Synthesis and Late-Stage Modification of (-)-Doliculide Derivatives Using Matteson's Homologation Approach.

(-)-Doliculide, a marine cyclodepsipeptide derived from the Japanese sea hare, Dolabella auricularia, exhibits potent cytotoxic properties, sparking interest in the field of synthetic chemistry. It is comprised of a peptide segment and a polyketide moiety, rendering it amenable to Matteson's homologation methodology. This technique facilitates the diversification of the distinctive polyketide side chain, thereby permitting the introduction of functional groups in late stages for modifications of the derived compounds and studies on structure-activity relationships.

Accraspiroketides A-B, Phenylnaphthacenoid-Derived Polyketides with Unprecedented [6 + 6+6 + 6] + [5 + 5] Spiro-Architecture.

Two novel polyketides, accraspiroketides A (1) and B (2), which feature unprecedented [6 + 6+6 + 6] + [5 + 5] spiro chemical architectures, were isolated from Streptomyces sp. MA37 ΔaccJ mutant strain. Compounds 1-2 exhibit excellent activity against Gram-positive bacteria (MIC = 1.5-6.3 µg/mL). Notably, 1 and 2 have superior activity against clinically isolated Enterococcus faecium K60-39 (MIC = 4.0 µg/mL and 4.7 µg/mL, respectively) than ampicillin (MIC = 25 µg/mL).

Evolution-Based Discovery of Polyketide Acylated Valine from a Cytochalasin-Like Gene Cluster in Simplicillium lamelliciola HDN13430.

Utilizing a gene evolution-oriented approach for gene cluster mining, a cryptic cytochalasin-like gene cluster (sla) in Antarctic-derived Simplicillium lamelliciola HDN13430 was identified. Compared with the canonical cytochalasin biosynthetic gene clusters (BGCs), the sla gene cluster lacks the key α,ß-hydrolase gene. Heterologous expression of the sla gene cluster led to the discovery of a new compound, slamysin (1), characterized by an N-acylated amino acid structure and demonstrating weak anti-Bacillus cereus activity. These findings underscore the potential of genetic evolution in uncovering novel compounds and indicating specific adaptive evolution within specialized habitats.

Colibactin-producing Escherichia coli enhance resistance to chemotherapeutic drugs by promoting epithelial to mesenchymal transition and cancer stem cell emergence.

Human colorectal cancers (CRCs) are readily colonized by colibactin-producing E. coli (CoPEC). CoPEC induces DNA double-strand breaks, DNA mutations, genomic instability, and cellular senescence. Infected cells produce a senescence-associated secretory phenotype (SASP), which is involved in the increase in tumorigenesis observed in CRC mouse models infected with CoPEC. This study investigated whether CoPEC, and the SASP derived from CoPEC-infected cells, impacted chemotherapeutic resistance. Human intestinal epithelial cells were infected with the CoPEC clinical 11G5 strain or with its isogenic mutant, which is unable to produce colibactin. Chemotherapeutic resistance was assessed in vitro and in a xenograft mouse model. Expressions of cancer stem cell (CSC) markers in infected cells were investigated. Data were validated using a CRC mouse model and human clinical samples. Both 11G5-infected cells, and uninfected cells incubated with the SASP produced by 11G5-infected cells exhibited an increased resistance to chemotherapeutic drugs in vitro and in vivo. This finding correlated with the induction of the epithelial to mesenchymal transition (EMT), which led to the emergence of cells exhibiting CSC features. They grew on ultra-low attachment plates, formed colonies in soft agar, and overexpressed several CSC markers (e.g. CD133, OCT-3/4, and NANOG). In agreement with these results, murine and human CRC biopsies colonized with CoPEC exhibited higher expression levels of OCT-3/4 and NANOG than biopsies devoid of CoPEC. Conclusion: CoPEC might aggravate CRCs by inducing the emergence of cancer stem cells that are highly resistant to chemotherapy.

Aspercitrininone A, novel antibacterial polyketide featuring unusual spiral skeleton from Aspergillus cristatus.

Aspercitrininone A (1), a novel polyketide featuring an unprecedented tetracyclic 6/6/6/5 spiral skeleton, was obtained from the rice fermentation cultures of the fungus Aspergillus cristatus together with five known compounds (2-6). Their structures were determined by HRESIMS data, 1D and 2D NMR spectroscopic analysis, and electronic circular dichroism (ECD) calculations. Aspercitrininone A was revealed as a new type of C/D cycle spiral structure and an unusual addition product of o-quinoid form citrinin with 2-methylterrefuranone. Compounds 1, 4, and 5 exhibited potent antibacterial activities with minimal inhibitory concentration (MIC) values from 13.2 to 67.3 µg/mL against four strains of human pathogenic bacteria in vitro.

