An enantioselective, modular, and general route to the cytochalasins: synthesis of L-696,474 and cytochalasin B

Synthesis and migrastatic activity of cytochalasin analogues lacking a macrocyclic moiety

Cytochalasans are known as inhibitors of actin polymerization and for their cytotoxic and migrastatic activity. In this study, we synthesized a series of cytochalasin derivatives that lack a macrocyclic moiety, a structural element traditionally considered essential for their biological activity. We focused on substituting the macrocycle with simple aryl-containing sidechains, and we have also synthesized compounds with different substitution patterns on the cytochalasin core. The cytochalasin analogues were screened for their migrastatic and cytotoxic activity. Compound 24 which shares the substitution pattern with natural cytochalasins B and D exhibited not only significant in vitro migrastatic activity towards BLM cells but also demonstrated inhibition of actin polymerization, with no cytotoxic effect observed at 50 μM concentration. Our results demonstrate that even compounds lacking the macrocyclic moiety can exhibit biological activities, albeit less pronounced than those of natural cytochalasins. However, our findings emphasize the pivotal role of substituting the core structure in switching between migrastatic activity and cytotoxicity. These findings hold significant promise for further development of easily accessible cytochalasan analogues as novel migrastatic agents.

A Review on Bioactive Compounds from Marine-Derived Chaetomium Species

Filamentous marine fungi have proven to be a plentiful source of new natural products. Chaetomium, a widely distributed fungal genus in the marine environment, has gained much interest within the scientific community. In the last 20 years, many potential secondary metabolites have been detected from marine-derived Chaetomium. In this review, we attempt to provide a comprehensive summary of the natural products produced by marine-derived Chaetomium species. A total of 122 secondary metabolites that were described from 2001 to 2021 are covered. The structural diversity of the compounds, along with details of the sources and relevant biological properties are also provided, while the relationships between structures and their bioactivities are discussed. It is our expectation that this review will be of benefit to drug development and innovation.

Secondary Metabolites from Marine-Derived Fungi and Actinobacteria as Potential Sources of Novel Colorectal Cancer Drugs

Colorectal cancer is one of the most common cancers diagnosed in the world. Chemotheraphy is one of the most common methods used for the pharmacological treatment of this cancer patients. Nevertheless, the adverse effect of chemotherapy is not optimized for improving the quality of life of people who are older, who are the most vulnerable subpopulation. This review presents recent updates regarding secondary metabolites derived from marine fungi and actinobacteria as novel alternatives for cytotoxic agents against colorectal cancer cell lines HCT116, HT29, HCT15, RKO, Caco-2, and SW480. The observed marine-derived fungi were from the species Aspergillus sp., Penicillium sp., Neosartorya sp., Dichotomomyces sp., Paradendryphiella sp., and Westerdykella sp. Additionally, Streptomyces sp. and Nocardiopsis sp. are actinobacteria discussed in this study. Seventy one compounds reviewed in this study were grouped on the basis of their chemical structures. Indole alkaloids and diketopiperazines made up most compounds with higher potencies when compared with other groups. The potency of indole alkaloids and diketopiperazines was most probably due to halogen-based functional groups and sulfide groups, respectively.

Berberine bridge enzyme-like oxidase-catalysed double bond isomerization acts as the pathway switch in cytochalasin synthesis

Cytochalasans (CYTs), as well as their polycyclic (pcCYTs) and polymerized (meCYTs) derivatives, constitute one of the largest families of fungal polyketide-nonribosomal peptide (PK-NRP) hybrid natural products. However, the mechanism of chemical conversion from mono-CYTs (moCYTs) to both pcCYTs and meCYTs remains unknown. Here, we show the first successful example of the reconstitution of the CYT core backbone as well as the whole pathway in a heterologous host. Importantly, we also describe the berberine bridge enzyme (BBE)-like oxidase AspoA, which uses Glu538 as a general acid biocatalyst to catalyse an unusual protonation-driven double bond isomerization reaction and acts as a switch to alter the native (for moCYTs) and nonenzymatic (for pcCYTs and meCYTs) pathways to synthesize aspochalasin family compounds. Our results present an unprecedented function of BBE-like enzymes and highly suggest that the isolated pcCYTs and meCYTs are most likely artificially derived products.

