Nagelamides K and L, Dimeric Bromopyrrole Alkaloids from Sponge Agelas Species

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.

Secondary metabolites from marine sponges of the genus Agelas: a comprehensive update insight on structural diversity and bioactivity

As one of the most common marine sponges in tropical and subtropical oceans, the sponges of the genus Agelas, have emerged as unique and yet under-investigated pools for discovery of natural products with fabulous molecular diversity and myriad interesting biological activities. The present review highlights the chemical structure and biological activity of 355 compounds that have been isolated and characterized from the members of Agelas sponges, over the period of about five decades (from 1971 to November 2021). For a better understanding, these numerous compounds are firstly classified and presented according to their carbon skeleton as well as their biosynthetic origins. Relevant summaries focusing on the source organism and the associated bioactivity of these compounds belonging to different chemical classes are also provided. This review highlights sponges of the genus Agelas as exciting source for discovery of intriguing natural compounds.

The marine sponges of the genus Agelas, are unique and yet under-investigated pools for discovery of natural products with fabulous molecular diversity and myriad interesting biological activities.

Efficient construction of the hexacyclic ring core of palau'amine: the pK a concept for proceeding with unfavorable equilibrium reactions

Palau'amine has received a great deal of attention as an attractive synthetic target due to its intriguing molecular architecture and significant immunosuppressive activity, and we achieved its total synthesis in 2015. However, the synthesized palau'amine has not been readily applicable to the mechanistic study of immunosuppressive activity, because it requires 45 longest linear steps from a commercially available compound. Here, we report the short-step construction of the ABCDEF hexacyclic ring core of palau'amine. The construction of the CDE tricyclic ring core in a single step is achieved by our pK_a concept for proceeding with unfavorable equilibrium reactions, and a palau'amine analog without the aminomethyl and chloride groups is synthesized in 20 longest linear steps from the same starting material. The palau'amine analog is confirmed to retain the immunosuppressive activity. The present synthetic approach for a palau'amine analog has the potential for use in the development of palau'amine probes for mechanistic elucidation.

A palau'amine analog (2) was synthesized from 2-cyclopentenone in 20 steps. The construction of the CDE tricyclic ring core in a single step is achieved by our pK_a concept for proceeding with the unfavorable equilibrium reactions.

Multifunctional Therapeutic Potential of Phytocomplexes and Natural Extracts for Antimicrobial Properties

Natural products have been known for their antimicrobial factors since time immemorial. Infectious diseases are a worldwide burden that have been deteriorating because of the improvement of species impervious to various anti-infection agents. Hence, the distinguishing proof of antimicrobial specialists with high-power dynamic against MDR microorganisms is central to conquer this issue. Successful treatment of infection involves the improvement of new drugs or some common source of novel medications. Numerous naturally occurring antimicrobial agents can be of plant origin, animal origin, microbial origin, etc. Many plant and animal products have antimicrobial activities due to various active principles, secondary metabolites, or phytochemicals like alkaloids, tannins, terpenoids, essential oils, flavonoids, lectins, phagocytic cells, and many other organic constituents. Phytocomplexes’ antimicrobial movement frequently results from a few particles acting in cooperative energy, and the clinical impacts might be because of the direct effects against microorganisms. The restorative plants that may furnish novel medication lead the antimicrobial movement. The purpose of this study is to investigate the antimicrobial properties of the phytocomplexes and natural extracts of the plants that are ordinarily being utilized as conventional medications and then recommended the chance of utilizing them in drugs for the treatment of multiple drug-resistant disease.

Total Synthesis of the Nagelamides - Synthetic Studies toward the Reported Structure of Nagelamide D and Nagelamide E Framework

The nagelamides are a small subset of the oroidin family of marine sponge-derived alkaloids and are, for the most part, dimeric in nature. As part of our efforts to develop synthetic access to this family, a Stille cross-coupling strategy is used to construct the bis-imidazolyl core skeleton. Reduction of the bis-vinylimidazole delivered the core framework of nagelamide D. Introduction of the 2-amino groups via the corresponding azides and introduction of the pyrrolecarboxamides through a double Mitsunobu reaction using a pyrrole hydantoin provided the putative structure of nagelamide D. The spectroscopic data for the synthetic and sponge-derived materials did not match well, whereas the spectroscopic data were a good match for closely related oroidin alkaloids, supporting the structure of the synthetic material. The structure of the synthetic material was further corroborated by obtaining an X-ray crystal structure of a derivative. Electrocyclization of an advanced precursor affords a dihydrobenzimidazole, which is expected to serve as a key intermediate en route to nagelamide E and ageliferin.

