Indole-based alkaloids from deep-sea bacterium Shewanella piezotolerans with antitumor activities

Microorganism-Derived Bisindole Alkaloids With Anticancer Potential and Their Mechanisms: A Comprehensive Review

Bisindole alkaloids constitute a significant class of natural compounds distinguished by their characteristic bisindole structure and renowned for their anticancer properties. Over the last six decades, researchers have isolated 425 microorganism-derived bisindole alkaloids (MDBAs). Among them, 187 MDBAs have demonstrated anticancer properties against various in vitro cancer cell lines, primarily by impeding the cell cycle, restraining cell proliferation, and inducing apoptosis and autophagy. These effects are mediated by regulating key targets and signaling pathways such as hypoxia-inducible factor (HIF)-1, MAPK, and phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR. This review provides a comprehensive examination of the sources, chemical diversity, and anticancer properties of these compounds. Furthermore, it summarizes the structure-activity relationship (SAR), druggability, and the mechanisms underlying MDBAs' anticancer effects. Ultimately, this article aims to furnish a thorough overview of the advancements in the investigation of microorganism-derived bisindole alkaloids for their continued development and utilization.

Copper-Catalyzed Oxidative Arylation and Hydroxylation of Indolin-2-ones for Direct Construction of Tetrasubstituted Carbon Centers

This study introduces a novel methodology for the direct construction of tetrasubstituted centers, utilizing secondary C(sp3)-H and C(sp2)-H substrates, specifically indolin-2-ones and indoles, through an innovative oxidative cross-coupling reaction. Facilitated by a straightforward copper salt catalyst, this reaction proceeds efficiently at a mild temperature of 40 °C under operationally streamlined conditions. Emphasizing sustainability, this method is notably enhanced by employing air (molecular oxygen) as an eco-friendly oxidant. In this approach, air (molecular oxygen) not only serves as the terminal oxidant but also as the oxygen donor in the synthesis of oxygen-containing compounds.

Indole alkaloids from marine resources: Understandings from therapeutic point of view to treat cancers

Cancer is the leading cause of mortality all over the world. Scientific investigation has demonstrated that disruptions in the process of autophagy are frequently interrelated with the emergence of cancer. Hence, scientists are seeking permanent solutions to counter the deadly disease. Indole alkaloids have been extensively studied and are acknowledged to exhibit several bioactivities. The current state of disease necessitates novel pharmacophores development. In recent decades, indole alkaloids have become increasingly significant in cancer treatment and are also used as adjuvants. A substantial amount of pharmacologically active molecules come from indole alkaloids, which are widely distributed in nature. Indole alkaloids derived from marine organisms show immense potential for therapeutic applications and seem highly effective in cancer treatment. A couple of experiments have been conducted preclinically to investigate the possibility of indole alkaloids in cancer treatment. Marine-derived indole alkaloids possess the ability to exhibit anticancer properties through diverse antiproliferative mechanisms. Certain indole alkaloids, including vincristine and vinblastine, were verified in clinical trials or are presently undergoing clinical assessments for preventing and treating cancer. Indole alkaloids from marine resources hold a significant functionality in identifying new antitumor agents. The current literature highlights recent advancements in indole alkaloids that appear to be anticancer agents and the underlying mechanisms.

Electrochemical oxidation of 3-substituted indoles

2-Oxindoles are an abundant heteroaromatic motif in natural products and pharmaceuticals. An appealing method for accessing 2-oxindoles is by oxidation of the corresponding indole, a transformation currently executed using stoichiometric quantities of unsafe chemical oxidants that can also form unwanted side-products. Herein, we report that 3-substituted indoles undergo a logistically straightforward, electrochemical oxidation to the corresponding 2-oxindole in the presence of potassium bromide (>20 examples), with only traces of the oxidative dimer detected. Cyclic voltammetry and control studies infer that the reaction proceeds by electrochemical generation of elemental bromine (Br₂) that upon reaction with indole, followed by hydrolysis, delivers the 2-oxindole. This procedure is an appealing alternative to existing methods used to access 2-oxindoles by oxidation of the parent indole.

One-Pot Synthesis of Core Structure of Shewanelline C Using an Azidoindoline

The unprecedented synthesis of the indolines bearing N3-quinazolin-2,4-dione moiety using an AZIN is reported. The concise synthesis features the tandem Staudinger/chemo-selective aza-Wittig/cyclization sequence of AZINs with isatoic anhydride by a one-pot protocol.

