Renieramide, a cyclic tripeptide from the Vanuatu sponge Reniera n. sp

Evolution in the asymmetric synthesis of biaryl ethers and related atropisomers

Axially chiral biaryl ethers and related compounds hold valuable potential in natural products, medicinal chemistry, and catalysis; however, their asymmetric syntheses have always been overlooked compared to other biaryl/hetero-biaryl atropisomers. Unlike the later class molecules bearing a single chiral axis, the former category possesses a unique type of atropisomerism bearing two potential axes. Due to their great importance in diverse research domains, catalytic atropselective biaryl ether synthesis has recently witnessed an upsurge. This highlight article provides an elaborated view on the developments of catalytic synthetic methods that have been explored to achieve dual axial chirality in biaryl ethers and related scaffolds.

Atroposelective Synthesis of Axially Chiral Diaryl Ethers by N-Heterocyclic-Carbene-Catalyzed Sequentially Desymmetric/Kinetic Resolution Process

We describe herein an N-heterocyclic-carbene-catalyzed atroposelective synthesis of axially chiral diaryl ethers. Through a sequentially enantioselective desymmetric process and a kinetic resolution process, the products could be constructed in good yields with excellent enantiopurities. Both alcohols and phenols were compatible with this catalytic system. The axially chiral carboxylic acids derived from the esters were proven to be potential chiral ligands for asymmetric synthesis, for example, Rh(III)-catalyzed enantioselective C-H functionalization.

The Biosynthetic Landscape of Triceptides Reveals Radical SAM Enzymes That Catalyze Cyclophane Formation on Tyr- and His-Containing Motifs

Peptide-derived cyclophanes inhabit a unique niche in the chemical space of macrocyclic peptides with several examples of pharmaceutical importance. Although both synthetic and biocatalytic methods are available for constructing these macrocycles, versatile (bio)catalysts able to incorporate a variety of amino acids that compose the macrocycle would be useful for the creation of diverse peptide cyclophanes. In this report, we synergized the use of bioinformatic tools to map the biosynthetic landscape of radical SAM enzymes (3-CyFEs) that catalyze three-residue cyclophane formation in the biosynthesis of a new family of RiPP natural products, the triceptides. This analysis revealed 3940 (3113 unique) putative precursor sequences predicted to be modified by 3-CyFEs. Several uncharacterized maturase systems were identified that encode unique precursor types. Functional studies were carried out in vivo in Escherichia coli to identify modified precursors containing His and Tyr residues. NMR analysis of the products revealed that Tyr and His can also be incorporated into cyclophane macrocycles by 3-CyFEs. Collectively, all aromatic amino acids can be incorporated by 3-CyFEs, and the cyclophane formation strictly occurs via a C(sp²)-C(sp³) cross-link between the (hetero)aromatic ring to Cβ. In addition to 3-CyFEs, we functionally validated an Fe(II)/α-ketoglutarate-dependent hydroxylase, resulting in β-hydroxylated residues within the cyclophane rings. This study reveals the potential breadth of triceptide precursors and a systematic approach for studying these enzymes to broaden the diversity of peptide macrocycles.

Natural Products from the Marine Sponge Subgenus Reniera

Marine sponges are one of the prolific producers of bioactive natural products with therapeutic potential. As an important subgenus of Haliclona, Reniera sponges are mainly distributed in the Mediterranean Sea and Atlantic area, and had been chemically investigated for over four decades. By an extensive literature search, this review first makes a comprehensive summary of all natural products from Reniera sponges and their endozoic microbes, as well as biological properties. Perspectives on strengthening the chemical study of Reniera sponges for new drug-lead discovery are provided in this work.

Oceans as a Source of Immunotherapy

Marine flora is taxonomically diverse, biologically active, and chemically unique. It is an excellent resource, which offers great opportunities for the discovery of new biopharmaceuticals such as immunomodulators and drugs targeting cancerous, inflammatory, microbial, and fungal diseases. The ability of some marine molecules to mediate specific inhibitory activities has been demonstrated in a range of cellular processes, including apoptosis, angiogenesis, and cell migration and adhesion. Immunomodulators have been shown to have significant therapeutic effects on immune-mediated diseases, but the search for safe and effective immunotherapies for other diseases such as sinusitis, atopic dermatitis, rheumatoid arthritis, asthma and allergies is ongoing. This review focuses on the marine-originated bioactive molecules with immunomodulatory potential, with a particular focus on the molecular mechanisms of specific agents with respect to their targets. It also addresses the commercial utilization of these compounds for possible drug improvement using metabolic engineering and genomics.

Bioactivities and molecular networking-based elucidation of metabolites of potent actinobacterial strains isolated from the Unkeshwar geothermal springs in India

