studies of Halogenated Constituents from Sponges

Marine organisms are abundant sources of bioactive natural products. Among metabolites produced by sponges and their associated microbial communities, halogenated natural compounds accounted for an important part due to their potent biological activities. The present review updates and compiles a total of 258 halogenated organic compounds isolated in the past three decades, especially brominated derivatives derived from 31 genera of marine sponges. These compounds can be classified as the following classes: brominated polyunsaturated lipids, nitrogen compounds, brominated tyrosine derivatives and other halogenated compounds. These substances were listed together with their source organisms, structures and bioactivities. For this purpose, 84 references were consulted.

Futunamine, a Pyrrole-Imidazole Alkaloid from the Sponge Stylissa aff. carteri Collected off the Futuna Islands

The chemical investigation of the sponge Stylissa aff. carteri collected around Futuna Islands in the Pacific Ocean led to the isolation of three new dimeric pyrrole 2-aminoimidazole alkaloids (PIAs). Futunamine (1) features an unprecedented pyrrolo[1,2-c]imidazole core, while two other new dimeric PIAs were identified as analogues of palau'amine. Together with other known PIAs isolated from this species, they were shown to exhibit anti-inflammatory and neuroprotective activities.

New Cytotoxic Natural Products from the Red Sea Sponge Stylissa carteri

Bioactivity-guided isolation supported by LC-HRESIMS metabolic profiling led to the isolation of two new compounds, a ceramide, stylissamide A (1), and a cerebroside, stylissoside A (2), from the methanol extract of the Red Sea sponge Stylissa carteri. Structure elucidation was achieved using spectroscopic techniques, including 1D and 2D NMR and HRMS. The bioactive extract's metabolomic profiling showed the existence of various secondary metabolites, mainly oleanane-type saponins, phenolic diterpenes, and lupane triterpenes. The in vitro cytotoxic activity of the isolated compounds was tested against two human cancer cell lines, MCF-7 and HepG2. Both compounds, 1 and 2, displayed strong cytotoxicity against the MCF-7 cell line, with IC50 values at 21.1 ± 0.17 µM and 27.5 ± 0.18 µM, respectively. They likewise showed a promising activity against HepG2 with IC50 at 36.8 ± 0.16 µM for 1 and IC50 30.5 ± 0.23 µM for 2 compared to the standard drug cisplatin. Molecular docking experiments showed that 1 and 2 displayed high affinity to the SET protein and to inhibitor 2 of protein phosphatase 2A (I2PP2A), which could be a possible mechanism for their cytotoxic activity. This paper spreads light on the role of these metabolites in holding fouling organisms away from the outer surface of the sponge, and the potential use of these defensive molecules in the production of novel anticancer agents.

Compositional variation between high and low prokaryotic diversity coral reef biotopes translates to different predicted metagenomic gene content

In a previous study, we identified host species that housed high and low diversity prokaryotic communities. In the present study, we expand on this and assessed the prokaryotic communities associated with seawater, sediment and 11 host species from 7 different phyla in a Taiwanese coral reef setting. The host taxa sampled included hard, octo- and black corals, molluscs, bryozoans, flatworms, fish and sea urchins. There were highly significant differences in composition among host species and all host species housed distinct communities from those found in seawater and sediment. In a hierarchical clustering analysis, samples from all host species, with the exception of the coral Galaxea astreata, formed significantly supported clusters. In addition to this, the coral G. astreata and the bryozoan Triphyllozoon inornatum on the one hand and the coral Tubastraea coccinea, the hermit crab Calcinus laevimanus and the flatworm Thysanozoon nigropapillosum on the other formed significantly supported clusters. In addition to composition, there were highly pronounced differences in richness and evenness among host species from the most diverse species, the bryozoan T. inornatum at 2518 ± 240 OTUs per 10,000 sequences to the least diverse species, the octocoral Cladiella sp. at 142 ± 14 OTUs per 10,000 sequences. In line with the differences in composition, there were significant differences in predicted metagenomic gene counts among host species. Furthermore, there were pronounced compositional and predicted functional differences between high diversity hosts (Liolophura japonica, G. astreata, T. coccinea, C. laevimanus, T. inornatum) and low diversity hosts (Antipathes sp., Pomacentrus coelestis, Modiolus auriculatus, T. nigropapillosum, Cladiella sp. and Diadema savigny). In particular, we found that all tested low diversity hosts were predicted to be enriched for the phosphotransferase system compared to high diversity hosts.