Saccharobisindole, Neoasterric Methyl Ester, and 7-Chloro-4(1H)-quinolone: Three New Compounds Isolated from the Marine Bacterium Saccharomonospora sp

Analysis of the chemical components from the culture broth of the marine bacterium Saccharomonospora sp. CNQ-490 has yielded three novel compounds: saccharobisindole (1), neoasterric methyl ester (2), and 7-chloro-4(1H)-quinolone (3), in addition to acremonidine E (4), pinselin (5), penicitrinon A (6), and penicitrinon E (7). The chemical structures of the three novel compounds were elucidated by the interpretation of 1D, 2D nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS) data. Compound 2 generated weak inhibition activity against Bacillus subtilis KCTC2441 and Staphylococcus aureus KCTC1927 at concentrations of 32 μg/mL and 64 μg/mL, respectively, whereas compounds 1 and 3 did not have any observable effects. In addition, compound 2 displayed weak anti-quorum sensing (QS) effects against S. aureus KCTC1927 and Micrococcus luteus SCO560.

Chiral Heterogeneous Scandium Lewis Acid Catalysts for Continuous-Flow Enantioselective Friedel-Crafts Carbon-Carbon Bond-Forming Reactions

While continuous-flow reactions with chiral heterogeneous catalysts provide a highly efficient method to synthesize optically active compounds, chiral heterogeneous Lewis acid catalysis has been less extensively explored. We have developed the first example of chiral heterogeneous Sc catalysts, which demonstrated excellent activity and selectivity for continuous-flow enantioselective Friedel-Crafts reactions of isatins with indoles. Noncovalent interactions between chiral Sc complexes and heteropoly acid-anchored amine-functionalized SiO₂ as support were utilized for the synthesis. The heteropoly acid was found to be crucial for the preparation, activity, and selectivity of the catalysts. The chiral ligand could be easily tuned without chemical modification and the continuous-flow synthesis of a biologically active compound was achieved.

Chemistry of trisindolines: natural occurrence, synthesis and bioactivity

Heterocyclic nitrogen compounds are privileged structures with many applications in the pharmaceutical and nutraceutical industries since they possess wide bioactivities. Trisindolines are heterocyclic nitrogen compounds consisting of an isatin core bearing two indole moieties. Trisindolines have been synthesized by reacting isatins with indoles using various routes and the yield greatly depends on the catalyst used, reaction conditions, and the substituents on both the isatin and indole moieties. Amongst the synthetic routes, acid-catalyzed condensation reaction between isatins and indoles are the most useful due to high yield, wide scope and short reaction times. Trisindolines are biologically active compounds and show anticancer, antimicrobial, antitubercular, antifungal, anticonvulsant, spermicidal, and antioxidant activities, among others. Trisindolines have not previously been reviewed. Therefore, this review aims to provide a comprehensive account of trisindolines including their natural occurrence, routes of synthesis, and biological activities. It aims to inspire the discovery of lead trisindoline drug candidates for further development.

This in-depth review of trisindolines covers their natural occurrence in addition to several routes of synthesis and catalysts used. The biological activities of trisindolines have been discussed with a special emphasis on the structure–activity relationship.

The Shewanella genus: ubiquitous organisms sustaining and preserving aquatic ecosystems

The Gram-negative Shewanella bacterial genus currently includes about 70 species of mostly aquatic γ­-proteobacteria, which were isolated around the globe in a multitude of environments such as surface freshwater and the deepest marine trenches. Their survival in such a wide range of ecological niches is due to their impressive physiological and respiratory versatility. Some strains are among the organisms with the highest number of respiratory systems, depending on a complex and rich metabolic network. Implicated in the recycling of organic and inorganic matter, they are important components of organism-rich oxic/anoxic interfaces, but they also belong to the microflora of a broad group of eukaryotes from metazoans to green algae. Examples of long-term biological interactions like mutualism or pathogeny have been described, although molecular determinants of such symbioses are still poorly understood. Some of these bacteria are key organisms for various biotechnological applications, especially the bioremediation of hydrocarbons and metallic pollutants. The natural ability of these prokaryotes to thrive and detoxify deleterious compounds explains their use in wastewater treatment, their use in energy generation by microbial fuel cells and their importance for resilience of aquatic ecosystems.