New Alpiniamide-Type Polyketide with Antibiofilm Activities from the Marine-Derived Streptomyces sp. ZS-A65.

Two new alpiniamide-type polyketides, alpiniamides H-I (1-2), in addition to four recognized compounds, were discovered in Streptomyces sp. ZSA65 derived from the marine sediments. The planar structure and absolute configuration of alpiniamides H-I were elucidated using a combination of 1D, 2D NMR, HRESIMS data analysis, Mosher's method and ECD calculations. The antibiofilm and antibacterial activities against P. aeruginosa were evaluated using the microdilution method. Notably, Compound 2 exhibited strong antibiofilm property.

A Tricyclic Aromatic Polyketide Isolated from the Marine-Derived Fungus Curvularia aeria.

A novel tricyclic polyketide, curvulanone (1), was isolated from the marine-derived fungus Curvularia aeria. The structure of 1 was determined by NMR and single-crystal X-ray crystallography. 1 had a cyclopentabenzopyranone with 3-acetic acid structure that is rarely found in natural compounds. Monoamine oxidase and sirtuin 1 inhibitory test was exhibited and 1 showed their inhibitory activity.

Antibiofilm activity of marine microbial natural products: potential peptide- and polyketide-derived molecules from marine microbes toward targeting biofilm-forming pathogens.

Controlling and treating biofilm-related infections is challenging because of the widespread presence of multidrug-resistant microbes. Biofilm, a naturally occurring matrix of microbial aggregates, has developed intricate and diverse resistance mechanisms against many currently used antibiotics. This poses a significant problem, especially for human health, including clinically chronic infectious diseases. Thus, there is an urgent need to search for and develop new and more effective antibiotics. As the marine environment is recognized as a promising reservoir of new biologically active molecules with potential pharmacological properties, marine natural products, particularly those of microbial origin, have emerged as a promising source of antibiofilm agents. Marine microbes represent an untapped source of secondary metabolites with antimicrobial activity. Furthermore, marine natural products, owing to their self-defense mechanisms and adaptation to harsh conditions, encompass a wide range of chemical compounds, including peptides and polyketides, which are primarily found in microbes. These molecules can be exploited to provide novel and unique structures for developing alternative antibiotics as effective antibiofilm agents. This review focuses on the possible antibiofilm mechanism of these marine microbial molecules against biofilm-forming pathogens. It provides an overview of biofilm development, its recalcitrant mode of action, strategies for the development of antibiofilm agents, and their assessments. The review also revisits some selected peptides and polyketides from marine microbes reported between 2016 and 2023, highlighting their moderate and considerable antibiofilm activities. Moreover, their antibiofilm mechanisms, such as adhesion modulation/inhibition targeting biofilm-forming pathogens, quorum sensing intervention and inhibition, and extracellular polymeric substance disruption, are highlighted herein.

Characterization of Bacillus velezensis 32a metabolites and their synergistic bioactivity against crown gall disease.

Crown gall disease caused by Agrobacterium tumefaciens is considered to be the main bacterial threat of stone fruit plants in Mediterranean countries. In a previous study, Bacillus velezensis strain 32a was isolated from Tunisian rhizosphere soil and revealed high antagonistic potential against A. tumefaciens strains. In order to better characterize the antagonistic activity of this strain against this important plant pathogen, the production of secondary metabolites was analyzed using liquid chromatography coupled with mass spectrometry. The results revealed the production of different compounds identified as surfactins, fengycins, iturins and bacillibactin belonging to the lipopeptide group, three polyketides (macrolactins, oxydifficidin and bacillaenes), bacilysin and its chlorinated derivative; chlorotetaine. The involvement of lipopeptides in this antagonistic activity was ruled out by performing agar and broth dilution tests with pure molecules. Thus, the construction of B. velezensis 32a mutants defective in polyketides and bacilysin biosynthesis and their antagonistic activity was performed and compared to a set of derivative mutants of a comparable strain, B. velezensis GA1. The defective difficidin mutants (△dfnA and △dfnD) were unable to inhibit the growth of A. tumefaciens, indicating the high-level contribution of difficidin in the antagonism process. While the macrolactin deficient mutant (∆mlnA) slightly decreased the activity, suggesting a synergetic effect with difficidin. Remarkably, the mutant △dhbC only deficient in bacillibactin production showed significant reduction in its capacity to inhibit the growth of Agrobacterium.Taken collectively, our results showed the strong synergetic effect of difficidin and macrolactins and the significant implication of siderophore to manage crown gall disease.