Agesasines A and B, Bromopyrrole Alkaloids from Marine Sponges Agelas spp

Exploration for specialized metabolites of Okinawan marine sponges Agelas spp. resulted in the isolation of five new bromopyrrole alkaloids, agesasines A (1) and B (2), 9-hydroxydihydrodispacamide (3), 9-hydroxydihydrooroidin (4), and 9E-keramadine (5). Their structures were elucidated on the basis of spectroscopic analyses. Agesasines A (1) and B (2) were assigned as rare bromopyrrole alkaloids lacking an aminoimidazole moiety, while 3-5 were elucidated to be linear bromopyrrole alkaloids with either aminoimidazolone, aminoimidazole, or N-methylated aminoimidazole moieties.

Bioactive Secondary Metabolites from the Marine Sponge Genus Agelas

The marine sponge genus Agelas comprises a rich reservoir of species and natural products with diverse chemical structures and biological properties with potential application in new drug development. This review for the first time summarized secondary metabolites from Agelas sponges discovered in the past 47 years together with their bioactive effects.

Hybrid Pyrrole-Imidazole Alkaloids from the Sponge Agelas sceptrum

A chemical investigation of the tropical sponge Agelas sceptrum from Plana Cays (Bahamas) led to the isolation of two hybrid pyrrole-imidazole alkaloids (PIAs), 15'-oxoadenosceptrin (1) and decarboxyagelamadin C (2). Herein, we report their challenging structure elucidation established by NMR and ECD spectroscopy. 15'-Oxoadenosceptrin (1) shows sceptrin merged with an adenine moiety, not yet encountered in the PIA family, whereas decarboxyagelamadin C (2) is a close derivative of agelamadins C to E recently isolated from an Agelas sp. from Okinawa.

Nagelamides X-Z, dimeric bromopyrrole alkaloids from a marine sponge Agelas sp

Three new dimeric bromopyrrole alkaloids, nagelamides X-Z (1-3), were isolated from a marine sponge Agelas sp. Nagelamides X (1) and Y (2) possess a novel tricyclic skeleton consisting of spiro-bonded tetrahydrobenzaminoimidazole and aminoimidazolidine moieties. Nagelamide Z (3) is the first dimeric bromopyrrole alkaloid involving the C-8 position in dimerization. The structures of 1-3 were elucidated on the basis of spectroscopic data. Nagelamides X-Z (1-3) exhibited antimicrobial activity.

The Chemistry of Marine Sponges∗

Marine sponges continue to attract wide attention from marine natural product chemists and pharmacologists alike due to their remarkable diversity of bioactive compounds. Since the early days of marine natural products research in the 1960s, sponges have notoriously yielded the largest number of new metabolites reported per year compared to any other plant or animal phylum known from the marine environment. This not only reflects the remarkable productivity of sponges with regard to biosynthesis and accumulation of structurally diverse compounds but also highlights the continued interest of marine natural product researchers in this fascinating group of marine invertebrates.

Among the numerous classes of natural products reported from marine sponges over the years, alkaloids, peptides, and terpenoids have attracted particularly wide attention due to their unprecedented structural features as well as their pronounced pharmacological activities which make several of these metabolites interesting candidates for drug discovery. This chapter consequently highlights several important groups of sponge-derived alkaloids, peptides, and terpenoids and describes their biological and/or pharmacological properties.

