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The antimicrobial activity of tumescenamide C against the scab-forming S. scabiei NBRC13768 was confirmed with a potent IC 50 value (1.5 μg/mL). Three tumescenamide C-resistant S. scabiei strains were generated to compare their gene variants. All three resistant strains contained nonsynonymous variants in genes related to cellobiose/cellotriose transport system components; cebF1, cebF2, and cebG2, which are responsible for the production of the phytotoxin thaxtomin A. Decrease in thaxtomin A production and the virulence of the three resistant strains were revealed by the LC/MS analysis and necrosis assay, respectively. Although the nonsynonymous variants were insufficient for identifying the molecular target of tumescenamide C, the cell wall component wall teichoic acid (WTA) was observed to bind significantly to tumescenamide C. Moreover, changes in the WTA contents were detected in the tumescenamide C-resistant strains. These results imply that tumescenamide C targets the cell wall system to exert antimicrobial effects on S. scabiei., (© 2024. The Author(s), under exclusive licence to the Japan Antibiotics Research Association.)

The development of targeted chemotherapeutic agents against colorectal cancer (CRC), one of the most common cancers with a high mortality rate, is in a constant need. Nannocystins are a family of myxobacterial secondary metabolites featuring a 21-membered depsipeptide ring. The in vitro anti-CRC activity of natural and synthetic nannocystins was well documented, but little is known about their in vivo efficacy and if positive, the underlying mechanism of action. In this study we synthesized a nitroaromatic nannocystin through improved preparation of a key fragment, and characterized its in vitro activity and in vivo efficacy against CRC. We first described the total synthesis of compounds 2-4 featuring Heck macrocyclization to forge their 21-membered macrocycle. In a panel of 7 cancer cell lines from different tissues, compound 4 inhibited the cell viability with IC values of 1-6 nM. In particular, compound 4 (1, 2, 4 nM) inhibited the proliferation of CRC cell lines (HCT8, HCT116 and LoVo) in both concentration and time dependent manners. Furthermore, compound 4 concentration-dependently inhibited the colony formation and migration of CRC cell lines. Moreover, compound 4 induced cell cycle arrest at sub-G 1 phase, apoptosis and cellular senescence in CRC cell lines. In three patient-derived CRC organoids, compound 4 inhibited the PDO with IC values of 3.68, 28.93 and 11.81 nM, respectively. In a patient-derived xenograft mouse model, injection of compound 4 (4, 8 mg/kg, i.p.) every other day for 12 times dose-dependently inhibited the tumor growth without significant change in body weight. We conducted RNA-sequencing, molecular docking and cellular thermal shift assay to elucidate the anti-CRC mechanisms of compound 4, and revealed that it exerted its anti-CRC effect at least in part by targeting AKT1., (© 2024. The Author(s), under exclusive licence to Shanghai Institute of Materia Medica, Chinese Academy of Sciences and Chinese Pharmacological Society.)

Antibiotics that use novel mechanisms are needed to combat antimicrobial resistance 1-3 . Teixobactin 4 represents a new class of antibiotics with a unique chemical scaffold and lack of detectable resistance. Teixobactin targets lipid II, a precursor of peptidoglycan 5 . Here we unravel the mechanism of teixobactin at the atomic level using a combination of solid-state NMR, microscopy, in vivo assays and molecular dynamics simulations. The unique enduracididine C-terminal headgroup of teixobactin specifically binds to the pyrophosphate-sugar moiety of lipid II, whereas the N terminus coordinates the pyrophosphate of another lipid II molecule. This configuration favours the formation of a β-sheet of teixobactins bound to the target, creating a supramolecular fibrillar structure. Specific binding to the conserved pyrophosphate-sugar moiety accounts for the lack of resistance to teixobactin 4 . The supramolecular structure compromises membrane integrity. Atomic force microscopy and molecular dynamics simulations show that the supramolecular structure displaces phospholipids, thinning the membrane. The long hydrophobic tails of lipid II concentrated within the supramolecular structure apparently contribute to membrane disruption. Teixobactin hijacks lipid II to help destroy the membrane. Known membrane-acting antibiotics also damage human cells, producing undesirable side effects. Teixobactin damages only membranes that contain lipid II, which is absent in eukaryotes, elegantly resolving the toxicity problem. The two-pronged action against cell wall synthesis and cytoplasmic membrane produces a highly effective compound targeting the bacterial cell envelope. Structural knowledge of the mechanism of teixobactin will enable the rational design of improved drug candidates., (© 2022. The Author(s).)