Putative Anticancer Compounds from Plant-Derived Endophytic Fungi: A Review

Endophytic fungi are microorganisms that exist almost ubiquitously inside the various tissues of living plants where they act as an important reservoir of diverse bioactive compounds. Recently, endophytic fungi have drawn tremendous attention from researchers; their isolation, culture, purification, and characterization have revealed the presence of around 200 important and diverse compounds including anticancer agents, antibiotics, antifungals, antivirals, immunosuppressants, and antimycotics. Many of these anticancer compounds, such as paclitaxel, camptothecin, vinblastine, vincristine, podophyllotoxin, and their derivatives, are currently being used clinically for the treatment of various cancers (e.g., ovarian, breast, prostate, lung cancers, and leukemias). By increasing the yield of specific compounds with genetic engineering and other biotechnologies, endophytic fungi could be a promising, prolific source of anticancer drugs. In the future, compounds derived from endophytic fungi could increase treatment availability and cost effectiveness. This comprehensive review includes the putative anticancer compounds from plant-derived endophytic fungi discovered from 1990 to 2020 with their source endophytic fungi and host plants as well as their antitumor activity against various cell lines.

Stereocontrolled Synthesis of Enantiopure cis-Fused Octahydroisoindolones via Chiral Oxazoloisoindolone Lactams

Kinetically controlled cyclocondensation of stereoisomeric and ring-chain tautomeric mixture of (±)-hydroxylactone 1 and 0.5 equiv of (R)-phenylglycinol provided tricyclic oxazoloisoindolone lactam (3R,5aS,9aR,9bS)-2a, a versatile intermediate for further stereocontrolled transformations to access enantiopure cis-fused octahydroisoindolones. An extension of this methodology was successfully applied to the synthesis of the 5,6-dihydroxy derivative (3aR,5R,6S,7aS)-17.

Biomimetic Synthesis of Natural Products: A Journey To Learn, To Mimic, and To Be Better

Total synthesis of natural products has been one of the most exciting and dynamic areas in synthetic organic chemistry. Nowadays, the major challenge in this field is not whether a given target of interest can be synthesized but how to make it with commendable efficiency and practicality. To meet this grand challenge, a wise way is to learn from Mother Nature who is recognized for her superb capability of forging complicated and sometimes beyond-imagination molecules in her own delicate way. Indeed, since Sir Robert Robinson published his groundbreaking synthesis of tropinone in 1917, biomimetic synthesis of natural products, a process of imitating nature's way to make molecules, has evolved into one of the most popular research directions in organic synthesis.Our group has been engaging in biomimetic synthesis of natural products in the past decade. During this time, we have come to realize that the successful implementation of a biomimetic synthesis entails the orchestrated combination of bioinspiration and rational design. On the one hand, we prefer to utilize some elegant bioinspired transformations (e.g., Diels-Alder dimerization, 6π-electrocyclization, and [2 + 2]-photocycloaddition) as the key steps of our synthesis, which enable rapid construction of the core skeletons of the chased targets with high efficiency; on the other hand, various powerful reactions (e.g., dyotropic rearrangement of β-lactone, tandem aldol condensation/Grob fragmentation reaction, and organocatalytic asymmetric Mukaiyama-Michael addition) are rationally designed by us, which allow for facile access to the requisite precursors for attempting biomimetic transformations. In some cases, the proposed biomimetic transformation may fail to give a satisfactory result in practice, and thus we opt to develop creative tactics (e.g., hydrogen atom transfer-triggered vinyl cyclobutane ring opening/oxygen insertion/cyclization cascade) that can meet the challenge. Guided by this synthesis concept, we have achieved the total syntheses of multiple families of natural products of great importance in both chemistry and biology, representatives of which include xanthanolides, cytochalasans, and plakortin-type polyketides. Of note, most of these targets could be accessed in a concise, efficient, and scalable manner, which paves the way for further exploration of their biological functions and medicinal potential. Moreover, owing to their biomimetic nature, our syntheses provide valuable information for deciphering the underlying biosynthetic pathways of the chased targets, which could not be attained by other synthetic modes.

