Hydroxamic Group Research Articles

A potent dual inhibitor targeting COX-2 and HDAC of acute myeloid leukemia cells.

Acute myeloid leukemia (AML) is an aggressive cancer with complex issues of drug resistance and a poor prognosis; thus, effective therapeutics is urgently needed for AML. In this study, we designed and synthesized dual cyclooxygenase-2 (COX-2) and histone deacetylase (HDAC) inhibitors, IMC-HA and IMC-OPD, and applied them for the treatment of AML. IMC-HA comprised a COX-2 inhibitor skeleton of indomethacin (IMC) and an HDAC inhibitor moiety of the hydroxamic group and was found to exhibit potent antiproliferative activity against AML cells (THP-1 and U937) and low cytotoxicity toward normal cells. Molecular docking simulations suggested that IMC-HA had a high binding affinity for HDAC and COX-2, with binding energies of -6.8 and -9.0kcal/mol, respectively. Mechanistic studies revealed that IMC-HA induced apoptosis and G0/G1 phase arrest in AML cells, which were characterized by alterations in the expression of apoptotic and cell cycle-related proteins. Further study demonstrated that IMC-HA also inhibited the MEK/ERK signaling pathway in AML cells. Overall, we believe that IMC-HA could serve as a potent COX-2/HDAC dual inhibitor and improve the treatment of AML.

Synthesis, characterization, molecular modeling, and antimicrobial study of copper(II) 2-chlorophenylacetohydroxamate

A copper(II) 2-chlorophenylacetohydroxamate complex has been synthesized using copper(II) chloride and potassium 2-chlorophenylacetohydroxamate in 1:2 molar ratio in methanol and characterized using CHN analysis, IR, 1H NMR, 13C NMR spectroscopy, and mass spectrometry. The hydroxamate ligand binds to metal via oxygen of carbonyl group and hydroxamic group (O, O bonding), and a distorted-square planar geometry has tentatively been proposed. The interactions between Staphylococcus aureus (bacterial receptor) ligand and complex, their inhibition constant, and binding energy values have been computed. The in vitro antimicrobial activity study against pathogenic gram –ve bacteria viz. Salmonella typhi and Escherichia coli; gram + ve S. aureus and Bacillus cereus by MIC method have revealed a significant antimicrobial potential.

In Vitro Evaluation of Pharmacokinetic Properties of Selected Dual COX-2 and 5-LOX Inhibitors.

Evaluation of pharmacokinetic properties is a significant step at the early stages of drug development. In this study, an in vitro evaluation of the pharmacokinetic properties of five newly synthesized compounds was performed. These compounds belong to N-hydroxyurea and hydroxamic acid derivatives and analogs of NSAIDs indomethacin, flurbiprofen, diclofenac, ibuprofen, and naproxen (compounds 1, 2, 3, 11, and 12, respectively) with dual COX-2 and 5-LOX inhibitory activity. Two in vitro methods (biopartitioning micellar chromatography (BMC) and PAMPA) were used to evaluate passive gastrointestinal absorption, while high-performance affinity chromatography (HPAC) and differential pulse voltammetry (DPV) were used to evaluate binding to human serum albumin (HSA). The introduction of N-hydroxyurea and hydroxamic acid groups into the structure of NSAIDs decreases both expected passive gastrointestinal absorption (BMC k values were from 3.02 to 9.50, while for NSAIDs were from 5.29 to 13.36; PAMPA -logPe values were between 3.81 and 4.76, while for NSAIDs were ≤3.46) and HSA binding (HPAC logk values were from 2.03 to 9.54, while for NSAIDs were ≥11.03; DPV peak potential shifts were between 7 and 34, while for NSAIDs were ≥54). Structural modifications of all tested compounds that increase lipophilicity could be considered to enhance their passive gastrointestinal absorption. Considering lower expected HSA binding and higher lipophilicity of tested compounds compared to corresponding NSAIDs, it can be expected that the volume of distribution of compounds 1, 2, 3, 11, and 12 will be higher. Reduced HSA binding may also decrease interactions with other drugs in comparison to corresponding NSAIDs. All tested compounds showed significant microsomal instability (25.07-58.44% decrease in concentration) in comparison to indomethacin (14.47%) and diclofenac (20.99%).

