[Show abstract][Hide abstract] ABSTRACT: The ever-increasing bacterial resistance to clinical antibiotics is making many drugs ineffective and creating significant treatment gaps. This can be only circumvented by the discovery of antibiotics with new mechanisms of action. We report here the identification of a new tetramic acid, ascosetin, from an Ascomycete using the Staphylococcus aureus fitness test screening method. The structure was elucidated by spectroscopic methods including 2D NMR and HRMS. Relative stereochemistry was determined by ROESY and absolute configuration was deduced by comparative CD spectroscopy. Ascosetin inhibited bacterial growth with 2-16 μg ml(-1) MIC values against Gram-positive strains including methicillin-resistant S. aureus. It also inhibited the growth of Haemophilus influenzae with a MIC value of 8 μg ml(-1). It inhibited DNA, RNA, protein and lipid synthesis with similar IC50 values, suggesting a lack of specificity; however, it produced neither bacterial membrane nor red blood cell lysis. It showed selectivity for bacterial growth inhibition compared with fungal but not mammalian cells. The isolation, structure and biological activity of ascosetin have been detailed here.The Journal of Antibiotics advance online publication, 2 April 2014; doi:10.1038/ja.2014.33.
The Journal of Antibiotics 04/2014; · 2.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bacteria continue to evade existing antibiotics by acquiring resistance by various mechanisms, leading to loss of antibiotic effectiveness. To avoid an epidemic from infections of incurable drug-resistant bacteria, new antibiotics with new modes of action are desperately needed. Using a genome-wide mechanism of action-guided whole cell screening approach based on antisense Staphylococcus aureus fitness test technology, we report herein the discovery of altersolanol P (1), a new tetrahydroanthraquinone from an unknown fungus from the Hypocreales isolated from forest litter collected in Puerto Rico. The structure was elucidated by high-resolution mass spectrometry and 2D NMR spectroscopy. Relative stereochemistry was established by NOESY correlations, and absolute configuration was deduced by the application of MPA ester-based methodology. Observed (1)H and (13)C NMR shifts were well aligned with the corresponding chemical shifts predicted by DFT calculations. Altersolanol P exhibited Gram-positive antibacterial activity (MIC range 1-8 μg/mL) and inhibited the growth of Gram-negative Haemophilus influenzae (MIC 2 μg/mL). The isolation, structure elucidation, and antibacterial activity of altersolanol P are described.
Journal of Natural Products 01/2014; · 3.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Natural products have been major sources of antibacterial agents and remain very promising. Frequent rediscoveries of known compounds hampers progress of new discoveries and demands development and utilization of new methods for rapid biological and chemical dereplication. This paper describes an efficient approach for discovery of new thiazolyl peptides by sensitive-resistant pair screening and dereplication in a time and cost-effective manner at industrial scale. A highly effective library-based dereplication of thiazolyl peptides by high resolution fourier transform liquid chromatography mass spectrometry (HRFTLCMS) has been developed, which can detect and dereplicate very low levels of thiazolyl peptides particularly when combined with miniaturized high-throughput 96-well solid-phase extraction separation, and as well can be automated. Combination of sensitive (susceptible)-resistant pair screening, diversified screening collection and miniaturized high-throughput SPE and HRFTLCMS techniques were applied for discovery of new thiazolyl peptides. The combined approach allowed for identification of over 24 thiazolyl peptides represented by three of the five structural subgroups, including three novel compounds. In addition, it is possible for the first time to mechanistically group three structural subgroups of over 24 thiazolyl peptides. Furthermore, these studies helped to understand natural frequency of distribution of these compounds and helped in discovery of new producing strains of many thiazolyl compounds.The Journal of Antibiotics advance online publication, 26 June 2013; doi:10.1038/ja.2013.54.
