Isolation of bisindole alkaloids that inhibit the cell cycle from Myxomycetes Arcyria ferruginea and Tubifera casparyi

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.

Biologically Active Compounds in True Slime Molds and Their Prospects for Sustainable Pest and Pathogen Control

True slime molds (Eumycetozoa) represent a monophyletic clade within the phylum Amoebozoa, comprising the lineages Myxogastria, Dictyostelia, and Protosporangiida. Although historically misclassified as fungi, recent molecular and biochemical studies underscore their distinct evolutionary trajectories and rich metabolomic profiles. In this review, we synthesize current knowledge on Eumycetozoa as a reservoir of bioactive compounds, detailing how secondary metabolites-including polysaccharides, amino acids, unsaturated fatty acids, terpenoids, and glycosides-vary across plasmodia, fruiting bodies, and spores. A systematic literature search in major scientific databases accounted for legacy nomenclature and leveraged chemoinformatic tools for compound verification. Our findings reveal 298 distinct metabolites that serve ecological roles in nutrient recycling and interspecies interactions, while also showing promise for controlling agricultural pests and pathogens. Notably, certain glycosides, lectins, and polyketides exhibit antimicrobial or cytotoxic activities, indicating their potential utility in managing these biological challenges. By consolidating current data and emphasizing the wide taxonomic range of Eumycetozoa, this review highlights the critical need for comprehensive biochemical and genomic investigations. Such efforts will not only advance our understanding of slime mold metabolomes and their evolutionary significance but also pave the way for innovative, eco-friendly applications.

Advances in the total synthesis of bis- and tris-indole alkaloids containing N-heterocyclic linker moieties

The past several years have seen an increase in the discovery and isolation of natural products of the indole alkaloid class. Bis- and tris-indole alkaloids are classes of natural products that have been shown to display diverse, potent biological activities. Of particular interest are bis- and tris-indole alkaloids containing N-heterocyclic linker moieties. It has been reported that more than 85% of biologically active compounds contain one or more heterocyclic moieties; of these, N-heterocycles have been identified as the most prevalent. The goal of this review is to provide a detailed overview of the recent advances in isolation and total synthesis of bis- and tris-indole alkaloids that contain N-heterocyclic linker moieties. The known biological activities of these natural products will also be discussed.

Metal-free, I2-promoted direct synthesis of 2-cyano-substituted maleimides via a unique 3,3-dicyano-2-arylacrylic acid intermediate

A robust, I₂-mediated cyclization reaction was developed for the synthesis of 2-cyano-substituted maleimides from arylethylidene malononitriles and amines via unique a 3,3-dicyano-2-arylacrylic acid intermediate. The reaction duration was short and devoid of an expensive transition-metal catalyst, ligands or toxic carbon monoxide. We executed an I₂/DMSO-mediated desirable oxidation of the C(sp³)-H bond of the carbonyl precursor followed by the formation of a 3,3-dicyano-2-arylacrylic acid intermediate. Use of readily available starting materials under mild and operationally simple reaction conditions are the major advantages of this strategy.

Microbial based natural compounds as potential inhibitors for SARS-CoV-2 Papain-like protease (PLpro): a molecular docking and dynamic simulation study

COVID-19 (Coronavirus disease of 2019) pandemic is one of the largest health threats the planet has faced in recent decades. Efforts are being continuously made to design a viable drug or a vaccine. Several natural and synthetic molecules are under study for their potency to inhibit viral replication. In order to emphasize the importance of microbial-based natural components in antiviral drug discovery, an attempt has been made through this study to find potential inhibitors for SARS-CoV-2 Papain-Like protease (PLpro) molecule from microbial sources. PLpro, with its multifunctional roles like viral polypeptide proteolysis and suppression of the host's innate immune response, is acting as a potential drug target. The X-ray crystal structure of PLpro and ligand molecules were retrieved from the protein structure database and Npatlas database, respectively. The molecules were screened based on drug likeliness and the pharmacophore model created in reference to a known potent PLpro inhibitor GRL0617. Totally 3272 molecules have undergone the docking process and the complexes of top hits were subjected to 100 ns molecular dynamic simulation. The results showed that Holyrine B, Dihydroarcyriarubin C, Baraphenazine C and 3-hydroxy-3'-N-acetylholyrine A had formed a stable complex in the active site of the PLpro with significant interaction efficiency. Earlier studies showed that Holyrine B could also be a possible inhibitor of the Main protease of SARS-CoV-2, which increases its significance in the process of COVID-19 drug development. In conclusion, these microbial compounds can be considered as possible SARS-CoV-2 inhibitors for further in vitro studies. Communicated by Ramaswamy H. Sarma.