Pithohirolide (1), a new depsipeptide, was isolated from an ascomycetous fungus Pithomyces chartarum TAMA 581. The planar structure of 1 was elucidated on the basis of NMR and MS analyses and the absolute configuration was determined by the advanced Marfey's analysis, chiral-phase HPLC analysis, and synthesis of degradation product. Compound 1 possesses a cyclic structure comprising (S)-2-hydroxy-3-phenylpropanoic acid, (S)-3-hydroxy-3-phenylpropanoic acid, (S)-2-hydroxyisovaleric acid, and N-methyl-L-alanine, connected via three ester and one amide linkages. Compound 1 exhibited antimicrobial activity against Staphylococcus aureus and Saccharomyces cerevisiae at MIC 3.1 μg ml -1 .

Multi-drug resistance is posing major challenges in suppressing the population of pests. Many herbivores develop resistance, causing a prolonged survival after exposure to a previously effective pesticide. Consequently, resistant pests reduce the yield of agricultural production, causing significant economic losses and reducing food security. Therefore, overpowering resistance acquisition of crop pests is a must. The ATP binding cassette transporters (ABC transporters) are considered as the main participants to the pesticide efflux and their neutralization will greatly contribute to potentiate failed treatments. Real-Time PCR analysis of 19 ABC transporter genes belonging to the ABCB, ABCC, ABCG, and ABCH revealed that a broad range of efflux pumps is activated in response to the exposure to pesticides. In this study, we used beauvericin (BEA), a known ABC transporters modulator, to resensitize different strains of Tetranychus urticae after artificial selection for resistance to cyflumetofen, bifenazate, and abamectin. Our results showed that the combinatorial treatment of pesticide (manufacturer's recommended doses) + BEA (sublethal doses: 0.15 mg/L) significantly suppressed the resistant populations of T. urticae when compared to single-drug treatments. Moreover, after selective pressure for 40 generations, the LC 50 values were significantly reduced from 36.5, 44.7, and 94.5 (pesticide) to 8.3, 12.5, and 23.4 (pesticide + BEA) for cyflumetofen, bifenazate, and abamectin, respectively. While the downstream targets for BEA are still elusive, we demonstrated hereby that it synergizes with sub-lethal doses of different pesticides and increases their effect by inhibiting ABC transporters. This is the first report to document such combinatorial activity of BEA against higher invertebrates paving the way for its usage in treating refractory cases of resistance to pesticides. Moreover, we demonstrated, for the first time, using in silico techniques, the higher affinity of BEA to ABC transformers subfamilies when compared to xenobiotics; thus, elucidating the pathway of the mycotoxin.

In this study, screening by LC-MS and cytotoxicity-guided isolation led to the identification of ulleungamide C (1), a previously unknown pipecolic acid-rich branched cyclic depsipeptide, from a soil actinobacterium Streptomyces sp. KCB13F003. The structure of 1 was determined by interpretation of spectroscopic and spectrometric data from 1D and 2D NMR and HRESIMS experiments. Antiproliferative assays using mammalian cancerous cells revealed that 1 inhibits the proliferation of HL-60 human promyelocytic leukemia cells. Cell cycle analysis showed an increased accumulation of cells in the G0/G1 phase after treatment with 1. Results of immunoblotting assays revealed that 1 reduced the expression levels of cyclin-dependent kinase 4 (CDK4), CDK6, retinoblastoma protein (Rb), and phosphorylated Rb, whereas it induced cyclin-dependent kinase inhibitor 1B (p27/Kip1) expression.

Pharmacological modulation of class I histone deacetylases (HDAC) has been evaluated as a therapeutic strategy for pulmonary hypertension (PH) in experimental models of PH. However, information of their expression, regulation and transcriptional targets in human PH and the therapeutic potential of isoform-selective enzyme modulation are lacking. Comprehensive analysis of expression and regulation of class I HDACs (HDAC1, HDAC2, HDAC3 and HDAC8) was performed in cardiopulmonary tissues and adventitial fibroblasts isolated from pulmonary arteries (PAAF) of idiopathic pulmonary arterial hypertension (IPAH) patients and healthy donors. Cellular functions and transcriptional targets of HDAC enzymes were investigated. Therapeutic effects of pan-HDAC (Vorinostat), class-selective (VPA) and isoform-selective (CAY10398, Romidepsin, PCI34051) HDAC inhibitors were evaluated ex vivo (IPAH-PAAF, IPAH-PASMC) and in vivo (rat chronic hypoxia-induced PH and zebrafish angiogenesis). Our screening identifies dysregulation of class I HDAC isoforms in IPAH. Particularly, HDAC1 and HDAC8 were consistently increased in IPAH-PAs and IPAH-PAAFs, whereas HDAC2 and HDAC8 showed predominant localization with ACTA2-expressing cells in extensively remodeled IPAH-PAs. Hypoxia not only significantly modulated protein levels of deacetylase (HDAC8), but also significantly caused dynamic changes in the global histone lysine acetylation levels (H3K4ac, H3K9/K14ac and H3K27ac). Importantly, isoform-specific RNA-interference revealed that HDAC isoforms regulate distinct subset of transcriptome in IPAH-PAAFs. Reduced transcript levels of KLF2 in IPAH-PAAFs was augmented by HDAC8 siRNA and HDAC inhibitors, which also attenuated IPAH-associated hyperproliferation and apoptosis-resistance ex vivo, and mitigated chronic hypoxia-induced established PH in vivo, at variable degree. Class I HDAC isoforms are significantly dysregulated in human PAH. Isoform-selective HDAC inhibition is a viable approach to circumvent off-target effects.