Synthesis of a Biomimetic Tetracyclic Precursor of Aspochalasins and Formal Synthesis of Trichoderone A

Aspochalasins are leucine-derived cytochalasins. Their complexity is associated with a high degree of biosynthetic oxidation, herein inspiring a two-phase strategy in total synthesis. We thus describe the synthesis of a putative biomimetic tetracyclic intermediate. The constructive steps are an intramolecular Diels-Alder reaction to install the isoindolone core of cytochalasins, whose branched precursor was obtained from a stereoselective Ireland-Claisen rearrangement performed from a highly unsaturated substrate. This also constitutes a formal synthesis of trichoderone A.

Bioinspired Network Analysis Enabled Divergent Syntheses and Structure Revision of Pentacyclic Cytochalasans

We accomplished the divergent total syntheses of ten pentacyclic cytochalasans (aspergillin PZ, trichodermone, trichoderones, flavipesines, and flavichalasines) from a common precursor aspochalasin D and revised the structures of trichoderone B, spicochalasin A, flavichalasine C, aspergilluchalasin based on structure network analysis of the cytochalasans biosynthetic pathways and DFT calculations. The key steps of the syntheses include transannular alkene/epoxyalkene and carbonyl-ene cyclizations to establish the C/D ring of pentacyclic aspochalasans. Our bioinspired approach to these pentacyclic cytochalasans validate the proposed biosynthetic speculation from a chemical view and provide a platform for the synthesis of more than 400 valuable cytochalasans bearing different macrocycles and amino-acid residues.

Applications of the Horner–Wadsworth–Emmons Olefination in Modern Natural Product Synthesis

The Horner–Wadsworth–Emmons (HWE) reaction is one of the most reliable olefination reaction and can be broadly applied in organic chemistry and natural product synthesis with excellent selectivity. Within the last few years HWE reaction conditions have been optimized and new reagents developed to overcome challenges in the total syntheses of natural products. This review highlights the application of HWE olefinations in total syntheses of structurally different natural products covering 2015 to 2020. Applied HWE reagents and reactions conditions are highlighted to support future synthetic approaches and serve as guideline to find the best HWE conditions for the most complicated natural products.

1 Introduction and Historical Background

2 Applications of HWE

2.1 Cyclization by HWE Reactions

2.2.1 Formation of Medium- to Larger-Sized Rings

2.2.2 Formation of Small- to Medium-Sized Rings

2.3 Synthesis of α,β-Unsaturated Carbonyl Groups

2.4 Synthesis of Substituted C=C Bonds

2.5 Late-Stage Modifications by HWE Reactions

2.6 HWE Reactions on Solid Supports

2.7 Synthesis of Poly-Conjugated C=C Bonds

2.8 HWE-Mediated Coupling of Larger Building Blocks

2.9 Miscellaneous

3 Summary and Outlook

Progress in the Chemistry of Cytochalasans

Cytochalasans are a group of fungal-derived natural products characterized by a perhydro-isoindolone core fused with a macrocyclic ring, and they exhibit a high structural diversity and a broad spectrum of bioactivities. Cytochalasans have attracted significant attention from the chemical and pharmacological communities and have been reviewed previously from various perspectives in recent years. However, continued interest in the cytochalasans and the number of laboratory investigations on these compounds are both growing rapidly. This contribution provides a general overview of the isolation, structural determination, biological activities, biosynthesis, and total synthesis of cytochalasans. In total, 477 cytochalasans are covered, including "merocytochalasans" that arise by the dimerization or polymerization of one or more cytochalasan molecules with one or more other natural product units. This contribution provides a comprehensive treatment of the cytochalasans, and it is hoped that it may stimulate further work on these interesting natural products.