Antifeedant, Antifungal Cryptic Polyketides with Six Structural Frameworks from Tea Endophyte Daldinia eschscholtzii Propelled by the Antagonistic Coculture with Phytopathogen Colletotrichum pseudomajus and Different Culture Methods.

The antagonistic coculture with tea phytopathogen Colletotrichum pseudomajus induces antifungal cryptic metabolites from isogenesis endophyte Daldinia eschscholtzii against tea phytopathogens. Sixteen new polyketides with six structural frameworks including ten cryptic ones, named coldaldols A-C (1-3), collediol (5), and daldinrins A-L (10-20 and 23), were found from the coculture of C. pseudomajus and D. eschscholtzii by different culture methods. The unique framework of compounds 11 and 12 featured a benzopyran-C7 polyketone hybrid, and compounds 13-16 were characterized by the novel benzopyran dimer. The structures were determined mainly by spectroscopic methods, including extensive one-dimensional (1D), two-dimensional (2D) NMR, high resolution electrospray ionisation mass spectroscopy (HRESIMS), ECD calculation, and single-crystal X-ray diffraction. The configuration of acyclic compounds 5 and 18 were determined by application of the universal NMR database. Most compounds showed significant antifungal activities against the tea pathogens C. pseudomajus and Alternaria sp. with MICs of 1-8 µg/mL. Compound 12 had stronger antifungal activity than that of positive drug nystatin. The ether bond at C-4 of the benzopyran derivative increased the antifungal activity. Compounds 4-9 and 11-23 showed antifeedant activities against silkworms with feeding deterrence indices of 15-100% at the concentration of 50 µg/cm2.

Diaphorin, a polyketide produced by a bacterial endosymbiont of the Asian citrus psyllid, adversely affects the in vitro gene expression with ribosomes from Escherichia coli and Bacillus subtilis.

Diaphorin is a polyketide produced by "Candidatus Profftella armatura" (Gammaproteobacteria), an obligate mutualist of an important agricultural pest, the Asian citrus psyllid Diaphorina citri (Hemiptera). Our previous study demonstrated that diaphorin, at physiological concentrations in D. citri, inhibits the growth and cell division of Bacillus subtilis (Firmicutes) but promotes the growth and metabolic activity of Escherichia coli (Gammaproteobacteria). This unique property of diaphorin may aid microbial mutualism in D. citri, potentially affecting the transmission of "Candidatus Liberibacter spp." (Alphaproteobacteria), the pathogens of the most destructive citrus disease Huanglongbing. Moreover, this property may be exploited to promote microbes' efficiency in producing industrial materials. However, the mechanism underlying this activity is unknown. Diaphorin belongs to the family of pederin-type compounds, which inhibit protein synthesis in eukaryotes by binding to eukaryotic ribosomes. Therefore, as a first step to assess diaphorin's direct influence on bacterial gene expression, this study examined the effect of diaphorin on the in vitro translation using ribosomes of B. subtilis and E. coli, quantifying the production of the green fluorescent protein. The results showed that the gene expression involving B. subtilis and E. coli ribosomes along with five millimolar diaphorin was 29.6% and 13.1%, respectively, less active than the control. This suggests that the diaphorin's adverse effects on B. subtilis are attributed to, at least partly, its inhibitory effects on gene expression. Moreover, as ingredients of the translation system were common other than ribosomes, the greater inhibitory effects observed with the B. subtilis ribosome imply that the ribosome is among the potential targets of diaphorin. On the other hand, the results also imply that diaphorin's positive effects on E. coli are due to targets other than the core machinery of transcription and translation. This study demonstrated for the first time that a pederin congener affects bacterial gene expression.

Natural Polyketides Act as Promising Antifungal Agents.

Invasive fungal infections present a significant risk to human health. The current arsenal of antifungal drugs is hindered by drug resistance, limited antifungal range, inadequate safety profiles, and low oral bioavailability. Consequently, there is an urgent imperative to develop novel antifungal medications for clinical application. This comprehensive review provides a summary of the antifungal properties and mechanisms exhibited by natural polyketides, encompassing macrolide polyethers, polyether polyketides, xanthone polyketides, linear polyketides, hybrid polyketide non-ribosomal peptides, and pyridine derivatives. Investigating natural polyketide compounds and their derivatives has demonstrated their remarkable efficacy and promising clinical application as antifungal agents.

New Cyclopiane Diterpenes and Polyketide Derivatives from Marine Sediment-Derived Fungus Penicillium antarcticum KMM 4670 and Their Biological Activities.

