Tunicamycins from Marine-Derived Streptomyces bacillaris Inhibit MurNAc-Pentapeptide Translocase in Staphylococcus aureus.

Four tunicamycin class compounds, tunicamycin VII (1), tunicamycin VIII (2), corynetoxin U17a (3), and tunicamycin IX (4), were isolated from the culture broth of the marine-derived actinomycete Streptomyces sp. MBTG32. The strain was identified using the 16S rDNA sequencing technique, and the isolated strain was closely related to Streptomyces bacillaris. The structures of the isolated compounds were elucidated based on spectroscopic data and comparisons with previously reported NMR data. Compounds 1-4 showed potent antibacterial activities against Gram-positive bacteria, especially Staphylococcus aureus, with MIC values of 0.13-0.25 µg/mL. Through a recombinant enzyme assay and overexpression analysis, we found that the isolated compounds exerted potent inhibitory effects on S. aureus MurNAc-pentapeptide translocase (MraY), with IC50 values of 0.08-0.21 µg/mL. The present results support that the underlying mechanism of action of tunicamycins isolated from marine-derived Streptomyces sp. is also associated with the inhibition of MraY enzyme activity in S. aureus.

Marinobazzanan, a Bazzanane-Type Sesquiterpenoid, Suppresses the Cell Motility and Tumorigenesis in Cancer Cells.

Marinobazzanan (1), a new bazzanane-type sesquiterpenoid, was isolated from a marine-derived fungus belonging to the genus Acremonium. The chemical structure of 1 was elucidated using NMR and mass spectroscopic data, while the relative configurations were established through the analysis of NOESY data. The absolute configurations of 1 were determined by the modified Mosher's method as well as vibrational circular dichroism (VCD) spectra calculation and it was determined as 6R, 7R, 9R, and 10R. It was found that compound 1 was not cytotoxic to human cancer cells, including A549 (lung cancer), AGS (gastric cancer), and Caco-2 (colorectal cancer) below the concentration of 25 µM. However, compound 1 was shown to significantly decrease cancer-cell migration and invasion and soft-agar colony-formation ability at concentrations ranging from 1 to 5 µM by downregulating the expression level of KITENIN and upregulating the expression level of KAI1. Compound 1 suppressed ß-catenin-mediated TOPFLASH activity and its downstream targets in AGS, A549, and Caco-2 and slightly suppressed the Notch signal pathway in three cancer cells. Furthermore, 1 also reduced the number of metastatic nodules in an intraperitoneal xenograft mouse model.

Nyuzenamide C, an Antiangiogenic Epoxy Cinnamic Acid-Containing Bicyclic Peptide from a Riverine Streptomyces sp.

A new nonribosomal peptide, nyuzenamide C (1), was discovered from riverine sediment-derived Streptomyces sp. DM14. Comprehensive analysis of the spectroscopic data of nyuzenamide C (1) revealed that 1 has a bicyclic backbone composed of six common amino acid residues (Asn, Leu, Pro, Gly, Val, and Thr) and four nonproteinogenic amino acid units, including hydroxyglycine, ß-hydroxyphenylalanine, p-hydroxyphenylglycine, and 3,ß-dihydroxytyrosine, along with 1,2-epoxypropyl cinnamic acid. The absolute configuration of 1 was proposed by J-based configuration analysis, the advanced Marfey's method, quantum mechanics-based DP4 calculations, and bioinformatic analysis of its nonribosomal peptide synthetase biosynthetic gene cluster. Nyuzenamide C (1) displayed antiangiogenic activity in human umbilical vein endothelial cells and induced quinone reductase in murine Hepa-1c1c7 cells.

Gwanakosides A and B, 6-Deoxy-α-l-talopyranose-Bearing Aromatic Metabolites from a Streptomyces sp. and Coculture with Pandoraea sp.

Single-strain cultivation of a mountain soil-derived Streptomyces sp. GA02 and its coculture with Pandoraea sp. GA02N produced two aromatic products, gwanakosides A and B (1 and 2, respectively). Their spectroscopic analysis revealed that 1 is a new dichlorinated naphthalene glycoside and 2 is a pentacyclic aromatic glycoside. The assignment of the two chlorine atoms in 1 was confirmed by the analysis of its band-selective CLIP-HSQMBC spectrum. The sugars in the gwanakosides were identified as 6-deoxy-α-l-talopyranose based on 1H-1H coupling constants, Rotating frame Overhauser enhancement spectroscopy (ROESY) NMR correlations, and chemical derivatization followed by spectroscopic and chromatographic analyses. The absolute configuration of 2, whose production was enhanced approximately 100-fold in coculture, was proposed based on a quantum mechanics-based chemical shift analysis method, DP4 calculations, and the chemically determined configuration of 6-deoxy-α-l-talopyranose. Gwanakoside A displayed inhibitory activity against pathogenic bacteria, including Staphylococcus aureus (MIC = 8 µg/mL) and Mycobacterium tuberculosis (MIC50 = 15 µg/mL), and antiproliferative activity against several human cancer cell lines (IC50 = 5.6-19.4 µM).