Natural Polyketides Isolated from the Endophytic Fungus Phomopsis sp. CAM212 with a Semisynthetic Derivative Downregulating the ERK/IκBα Signaling Pathways

Three previously undescribed natural products, phomopsinin A - C (1:  - 3: ), together with three known compounds, namely, cis-hydroxymellein (4: ), phomoxanthone A (5: ) and cytochalasin L-696,474 (6: ), were isolated from the solid culture of Phomopsis sp. CAM212, an endophytic fungus obtained from Garcinia xanthochymus. Their structures were determined on the basis of spectroscopic data, including IR, NMR, and MS. The absolute configurations of 1: and 2: were assigned by comparing their experimental and calculated ECD spectra. Acetylation of compound 1: yielded 1A: , a new natural product derivative that was tested together with other isolated compounds on lipopolysaccharide-stimulated RAW 264.7 cells. Cytochalasin L-696,474 (6: ) was found to significantly inhibit nitric oxide production, but was highly cytotoxic to the treated cells, whereas compound 1: slightly inhibited nitric oxide production, which was not significantly different compared to lipopolysaccharide-treated cells. Remarkably, the acetylated derivative of 1: , compound 1A: , significantly inhibited nitric oxide production with an IC₅₀ value of 14.8 µM and no cytotoxic effect on treated cells, thereby showing the importance of the acetyl group in the anti-inflammatory activity of 1A: . The study of the mechanism of action revealed that 1A: decreases the expression of inducible nitric oxide synthase, cyclooxygenase 2, and proinflammatory cytokine IL-6 without an effect on IL-1β expression. Moreover, it was found that 1A: exerts its anti-inflammatory activity in lipopolysaccharide-stimulated RAW 264.7 macrophage cells by downregulating the activation of ERK1/2 and by preventing the translocation of nuclear factor κB. Thus, derivatives of phomopsinin A (1: ), such as compound 1A: , could provide new anti-inflammatory leads.

Intracellular G-actin targeting of peripheral sensory neurons by the multifunctional engineered protein C2C confers relief from inflammatory pain

The engineered multifunctional protein C2C was tested for control of sensory neuron activity by targeted G-actin modification. C2C consists of the heptameric oligomer, C2II-CI, and the monomeric ribosylase, C2I. C2C treatment of sensory neurons and SH-SY5Y cells in vitro remodeled actin and reduced calcium influx in a reversible manner. C2C prepared using fluorescently labeled C2I showed selective in vitro C2I delivery to primary sensory neurons but not motor neurons. Delivery was dependent on presence of both C2C subunits and blocked by receptor competition. Immunohistochemistry of mice treated subcutaneously with C2C showed colocalization of subunit C2I with CGRP-positive sensory neurons and fibers but not with ChAT-positive motor neurons and fibers. The significance of sensory neuron targeting was pursued subsequently by testing C2C activity in the formalin inflammatory mouse pain model. Subcutaneous C2C administration reduced pain-like behaviors by 90% relative to untreated controls 6 h post treatment and similarly to the opioid buprenorphene. C2C effects were dose dependent, equally potent in female and male animals and did not change gross motor function. One dose was effective in 2 h and lasted 1 week. Administration of C2I without C2II-CI did not reduce pain-like behavior indicating its intracellular delivery was required for behavioral effect.

Antiproliferative and Enzyme Docking Analysis of Engleromycin from Engleromyces goetzei

Engleromyces goetzei P. Henn. (E. goetzei) has been widely used as a traditional herb for many years in Kenya due to its diverse biological effects. Although engleromycin was first isolated from E. goetzei in 1980, its pharmacological activity is still unknown. In this study, engleromycin from E. goetzei was identified by spectroscopic analyses, and subsequently examined for its antiproliferative activity using human cancer cell lines of SGC-7901, HT-29, HeLa and A549. As a result, it was revealed that engleromycin strongly inhibited the growth of SGC-7901, HT-29, HeLa and A549 cells with IC₅₀ values at 26.77 ± 1.69 µM, 7.73 ± 0.18 µM, 7.00 ± 0.12 µM and 3.14 ± 0.03 µM, respectively. The results of topoisomerase II (Top II) inhibition assay in vitro implied that engleromycin might be a Top II inhibitor. Further insights into the potential mechanism of antiproliferative activity displayed that engleromycin could dock into the binding pockets of Top II, like the clinical inhibitor doxorubicin, and then inhibit the biological activity of Top II. Taken together, our findings suggest that engleromycin has an anticancer potential, and may serve as a leading compound for the development of antitumor agents.