Probing class I histone deacetylases (HDAC) with proteolysis targeting chimera (PROTAC) for the development of highly potent and selective degraders

Class I HDACs are considered promising targets for cancer due to their role in epigenetic modifications. The main challenges in developing a new, potent and non-toxic class I HDAC inhibitor are selectivity and appropriate pharmacokinetics. The PROTAC technique (Proteolysis Targeting Chimera) is a new method in drug development for the production of active substances that can degrade a protein of interest (POI) instead of inhibiting it. This technique will open the era to produce selective and potent drugs with a high margin of safety. Previously, we reported different inhibitors targeting class I HDACs functionalized with aminobenzamide or hydroxamate groups. In the current research work, we will employ PROTAC technique to develop class I HDAC degraders based on our previously reported inhibitors. We synthesized two series of aminobenzamide-based PROTACs and hydroxamate-based PROTACs and tested them in vitro against class I HDACs. To ensure their degradation, all of them were screened against HDAC2 as representative example of class I. The best candidates were evaluated at different concentrations at various HDAC subtypes. This resulted in the PROTAC (32a) (HI31.1) that degrades HDAC8 with a DC50 of 8.9 nM with a proper margin of selectivity against other isozymes. Moreover, PROTAC 32a is able to degrade HDAC6 with DC50 = 14.3 nM. Apoptotic study on leukemic cells (MV-4–11) displayed more than 50 % apoptosis took place at 100 nM. PROTAC 32a (HI31.1) showed a good margin of safety against normal cell line and proper chemical stability.

Design and synthesis of non-hydroxamate lipophilic inhibitors of 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR): in silico, in vitro and antibacterial studies.

1-Deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) is a key enzyme of the 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway operating in several pathogens, including Mycobacterium and Plasmodium. Since a DXR homologue is not present in humans, it is an important antimicrobial target. Fosmidomycin (FSM) and its analogues inhibit DXR function by chelating the divalent metal (Mn2+ or Mg2+) in its active site via a hydroxamate metal binding group (MBG). The latter, however, enhances the polarity of molecules and is known to display metabolic instability and toxicity issues. While attempts have been made to increase the lipophilicity of FSM by substituting the linker chain and prodrug approach, very few efforts have been made to replace the hydroxamate group with other lipophilic MBGs. We report a systematic in silico and experimental investigation to identify novel MBGs for designing non-hydroxamate lipophilic DXR inhibitors. The SAR studies with selected MBG fragments identified novel inhibitors of E. Coli DXR with IC50 values ranging from 0.29 to 106 μM. The promising inhibitors were also screened against ESKAPE pathogens and M. tuberculosis.

Investigation into the impact of Mn2+ and its interaction with calcite in the flotation of rhodochrosite

The unavoidable Mn2+ ions in pulp were considered in the flotation of rhodochrosite, and its effect and relative interaction mechanism on the floatability of calcite served as a typical gangue mineral were investigated through microflotation tests, zeta potential measurements, SEM-EDS detection, solution chemistry calculation, adsorption experiments, FTIR and XPS analyses. There exhibited a good separation performance of rhodochrosite against calcite with OHA collector, but in the presence of Mn2+ ions, the floatability of calcite was closed to rhodochrosite within a pH of 8.0–10.0, which resulted in the separation difficulty between them. As evidenced, the surface of calcite could be modified by Mn2+ ions, its isoelectric point shifted positively from 8.91 to 10.06, and Mn2+ species detected on calcite surfaces were in close proximity to rhodochrosite. It indicated that MnCO3 precipitates were generated on the surface of calcite. After modified by Mn2+, the calcite surface became more active and obviously increased the adsorption amount of OHA. It was verified from zeta potential and XPS analyses that Mn species on the surface of calcite were active sites for OHA adsorption, likely the hydroxamate group of OHA collector chelated with Mn species to form hydrophobic compounds. As a result, Mn2+ ions in pulp would reduce the flotation selectivity of rhodochrosite from calcite, thus it is necessary to eliminate the disadvantage of Mn2+ for strengthening flotation.