Bisindole natural products: A vital source for the development of new anticancer drugs

Currently, the number of new cancer cases and deaths worldwide is increasing year on year. In addition to the requirement for cancer prevention, the top priority is still to seek the effective cure of cancer. In over a half century of constant exploration, increasing attention has been paid to the excellent anticancer activity of natural products, with more and more natural products isolated, identified and detected. For this study, the focus lies the natural products of bisindole, where two indole molecules are indirectly linked or directly polymerized, developing the diversity of structure and mechanism, accompanied with the better anticancer activity than monomers. There has been a long history of applying indirubin and vincristine in cancer treatment, verifying the anticancer effect of bisindoles. Vincribine, midostaurin and other anticancer drugs have also been developed and commercialized. In this paper, a review regarding the potential therapeutic effect of bisindole alkaloids extracted from various natural products was carried out, in which the progress made in research of 242 bisindole alkaloids for cancer treatment was introduced. These compounds may be applicable as medicinal products for clinical research in the future.

Total Synthesis of Aqabamycin G, a Nitrophenyl Indolylmaleimide Marine Alkaloid from Vibrio sp. WMBA

The first total synthesis of the marine alkaloid aqabamycin G is disclosed. The synthetic sequence involved the stepwise addition to maleimide of an indole motif and a substituted diazo-benzenoid unit derived from acetaminophen. An alternative strategy using a protected phenol is also reported.

[Novel Tyrosine Phosphorylation Signals in the Nucleus and on Mitotic Spindle Fibers and Lysosomes Revealed by Strong Inhibition of Tyrosine Dephosphorylation]

Protein-tyrosine phosphorylation is one of the posttranslational modifications and plays critical roles in regulating a wide variety of cellular processes, such as cell proliferation, differentiation, adhesion, migration, survival, and apoptosis. Protein-tyrosine phosphorylation is reversibly regulated by protein-tyrosine kinases and protein-tyrosine phosphatases. Strong inhibition of protein-tyrosine phosphatase activities is required to undoubtedly detect tyrosine phosphorylation. Our extremely careful usage of Na₃VO₄, a potent protein-tyrosine phosphatase inhibitor, has revealed not only the different intracellular trafficking pathways of Src-family tyrosine kinase members but also novel tyrosine phosphorylation signals in the nucleus and on mitotic spindle fibers and lysosomes. Furthermore, despite that the first identified oncogene product v-Src is generally believed to induce transformation through continuous stimulation of proliferation signaling by its strong tyrosine kinase activity, v-Src-driven transformation was found to be caused not by continuous proliferation signaling but by v-Src tyrosine kinase activity-dependent stochastic genome alterations. Here, I summarize our findings regarding novel tyrosine phosphorylation signaling in a spatiotemporal sense and highlight the significance of the roles of tyrosine phosphorylation in transcriptional regulation inside the nucleus and chromosome dynamics.

A Co-Culturing Approach Enables Discovery and Biosynthesis of a Bioactive Indole Alkaloid Metabolite

Whole-genome sequence data of the genus Streptomyces have shown a far greater chemical diversity of metabolites than what have been discovered under typical laboratory fermentation conditions. In our previous natural product discovery efforts on Streptomyces sp. MA37, a bacterium isolated from the rhizosphere soil sample in Legon, Ghana, we discovered a handful of specialised metabolites from this talented strain. However, analysis of the draft genome of MA37 suggested that most of the encoded biosynthetic gene clusters (BGCs) remained cryptic or silent, and only a small fraction of BGCs for the production of specialised metabolites were expressed when cultured in our laboratory conditions. In order to induce the expression of the seemingly silent BGCs, we have carried out a co-culture experiment by growing the MA37 strain with the Gram-negative bacterium Pseudomonas sp. in a co-culture chamber that allows co-fermentation of two microorganisms with no direct contact but allows exchange of nutrients, metabolites, and other chemical cues. This co-culture approach led to the upregulation of several metabolites that were not previously observed in the monocultures of each strain. Moreover, the co-culture induced the expression of the cryptic indole alkaloid BGC in MA37 and led to the characterization of the known indolocarbazole alkaloid, BE-13793C 1. Neither bacterium produced compound 1 when cultured alone. The structure of 1 was elucidated by Nuclear Magnetic Resonance (NMR), mass spectrometry analyses and comparison of experimental with literature data. A putative biosynthetic pathway of 1 was proposed. Furthermore, BE-13793C 1 showed strong anti-proliferative activity against HT-29 (ATCC HTB-38) cells but no toxic effect to normal lung (ATCC CCL-171) cells. To the best of our knowledge, this is the first report for the activity of 1 against HT-29. No significant antimicrobial and anti-trypanosomal activities for 1 were observed. This research provides a solid foundation for the fact that a co-culture approach paves the way for increasing the chemical diversity of strain MA37. Further characterization of other upregulated metabolites in this strain is currently ongoing in our laboratory.