Biomimetic Synthesis of (+)-Aspergillin PZ

The cytochalasans are a large family of polyketide natural products with potent bioactivities. Amongst them, the aspochalasins show particularly intricate and fascinating structures. To gain insight into their structural diversity and innate reactivity, we have developed a rapid synthesis of aspochalasin D, the central member of the family. It proceeded in 13 steps starting from divinyl carbinol and utilized a high pressure Diels-Alder reaction that features high regio- and stereoselectivity. So far, our work has culminated in a biomimetic synthesis of aspergillin PZ, an intricate pentacyclic aspochalasan.

Evaluation of Tumor Regulatory Genes and Apoptotic Pathways in The Cytotoxic Effect of Cytochalasin H on Malignant Human Glioma Cell Line (U87MG)

Objective

The aim of current study was to provide a proof-of-concept on the mechanism of PLAU and PCDH10 gene expressions and caspases-3, -8, and -9 activities in the apoptotic pathway after treatment of malignant human glioma cell line (U87MG) with cytochalasin H.

Materials and Methods

In the present experimental study, we have examined cytochalasin H cytotoxic activities as a new therapeutic agent on U87MG cells in vitro for the first time. The cells were cultured and treated with 10^-5-10^-9 M of cytochalasin H for 24, 48 and 72 hours. The assessment of cell viability was carried out by (3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazoliumbromide (MTT) assay at 578 nm. The data are the average of three independent tests. mRNA expression changes of PLAU and PCDH10 were then evaluated by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). The fluorometric of caspases-3, -8, and -9 activities were carried out. The morphology changes in the U87MG cells were observed by fluorescence microscope.

Results

MTT assay showed that cytochalasin H (10^-5 M) inhibited the U87MG cancer cells proliferation after 48 hours. Analysis of qRT-PCR showed that the PLAU expression was significantly decreased in comparison with the control (P<0.05). The expression of PCDH10 also showed a significant increase when compared to the control (P<0.001). Fluorescence microscope indicated morphological changes due to apoptosis in U87MG cancer cells, after treatment with cytochalasin H (10^-5 M, 48 hours). The fluorometric evaluation of caspase-3, -8, and -9 activities showed no significant difference between the caspases and the control group.

Conclusion

This study shows the effect of caspase-independent pathways of the programmed cell death on the U87MG cancer cell line under cytochalasin H treatment. Further studies are needed to explore the exact mechanism.

The potential of compounds isolated from Xylaria spp. as antifungal agents against anthracnose

Anthracnose is a crop disease usually caused by fungi in the genus Colletotrichum or Gloeosporium. These are considered one of the main pathogens, causing significant economic losses, such as in peppers and guarana. The current forms of control include the use of resistant cultivars, sanitary pruning and fungicides. However, even with the use of some methods of controlling these cultures, the crops are not free of anthracnose. Additionally, excessive application of fungicides increases the resistance of pathogens to agrochemicals and cause harm to human health and the environment. In order to find natural antifungal agents against guarana anthracnose, endophytic fungi were isolated from Amazon guarana. The compounds piliformic acid and cytochalasin D were isolated by chromatographic techniques from two Xylaria spp., guided by assays with Colletotrichum gloeosporioides. The isolated compounds were identified by spectrometric techniques, as NMR and mass spectrometry. This is the first report that piliformic acid and cytochalasin D have antifungal activity against C. gloeosporioides with MIC 2.92 and 2.46 μmol mL⁻¹ respectively. Captan and difenoconazole were included as positive controls (MIC 16.63 and 0.02 μmol mL⁻¹, respectively). Thus, Xylaria species presented a biotechnological potential and production of different active compounds which might be promising against anthracnose disease.

Synthesis of C14–C21 acid fragments of cytochalasin Z8via anti-selective aldol condensation and B-alkyl Suzuki–Miyaura cross-coupling

An efficient synthesis of the C14–C21 acid fragment of cytochalasin Z₈ was accomplished in 10 steps with 14% overall yield.