The Journal of Antibiotics 06/2013; · 2.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Phaeofungin (1), a new cyclic depsipeptide isolated from Phaeosphaeria sp., was discovered by application of reverse genetics technology, using the Candida albicans fitness test (CaFT). Phaeofungin is comprised of seven amino acids and a β,γ-dihydroxy-γ-methylhexadecanoic acid arranged in a 25-membered cyclic depsipeptide. Five of the amino acids were assigned with d-configurations. The structure was elucidated by 2D-NMR and HRMS-MS analysis of the natural product and its hydrolyzed linear peptide. The absolute configuration of the amino acids was determined by Marfey's method by complete and partial hydrolysis of 1. The CaFT profile of the phaeofungin-containing extract overlapped with that of phomafungin (3), another structurally different cyclic lipodepsipeptide isolated from a Phoma sp. using the same approach. Comparative biological characterization further demonstrated that these two fungal lipodepsipeptides are functionally distinct. While phomafungin was potentiated by cyclosporin A (an inhibitor of the calcineurin pathway), phaeofungin was synergized with aureobasidin A (2) (an inhibitor of the sphingolipid biosynthesis) and to some extent caspofungin (an inhibitor of glucan synthase). Furthermore, phaeofungin caused ATP release in wild-type C. albicans strains but phomafungin did not. It showed modest antifungal activity against C. albicans (MIC 16-32 μg/mL) and better activity against Aspergillus fumigatus (MIC 8-16 μg/mL) and Trichophyton mentagrophytes (MIC 4 μg/mL). The linear peptide was inactive, suggesting that the macrocyclic depsipeptide ring is essential for target engagement and antifungal activity.
Journal of Natural Products 03/2013; 76(3):334-45. · 3.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In a whole-cell mechanism of action (MOA)-based screening strategy for discovery of antifungal agents, Candida albicans was used, followed by testing of active extracts in the C. albicans fitness test (CaFT), which provides insight into the mechanism of action. A fermentation extract of an undescribed species of Metulocladosporiella that inhibited proteasome activity in a C. albicans fitness test was identified. The chemical genomic profile of the extract contained hypersensitivity of heterozygous deletion strains (strains that had one of the genes of the diploid genes knocked down) of genes represented by multiple subunits of the 25S proteasome. Two structurally related peptide aldehydes, named fellutamides C and D, were isolated from the extract. Fellutamides were active against C. albicans and Aspergillus fumigatus with MICs ranging from 4 to 16 μg/mL and against fungal proteasome (IC₅₀ 0.2 μg/mL). Both compounds showed proteasome activity against human tumor cell lines, potently inhibiting the growth of PC-3 prostate carcinoma cells, but not A549 lung carcinoma cells. In PC-3 cells compound treatment produced a G2M cell cycle block and induced apoptosis. Preliminary SAR studies indicated that the aldehyde group is critical for the antifungal activity and that the two hydroxy groups are quantitatively important for potency.
Journal of Natural Products 07/2011; 74(8):1721-30. · 3.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Platensimycin (1a) and platencin (2) are inhibitors of FabF and FabF/H bacterial fatty acid synthase. The discovery of natural congeners is an approach that can render a better understanding of the structure-function relationships of complex natural products. The isolation and structure elucidation of nine new congeners (11-20) of platensimycin and platencin are described from a fermentation broth of Streptomyces platensis. These hydroxylated congeners are likely derived by cytochrome P450 oxidation of the terpenoid units post-cyclization. Polar groups in the terpenoid portion of the molecule produce negative interactions with the hydrophobic pocket of FabF, resulting in poor activities. However, the discovery of these compounds serves an important purpose, not only to understand structure-function relationships, which cannot be easily accessed by chemical modification, but also to provide access to compounds that could be used for structural identification/confirmation of the oxidative trace metabolites produced in vivo during animal experiments.
Journal of Natural Products 01/2011; 74(3):329-40. · 3.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Natural products serve as a great reservoir for chemical diversity and are the greatest source for antibacterial agents. Recent discoveries of platensimycin and platencin as inhibitors of bacterial fatty acid biosynthesis enzymes supplied new chemical scaffolds for potential antibacterial agents to overcome resistant pathogens. Discovery of natural congeners augment chemical modification in understanding of structure-activity relationship (SAR). Chemical and biological screening of the extracts led to isolation of three hydroxylated analogs of platencin. The C-12, C-14 and C-15 hydroxylated analogs showed attenuated activities which provided significant understanding of functional tolerance in the diterpenoid portion of the molecule. A truncated and oxidized C-13 natural congener was isolated which suggested direct intermediacy of ent-copalyl diphosphate for the biosynthesis of platensimycins and platencins.