Zn(OAc)2-catalyzed tandem cyclization of isocyanides, α-diazoketones, and anhydrides: a general route to polysubstituted maleimides

A zinc-catalyzed three-component reaction of isocyanides, α-diazoketones, and anhydrides has been realized as a novel and efficient method for the synthesis of polysubstituted maleimides.

GLI1 Inhibitors Identified by Target Protein Oriented Natural Products Isolation (TPO-NAPI) with Hedgehog Inhibition

This report describes the development of a target-protein-oriented natural-products-isolation (TPO-NAPI) method for Hedgehog inhibitors and the direct GLI1 inhibitor, 5'- O-methyl-3-hydroxyflemingin A (3), which inhibited hedgehog (Hh) signal transduction and diminished characteristics of cancer stem cells. Eight natural products (including three newly described products) that directly bind to GLI1 were rapidly obtained via the TPO-NAPI method developed using GLI1 protein-immobilized beads. 5'- O-Methyl-3-hydroxyflemingin A (3) inhibited Hh signaling (IC₅₀ 7.3 μM), leading to decreasing production of the Hh target proteins BCL2, PTCH1, and BMI1. 5'- O-Methyl-3-hydroxyflemingin A (3) was cytotoxic to Hh-related cancer cells. CD experiments revealed that 5'- O-methyl-3-hydroxyflemingin A (3) directly bound GLI1 ( K_d = 7.7 μM). Moreover, 5'- O-methyl-3-hydroxyflemingin A (3) diminished cancer stem cell characters of Huh7 such as sphere formation and production of the cancer stem cell marker EpCAM. These results suggest that Hh inhibitors can efficiently suppress the activity of cancer stem cells.

Palladium-catalyzed aerobic oxidative carbonylation of alkynes with amines: a general access to substituted maleimides

A catalytic oxidative carbonylation reaction was developed for the synthesis of polysubstituted maleimides from alkynes and amines with air as a green oxidant.

Synthesis of pyrazolylbisindoles over mesoporous Lewis acidic ZrTUD-1: Potential application in selective Cu(2+) colorimetric detection

A series of pyrazolylbisindole (PBI) derivatives were prepared by simple condensation of indole and pyrazole aldehyde utilizing amorphous mesoporous ZrTUD-1 having predominant Lewis acid sites. The applicability of pyrazolylbisindolyl derivate as a colorimetric chemosensor with high selectivity toward Cu(2+) over other cations were tested. Among heavy and transition metal (HTM) ions in CH3CN solution, the probe only sensed Cu(2+) detectable by naked eye. The sensor exhibited a new absorption band at 488 nm (a red shift of 206 nm from 282 nm) with a large colorimetric response and affinity to Cu(2+) over other cations tested (Al(3+), Pb(2+), Cd(2+), Mg(2+), Mn(2+), Zn(2+), K(+), Fe(2+), Ca(2+), Cu(2+) and Hg(2+)).

Naturally occurring small-molecule inhibitors of hedgehog/GLI-mediated transcription

The aberrant hedgehog (Hh)/GLI signaling pathway causes the formation and progression of a variety of tumors. To search for Hh/GLI inhibitors, we screened for naturally occurring inhibitors of the transcriptional activator GLI1 by using a cell-based assay. We identified zerumbone (1), zerumbone epoxide (2), staurosporinone (9), 6-hydroxystaurosporinone (10), arcyriaflavin C (11) and 5,6-dihydroxyarcyriaflavin A (12) as inhibitors of GLI-mediated transcription. In addition, we isolated physalins F (17) and B (18) from Physalis minima, which are also potent inhibitors. These compounds also inhibited GLI2-mediated transactivation. Semiquantitative RT-PCR and Western blotting analysis further revealed that 1, 9, 17, and 18 decreased Hh-related component expressions. We also show that inhibitors of GLI-mediated transactivation reduce the level of the antiapoptosis Bcl2 expression. Finally, these identified compounds were cytotoxic to PANC1 pancreatic cancer cells, which express Hh/GLI components. These results strongly suggest that the cytotoxicity of the compounds to PANC1 cells correlates with their inhibition of GLI-mediated transcription.