Occurrence of halogenated alkaloids

Once considered to be isolation artifacts or chemical "mistakes" of nature, the number of naturally occurring organohalogen compounds has grown from a dozen in 1954 to >5000 today. Of these, at least 25% are halogenated alkaloids. This is not surprising since nitrogen-containing pyrroles, indoles, carbolines, tryptamines, tyrosines, and tyramines are excellent platforms for biohalogenation, particularly in the marine environment where both chloride and bromide are plentiful for biooxidation and subsequent incorporation into these electron-rich substrates. This review presents the occurrence of all halogenated alkaloids, with the exception of marine bromotyrosines where coverage begins where it left off in volume 61 of The Alkaloids. Whereas the biological activity of these extraordinary compounds is briefly cited for some examples, a future volume of The Alkaloids will present full coverage of this topic and will also include selected syntheses of halogenated alkaloids. Natural organohalogens of all types, especially marine and terrestrial halogenated alkaloids, comprise a rapidly expanding class of natural products, in many cases expressing powerful biological activity. This enormous proliferation has several origins: (1) a revitalization of natural product research in a search for new drugs, (2) improved compound characterization methods (multidimensional NMR, high-resolution mass spectrometry), (3) specific enzyme-based and other biological assays, (4) sophisticated collection methods (SCUBA and remote submersibles for deep ocean marine collections), (5) new separation and purification techniques (HPLC and countercurrent separation), (6) a greater appreciation of traditional folk medicine and ethobotany, and (7) marine bacteria and fungi as novel sources of natural products. Halogenated alkaloids are truly omnipresent in the environment. Indeed, one compound, Q1 (234), is ubiquitous in the marine food web and is found in the Inuit from their diet of whale blubber. Given the fact that of the 500,000 estimated marine organisms--which are the source of most halogenated alkaloids--only a small percentage have been investigated for their chemical content, it is certain that myriad new halogenated alkaloids are awaiting discovery. For example, it is estimated that nearly 4000 species of bryozoans have not been examined for their chemical content. The few species that have been studied contain some extraordinary halogenated alkaloids, such as hinckdentine A (610) and the chartellines (611-613). Of the estimated 1.5 million species of fungi, secondary metabolites have been characterized from only 5000 species. The future seems bright for the collector of halogenated alkaloids!

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.

Chemistry and biology of Okinawan marine natural products

Marine macro- and micro-organisms collected in Okinawa are good sources of compounds with intriguing structures and interesting biological activities. Synthetic hybrid molecules of caffeine and eudistomin D from tunicates Eudistoma sp. were found to show better potency as adenosine receptor ligands than caffeine, and one of them exhibits potent activity for adenosine receptors tested, especially for A3 subtype. Potent cytotoxic polyene macrolides from a tunicate Cystodytes sp. were found to be potent osteoclast inhibitors and to inhibit vacuolar type H+-ATPase (V-ATPase) of both mammalian and yeast cells. Amphidinolactones A and B are new macrolides from a dinoflagellate Amphidinium sp., and a potent cytotoxic macrolide from another strain was found to target actin cytoskeleton. Theonezolide A, a long-chain polyketide from a sponge Theonella sp., induces a drastic shape change in platelets by reorganization of microtubules. The stereochemistry of many chiral centers in theonezolide A was elucidated by spectral data and chemical means. Metachromins L-Q are new sesquiterpenoid quinones with an amino acid residue, while nakijiquinones E and F were the first dimeric sesquiterpenoid quinones possessing a 3-aminobenzoate moiety. Halichonadin E is the first hetero-dimeric sesquiterpenoid with eudesmane and aromadendrane skeletons linked through a urea fragment isolated from a sponge Halichondria sp. Pyrinadine A and nakinadine A are novel bis-pyridine alkaloids from sponges, while nagelamides are new bromopyrrole alkaloids from a sponge Agelas sp. Here, the structures and bioactivities of these interesting marine natural products will be described.

Total synthesis of the putative structure of nagelamide D

A total synthesis of the putative structure of nagelamide D from imidazole is described. A Stille cross-coupling is used to construct the bis imidazole skeleton, and the pyrrolecarboxamides are introduced via a double Mitsunobu reaction using a pyrrolehydantoin derivative. Discrepancies between the published spectroscopic data and that reported in the literature cast doubts either on the assigned structure or the reported data.

Bromopyrrole alkaloids from marine sponges of the genus Agelas

Four new bromopyrrole alkaloids, nagelamides O (1) and P (2) and mukanadins E (3) and F (4), were isolated from three collections of Okinawan marine sponges of the genus Agelas. The structures and stereochemistry of 1-4 were elucidated on the basis of their spectroscopic data.