Mixed Liquid and Solid Phase Synthesis of Isopeptidic Desferrioxamine Analogues for Complexation of Zirconium

Abstract89Zr has a number of advantageous properties for PET‐imaging, but optimal chelators for its widespread clinical application still need to be found. Tetrahydroxamates derived from the natural siderophore DFOB are promising candidates in this context. This study describes a solid‐phase approach to isopeptide analogs of DFOB (termed ipDFO*) with four hydroxamate groups for stable Zr(IV)‐chelation. The route uses either commercial or easily available Fmoc‐protected precursors and allows the synthesis of ipDFO* and clickable AZA−ipDFO* derivatives in only a few hours. The solid‐phase synthesis reduces the workload for the synthesis of ipDFO* and AZA−ipDFO* derivatives thus significantly compared to a previous multistep solution synthesis. The route is also modular and allows the synthesis of various ipDFO* derivatives with variation in the spacer length between the hydroxamate groups. This spacing is a critical parameter for finding the optimal chelator for hard metal cations like Zr(IV). It might thus help to speed up the search for an ideal Zr‐chelator for PET‐imaging and might also allow the extension to other metal cations of different size.

Molecular design of hydroxamic acid-based derivatives as urease inhibitors of Helicobacter pylori.

Helicobacter pylori is the main causative agent of gastric cancer, especially non-cardiac gastric cancers. This bacterium relies on urease producing much ammonia to colonize the host. Herein, the study provides valuable insights into structural patterns driving urease inhibition for high-activity molecules designed via exploring known inhibitors. Firstly, an ensemble model was devised to predict the inhibitory activity of novel compounds in an automated workflow (R2 = 0.761) that combines four machine learning approaches. The dataset was characterized in terms of chemical space, including molecular scaffolds, clustering analysis, distribution for physicochemical properties, and activity cliffs. Through these analyses, the hydroxamic acid group and the benzene ring responsible for distinct activity were highlighted. Activity cliff pairs uncovered substituents of the benzene ring on hydroxamic acid derivatives are key structures for substantial activity enhancement. Moreover, 11 hydroxamic acid derivatives were designed, named mol1-11. Results of molecular dynamic simulations showed that the mol9 exhibited stabilization of the active site flap's closed conformation and are expected to be promising drug candidates for Helicobacter pylori infection and further in vitro, in vivo, and clinical trials to demonstrate in future.

Preparation of 6-Amino-N-hydroxyhexanamide-Modified Porous Chelating Resin for Adsorption of Heavy Metal Ions.

The pollution of water bodies by heavy metal ions has recently become a global concern. In this experiment, a novel chelating resin, D851-6-AHHA, was synthesized by grafting 6-amino-N-hydroxyhexanamide (6-AHHA) onto the (-CH2N-(CH2COOH)2) group of the D851 resin, which contained a hydroxamic acid group, amide group, and some carboxyl groups. This resin was developed for the purpose of removing heavy metal ions, such as Cr(III) and Pb(II), from water. The findings from static adsorption experiments demonstrated the remarkable adsorption effectiveness of D851-6-AHHA resin towards Cr(III) and Pb(II). Specifically, the maximum adsorption capacities for Cr(III) and Pb(II) were determined to be 91.50 mg/g and 611.92 mg/g, respectively. Furthermore, the adsorption kinetics of heavy metal ions by D851-6-AHHA resin followed the quasi-second-order kinetic model, while the adsorption isotherms followed the Langmuir model. These findings suggest that the adsorption process was characterized by monolayer chemisorption. The adsorption mechanism of D851-6-AHHA resin was comprehensively investigated through SEM, XRD, FT-IR, and XPS analyses, revealing a high efficiency of D851-6-AHHA resin in adsorbing Cr(III) and Pb(II). Specifically, the (-C(=O)NHOH) group exhibited a notable affinity for Cr(III) and Pb(II), forming stable multi-elemental ring structures with them. Additionally, dynamic adsorption experiments conducted using fixed-bed setups further validated the effectiveness of D851-6-AHHA resin in removing heavy metal ions from aqueous solutions. In conclusion, the experimental findings underscored the efficacy of D851-6-AHHA resin as a highly efficient adsorbent for remediating water bodies contaminated by heavy metal ions.