Two novel depsipeptides xenematides F and G (1, 2), were isolated from entomopathogenic Xenorhabdus budapestensis SN84 along with a known compound xenematide B. The structures of the two new molecules were elucidated using NMR, MS and Marfey's method. The xenematide G (2) contains α-aminoheptanoic acid, a non-protein amino acid that is rarely found in secondary metabolites from entomopathogenic bacteria. Xenematides F and G were tested for antibacterial activity. Xenematide G (2) exhibited moderate antibacterial activity.

Actin binding compounds are widely used tools in cell biology. We compare the biological and biochemical effects of miuraenamide A and jasplakinolide, a structurally related prototypic actin stabilizer. Though both compounds have similar effects on cytoskeletal morphology and proliferation, they affect migration and transcription in a distinctive manner, as shown by a transcriptome approach in endothelial cells. In vitro, miuraenamide A acts as an actin nucleating, F-actin polymerizing and stabilizing compound, just like described for jasplakinolide. However, in contrast to jasplakinolide, miuraenamide A competes with cofilin, but not gelsolin or Arp2/3 for binding to F-actin. We propose a binding mode of miuraenamide A, explaining both its similarities and its differences to jasplakinolide. Molecular dynamics simulations suggest that the bromophenol group of miurenamide A interacts with residues Tyr133, Tyr143, and Phe352 of actin. This shifts the D-loop of the neighboring actin, creating tighter packing of the monomers, and occluding the binding site of cofilin. Since relatively small changes in the molecular structure give rise to this selectivity, actin binding compounds surprisingly are promising scaffolds for creating actin binders with specific functionality instead of just "stabilizers".

Melanogenesis is the process of production of melanin pigments that are responsible for the colors of skin, eye, and hair and provide protection from ultraviolet radiation. However, excessive levels of melanin formation cause hyperpigmentation disorders such as freckles, melasma, and age spots. Liver X receptors (LXR) are nuclear oxysterol receptors belonging to the family of ligand-activated transcription factors and physiological regulators of lipid and cholesterol metabolism. In the skin, activation of LXRs stimulates differentiation of keratinocytes and augments lipid synthesis in sebocytes. However, the function of LXRs in melanogenesis has not been clearly elucidated. In addition, although beauvericin, a well-known mycotoxin primarily isolated from several fungi, has various biological properties, its involvement in melanogenesis has not been reported. Therefore, in this study, we examined the effects of beauvericin on melanogenesis and its molecular mechanisms. Beauvericin decreased melanin content and tyrosinase activity without any cytotoxicity. Beauvericin also reduced protein levels of MITF, tyrosinase, TRP1, and TRP2. In addition, beauvericin suppressed cAMP-PKA-CREB signaling and upregulated expression of LXR-α, resulting in the suppression of p38 MAPK. Our results indicate that beauvericin attenuates melanogenesis by regulating both cAMP/PKA/CREB and LXR-α/p38 MAPK pathways, consequently leading to a reduction of melanin levels.

The Chromobacterium sp. Panama bacterium has in vivo and in vitro anti-Plasmodium properties. To assess the nature of the Chromobacterium-produced anti-Plasmodium factors, chemical partition was conducted by bioassay-guided fractionation where different fractions were assayed for activity against asexual stages of P. falciparum. The isolated compounds were further partitioned by reversed-phase FPLC followed by size-exclusion chromatography; high resolution UPLC and ESI/MS data were then collected and revealed that the most active fraction contained a cyclic depsipeptide, which was identified as romidepsin. A pure sample of this FDA-approved HDAC inhibitor allowed us to independently verify this finding, and establish that romidepsin also has potent effect against mosquito stages of the parasite's life cycle. Genomic comparisons between C. sp. Panama and multiple species within the Chromobacterium genus further demonstrated a correlation between presence of the gene cluster responsible for romidepsin production and effective antiplasmodial activity. A romidepsin-null Chromobacterium spp. mutant loses its anti-Plasmodium properties by losing the ability to inhibit P. falciparum HDAC activity, and romidepsin is active against resistant parasites to commonly deployed antimalarials. This independent mode of action substantiates exploring a chromobacteria-based approach for malaria transmission-blocking.