Cytoglobosins H and I, New Antiproliferative Cytochalasans from Deep-Sea-Derived Fungus Chaetomium globosum

Cytoglobosins H (1) and I (2), together with seven known cytochalasan alkaloids (3–9), were isolated from the deep-sea-derived fungus Chaetomium globosum. The structures of new compounds 1 and 2 were elucidated by extensive 1D and 2D NMR and mass spectroscopic data. All the compounds were evaluated for their antiproliferative activities against MDA-MB-231 human breast cancer cells, LNCaP human prostate cancer cells, and B16F10 mouse melanoma cells. Compound 6 showed significant antiproliferative activity against LNCaP and B16F10 cell lines with IC₅₀ values of 0.62 and 2.78 μM, respectively. Further testing confirmed that compound 6 inhibited the growth of LNCaP cells by inducing apoptosis.

Mechanisms underlying effect of the mycotoxin cytochalasin B on induction of cytotoxicity, modulation of cell cycle, Ca2+ homeostasis and ROS production in human breast cells

Cytochalasin B, a cell-permeable mycotoxin isolated from the fungus Phoma spp., shows a wide range of biological effects, among which its potent antitumor activity has raised great interests in different models. However, the cytotoxic activity of cytochalasin B and its underlying mechanisms have not been elucidated in breast cells. This study examined the effect of cytochalasin B on MCF 10A human breast epithelial cells and ZR-75-1 human breast cancer cells. Cytochalasin B (10-20μM) concentration-dependently induced cytotoxicity, cell cycle arrest, and [Ca²⁺]_i rises in ZR-75-1 cells but not in MCF 10A cells. In ZR-75-1 cells, cytochalasin B triggered G2/M phase arrest through the modulation of CDK1, cyclin B1, p53, p27 and p21 expressions. The Ca²⁺ signal response induced by cytochalasin B was reduced by removing extracellular Ca²⁺ and was inhibited by the store-operated Ca²⁺ channel blocker 2-APB and SKF96365. In Ca²⁺-free medium, cytochalasin B induced Ca²⁺ release through thapsigargin-sensitive endoplasmic reticulum stores. Moreover, cytochalasin B increased H₂O₂ levels but reduced GSH levels. The apoptotic effects evoked by cytochalasin B were partially inhibited by prechelating cytosolic Ca²⁺ with BAPTA-AM and the antioxidant NAC. Together, in ZR-75-1 cells but not in MCF 10A cells, cytochalasin B activated Ca²⁺-associated mitochondrial apoptotic pathways that involved G2/M phase arrest and ROS signaling. Furthermore, cytochalasin B induced [Ca²⁺]_i rises by releasing Ca²⁺ from the endoplasmic reticulum and causing Ca²⁺ influx through 2-APB or SKF96365-sensitive store-operated Ca²⁺ entry. Our findings provide new insights into the possible application of cytochalasin B in human breast cancer therapy.

Coordinated and Iterative Enzyme Catalysis in Fungal Polyketide Biosynthesis

Fungal polyketides are natural products with great chemical diversity that exhibit a wide range of biological activity. This chemical diversity stems from specialized enzymes encoded in the biosynthetic gene cluster responsible for the natural product biosynthesis. Fungal polyketide synthases (PKS) are the megasynthases that produce the carbon scaffolds for the molecules. Subsequent downstream tailoring enzymes such as oxygenases will then further modify the organic framework. In fungi, many of these enzymes have been found to work iteratively-catalyzing multiple reactions on different sites of the substrate. This perspective will analyze several examples of fungal polyketides that are assembled from a scaffold-building iterative PKS and an accompanying iterative tailoring oxygenase. In these examples, the PKS product is designed for downstream iterative oxygenations to generate additional complexity. Together, these iterative enzymes orchestrate the efficient biosynthesis of elaborate natural products such as lovastatin, chaetoglobosin A, cytochalasin E, and aurovertin E.

Trienamine catalyzed asymmetric synthesis and biological investigation of a cytochalasin B-inspired compound collection

Due to their enhanced metabolic needs many cancers need a sufficient supply of glucose, and novel inhibitors of glucose import are in high demand. Cytochalasin B (CB) is a potent natural glucose import inhibitor which also impairs the actin cytoskeleton leading to undesired toxicity. With a view to identifying selective glucose import inhibitors we have developed an enantioselective trienamine catalyzed synthesis of a CB-inspired compound collection. Biological analysis revealed that indeed actin impairment can be distinguished from glucose import inhibition and led to the identification of the first selective glucose import inhibitor based on the basic structural architecture of cytochalasin B.