Multimechanism biological profiling of tetrahydro-β-carboline analogues as selective HDAC6 inhibitors for the treatment of Alzheimer's disease

With the intensive research on the pathogenesis of Alzheimer's disease (AD), inhibition of HDAC6 appears to be a potential therapeutic approach for AD. In this paper, a series of tetrahydro-β-carboline derivatives with hydroxamic acid group were fast synthesized. Among all, the most potent 15 selectively inhibited HDAC6 with IC50 of 15.2 nM and markedly increased acetylated alpha-tubulin levels. In cellular assay, 15 showed excellent neurotrophic effect by increasing the expression of GAP43 and Beta-3 tubulin markers. Besides, 15 showed neuroprotective effects in PC12 or SH-SY5Y cells against H2O2 and 6-OHDA injury through activation of Nrf2, catalase and Prx II, and significantly reduced H2O2-induced reactive oxygen species (ROS) production. In vivo, 15 significantly attenuated zebrafish anxiety-like behaviour and memory deficits in a SCOP-induced zebrafish model of AD. To sum up, multifunctional 15 might be a good lead to develop novel tetrahydrocarboline-based agents for the treatment of AD.

Highly efficient flotation of ilmenite with a novel dithiocarbamate-hydroxamate collector

The pre-activation of lead nitrate has been extensively proved to be an effective technique in ilmenite flotation, and sodium oleate is the preferred collector. Realization the clean flotation of ilmenite is an important aspect to respond the green and low-carbon policy. In this work, a dithiocarbamate-hydroxamate collector OAHD was pioneeringly added into the direct flotation of ilmenite as an efficient collector. The micro-flotation performance found that OAHD realized an efficient flotation of ilmenite under low concentration of 1.0 × 10−5 mol/L under around pH 8.0, and the flotation recovery rate of ilmenite reached about 94.2%, which was about 35.8% higher than that of NaOL. The morphology of ilmenite observed by AFM probed the self-assemble adsorption behavior of OAHD on ilmenite surface. DFT (density functional theory) calculations suggested that both dithiocarbamate and hydroxamate groups are the chemical active centers and have strong electron acceptability of d-orbital electrons of Fe atoms at/on the interface of ilmenite. UV–Vis spectra demonstrated that dithiocarbamte and hydroxamate groups simultaneously has strong chemical reaction with Fe2+ ions. XPS analysis recommended that OAHD chemisorbed on ilmenite surface to produce the surface Fe(II)-OAHD complexes where the O,O-five membered ring of Fe(II)-hydroxamate compounds were formed.

Replacement of the hydroxamic acid group in the selective HDAC8 inhibitor PCI-34051

PCI-34051 is a valuable tool to interrogate the therapeutic effects of selective inhibition of HDAC8. However, it has not advanced to clinical trials, perhaps due to poor PK or off-target effects. We hypothesized that the presence of a hydroxamic acid (HA) group in PCI-34051 contributed to its lack of advancement. Therefore, we replaced the HA in the PCI-34051 scaffold with a series of moieties that have the potential to bind to Zn and evaluated their activity in a HDAC8 assay. Surprisingly, none of the replacements effectively mimicked the HA, and analogs lost significant potency. Evaluation of the analogs’ affinity to Zn indicated that none had affinity for Zn within the same range as the HA. These studies point to the difficulty in the application of bioisosteric replacements for Zn binding motifs.

KAJIAN SINTESIS ASAM LEMAK HIDROKSAMAT MENGGUNAKAN MINYAK GORENG BEKAS

Fatty Hydroxamic Acids (FHA) has been successfully synthesized from used cooking oil. The purpose of this research was the enzymatic synthesis of fatty hydroxamic acids from used cooking oil and determine the optimum conditions, which includes three stages of processing, namely the oil preparation stage, the synthesis optimization stage and the characterization stage. At the oil preparation stage, the yield of used cooking oil was 29%. At the optimization stage, the optimum conditions for the synthesis of fatty hydroxamic acids from used cooking oil were at a temperature of 35oC for 25 hours with a ratio of lipase (gram) : hydroxylamine (mmol) equal to 1:500 and the ratio of lipase (gram) : crude bran rice (gram) was equal to 1:75. The number of hydroxamic acid groups in 1 gram of dry sample of fatty hydroxamic acid was 3,16 mmol. Based on the results of the analysis of the color test with Cu (II) and Fe (III), a complex color that is typical for the two metals which obtained with fatty hydroxamic acids, they were green and dark red. Whereas, from the FTIR analysis, the spectrum of the functional groups of hydroxamic acid was obtained.