Current antiretroviral therapy (ART) for HIV/AIDS slows disease progression by reducing viral loads and increasing CD4 counts. Yet ART is not curative due to the persistence of CD4+ T-cell proviral reservoirs that chronically resupply active virus. Elimination of these reservoirs through the administration of synergistic combinations of latency reversing agents (LRAs), such as histone deacetylase (HDAC) inhibitors and protein kinase C (PKC) modulators, provides a promising strategy to reduce if not eradicate the viral reservoir. Here, we demonstrate that largazole and its analogues are isoform-targeted histone deacetylase inhibitors and potent LRAs. Significantly, these isoform-targeted HDAC inhibitors synergize with PKC modulators, namely bryostatin-1 analogues (bryologs). Implementation of this unprecedented LRA combination induces HIV-1 reactivation to unparalleled levels and avoids global T-cell activation within resting CD4+ T-cells.

Beauveriolide III (BeauIII) inhibited sterol O-acyltransferases 1 and 2 (SOAT1 and SOAT2), which are endoplasmic reticulum (ER) membrane proteins, in an enzyme-based assay, and selectively inhibited SOAT1 in a cell-based assay using SOAT1-/SOAT2-CHO cells. This discrepancy in SOAT inhibition by BeauIII was investigated. In the enzyme-based assay, BeauIII inhibited SOAT1 and SOAT2 to a similar extent using microsomes prepared from cells disrupted under the strongest sonication condition. In semi-intact SOAT1-/SOAT2-CHO cells prepared by a treatment with digitonin (plasma membrane permeabilized), BeauIII selectively inhibited SOAT1 (IC 50 ; 5.0 µM (SOAT1) vs >90 µM (SOAT2)), while in those treated with saponin (plasma membrane and ER membrane permeabilized), BeauIII inhibited SOAT1 (IC 50 , 1.8 µM) and SOAT2 (5.9 µM). SOAT1-selective inhibition by BeauIII was reproduced in intact ER fractions prepared from SOAT1/SOAT2-CHO cells. A Western blotting analysis revealed that biotin-labeled beauveriolide bound to the SOAT1 protein prepared from SOAT1-CHO cells. We concluded that BeauIII binds to a putative active site responsible for SOAT1 that is located on the cytosolic side of the ER, while BeauIII is not accessible to the corresponding active site for SOAT2 located on the luminal side.

Cereulide and isocereulides A-G are biosynthesized as emetic toxins by Bacillus cereus via a non-ribosomal peptide synthetase (NRPS) called Ces. Although a thiotemplate mechanisms involving cyclo-trimerization of ready-made D-O-Leu-D-Ala-L-O-Val-L-Val via a thioesterase (TE) domain is proposed for cereulide biosynthesis, the exact mechanism is far from being understood. UPLC-TOF MS analysis of B. cereus strains in combination with (13)C-labeling experiments now revealed tetra-, octa-, and dodecapeptides of a different sequence, namely (L-O-Val-L-Val-D-O-Leu-D-Ala)1-3, as intermediates of cereulide biosynthesis. Surprisingly, also di-, hexa-, and decadepsipeptides were identified which, together with the structures of the previously reported isocereulides E, F, and G, do not correlate to the currently proposed mechanism for cereulide biosynthesis and violate the canonical NRPS biosynthetic logic. UPLC-TOF MS metabolite analysis and bioinformatic gene cluster analysis highlighted dipeptides rather than single amino or hydroxy acids as the basic modules in tetradepsipeptide assembly and proposed the CesA C-terminal C* domain and the CesB C-terminal TE domain to function as a cooperative esterification and depsipeptide elongation center repeatedly recruiting the action of the C* domain to oligomerize tetradepsipeptides prior to the release of cereulide from the TE domain by macrocyclization.

Enniatins (ENs), a group of antibiotics commonly produced by various strains of Fusarium, are six-membered cyclic depsipeptides formed by the union of three molecules of D-α-hydroxyisovaleric acid and three N-methyl-L-amino acids. The endophyte Fusarium tricinctum Corda was isolated from the fruits of Hordeum sativum Jess. and cultivated on a rice medium. The fungal metabolites were extracted with methanol and were identified, employing liquid chromatography-mass spectrometry as ENs A, A1, B, B1, B2 and Q. EN Q is a new analog of EN A and the occurrence of EN B2 is reported for the first time from this endophyte, in addition to four well-known ENs (A, A1, B and B1). The methanol extract of F. tricinctum showed mild antibacterial and antileishmanial activities. Additionally the tested extract displayed inhibition of the activity of thioredoxin reductase enzyme of Plasmodium falciparum.