Cave Actinobacteria as Producers of Bioactive Metabolites

Recently, there is an urgent need for new drugs due to the emergence of drug resistant pathogenic microorganisms and new infectious diseases. Members of phylum Actinobacteria are promising source of bioactive compounds notably antibiotics. The search for such new compounds has shifted to extreme or underexplored environments to increase the possibility of discovery. Cave ecosystems have attracted interest of the research community because of their unique characteristics and the microbiome residing inside including actinobacteria. At the time of writing, 47 species in 30 genera of actinobacteria were reported from cave and cave related habitats. Novel and promising bioactive compounds have been isolated and characterized. This mini-review focuses on the diversity of cultivable actinobacteria in cave and cave-related environments, and their bioactive metabolites from 1999 to 2018.

Recent advances in the tandem reaction of azides with alkynes or alkynols

Over the past few decades, the development of versatile methodologies to employ azides as aminating agents for the formation of nitrogen-containing compounds has attracted significant attention in synthetic chemistry.

Composition and Predictive Functional Analysis of Bacterial Communities in Seawater, Sediment and Sponges in the Spermonde Archipelago, Indonesia

In this study, we used a 16S rRNA gene barcoded pyrosequencing approach to sample bacterial communities from six biotopes, namely, seawater, sediment and four sponge species (Stylissa carteri, Stylissa massa, Xestospongia testudinaria and Hyrtios erectus) inhabiting coral reefs of the Spermonde Archipelago, South Sulawesi, Indonesia. Samples were collected along a pronounced onshore to offshore environmental gradient. Our goals were to (1) compare higher taxon abundance among biotopes, (2) test to what extent variation in bacterial composition can be explained by the biotope versus environment, (3) identify dominant (>300 sequences) bacterial operational taxonomic units (OTUs) and their closest known relatives and (4) assign putative functions to the sponge bacterial communities using a recently developed predictive metagenomic approach. We observed marked differences in bacterial composition and the relative abundance of the most abundant phyla, classes and orders among sponge species, seawater and sediment. Although all biotopes housed compositionally distinct bacterial communities, there were three prominent clusters. These included (1) both Stylissa species and seawater, (2) X. testudinaria and H. erectus and (3) sediment. Bacterial communities sampled from the same biotope, but different environments (based on proximity to the coast) were much more similar than bacterial communities from different biotopes in the same environment. The biotope thus appears to be a much more important structuring force than the surrounding environment. There were concomitant differences in the predicted counts of KEGG orthologs (KOs) suggesting that bacterial communities housed in different sponge species, sediment and seawater perform distinct functions. In particular, the bacterial communities of both Stylissa species were predicted to be enriched for KOs related to chemotaxis, nitrification and denitrification whereas bacterial communities in X. testudinaria and H. erectus were predicted to be enriched for KOs related to the toxin-antitoxin (TA) system, nutrient starvation and heavy metal export.

Unprecedented biomimetic homodimerization of oroidin and clathrodin marine metabolites in the presence of HMPA or phosphonate salt tweezers

The first biomimetic homodimerization of oroidin and clathrodin was effected in the presence HMPA and diphosphonate salts, strong guanidinium and amide chelating agents. The intermolecular associations probably interfere with the entropically and kinetically favored intramolecular cyclizations. Use of oroidin·(1)/2HCl salt or clathrodin·(1)/2HCl was indicative in the presence of the ambident nucleophilic and electrophilic tautomers of the 2-aminoimidazolic oroidin and clathrodin precursors. Surprisingly, the homodimerization of oroidin led to the nagelamide D skeleton, while the homodimerization of clathrodin gave the benzene para-symmetrical structure 19. The common process was rationalized from tautomeric precursors I and III.

The chemistry and biology of organic guanidine derivatives

The chemistry and biology of organic natural guanidines are reviewed, including the isolation, structure determination, synthesis, biosynthesis and biological activities of alkaloids, non-ribosomal peptides, guanidine-bearing terpenes, polyketides and shikimic acid derivatives from natural sources.

Marine natural products

Covering: 2010. Previous review: Nat. Prod. Rep., 2011, 28, 196. This review covers the literature published in 2010 for marine natural products, with 895 citations (590 for the period January to December 2010) 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 (1003 for 2010), 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.

Biosynthesis, asymmetric synthesis, and pharmacology, including cellular targets, of the pyrrole-2-aminoimidazole marine alkaloids

The pyrrole-2-aminoimidazole (P-2-AI) alkaloids are a growing family of marine alkaloids, now numbering well over 150 members, with high topographical and biological information content. Their intriguing structural complexity, rich and compact stereochemical content, high N to C ratio (~1 : 2), and increasingly studied biological activities are attracting a growing number of researchers from numerous disciplines world-wide. This review surveys advances in this area with a focus on the structural diversity, biosynthetic hypotheses with increasing, but still rare, verifying experimental studies, asymmetric syntheses, and biological studies, including cellular target receptor isolation studies, of this stimulating and exciting alkaloid family.