Synthesis of polyacrylate-divinylbenzene hydroxamic resins and its gallium adsorption performance in sulfuric acid solution

In this study, the adsorption behavior of gallium ions on a synthesized hydroxamic acid resin from sulfuric acid solution was investigated, aiming to recover Ga directly from pressure leaching solution in zinc hydrometallurgical plant. Hydroxamic acid chelating resin (HA-PDR) was prepared by introducing hydroxamic acid groups into the pre-made polyacrylate resin (PDR) with methyl ester group through hydroxylamine reaction. Polyacrylate-divinylbenzene hydroxamic resins with a nitrogen content of up to 3.85 % were obtained at a divinylbenzene (DVB) content of 13 % and an optimal raw material ratio of NH2OH·HCl: NaOH: −CH3 = 4:4.5:1 (molar ratio). The obtained materials was characterized using FTIR, XPS and SEM to verify the successful introduction of hydroxamic acid groups. The results of adsorption experiments showed that the adsorption capacity of 27.65 mg/g could be obtained with a chemical, multilayered, and heterogeneous adsorption process, and film diffusion and intra-particle diffusion rate controlled mainly the adsorption efficiency. It has been proven that polyacrylate-divinylbenzene hydroxamic resins has extremely high adsorption selectivity for gallium in sulfuric acid solution, and the desorption effect is obvious, which can be applied promisingly in the industrial development of gallium extraction technology from zinc leaching residue in sulfuric acid system.

Efficient removal of U(VI) from aqueous solution using poly(amidoxime-hydroxamic acid) functionalized graphene oxide.

The efficient development of selective materials for uranium recovery from wastewater and seawater is crucial for the utilization of uranium resources and environmental protection. The potential of graphene oxide (GO) as an effective adsorbent for the removal of environmental contaminants has been extensively investigated. Further modification of the functional groups on the basal surface of GO can significantly enhance its adsorption performance. In this study, a novel poly(amidoxime-hydroxamic acid) functionalized graphene oxide (pAHA-GO) was synthesized via free radical polymerization followed by an oximation reaction, aiming to enhance its adsorption efficiency for U(VI). A variety of characterization techniques, including SEM, Raman spectroscopy, FT-IR, and XPS, were employed to demonstrate the successful decoration of amidoxime and hydroxamic acid functional groups onto GO. Meanwhile, the adsorption of U(VI) on pAHA-GO was studied as a function of contact time, adsorbent dosage, pH, ionic strength, initial U(VI) concentration, and interfering ions by batch-type experiments. The results indicated that the pAHA-GO exhibited excellent reuse capability, high stability, and anti-interference ability. Specially, the U(VI) adsorption reactions were consistent with pseudo-second-order and Langmuir isothermal adsorption models. The maximum U(VI) adsorption capacity was evaluated to be 178.7mg/g at pH 3.6, displaying a higher U(VI) removal efficiency compared with other GO-based adsorbents in similar conditions. Regeneration of pAHA-GO did not significantly influence the adsorption towards U(VI) for up to four sequential cycles. In addition, pAHA-GO demonstrated good adsorption capacity stability when it was immersed in HNO3 solution at different concentrations (0.1-1.0mol/L) for 72h. pAHA-GO was also found to have anti-interference ability for U(VI) adsorption in seawater with high salt content at near-neutral pH condition. In simulated seawater, the adsorption efficiency was above 94% for U(VI) across various initial concentrations. The comprehensive characterization results demonstrated the involvement of oxygen- and nitrogen-containing functional groups in pAHA-GO in the adsorption process of U(VI). Overall, these findings demonstrate the feasibility of the pAHA-GO composite used for the capture of U(VI) from aqueous solutions.

Biosynthesis of novel desferrioxamine derivatives requires unprecedented crosstalk between separate NRPS-independent siderophore pathways.