Study on Myxomycetes as a New Source of Bioactive Natural Products

The Myxomycetes (true slime molds) are an unusual group of primitive organisms that may be assigned to one of the lowest classes of eukaryotes. As their fruit bodies are very small and it is very difficult to collect much quantity, few studies have been made on the chemistry of myxomycetes. We studied spore germination experiments of hundreds of field-collected myxomycetes collected in Japan, and succeeded in laboratory culture of plasmodia of several myxomycetes in a practical scale for natural products chemistry studies. Pyrroloiminoquinones, polyene yellow pigments, and a peptide lactone were isolated from cultured plasmodia of myxomycetes, while new naphthoquinone pigments, cycloanthranilylprolines, tyrosine-kinase inhibitory bisindoles, a cytotoxic triterpenoid aldehyde lactone, a dibenzofuran glycoside, and sterols possessing an unprecedented 2,6-dioxabicyclo[2.2.2] octan-3-one ring system, were also isolated from field-collected fruit bodies of myxomycetes.

Synthesis, determination of stereochemistry, and evaluation of new bisindole alkaloids from the myxomycete Arcyria ferruginea: An approach for Wnt signal inhibitor

To determine the stereochemistry of dihydroarcyriarubin C (1), new bisindole alkaloid isolated from the myxomycete Arcyria ferruginea, cis- (2) and trans-dihydroarcyriarubin C (3) were synthesized. Comparison of their NMR characteristics allowed the trans stereochemistry of the natural product to be confirmed. Moreover, the Wnt signal inhibitory activities of 2 and 3 were compared with that of arcyriaflavin C (4), which is a natural product containing a bond between C-2 and C-2'. The cis-dihydroarcyriarubin C (2) showed moderate inhibition of Wnt signal transcription, which suggests that bisindole frameworks might be useful as small-molecule Wnt signal inhibitors.

Indolocarbazole natural products: occurrence, biosynthesis, and biological activity

The indolocarbazole family of natural products, including the biosynthetically related bisindolylmaleimides, is reviewed (with 316 references cited). The isolation of indolocarbazoles from natural sources and the biosynthesis of this class of compounds are thoroughly reviewed, including recent developments in molecular genetics, enzymology and metabolic engineering. The biological activities and underlying modes of action displayed by natural and synthetic indolocarbazoles is also presented, with an emphasis on the development of analogs that have entered clinical trials for its future use against cancer or other diseases.

Bisindole alkaloids from myxomycetes Arcyria denudata and Arcyria obvelata

A new bisindole sulfate (1) and arcyroxocin B (2) were isolated from wild fruiting bodies of Arcyria denudate, along with three known bisindoles (4-6). Dihydroarcyriacyanin A (3) was obtained from wild fruiting bodies of Arcyria obvelata, along with a known bisindole (7). The structures of these compounds were elucidated on the basis of spectroscopic data, and this is the first report of full characterizations of arcyroxocin B (2) and dihydroarcyriacyanin A (3). Compounds 2, 3, and 6 showed cytotoxicity against Jurkat cells.

New cytotoxic bisindole alkaloids with protein tyrosine kinase inhibitory activity from a myxomycete Lycogala epidendrum

Two new bisindole alkaloids, 6-hydroxystaurosporinone (1) and 5,6-dihydroxyarcyriaflavin A (2) were isolated from field-collected fruit bodies of a myxomycete Lycogala epidendrum, along with eight known bisindoles (3-10). The structures of these new compounds were determined on the basis of spectroscopic data. Compounds 1 and 2 showed cytotoxicity against HeLa, Jurkat, and vincristine resistant KB/VJ300 cells, and compound 1, particularly, inhibited protein tyrosine kinase activity.

Secondary metabolites of slime molds (myxomycetes)

The compounds reported from the slime molds (myxomycetes) species are described. Almost 100 natural compounds including their chemical structures and biological activities are described in this review article. Only metabolites with a well-defined structure are included.

Cycloanthranilylproline-Derived Constituents from a Myxomycete Fuligo candida

Cycloanthranilylproline (1) and its derivatives (2--4) were isolated from field-collected fruit-bodies of a myxomycete Fuligo candida and their structures were elucidated by spectral data. Compound 4, which was contained in the water-soluble fraction of the extract of this myxomycete, was unstable and quite susceptible to decarboxylation to yield compound 2, which was a major constituent of the EtOAc-soluble fraction of this extract.