Antibiotic resistance is spreading faster than the introduction of new compounds into clinical practice, causing a public health crisis. Most antibiotics were produced by screening soil microorganisms, but this limited resource of cultivable bacteria was overmined by the 1960s. Synthetic approaches to produce antibiotics have been unable to replace this platform. Uncultured bacteria make up approximately 99% of all species in external environments, and are an untapped source of new antibiotics. We developed several methods to grow uncultured organisms by cultivation in situ or by using specific growth factors. Here we report a new antibiotic that we term teixobactin, discovered in a screen of uncultured bacteria. Teixobactin inhibits cell wall synthesis by binding to a highly conserved motif of lipid II (precursor of peptidoglycan) and lipid III (precursor of cell wall teichoic acid). We did not obtain any mutants of Staphylococcus aureus or Mycobacterium tuberculosis resistant to teixobactin. The properties of this compound suggest a path towards developing antibiotics that are likely to avoid development of resistance.

A novel depsipeptide (PM181110) was purified from an endophytic fungus Phomopsis glabrae isolated from the leaves of Pongamia pinnata (family Fabaceae). The chemical structure of PM181110 was elucidated using physiochemical properties, 2D NMR and other spectroscopic methods. PM181110 is very close in structure to FE399. The compound exhibited in vitro anticancer activity against 40 human cancer cell lines with a mean IC50 value of 0.089 μM and ex vivo efficacy towards 24 human tumor xenografts (mean IC50=0.245 μM).

In the course of our screening for inhibitors of lipopolysaccharide (LPS) binding to cellular receptor CD14, potent inhibitory activity was detected in the cultured broth of Pedobacter sp. SANK 72003. Three active compounds, pedopeptin A, B and C, were isolated from the broth and their structures were elucidated by physicochemical and spectral data to be new cyclic depsipeptides.

The disulfide bond is unusual in natural products and critical for thermal stability, cell permeability and bioactivity. DepH from Chromobacterium violaceum No. 968 is an FAD-dependent enzyme responsible for catalyzing the disulfide bond formation of FK228, an anticancer prodrug approved for the treatment of cutaneous T-cell lymphoma. Here we report the crystal structures of DepH and DepH complexed with a substrate analogue S,S'-dimethyl FK228 at 1.82 Å and 2.00 Å, respectively. Structural and biochemical analyses revealed that DepH, in contrast to the well characterized low molecular weight thioredoxin reductases (LMW TrxRs), is an NADP(+)-independent dithiol oxidase. DepH not only lacks a conserved GGGDXAXE motif necessary for NADP(+) binding in the canonical LMW TrxRs, but also contains a 11-residue sequence which physically impedes the binding of NADP(+). These observations explain the difference between NADP(+)-independent small molecule dithiol oxidases and NADP(+)-dependent thioredoxin reductases and provide insights for understanding the catalytic mechanism of dithiol oxidases involved in natural product biosynthesis.

During the search for new antitrypanosomal drug leads, three new antitrypanosomal compounds, cardinalisamides A-C (1-3), were isolated from cultures of the insect pathogenic fungus Cordyceps cardinalis NBRC 103832. Their structures were elucidated using MS analyses and extensive 2D-heteronuclear NMR. The absolute configurations of 1-3 were addressed by chemical degradation and Marfey's analysis. 1-3 showed in vitro antitrypanosomal activity against Trypanosoma brucei brucei with IC50 values of 8.56, 8.65 and 8.63 μg ml(-1), respectively.

Kutznerides are hexadepsipeptide antifungal and antimicrobial agents containing O-methyl-L-serine in their very unique peptidic backbone. During kutznerides biosynthesis, this O-methylated amino-acid residue is proposed to result from the action of an adenylation (A) domain present in KtzH, which is interrupted by the S-adenosylmethionine-binding-containing part of a methyltransferase. In this study, we co-expressed recombinant KtzH(A4MA4T4) with its MbtH-like protein partner KtzJ and demonstrated the requirement for KtzJ in producing soluble and active KtzH(A4MA4T4). We demonstrated the specificity of KtzH(A4MA4T4) toward L-Ser and showed the activity of the partial methyltransferase enzyme in O-methylation of L-Ser after its covalent attachment to the thiolation domain of KtzH(A4MA4T4). The insights gained from this work may guide future study and development of engineered interrupted adenylation domains for combinatorial biosynthetic methodologies.