Using cytochalasins to improve current chemotherapeutic approaches

Although the amount of progress cancer therapy has made in recent years is commendable, considerable limitations still remain. Most agents preferentially target rapidly proliferating cells, thereby destroying tumorigenic growths. Unfortunately, there are many labile cells in the patient that are also rapidly dividing, ultimately perpetuating significant side effects, including immunosuppression. Cytochalasins are microfilament-directed agents most commonly known for their use in basic research to understand cytoskeletal mechanisms. However, such agents also exhibit profound anticancer activity, as indicated by numerous in vitro and in vivo studies. Cytochalasins appear to preferentially damage malignant cells, as shown by their minimal effects on normal epithelial and immune cells. Further, cytochalasins influence the end stages of mitosis, suggesting that such agents could be combined with microtubule-directed agents to elicit a profound synergistic effect on malignant cells. Therefore, it is likely that cytochalasins could be used to supplement current chemotherapeutic measures to improve efficacy rates, as well as decrease the prevalence of drug resistance in the clinical setting.

Miniaturized Cultivation of Microbiota for Antimalarial Drug Discovery

The ongoing search for effective antiplasmodial agents remains essential in the fight against malaria worldwide. Emerging parasitic drug resistance places an urgent need to explore chemotherapies with novel structures and mechanisms of action. Natural products have historically provided effective antimalarial drug scaffolds. In an effort to search nature's chemical potential for antiplasmodial agents, unconventionally sourced organisms coupled with innovative cultivation techniques were utilized. Approximately 60,000 niche microbes from various habitats (slow-growing terrestrial fungi, Antarctic microbes, and mangrove endophytes) were cultivated on a small-scale, extracted, and used in high-throughput screening to determine antimalarial activity. About 1% of crude extracts were considered active and 6% partially active (≥ 67% inhibition at 5 and 50 μg/mL, respectively). Active extracts (685) were cultivated on a large-scale, fractionated, and screened for both antimalarial activity and cytotoxicity. High interest fractions (397) with an IC50 < 1.11 μg/mL were identified and subjected to chromatographic separation for compound characterization and dereplication. Identifying active compounds with nanomolar antimalarial activity coupled with a selectivity index tenfold higher was accomplished with two of the 52 compounds isolated. This microscale, high-throughput screening project for antiplasmodial agents is discussed in the context of current natural product drug discovery efforts.

The chemistry of isoindole natural products

This review highlights the chemical and biological aspects of natural products containing an oxidized or reduced isoindole skeleton. This motif is found in its intact or modified form in indolocarbazoles, macrocyclic polyketides (cytochalasan alkaloids), the aporhoeadane alkaloids, meroterpenoids from Stachybotrys species and anthraquinone-type alkaloids. Concerning their biological activity, molecular structure and synthesis, we have limited this review to the most inspiring examples. Within different congeners, we have selected a few members and discussed the synthetic routes in more detail. The putative biosynthetic pathways of the presented isoindole alkaloids are described as well.

Iridium-catalyzed allylation of chiral β-stereogenic alcohols: bypassing discrete formation of epimerizable aldehydes

The cyclometalated π-allyliridium 3,4-dinitro-C,O-benzoate complex modified by (R)- or (S)-Cl,MeO-BIPHEP promotes the transfer hydrogenative coupling of allyl acetate to β-stereogenic alcohols with good to excellent levels of catalyst-directed diastereoselectivity to furnish homoallylic alcohols. Remote electronic effects of the C,O-benzoate of the catalyst play a critical role in suppressing epimerization of the transient α-stereogenic aldehyde.