Protocols for the Syntheses of 2,2'-Bis(indolyl)arylmethanes, 2-Benzylated Indoles, and 5,7-Dihydroindolo[2,3-b]carbazoles

The electrophilic substitution reaction of 4,7-dihydroindole with aryl-aldehydes as an electrophilic partner followed by an oxidation step to deliver 2,2'-bis(indolyl)arylmethanes was studied for the first time. The reaction afforded regioselectivity at the 2,2'-positions of indole in an operationally simple and inexpensive procedure with a variety of substrates. To the best of our knowledge, this is the first set of examples of 2,2'-bis(indolyl)arylmethanes obtained in a substituent-free manner. A facile method from dipyrromethanes to the corresponding 2-benzylindoles was also reported. In addition, 2,2'-bis(indolyl)arylmethanes were converted to 5,7-dihydroindolo[2,3-b]carbazoles.

Two New Cytotoxic Compounds from a Deep-Sea Penicillum citreonigrum XT20-134

Penicillum citreonigrum XT20-134 (MCCC 3A00956) is a fungus with cytotoxic activity, derived from deep-sea sediment. Five new compounds, adeninylpyrenocine (1), 2-hydroxyl-3-pyrenocine-thio propanoic acid (2), ozazino-cyclo-(2,3-dihydroxyl-trp-tyr) (3), 5,5-dichloro-1-(3,5-dimethoxyphenyl)-1,4-dihydroxypentan-2-one (4), and 2,3,4-trihydroxybutyl cinnamate (5), together with 19 known compounds (6-24), were isolated from an ethyl acetate (EtOAc) extract of its fermentation. The structures of the new compounds were comprehensively characterized by high-resolution electrospray ionization-mass spectrometry (HR-ESI-MS), 1D and 2D nuclear magnetic resonance (NMR). All isolates were evaluated for their cytotoxic activities. The heteroatom-containing new compounds 2 and 4 showed potent cytotoxicity to the human hepatoma tumor cell Bel7402 with IC₅₀ values of 7.63 ± 1.46, 13.14 ± 1.41 μM and the human fibrosarcoma tumor cell HT1080 with IC₅₀ values of 10.22 ± 1.32, 16.53 ± 1.67 μM, respectively.

Bioactive Brominated Oxindole Alkaloids from the Red Sea Sponge Callyspongia siphonella

In the present study, LC-HRESIMS-assisted dereplication along with bioactivity-guided isolation led to targeting two brominated oxindole alkaloids (compounds 1 and 2) which probably play a key role in the previously reported antibacterial, antibiofilm, and cytotoxicity of Callyspongia siphonella crude extracts. Both metabolites showed potent antibacterial activity against Gram-positive bacteria, Staphylococcus aureus (minimum inhibitory concentration (MIC) = 8 and 4 µg/mL) and Bacillus subtilis (MIC = 16 and 4 µg/mL), respectively. Furthermore, they displayed moderate biofilm inhibitory activity in Pseudomonasaeruginosa (49.32% and 41.76% inhibition, respectively), and moderate in vitro antitrypanosomal activity (13.47 and 10.27 µM, respectively). In addition, they revealed a strong cytotoxic effect toward different human cancer cell lines, supposedly through induction of necrosis. This study sheds light on the possible role of these metabolites (compounds 1 and 2) in keeping fouling organisms away from the sponge outer surface, and the possible applications of these defensive molecules in the development of new anti-infective agents.

Direct Csp3-H methylenation of 2-arylacetamides using DMF/Me2NH-BH3 as the methylene source

A direct Csp3-H methylenation of 2-arylacetamides using DMF/Me2NH-BH3 as the methylene source was developed. The formyl group of DMF delivered the carbon and one hydrogen atoms, and the Me2NH-BH3 donated the remaining one hydrogen atom. This protocol offers a new alternative to make useful 2-arylacrylamides from simple starting materials.

Bioactive Compounds Isolated from Marine-Derived Microbes in China: 2009-2018

This review outlines the research that was carried out regarding the isolation of bioactive compounds from marine-derived bacteria and fungi by China-based research groups from 2009-2018, with 897 publications being surveyed. Endophytic organisms featured heavily, with endophytes from mangroves, marine invertebrates, and marine algae making up more than 60% of the microbial strains investigated. There was also a strong focus on fungi as a source of active compounds, with 80% of publications focusing on this area. The rapid increase in the number of publications in the field is perhaps most notable, which have increased more than sevenfold over the past decade, and suggests that China-based researchers will play a major role in marine microbial natural products drug discovery in years to come.

Thermal-mediated catalyst-free heterolytic cleavage of 3-halooxindoles: rapid access to 3-functionalized-2-oxindoles

Herein a previously unreported catalyst-free S_N1 reaction of the 3-halooxindoles to build 3-functionalized-2-oxindoles is described.