Two new cyclopiane diterpenes and a new cladosporin precursor, together with four known related compounds, were isolated from the marine sediment-derived fungus Penicillium antarcticum KMM 4670, which was re-identified based on phylogenetic inference from ITS, BenA, CaM, and RPB2 gene regions. The absolute stereostructures of the isolated cyclopianes were determined using modified Mosher's method and quantum chemical calculations of the ECD spectra. The isolation from the natural source of two biosynthetic precursors of cladosporin from a natural source has been reported for the first time. The antimicrobial activities of the isolated compounds against Staphylococcus aureus, Escherichia coli, and Candida albicans as well as the inhibition of staphylococcal sortase A activity were investigated. Moreover, the cytotoxicity of the compounds to mammalian cardiomyocytes H9c2 was studied. As a result, new cyclopiane diterpene 13-epi-conidiogenone F was found to be a sortase A inhibitor and a promising anti-staphylococcal agent.

Advances on structure, bioactivity, and biosynthesis of amino acid-containing trans-AT polyketides.

Trans-AT polyketides represent a class of natural compounds utilizing independent acyltransferase during their biosynthesis. They are well known for their diverse chemical structures and potent bioactivities. Trans-AT polyketides are synthesized through biosynthetic gene clusters predominantly composed of polyketide synthases (PKS), but often found in hybrid with non-ribosomal peptide synthetases (NRPS). This genetic hybridization results in the incorporation of amino acid residues into polyketide structures, significantly enhancing their structural diversity. Numerous amino acid-containing trans-AT polyketides have been identified, drawing significant attention to the mechanisms underlying amino acid incorporation and their impact on the biological activity of polyketides. Here, we discussed their origins, structures, biological activities, and the specific roles of amino acids in modulating both the bioactivity and biosynthesis of 38 trans-AT polyketides containing amino acids for the first time. This comprehensive analysis will serve as a crucial reference for the exploration of novel compounds and the improvement of structures and activities.

Induction of New Aromatic Polyketides from the Marine Actinobacterium Streptomyces griseorubiginosus through an OSMAC Approach.

Using the OSMAC (One Strain Many Compounds) approach, the actinobacterium Streptomyces griseorubiginosus, derived from an unidentified cnidarian collected from a reef near Pointe de Bellevue in Réunion Island (France), was subjected to cultivation under diverse conditions. This endeavour yielded the isolation of a repertoire of 23 secondary metabolites (1-23), wherein five compounds were unprecedented as natural products (19-23). Specifically, compounds 19 and 20 showcased novel anthrone backbones, while compound 23 displayed a distinctive tetralone structure. Additionally, compounds 21 and 22 presented an unusual naphtho [2,3-c]furan-4(9H)-one chromophore. Interestingly, the detection of all these novel compounds (19-23) was exclusively achieved when the bacterium was cultured in FA-1 liquid medium supplemented with the epigenetic modifier γ-butyrolactone. The elucidation of the structural features of the newfound compounds was accomplished through a combination of HRESIMS, 1D and 2D NMR spectroscopy, as well as QM-NMR (Quantum Mechanical-Nuclear Magnetic Resonance) methods and by comparison with existing literature. Moreover, the determination of the relative configuration of compound 23 was facilitated by employing the mix-J-DP4 computational approach.

Penidihydrocitrinins A-C: New Polyketides from the Deep-Sea-Derived Penicillium citrinum W17 and Their Anti-Inflammatory and Anti-Osteoporotic Bioactivities.

Three new polyketides (penidihydrocitrinins A-C, 1-3) and fourteen known compounds (4-17) were isolated from the deep-sea-derived Penicillium citrinum W17. Their structures were elucidated by comprehensive analyses of 1D and 2D NMR, HRESIMS, and ECD calculations. Compounds 1-17 were evaluated for their anti-inflammatory and anti-osteoporotic bioactivities. All isolates exhibited significant inhibitory effects on LPS-stimulated nitric oxide production in murine brain microglial BV-2 cells in a dose-response manner. Notably, compound 14 displayed the strongest effect with the IC50 value of 4.7 µM. Additionally, compounds 6, 7, and 8 significantly enhanced osteoblast mineralization, which was comparable to that of the positive control, purmorphamine. Furthermore, these three compounds also suppressed osteoclastogenesis in a dose-dependent manner under the concentrations of 2.5 µM, 5.0 µM, and 10 µM.

Turonicin A, an Antifungal Linear Polyene Polyketide from an Australian Streptomyces sp.