Inhibitory Effects of Nitrogenous Metabolites from a Marine-Derived Streptomyces bacillaris on Isocitrate Lyase of Candida albicans.

Two nitrogenous metabolites, bacillimide (1) and bacillapyrrole (2), were isolated from the culture broth of the marine-derived actinomycete Streptomyces bacillaris. Based on the results of combined spectroscopic and chemical analyses, the structure of bacillimide (1) was determined to be a new cyclopenta[c]pyrrole-1,3-dione bearing a methylsulfide group, while the previously reported bacillapyrrole (2) was fully characterized for the first time as a pyrrole-carboxamide bearing an alkyl sulfoxide side chain. Bacillimide (1) and bacillapyrrole (2) exerted moderate (IC50 = 44.24 µM) and weak (IC50 = 190.45 µM) inhibitory effects on Candida albicans isocitrate lyase, respectively. Based on the growth phenotype using icl-deletion mutants and icl expression analyses, we determined that bacillimide (1) inhibits the transcriptional level of icl in C. albicans under C2-carbon-utilizing conditions.

Discovery and Photoisomerization of New Pyrrolosesquiterpenoids Glaciapyrroles D and E, from Deep-Sea Sediment Streptomyces sp.

Two new pyrrolosesquiterpenes, glaciapyrroles D (1) and E (2) were discovered along with the previously reported glaciapyrrole A (3) from Streptomyces sp. GGS53 strain isolated from deep-sea sediment. This study elucidated the planar structures of 1 and 2 using nuclear magnetic resonance (NMR), mass spectrometry (MS), ultraviolet (UV), and infrared (IR) spectroscopic data. The absolute configurations of the glaciapyrroles were determined by Mosher's method, circular dichroism spectroscopy, and X-ray crystallography. Under 366 nm UV irradiation, the glaciapyrroles were systematically converted to the corresponding photoglaciapyrroles (4-6) via photoisomerization, resulting in the diversification of the glaciapyrrole family compounds. The transformation of the glaciapyrrole Z to E isomers occurred in a 1:1 ratio, based on virtual validation of the photoisomerization of these olefinic compounds by 1H-NMR spectroscopy and liquid chromatography/mass spectrometry (LC/MS) analysis. Finally, when encapsulated in poly(lactic-co-glycolic acid) nanoparticles, glaciapyrrole E and photoglaciapyrrole E displayed significant inhibitory activity against influenza A virus. This is the first report of antiviral effects from glaciapyrrole family compounds, whose biological functions have only been subjected to limited studies so far.

The Alleviating Effect of Lagerstroemia indica Flower Extract on Stretch Marks through Regulation of Mast Cells.

Striae distensae (SD) or stretch marks are common linear scars of atrophic skin with disintegrating extracellular matrix (ECM) structures. Although fibroblasts contribute to the construction of ECM structure in SD, some studies have reported that mast cell degranulation causes the disruption of ECM in early SD lesions. Lagerstroemia indica flower (LIF) has traditionally been used in India as a diuretic. However, little is known about the effect and molecular action of Lagerstroemia indica flower extract (LIFE) on alleviating SD. This study evaluated the effects of LIFE on mast cell degranulation and the synthesis of ECM components in fibroblasts. LIFE inhibits the adhesion of rat basophilic leukemia (RBL) cells, RBL-2H3 on fibronectin (FN) and the expression of integrin, a receptor for FN, thereby reducing focal adhesion kinase (FAK) phosphorylation. In addition, LIFE attenuated the allergen-induced granules and cytokine interleukin 3 (IL-3) through the adhesion with FN. Moreover, the conditioned medium (CM) of activated mast cells decreases the synthesis of ECM components, and LIFE restores the abnormal expressions induced by activated mast cells. These results demonstrate that LIFE suppresses FN-induced mast cell activation and promotes the synthesis of ECM components in fibroblast, which indicates that LIFE may be a useful cosmetic agent for SD treatment.

Azetidine-Bearing Non-Ribosomal Peptides, Bonnevillamides D and E, Isolated from a Carrion Beetle-Associated Actinomycete.