An immunodominant membrane protein (Imp) of 'Candidatus Phytoplasma mali' binds to plant actin

The phytopathogenic, cell-wall-less phytoplasmas exhibit a dual life cycle: they multiply in the phloem of their host plant and in the body of their insect vector. Their membrane proteins are in direct contact with both hosts and are supposed to play a crucial role in the phytoplasma spread within the plant as well as by the insect vector. Three types of nonhomologous but highly abundant and immunodominant membrane proteins (IDP) have been identified within the phytoplasmas: Amp, IdpA, and Imp. Although recent results indicate that Amp is involved in vector specificity interacting with insect proteins such as actin, little is known about the interaction of IDP with the plant. We could demonstrate that transiently expressed Imp of 'Candidatus Phytoplasma mali' as well as the Imp without transmembrane domain (Imp▴Tm) bind with plant actins in vivo. Moreover, in vitro co-sediment and binding assays showed that Escherichia coli-expressed recombinant Imp▴Tm-His binds to both G- and F-actins isolated from rabbit muscle. Transgenic plants expressing Imp- or Imp▴Tm-green fluorescent protein did not exhibit any remarkable change of phenotype compared with the wild-type plant. These results indicate that Imp specifically binds to plant actin and a role of Imp-actin binding in phytoplasma motility is hypothesized.

Depth-sensing analysis of cytoskeleton organization based on AFM data

Atomic force microscopy is a common technique used to determine the elastic properties of living cells. It furnishes the relative Young's modulus, which is typically determined for indentation depths within the range 300-500 nm. Here, we present the results of depth-sensing analysis of the mechanical properties of living fibroblasts measured under physiological conditions. Distributions of the Young's moduli were obtained for all studied cells and for every cell. The results show that for small indentation depths, histograms of the relative values of the Young's modulus described the regions rich in the network of actin filaments. For large indentation depths, the overall stiffness of a whole cell was obtained, which was accompanied by a decrease of the modulus value. In conclusion, the results enable us to describe the non-homogeneity of the cell cytoskeleton, particularly, its contribution linked to actin filaments located beneath the cell membrane. Preliminary results showing a potential application to improve the detection of cancerous cells, have been presented for melanoma cell lines.

Inhibition of LuxS by S-ribosylhomocysteine analogues containing a [4-aza]ribose ring

LuxS (S-ribosylhomocysteinase) catalyzes the cleavage of the thioether linkage of S-ribosylhomocysteine (SRH) to produce homocysteine and 4,5-dihydroxy-2,3-pentanedione (DPD), the precursor to a small signaling molecule that mediates interspecies bacterial communication called autoinducer 2 (AI-2). Inhibitors of LuxS should interfere with bacterial interspecies communication and potentially provide a novel class of antibacterial agents. In this work, SRH analogues containing substitution of a nitrogen atom for the endocyclic oxygen as well as various deoxyriboses were synthesized and evaluated for LuxS inhibition. Two of the [4-aza]SRH analogues showed modest competitive inhibition (K(I) ∼40 μM), while most of the others were inactive. One compound that contains a hemiaminal moiety exhibited time-dependent inhibition, consistent with enzyme-catalyzed ring opening and conversion into a more potent species (K(I)(∗)=3.5 μM). The structure-activity relationship of the designed inhibitors highlights the importance of both the homocysteine and ribose moieties for high-affinity binding to LuxS active site.

Substituted lactam and cyclic azahemiacetals modulate Pseudomonas aeruginosa quorum sensing

Quorum sensing (QS) is a population-dependent signaling process bacteria use to control multiple processes including virulence that is critical for establishing infection. The most common QS signaling molecule used by Gram-negative bacteria are acylhomoserine lactones. The development of non-native acylhomoserine lactone (AHL) ligands has emerged as a promising new strategy to inhibit QS in Gram-negative bacteria. In this work, we have synthesized a set of optically pure γ-lactams and their reduced cyclic azahemiacetal analogues, bearing the additional alkylthiomethyl substituent, and evaluated their effect on the AHL-dependent Pseudomonas aeruginosa las and rhl QS pathways. The concentration of these ligands and the simple structural modification such as the length of the alkylthio substituent has notable effect on activity. The γ-lactam derivatives with nonylthio or dodecylthio chains acted as inhibitors of las signaling with moderate potency. The cyclic azahemiacetal with shorter propylthio or hexylthio substituent was found to strongly inhibit both las and rhl signaling at higher concentrations while the propylthio analogue strongly stimulated the las QS system at lower concentrations.