The bioactive potential of Actinobacteria endemic to hot springs has rarely been investigated. This study highlights the cultivable diversity and bioactivities of Actinobacteria associated with the Unkeshwar hot springs, India. Potent strains were evaluated for their biosynthetic potentials and metabolite analysis was performed using effective dereplication molecular networking tools. A total of 86 actinobacterial strains were isolated and grouped into 21 distinct genera, based on 16S rRNA gene sequence analysis. These strains included rare members such as Micromonospora, Marmoricola, Actinomadura, Cellulomonas, Cellulosimicrobium, Janibacter, Rothia, Barrentisimonas, Dietzia and Glycomyces. In antimicrobial screening, Micromonospora sp. strain GH99 and Streptomyces sp. strain GH176 were found to be potent antimicrobial strains. The metabolic extracts of these strains exhibited strong antimicrobial activity against Staphylococcus epidermidis (NCIM 2493), Shigella flexneri (NCIM 5265), Klebsiella pneumonia (NCIM 2098), and Salmonella abony (NCIM 2257). The extracts also displayed strong anti-biofilm and anticancer activities against Pseudomonas aeruginosa (NCIM 5029), Acinetobacter junii (NCIM 5188) and breast cancer cell line MCF7, respectively. Both strains also tested positive for the presence of the PKS biosynthetic gene cluster in their genomes. To effectively delineate the secondary metabolites, the extracts were subjected to MS/MS-guided molecular networking analysis. Structurally diverse compounds including the polyketides 22-dehydroxymethyl-kijanolide (GH99 strain) and Abyssomicin I (GH176 strain) were detected in the extracts. Interestingly, Brevianamide F was detected in the extract of Micromonospora, which has previously been mostly found in fungal species. Other compounds such as cyclic tripeptides, Cyclo(l-Pro-d-Ile) and Cyclo(d-Pro-l-Phe), were also identified in this strain. In summary, for the first time, we explored the diversity of Actinobacteria and evaluated their bioactive potential from the Unkeshwar hot springs. The potent strains isolated in the study could be useful in drug discovery programs.

The bioactive potential of Actinobacteria endemic to hot springs has rarely been investigated.

Natalenamides A⁻C, Cyclic Tripeptides from the Termite-Associated Actinomadura sp. RB99

In recent years, investigations into the biochemistry of insect-associated bacteria have increased. When combined with analytical dereplication processes, these studies provide a powerful strategy to identify structurally and/or biologically novel compounds. Non-ribosomally synthesized cyclic peptides have a broad bioactivity spectrum with high medicinal potential. Here, we report the discovery of three new cyclic tripeptides: natalenamides A–C (compounds 1–3). These compounds were identified from the culture broth of the fungus-growing termite-associated Actinomadura sp. RB99 using a liquid chromatography (LC)/ultraviolet (UV)/mass spectrometry (MS)-based dereplication method. Chemical structures of the new compounds (1–3) were established by analysis of comprehensive spectroscopic methods, including one-dimensional (¹H and ¹³C) and two-dimensional (¹H-¹H-COSY, HSQC, HMBC) nuclear magnetic resonance spectroscopy (NMR), together with high-resolution electrospray ionization mass spectrometry (HR-ESIMS) data. The absolute configurations of the new compounds were elucidated using Marfey’s analysis. Through several bioactivity tests for the tripeptides, we found that compound 3 exhibited significant inhibitory effects on 3-isobutyl-1-methylxanthine (IBMX)-induced melanin production. The effect of compound 3 was similar to that of kojic acid, a compound extensively used as a cosmetic material with a skin-whitening effect.

Photo-induced synthesis and in vitro antitumor activity of Fenestin A analogs

Two bioactive Fenestin A analogs were synthesized by photo-induced cyclization.

The Pharmacological Potential of Non-ribosomal Peptides from Marine Sponge and Tunicates

Marine biodiversity is recognized by a wide and unique array of fascinating structures. The complex associations of marine microorganisms, especially with sponges, bryozoans, and tunicates, make it extremely difficult to define the biosynthetic source of marine natural products or to deduce their ecological significance. Marine sponges and tunicates are important source of novel compounds for drug discovery and development. Majority of these compounds are nitrogen containing and belong to non-ribosomal peptide (NRPs) or mixed polyketide-NRP natural products. Several of these peptides are currently under trial for developing new drugs against various disease areas, including inflammatory, cancer, neurodegenerative disorders, and infectious disease. This review features pharmacologically active NRPs from marine sponge and tunicates based on their biological activities.

Characterization and NMR solution structure of a novel cyclic pentapeptide inhibitor of pathogenic hantaviruses

Hantavirus-induced diseases such as hantavirus cardiopulmonary syndrome and hemorrhagic fever with renal syndrome are a global health concern. Hantavirus cardiopulmonary syndrome caused by Sin Nombre virus lacks specific therapy and its high mortality makes Sin Nombre virus a potential bioweapon agent. Sin Nombre virus entry into susceptible cells requires expression of alpha(v)beta(3) integrin. We recently reported the sequence of a cyclic nonapeptide that inhibited Sin Nombre virus entry into Vero E6 cells at a level comparable to ReoPro, a Fab fragment of the anti-beta(3) antibody c7E3. Here, we refine the parental peptide, cyclo-[CPFVKTQLC], using alanine scanning and amino acid deletions, by optimizing for viral inhibition. The IC(50) of the resulting peptide, cyclo-[CPFVC], was 267 microM compared with 263 microM for the parental peptide. The solution structure of cyclo-[CPFVC] was determined by two-dimensional nuclear magnetic resonance spectroscopy, revealing the Phe ring in an extended conformation stacked against the Pro ring and containing a beta-turn encompassing Val-4 through Cys-1. As an initial step in identifying interactions between cyclo-[CPFVC] and its target cellular receptor, the refined peptide structure was docked into the ReoPro binding site of integrin beta(3). This structure will provide the basis for designing more potent peptidomimetic therapeutics to prevent Sin Nombre virus entry and treat hantavirus cardiopulmonary syndrome.

Discovery of halogenated eurypamide B analogues as inhibitors of lipid droplet accumulation in macrophages

Halogenated cyclic isodityrosine-tripeptides were synthesized as analogues of a marine natural product, eurypamide B. Although the original eurypamides showed no inhibitory activity, the new analogues were found to inhibit lipid droplet accumulation in macrophages with a low micromolar IC50 value.