The novel antifungal macrocyclic lipopeptidolactone, KB425796-A (1), was isolated from the fermentation broth of bacterial strain 530603, which was identified as a new Paenibacillus species based on morphological and physiological characteristics, and 16S rRNA sequences. KB425796-A (1) was isolated as white powder by solvent extraction, HP-20 and ODS-B column chromatography, and lyophilization, and was determined to have the molecular formula C79H115N19O18. KB425796-A (1) showed antifungal activities against Aspergillus fumigatus and the micafungin-resistant infectious fungi Trichosporon asahii, Rhizopus oryzae, Pseudallescheria boydii and Cryptococcus neoformans.

KB425796-C is a novel antifungal metabolite produced by the newly isolated bacterial strain Paenibacillus sp. No. 530603. This compound is a 40-membered macrocyclic lipopeptidolactone consisting of 12 amino acids and a 3-hydroxy-15-methylpalmitoyl moiety. KB425796-C displayed antifungal activity against micafungin-resistant fungi and was fungicidal to Trichosporon asahii in vitro. In a murine systemic infection model of T. asahii, KB425796-C showed excellent efficacy upon i.p. administration at 32 mg kg(-1). In addition, KB425796-C induced morphological changes in the hyphae of Aspergillus fumigatus and had fungicidal effects in combination with micafungin. In a mouse model of septic A. fumigatus infection, although non-treated mice survived for a maximum of only 6 days, the survival rate of micafungin-treated mice (0.1 mg kg(-1)) increased to 20%, while the survival rate of mice treated with a combination of micafungin (0.1 mg kg(-1)) and KB425796-C (32 mg kg(-1)) increased to 100% during the 31-day post-infection period. Our findings suggest that KB425796-C is a good candidate for the treatment of aspergillosis in combination with micafungin.

The discovery and characterization of natural congeners is one approach for understanding the relationship between chemical structure and biological function. We recently isolated the novel antifungal metabolite KB425796-A produced by the recently isolated bacterium Paenibacillus sp. 530603. On the basis of morphological changes of Aspergillus fumigatus induced by KB425796-A in combination with micafungin, we developed a highly sensitive screening method for the specific detection of KB425796-A congeners. Using this method, we isolated ten congeners of KB425796-A, named KB425796-B, -C, -D, -E, -F, -G, -H, -I, -J and -K, which exhibited diverse antifungal potencies against A. fumigatus. One of the most potent congeners, KB425796-C, had antifungal activities against several micafungin-resistant infectious fungi. KB425796-C can be a potential drug candidate for treating micafungin-resistant fungal infections.

Enniatins are cyclohexadepsipeptides isolated largely from Fusarium species of fungi, although they have been isolated from other genera, such as Verticillium and Halosarpheia. They were first described over 60 years ago, and their range of biological activities, including antiinsectan, antifungal, antibiotic and cytotoxic, drives contemporary interest. To date, 29 enniatins have been isolated and characterized, either as a single compound or mixtures of inseparable homologs. Structurally, these depsipeptides are biosynthesized by a multifunctional enzyme, termed enniatin synthetase, and are composed of six residues that alternate between N-methyl amino acids and hydroxy acids. Their structure elucidation can be challenging, particularly for enniatins isolated as inseparable homologs; however, several strategies and tools have been utilized to solve these problems. Currently, there is one drug that has been developed from a mixture of enniatins, fusafungine, which is used as a topical treatment of upper respiratory tract infections by oral and/or nasal inhalation. Given the range of biological activities observed for this class of compounds, research on enniatins will likely continue. This review strives to digest the past studies, as well as, describe tools and techniques that can be utilized to overcome the challenges associated with the structure elucidation of mixtures of enniatin homologs.

Verticillium sp. FKI-2679, a soil isolate, was found to produce inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT) in a cell-based assay using ACAT1- and ACAT2-expressing CHO cells. Three new compounds, verticilides A2, A3 and B1, were isolated along with a known compound, verticilide A1, from the fermentation broth of the fungus by solvent extraction, ODS column chromatography, silica gel column chromatography and preparative HPLC. Structure elucidation showed that these compounds were new cyclic depsipeptide. Verticilides A1, A2, A3 and B1 showed a degree of selectivity towards ACAT2, with IC(50)s 8.5-11-fold more potent than observed against ACAT1.