[Show abstract][Hide abstract] ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
[Show abstract][Hide abstract] ABSTRACT: Platensimycin and platencin are inhibitors of FabF and FabF/H bacterial fatty acid synthesis enzymes, respectively. Discovery of natural congeners provides one of the ways to understand the relationship of chemical structure and biological function. Efforts to discover the natural analogs of platensimycin by chemical screening led to the isolation of platensimycin B(4), a glucoside congener of platensimycin. This analog showed significantly attenuated activity and critically defined the limited binding space around the aromatic ring and established the importance of the free phenolic and carboxyl group for the activity.
The Journal of Antibiotics 11/2009; 62(12):699-702. · 2.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Natural products continue to serve as one of the best sources for discovery of antibacterial agents as exemplified by the recent discoveries of platensimycin and platencin. Chemical modifications as well as discovery of congeners are the main sources for gaining knowledge of structure-activity relationship of natural products. Screening for congeners in the extracts of the fermentation broths of Streptomyces platensis led to the isolation of platencin A(1), a hydroxy congener of platencin. The hydroxylation of the tricyclic enone moiety negatively affected the antibacterial activity and appears to be consistent with the hydrophobic binding pocket of the FabF. Isolation, structure, enzyme-bound structure and activity of platencin A(1) and two other congeners have been described.
[Show abstract][Hide abstract] ABSTRACT: Platensimycin and platencin are novel natural product antibiotics that inhibit bacterial growth by inhibiting condensing enzymes FabF and FabF/FabH of fatty acid biosynthesis pathways, respectively. Continued search for the natural congeners of these compounds led to the isolation of platensic acid, the free C-17 tetracyclic enoic acid, and platensimide A, a 2,4-diaminobutyric acid amide derivative. Isolation, structure, semisynthesis, and activity of these compounds are described.
[Show abstract][Hide abstract] ABSTRACT: Thiazolyl peptides are a class of highly rigid trimacrocyclic compounds consisting of varying but large numbers of thiazole rings. The need for new antibacterial agents to treat infections caused by resistant bacteria prompted a reinvestigation of this class, leading to the previous isolation of thiazolyl peptides, namely, thiazomycin (5) and thiazomycin A (6), congeners of nocathiacins (1-4). Continued chemical screening led to the isolation of six new thiazolyl peptide congeners (8-13), of which three had truncated structures lacking an indole residue. From these, compound 8 showed activity similar to thiazomycin. Two compounds (9 and 10) showed intermediate activities, and the three truncated compounds (11-13) were essentially inactive. The discovery of the truncated compounds revealed the minimal structural requirements for activity and suggested probable biosynthetic pathways for more advanced compounds. The isolation, structure elucidation, antibacterial activity, and proposed biogenesis of thiazomycins are herein described.
Journal of Natural Products 04/2009; 72(5):841-7. · 3.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Protein synthesis inhibition is a highly successful target for developing clinically effective and safe antibiotics. There are several targets within the ribosomal machinery, and small ribosomal protein S4 (RPSD) is one of the newer targets. Screening of microbial extracts using antisense-sensitized rpsD Staphylococcus aureus strain led to isolation of okilactomycin and four new congeners from Streptomyces scabrisporus. The major compound, okilactomycin, was the most active, with a minimum detection concentration of 3-12 microg ml(-1) against antisense assay, and showed an MIC of 4-16 microg ml(-1) against Gram-positive bacteria, including S. aureus. The congeners were significantly less active in all assays, and all compounds showed a slight preferential inhibition of RNA synthesis over DNA and protein synthesis. Antisense technology, due to increased sensitivity, continues to yield new, even though weakly active, antibiotics.
The Journal of Antibiotics 02/2009; 62(2):55-61. · 2.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inhibition of fatty acid synthesis is emerging as a valuable target for antibacterial agents. Platensimycin and platencin are novel natural products that were reported recently to inhibit the FabF and FabF/FabH condensing enzymes, respectively, present in the fatty acid biosynthetic pathway. Selective inhibition of these enzymes by platensimycin and platencin accounts for their potent antibiotic activity. We have continued our quest to find additional members of this class of compounds leading to discovery of platensimycin A1, a hydroxylated congener. We report herein the isolation, structure, antibacterial and enzymatic activities, and co-crystal structure bound to Escherichia coli FabF. The lower activity of platensimycin A1 suggests that substitution at C-14 is detrimental for the activity.
Tetrahedron Letters - TETRAHEDRON LETT. 01/2009; 50(37):5182-5185.