Turonicin A (1) was isolated from Streptomyces sp. MST-123921, which was recovered from soil collected on the banks of the Turon River in New South Wales, Australia. Turonicin A (1) is an amphoteric linear polyene polyketide featuring independent pentaene and tetraenone chromophores and is structurally related to linearmycins A-C (2-4). The structure of 1 was determined by detailed spectroscopic analysis and comparison to literature data. Bioinformatic analysis of the linearmycin biosynthetic gene cluster also allowed the previously unresolved absolute stereostructures of 2-4 to be elucidated. Turonicin A (1) exhibited very potent activity against the fungi Candida albicans (MIC 0.0031 µg/mL, 2.7 nM) and Saccharomyces cerevisiae (MIC 0.0008 µg/mL, 0.7 nM), moderate activity against the bacteria Bacillus subtilis (MIC 0.097 µg/mL, 85 nM) and Staphylococcus aureus (MIC 0.39 µg/mL, 340 nM), and no cytotoxicity against human fibroblasts, making it an attractive candidate for further development as a potential next-generation antibiotic scaffold.

Discovery of a Natural Hybrid Polyketide Produced by Endophytic Cladosporium sphaerospermum for Biocontrol of Phytopathogenic Fungus Botrytis cinerea.

The endophytic fungus Cladosporium sphaerospermum WBS017 exhibits broad-spectrum activity against plant pathogens, with particular effectiveness against Botrytis cinerea. Subsequently, a compound is isolated from strain WBS017 as the main active ingredient against B. cinerea using activity-guided separation and identified as hybrid polyketide (namely cladodionen, CLD) using UV, MS, NMR, etc. In vitro and in vivo antifungal activity tests demonstrate that CLD effectively inhibits the mycelial growth and spore germination, with an IC50 value of 1.13 and 0.095 mM, respectively, and exerts antifungal and fresh-keeping effects on both strawberry and tomato. Microscopy analysis reveals that the inhibitory effects of CLD on hyphae and spore germination are attributed to a decrease in structural stability of mycelia cells as well as the accumulation of reactive oxygen species (ROS). Furthermore, transcriptome analysis further indicates that spore germination is inhibited by suppressing the transcription levels of membrane or membrane-related genes, disturbing the balance of ROS metabolism, altering the primary metabolic pathways, genetic information processing, and cellular processes. Importantly, CLD demonstrates no significant toxicity on zebrafish embryos even at a concentration of 0.226 mM, indicating its potential as a safe biological-control agent. In summary, CLD would be a novel potential biological-control agent and can be considered as a promising fungicide to control B. cinerea.

Daldipyrenones A-C: Caged [6,6,6,6,6] Polyketides Derived from an Endolichenic Fungus Daldinia pyrenaica 047188.

Daldipyrenones A-C (1-3), three unprecedented caged xanthone [6,6,6,6,6] polyketides featuring a spiro-azaphilone unit, were discovered from an endolichenic fungus, Daldinia pyrenaica 047188. The structures of 1-3 were determined by using spectroscopic analysis and chemical derivatization. Daldipyrenones are likely derived by combining a chromane biosynthesis intermediate, 1-(2,6-dihydroxyphenyl)but-2-en-2-one, and a spiro-azaphilone, pestafolide A, via radical coupling or Michael addition to form a bicyclo[2.2.2]octane ring. Genome sequencing of the strain revealed two separate biosynthetic gene clusters responsible for forming two biosynthetic intermediates, suggesting a proposed biosynthetic pathway. Daldipyrenone A (1) exhibited significant antimelanogenic activity with lower EC50's than positive controls and moderate adiponectin-secretion promoting activity.

Tetracenomycin X sequesters peptidyl-tRNA during translation of QK motifs.

As antimicrobial resistance threatens our ability to treat common bacterial infections, new antibiotics with limited cross-resistance are urgently needed. In this regard, natural products that target the bacterial ribosome have the potential to be developed into potent drugs through structure-guided design, provided their mechanisms of action are well understood. Here we use inverse toeprinting coupled to next-generation sequencing to show that the aromatic polyketide tetracenomycin X primarily inhibits peptide bond formation between an incoming aminoacyl-tRNA and a terminal Gln-Lys (QK) motif in the nascent polypeptide. Using cryogenic electron microscopy, we reveal that translation inhibition at QK motifs occurs via an unusual mechanism involving sequestration of the 3' adenosine of peptidyl-tRNALys in the drug-occupied nascent polypeptide exit tunnel of the ribosome. Our study provides mechanistic insights into the mode of action of tetracenomycin X on the bacterial ribosome and suggests a path forward for the development of novel aromatic polyketide antibiotics.