Romidepsin (Istodax), a selective inhibitor of histone deacetylases (HDACs), was approved for the treatment of cutaneous T-cell lymphoma in November 2009 by the US Food and Drug Administration. This unique natural product was discovered from cultures of Chromobacterium violaceum, a Gram-negative bacterium isolated from a Japanese soil sample. This bicyclic compound acts as a prodrug, its disulfide bridge being reduced by glutathione on uptake into the cell, allowing the free thiol groups to interact with Zn ions in the active site of class I and II HDAC enzymes. Due to the synthetic complexity of the compound, as well as the low yield from the producing organism, analogs are sought to create synthetically accessible alternatives. As a T-cell lymphoma drug, romidepsin offers a valuable new treatment for diseases with few effective therapies.

The anti-MRSA antibiotic, WAP-8294A, was isolated from the fermentation broth of Lysobacter sp. The major component, WAP-8294A2, is composed of 1 mol of Gly, L-Leu, L-Glu, D-Asn, D-Trp, D-threo-β-hydroxyasparagine, N-Me-D-Phe and N-Me-L-Val, and 2 mol of L-Ser, D-Orn and D-3-hydroxy-7-Me-octanoic acid. The structure of the WAP-8294A2 was mainly determined as a cyclic depsipeptide by 2D NMR experiments. However, it was difficult to use the NMR experiment to determine the minor components, A1, A4 and Ax13, isolated in small amounts. In the present study, ESI MS/MS was applied to the structure elucidation of these minor components. The structures of these minor components were determined on the basis of the fragmentation pattern of the product ions of WAP-8294A2 in the ESI MS/MS. As a result, it was confirmed that A1 and A4 had the same amino acid sequence as A2, while A1 and A4 had the 3-OH-octanoic acid and 3-OH-8-Me-nonanoic acid, respectively, in the place of the 3-OH-7-Me-octanoic acid in A2. In the structure of Ax13, it was found that Gly of A2 was changed to β-Ala of Ax13., (© 2011 Japan Antibiotics Research Association All rights reserved)

Two peptides, tumescenamides A and B, were isolated from the fermentation broth of a marine bacterium, Streptomyces tumescens YM23-260. The structure of tumescenamide A was determined to be a cyclic depsipeptide consisting of α-amino-2-butenoic acid, tyrosine, valine, leucine and threonine, substituted with a 2,4-dimethylheptanoyl residue at the α-NH(2) position. Tumescenamide B possesses a 2,4,6-trimethylnonanoyl residue in place of the 2,4-dimethylheptanoyl substituent in tumescenamide A. Tumescenamide A induced reporter gene expression under the control of the insulin-degrading enzyme promoter.

NW-G01 is a novel cyclic hexapeptide antibiotic produced by Streptomyces alboflavus 313. Its relative structure was established by HR-ESI-MS, IR, 1D and 2D NMR techniques, the absolute structure was determined using a combination of single-crystal X-ray diffraction and Marfey's method finally. The antibiotic consists of L-valine, (3S)- and (3R)-piperazic acids, N-methyl-D-alanine and (2S,3aR,8aS)-6-chloro-3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid.

A new ryanodine-binding inhibitor, verticilide, was isolated from the cultured broth of a fungus, Verticillium sp. FKI-1033. It is a 24-membered ring cyclic depsipeptide, its structure being elucidated as cyclo[(2R)-2-hydroxyheptanoyl-N-methyl- L-alanyl](4). Verticilide inhibited ryanodine binding to ryanodine receptors in the cockroach at an IC(50) value of 4.2 microM, whereas inhibition against mouse ryanodine receptors was weak (IC(50)=53.9 microM).

Chemical investigation of the marine-derived Streptomyces sp. Act8015 led to the isolation of two cyclic peptide antibiotics, piperazimycins A and B (1a, 1b). Their structures were confirmed on the basis of a detailed HRESI-MS/MS analysis. Additionally, a new butanolide, 4,10-dihydroxy-10-methyl-dodecan-4-olide (2), and the respective acid, 4,10-dihydroxy-10-methyl-dodecanoic acid (3a) were identified. Further isolated compounds were staurosporin, adenine, indole-3-carboxylic acid, ferulic acid, tryptophol, and three gamma-butyrolactones: virginiae butanolide E (4e) and Graefe's Factors I (4f) and III (4g). The structures of 2 and 3a were confirmed by detailed 1D and 2D NMR studies and MS spectra and by comparison with related structures. A full signal assignment of virginiae butanolide E (4e) is reported here for the first time.

Branched chain amino acids are often utilized as the precursors of many lipid-containing bacterial secondary metabolites. The effect of isoleucine on the composition of the mixture of cyclic lipopeptide antibiotics, tripropeptins from Lysobacter sp. BMK333-48F3 was evaluated. As expected, a novel tripropeptin analog with an anteiso-branched fatty acid was produced. The new compound, TPPaiC shows potent antibacterial activity against Gram-positive bacteria including MRSA and VRE. On the other hand, no increase was observed in the production of other tripropeptins by the addition of isoleucine.