Two new nonribosomal peptides, bonnevillamides D and E (1 and 2), have been discovered in Streptomyces sp. UTZ13 isolated from the carrion beetle, Nicrophorus concolor. Combinational analysis of the UV, MS, and NMR spectroscopic data revealed that their planar structures were comprised of dichlorinated linear peptides containing nonproteinogenic amino acid residues, such as 4-methylazetidinecarboxylic acid and 4-O-acetyl-5-methylproline. The configurations of bonnevillamides D and E (1 and 2) were determined based on ROESY correlations, the advanced Marfey's method, phenylglycine methyl ester derivatization, molecular modeling, and circular dichroism spectroscopy. The nonribosomal peptide synthetase biosynthetic pathway of bonnevillamides D and E has been proposed using bioinformatic analysis of the whole-genome sequence data of Streptomyces sp. UTZ13. Their biological activity toward the aggregation of amyloid-ß, which is one of the key pathogenic proteins in Alzheimer's disease, was evaluated using a thioflavin T assay and gel electrophoresis. Bonnevillamides D and E reversed the fibril formation by inducing the monomerization of amyloid-ß aggregates.

Synthesis and biological activity of selenopsammaplin A and its analogues as antitumor agents with DOT1L inhibitory activity.

Disruptor of telomeric silencing-1 like (DOT1L) is a histone H3 methyltransferase which specifically catalyzes the methylation of histone H3 lysine-79 residue. Recent findings demonstrate that DOT1L is abnormally overexpressed and the upregulated DOT1L evokes the proliferation and metastasis in human breast cancer cells. Therefore, the DOT1L inhibitor is considered a promising strategy to treat breast cancers. Non-nucleoside DOT1L inhibitors, selenopsammaplin A and its analogues, were firstly reported in the present study. Selenopsammaplin A was newly designed and synthesized with 25% overall yield in 8 steps from 3-bromo-4-hydroxybenzaldahyde, and thirteen analogues of selenopsammaplin A were prepared for structure-activity relationship studies of their cytotoxicity against cancer cells and inhibitory activity toward DOT1L for antitumor potential. All synthetic selenopsammaplin A analogues exhibited the higher cytotoxicity compared to psammaplin A with up to 6 - 60 times depending on cancer cells, and most analogues showed significant inhibitory activities against DOT1L. Among the prepared analogues, the phenyl analogue (10) possessed the most potent activity with both cytotoxicity and inhibition of DOT1L. Compound 10 also exhibited the antitumor and antimetastatic activity in an orthotopic mouse metastasis model implanted with MDA-MB-231 human breast cancer cells. These biological findings suggest that analogue 10 is a promising candidate for development as a cancer chemotherapeutic agent in breast cancers.

Antitumor Activity of Asperphenin B by Induction of Apoptosis and Regulation of Glyceraldehyde-3-phosphate Dehydrogenase in Human Colorectal Cancer Cells.

Colorectal cancer (CRC) is a common and intractable malignancy with a high mortality risk. Conventional chemotherapeutics are effective for patients with early stage CRC, but the majority of deaths of CRC patients are linked to acquired drug resistance or metastasis occurrence. Asperphenin B (1), a lipopeptidyl benzophenone isolated from a marine-derived Aspergillus sp. fungus, reportedly possesses antiproliferative activity against cancer cells. However, its antitumor activity and the underlying molecular mechanisms remain unexplored. In this study, 1 induced G2/M phase cell cycle arrest and subsequent apoptotic cell death and inhibited tumor growth in a xenograft model. The 1-induced G2/M phase arrest was associated with the regulation of checkpoint proteins, including Chk1/2 and Cdc25c. The 1-induced apoptosis was correlated with an upregulation of p53 and cleaved caspases and a downregulation of survivin. Further experiments revealed that 1-mediated suppression of migration and invasion of metastatic HCT116 cells was partially associated with the downregulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression. The antimetastatic potential of 1 was also confirmed by E-cadherin upregulation and N-cadherin and Snail downregulation, which were in turn associated with the GAPDH regulation. These findings highlight the potential use of 1 as a novel candidate for treating metastatic CRC with the modulation of GAPDH function.

Structures and Biosynthetic Pathway of Coprisamides C and D, 2-Alkenylcinnamic Acid-Containing Peptides from the Gut Bacterium of the Carrion Beetle Silpha perforata.