Indole Derivative-Capped Gold Nanoparticles as an Effective Bactericide in Vivo

We synthesize indole derivative-capped gold nanoparticles (Au_IDs) via a straightforward route to fight multidrug-resistant (MDR) bacteria. When gold nanoparticles are modified with two indole derivatives, tryptophan and 5-aminoindole, they exhibit excellent antibacterial activities against both laboratory antibiotic-sensitive and MDR bacteria. Au_IDs possess remarkable bactericidal activities against MDR bacteria killing 99.9% of MDR Escherichia coli and polymyxin-resistant Klebsiella pneumoniae after 0.5 h of incubation, which are superior to clinical antibiotics including polymyxin B and cefotaxime. By evaluating the potential of Au_IDs in wound cure, Au_IDs show outstanding capability in MDR bacterial wound infection. Our findings provide new candidates for the development of bactericides and the fabrication of wound dressings for treating MDR infection.

2,3-Dihydroquinazolin-4(1H)-one as a privileged scaffold in drug design

2,3-Dihydroquinazolin-4-one (DHQ) belongs to the class of nitrogen-containing heterocyclic compounds representing a core structural component in various biologically active compounds. In the past decades, several methodologies have been developed for the synthesis of the DHQ framework, especially the 2-substituted derivatives. Unfortunately, multistep syntheses, harsh reaction conditions, and the use of toxic reagents and solvents have limited their full potential as a versatile fragment. Recently, use of green chemistry and alternative strategies are being explored to prepare diverse DHQ derivatives. This fragment is used as a synthon for the preparation of biologically active quinazolinones and as a functional substrate for the synthesis of modified DHQ derivatives exhibiting different biological properties. In this review, we provide a comprehensive assessment of the synthesis and biological evaluations of DHQ derivatives.

Alcohols as Substrates and Solvents for the Construction of 3-Alkoxylated-2-Oxindoles by Direct Alkoxylation of 3-Halooxindoles

Described herein is an environmentally benign method for the synthesis of multisubstituted 3-alkoxylated-2-oxindoles 3 via direct alkoxylation of 3-halooxindoles 1. A wide variety of such multisubstituted 3-alkoxylated-2-oxindole scaffolds were smoothly obtained in good yields (up to 94%) by heating in an oil bath at 35 °C for 24 h. A particularly valuable feature of this method was the development of environment-friendly chemistry using alcohols 2 as both the substrates and solvents in the presence of a catalytic amount of base.

5,5′-Bistriazoles as axially chiral, multidentate ligands: synthesis, configurational stability and catalytic application of their scandium(iii) complexes

The design and development of 5,5′-bistriazoles featuring aminomethyl substituents is discussed.

Biosynthetic Functional Gene Analysis of Bis-Indole Metabolites from 25D7, a Clone Derived from a Deep-Sea Sediment Metagenomic Library

This work investigated the metabolites and their biosynthetic functional hydroxylase genes of the deep-sea sediment metagenomic clone 25D7. 5-Bromoindole was added to the 25D7 clone derived Escherichia coli fermentation broth. The new-generated metabolites and their biosynthetic byproducts were located through LC-MS, in which the isotope peaks of brominated products emerged. Two new brominated bis-indole metabolites, 5-bromometagenediindole B (1), and 5-bromometagenediindole C (2) were separated under the guidance of LC-MS. Their structures were elucidated on the basis of 1D and 2D NMR spectra (COSY, HSQC, and HMBC). The biosynthetic functional genes of the two new compounds were revealed through LC-MS and transposon mutagenesis analysis. 5-Bromometagenediindole B (1) also demonstrated moderately cytotoxic activity against MCF7, B16, CNE2, Bel7402, and HT1080 tumor cell lines in vitro.

Marine natural products

This review covers the literature published in 2014 for marine natural products (MNPs), with 1116 citations (753 for the period January to December 2014) 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 (1378 in 456 papers for 2014), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Marine Indole Alkaloids

Marine indole alkaloids comprise a large and steadily growing group of secondary metabolites. Their diverse biological activities make many compounds of this class attractive starting points for pharmaceutical development. Several marine-derived indoles were found to possess cytotoxic, antineoplastic, antibacterial and antimicrobial activities, in addition to the action on human enzymes and receptors. The newly isolated indole alkaloids of marine origin since the last comprehensive review in 2003 are reported, and biological aspects will be discussed.

Friedel–Crafts alkylation of heteroarenes and arenes with indolyl alcohols for construction of 3,3-disubstituted oxindoles

An intriguing camphorsulfonic acid catalyzed Friedel–Crafts alkylation of arenes with indolyl alcohols has been developed featuring mild reaction conditions, wide substrate scope and high yields.