Two new antibiotic depsipeptides, unnarmicins C (1) and A (2), were isolated from the fermentation broth of a marine bacterium, Photobacterium sp. strain MBIC06485. The structure of 1 was established by spectroscopic studies and chiral analyses of its chemical degradation/conversion products, and that of 2 by comparing its NMR, MS, and CD data with those of 1. Both compounds selectively inhibited the growth of two strains belonging to the genus Pseudovibrio, one of the most prevalent genera in the marine environments within the class Alphaproteobacteria.

Pleofungins (formerly called F-15078) A, B, C and D, novel depsipeptide antifungal antibiotics, were found in a mycelium extract of the producing fungus, Phoma sp. SANK 13899. The structures of pleofungins A, B, C and D were elucidated mainly by various NMR studies. The absolute configurations of the amino acids and N-methyl amino acids of pleofungin A constituents in the hydrolysate were determined by the application of advanced Marfey's method in combination with gas chromatography/mass spectrometry analysis of their silylation products with N-methyl-N-(tert-butylsilyl)trifluoroacetamide. Two alpha-hydroxy acid constituents, alpha-hydroxyisocaproic acid and alpha-hydroxyisovaleric acid, were isolated from the hydrolysate and their stereochemistries were determined by their specific rotations.

The marine strain Pseudoalteromonas maricaloris KMM 636T was found to produce an inseparable mixture of two brominated yellow main pigments, bromoalterochromide A and A', in a ratio of 3: 1. Both pigments are Thr-Val-Asn-Asn-X pentapeptide lactones, where the amino group of Thr is acylated with 9-(3-bromo-4-hydroxyphenyl)-nona-2,4,6,8-tetraenoic acid, and X is aIle and Leu, respectively. They possess cytotoxic effects on developing eggs of the sea urchin Strongylocentrotus intermedius, but no antibiotic activity.

Chemical investigation of the cytotoxic and anti-tuberculosis active butanone extract obtained from the growth media of the marine-derived fungus Beauveria felina led to the isolation of two new destruxins, [beta-Me-Pro] destruxin E chlorohydrin (1) and pseudodestruxin C (3), along with five known cyclic depsipeptides. The structures of the new destruxin derivatives were established by analysis of spectroscopic data, while the absolute configuration of the common amino acid residues was established by Marfey's analysis. The absolute configuration of the 2(R),4(S)-5-chloro-2,4-dihydroxypentanoic acid residue in 1 could be established by application of a J-based configuration method followed by derivatization with R-MPA-Cl and NMR analysis.

A slightly halophilic myxobacterial strain, SMH-27-4, was isolated from nearshore soil and shown to belong to a new myxobacterium genus based on phylogenetic analysis. This slowly-growing myxobacterium produced the novel antibiotic depsipeptides miuraenamides A and B. Their physico-chemical properties and molecular formulas, C34H42N3O7Br and C34H42N3O7I, were determined. Miuraenamides A exhibited potent and selective inhibition against a phytopathogenic microorganism, Phytophthora sp., and moderate inhibition against some fungi and yeasts, but was ineffective against bacteria. Both of the metabolites inhibited NADH oxidase at IC50 values of 50 microM, suggesting, like beta-methoxyacrylate-type antibiotics, the electron transfer system of the mitochondrial respiratory chain as the cellular target.

The ethyl acetate extract of the Streptomyces sp. isolate GW99/1572 exhibited significant biological activity against Gram-positive bacteria and delivered kettapeptin (1), a new hexadepsipeptide antibiotic of the azinothricin type. The structure was elucidated by various 1D and 2D NMR techniques, mass spectrometry and by comparison of the NMR data with those of closely related antibiotics. The absolute configuration of the compound was derived by crystal structure analysis and by comparison with the optical rotation data of related compounds.

Ramoplanin is a glycolipodepsipeptide antibiotic obtained by fermentation of the Actinoplanes sp. ATCC 33076, isolated as a complex of three closely related components A1, A2 and A3, which differ in their fatty acid moiety. We have investigated the influence of L-leucine and L-valine, the biosynthetic precursors of the fatty acids in A2 and A3 factors, on the complex composition and antibiotic productivity. Addition of 5 g/litre of L-leucine at the time of inoculation increases antibiotic production and improves the production of A2 factor, which represents the active principle component under clinical development. Addition of L-valine in the same conditions modifies the composition of the complex towards the A3 factor but does not improve total antibiotic productivity. A possible explanation for the different actions of the two amino acids is presented.