Coprisamides C and D (1 and 2) were isolated from a gut bacterium, Micromonospora sp. UTJ3, of the carrion beetle Silpha perforata. Based on the combined analysis of UV, MS, and NMR spectral data, the planar structures of 1 and 2 were elucidated to be unreported derivatives of coprisamides A and B, cyclic depsipeptides bearing a 2-alkenylcinnamic acid unit and the unusual amino acids ß-methylaspartic acid and 2,3-diaminopropanoic acid. The absolute configuration of 1 was determined using the advanced Marfey's method, phenylglycine methyl ester derivatization, and J-based configuration analysis. The biosynthetic gene clusters for the coprisamides were investigated based on genomic data from coprisamide-producing strains Micromonospora sp. UTJ3 and Streptomyces sp. SNU533. Coprisamide C (1) was active against the Mycobacterium tuberculosis mc2 6230 strain.

Tropolone-Bearing Sesquiterpenes from Juniperus chinensis: Structures, Photochemistry and Bioactivity.

The tropolone-bearing sesquiterpenes juniperone A (1) and norjuniperone A (2) were isolated from the folk medicinal plant Juniperus chinensis, and their structures were determined by a combination of spectroscopic and crystallographic methods. Photojuniperones A1 (3) and A2 (4), bearing bicyclo[3,2,0]heptadienones derived from tropolone, were photochemically produced and structurally identified by spectroscopic methods. Predicted by the machine learning-based assay, 1 significantly inhibited the action of tyrosinase. The new compounds also inhibited lipid accumulation and enhanced the extracellular glycerol excretion.

Ochraceopetalin, a Mixed-Biogenetic Salt of Polyketide and Amino Acid Origins from a Marine-Derived Aspergillus ochraceopetaliformis Fungus.

Ochraceopetalin (1), a mixed-biogenetic salt compound and its component 2 were isolated from the culture broths of a marine-derived fungus, Aspergillus ochraceopetaliformis. Based on combined spectroscopic and chemical analyses, the structure of 1 was determined to be a sulfonated diphenylether-aminol-amino acid ester guanidinium salt of an unprecedented structural class, while 2 was determined to be the corresponding sulfonated diphenylether. Ochraceopetaguanidine (3), the other guanidine-bearing aminol amino acid ester component, was also prepared and structurally elucidated. Compound 1 exhibited significant cytotoxicity against K562 and A549 cells.

Inhibitory Effects of Epipolythiodioxopiperazine Fungal Metabolites on Isocitrate Lyase in the Glyoxylate Cycle of Candida albicans.

Four epipolythiodioxopiperazine fungal metabolites (1-4) isolated from the sponge-derived Aspergillus quadrilineatus FJJ093 were evaluated for their capacity to inhibit isocitrate lyase (ICL) in the glyoxylate cycle of Candida albicans. The structures of these compounds were elucidated using spectroscopic techniques and comparisons with previously reported data. We found secoemestrin C (1) (an epitetrathiodioxopiperazine derivative) to be a potent ICL inhibitor, with an inhibitory concentration of 4.77 ± 0.08 µM. Phenotypic analyses of ICL-deletion mutants via growth assays with acetate as the sole carbon source demonstrated that secoemestrin C (1) inhibited C. albicans ICL. Semi-quantitative reverse-transcription polymerase chain reaction analyses indicated that secoemestrin C (1) inhibits ICL mRNA expression in C. albicans under C2-assimilating conditions.

Svalbamides A and B, Pyrrolidinone-Bearing Lipodipeptides from Arctic Paenibacillus sp.

Two new secondary metabolites, svalbamides A (1) and B (2), were isolated from a culture extract of Paenibacillus sp. SVB7 that was isolated from surface sediment from a core (HH17-1085) taken in the Svalbard archipelago in the Arctic Ocean. The combinational analysis of HR-MS and NMR spectroscopic data revealed the structures of 1 and 2 as being lipopeptides bearing 3-amino-2-pyrrolidinone, d-valine, and 3-hydroxy-8-methyldecanoic acid. The absolute configurations of the amino acid residues in svalbamides A and B were determined using the advanced Marfey's method, in which the hydrolysates of 1 and 2 were derivatized with l- and d- forms of 1-fluoro-2,4-dinitrophenyl-5-alanine amide (FDAA). The absolute configurations of 1 and 2 were completely assigned by deducing the stereochemistry of 3-hydroxy-8-methyldecanoic acid based on DP4 calculations. Svalbamides A and B induced quinone reductase activity in Hepa1c1c7 murine hepatoma cells, indicating that they represent chemotypes with a potential for functioning as chemopreventive agents.

Structure Revision and the Biosynthetic Pathway of Tripartilactam.

Tripartilactam (1) is a natural macrocyclic lactam originally reported to have a unique [18,8,4]-tricyclic framework. However, the validity of this structure has been contested since niizalactam C (2), bearing a [18,6,6]-tricyclic skeleton, was proposed as an alternative structure in 2015. In the present study, a comprehensive reinvestigation of NMR spectroscopic data and a 13C-13C COSY NMR experiment identified direct 13C-13C coupling, thus leading to the unequivocal revision of the structure of tripartilactam as niizalactam C (2). In addition, whole-genome sequencing analysis of the tripartilactam-producing bacterial strain and subsequent bioinformatics and mutagenesis analyses identified its biosynthetic pathway, which probably utilizes one of the type I polyketide synthase (PKS) modules iteratively during its biosynthesis and exhibits spontaneous [4+2] cycloaddition from the precursor compound, sceliphrolactam, in the post-PKS process.

Sortase A-Inhibitory Coumarins from the Folk Medicinal Plant Poncirus trifoliata.

Thirteen coumarins (1-13), including five new compounds (1-5), were isolated from the folk medicinal plant Poncirus trifoliata. Combined spectroscopic analyses revealed that coumarins 1-4 are bis-isoprenylated coumarins with diverse oxidation patterns, while 5 is an enantiomeric di-isoprenylated coumarin. The absolute configurations of the stereogenic centers in the isoprenyl chains were assigned through MTPA and MPA methods, and those of the known compounds triphasiol (6) and ponciol (7) were also assigned using similar methods. These coumarins inhibited significantly Staphylococcus aureus-derived sortase A (SrtA), a transpeptidase responsible for anchoring surface proteins to the peptidoglycan cell wall in Gram-positive bacteria. The present results obtained indicated that the bioactivity and underlying mechanism of action of these coumarins are associated with the inhibition of SrtA-mediated S. aureus adhesion to eukaryotic cell matrix proteins including fibrinogen and fibronectin, thus potentially serving as SrtA inhibitors.

Isocadiolides A-H: Polybrominated Aromatics from a Synoicum sp. Ascidian.

Isocadiolides A-H (1-8) and cadiolide N (9), new polybrominated aromatic compounds, were isolated from a Korean Synoicum sp. ascidian. On the basis of the results of extensive spectroscopic analyses, these compounds possessed tris-bromohydroxyphenyl moieties as a common structural motif, while their cores varied [cyclopentenedione (1-5), dihydrofuran (6 and 7), pyranone (8), and furanone (9)], reflecting different extents of rearrangement and oxidation. Several of these compounds exhibited weak antibacterial activities and moderate abilities to inhibit the microbial enzymes sortase A and isocitrate lyase.

Formicolides A and B, Antioxidative and Antiangiogenic 20-Membered Macrolides from a Wood Ant Gut Bacterium.

Two new macrolides, formicolides A (1) and B (2), were isolated from Streptomyces sp. BA01, a gut bacterial strain of the wood ant (Formica yessensis). Their 20-membered macrocyclic lactone structures were established using NMR and mass spectrometric data. The relative configurations of the formicolides were determined by J-based configuration analysis utilizing ROESY, HETLOC, and HECADE NMR spectroscopic data. Genomic and bioinformatics analysis of the bacterial strain enabled us to identify the type-I polyketide synthase pathway employing a trans-acyltransferase system. The absolute configurations of 1 and 2 are proposed based on detailed analysis of the sequences of the ketoreductases in the modular gene cluster and statistical comparative analysis of the experimental NMR chemical shifts and quantum mechanical calculations. Formicolides A and B (1 and 2) induced quinone reductase activity in murine Hepa-1c1c7 cells and antiangiogenic activity by suppression of tube formation in human umbilical vein endothelial cells.

Absolute Configuration and Antibiotic Activity of Piceamycin.

The cultivation of a Streptomyces sp. SD53 strain isolated from the gut of the silkworm Bombyx mori produced two macrolactam natural products, piceamycin (1) and bombyxamycin C (2). The planar structures of 1 and 2 were identified by a combination of NMR, MS, and UV spectroscopic analyses. The absolute configurations were assigned based on chemical and chromatographic methods as well as ECD calculations. A new chromatography-based experimental method for determining the configurations of stereogenic centers ß to nitrogen atoms in macrolactams was established and successfully applied in this report. These compounds exhibited significant bioactivities against the silkworm entomopathogen Bacillus thuringiensis and various human pathogens as well as human cancer cell lines. In particular, piceamycin potently inhibited Salmonella enterica and Proteus hauseri with MIC values of 0.083 µg/mL and 0.025 µg/mL, respectively. The biosynthetic pathway involved in the formation of the cyclopentenone moiety in piceamycin is discussed.