Iron is essential to many biological processes but its poor solubility in aerobic environments restricts its bioavailability. To overcome this limitation, bacteria have evolved a variety of strategies, including the production and secretion of iron-chelating siderophores. Here, we describe the discovery of four series of siderophores from Streptomyces ambofaciens ATCC23877, three of which are unprecedented. MS/MS-based molecular networking revealed that one of these series corresponds to acylated desferrioxamines (acyl-DFOs) recently identified from S. coelicolor. The remaining sets include tetra- and penta-hydroxamate acyl-DFO derivatives, all of which incorporate a previously undescribed building block. Stable isotope labeling and gene deletion experiments provide evidence that biosynthesis of the acyl-DFO congeners requires unprecedented crosstalk between two separate non-ribosomal peptide synthetase (NRPS)-independent siderophore (NIS) pathways in the producing organism. Although the biological role(s) of these new derivatives remain to be elucidated, they may confer advantages in terms of metal chelation in the competitive soil environment due to the additional bidentate hydroxamic functional groups. The metabolites may also find application in various fields including biotechnology, bioremediation, and immuno-PET imaging.IMPORTANCEIron-chelating siderophores play important roles for their bacterial producers in the environment, but they have also found application in human medicine both in iron chelation therapy to prevent iron overload and in diagnostic imaging, as well as in biotechnology, including as agents for biocontrol of pathogens and bioremediation. In this study, we report the discovery of three novel series of related siderophores, whose biosynthesis depends on the interplay between two NRPS-independent (NIS) pathways in the producing organism S. ambofaciens-the first example to our knowledge of such functional cross-talk. We further reveal that two of these series correspond to acyl-desferrioxamines which incorporate four or five hydroxamate units. Although the biological importance of these novel derivatives is unknown, the increased chelating capacity of these metabolites may find utility in diagnostic imaging (for instance, 89Zr-based immuno-PET imaging) and other applications of metal chelators.

Chelating Effect of Siderophore Desferrioxamine-B on Uranyl Biomineralization Mediated by Shewanella putrefaciens.

In contaminated water and soil, little is known about the role and mechanism of the biometabolic molecule siderophore desferrioxamine-B (DFO) in the biogeochemical cycle of uranium due to complicated coordination and reaction networks. Here, a joint experimental and quantum chemical investigation is carried out to probe the biomineralization of uranyl (UO22+, referred to as U(VI) hereafter) induced by Shewanella putrefaciens (abbreviated as S. putrefaciens) in the presence of DFO and Fe3+ ion. The results show that the production of mineralized solids {hydrogen-uranium mica [H2(UO2)2(PO4)2·8H2O]} via S. putrefaciens binding with UO22+ is inhibited by DFO, which can both chelate preferentially UO22+ to form a U(VI)-DFO complex in solution and seize it from U(VI)-biominerals upon solvation. However, with Fe3+ ion introduced, the strong specificity of DFO binding with Fe3+ causes re-emergence of biomineralization of UO22+ {bassetite [Fe(UO2)2(PO4)2·8(H2O)]} by S. putrefaciens, owing to competitive complexation between Fe3+ and UO22+ for DFO. As DFO possesses three hydroxamic functional groups, it forms hexadentate coordination with Fe3+ and UO22+ ions via these functional groups. The stability of the Fe3+-DFO complex is much higher than that of U(VI)-DFO, resulting in some DFO-released UO22+ to be remobilized by S. putrefaciens. Our finding not only adds to the understanding of the fate of toxic U(VI)-containing substances in the environment and biogeochemical cycles in the future but also suggests the promising potential of utilizing functionalized DFO ligands for uranium processing.

Iron uptake pathway of Escherichia coli as an entry route for peptide nucleic acids conjugated with a siderophore mimic.

Bacteria secrete various iron-chelators (siderophores), which scavenge Fe3+ from the environment, bind it with high affinity, and retrieve it inside the cell. After the Fe3+ uptake, bacteria extract the soluble iron(II) from the siderophore. Ferric siderophores are transported inside the cell via the TonB-dependent receptor system. Importantly, siderophore uptake paths have been also used by sideromycins, natural antibiotics. Our goal is to hijack the transport system for hydroxamate-type siderophores to deliver peptide nucleic acid oligomers into Escherichia coli cells. As siderophore mimics we designed and synthesized linear and cyclic Nδ-acetyl-Nδ-hydroxy-l-ornithine based peptides. Using circular dichroism spectroscopy, we found that iron(III) is coordinated by the linear trimer with hydroxamate groups but not by the cyclic peptide. The internal flexibility of the linear siderophore oxygen atoms and their interactions with Fe3+ were confirmed by all-atom molecular dynamics simulations. Using flow cytometry we found that the designed hydroxamate trimer transports PNA oligomers inside the E. coli cells. Growth recovery assays on various E. coli mutants suggest the pathway of this transport through the FhuE outer-membrane receptor, which is responsible for the uptake of the natural iron chelator, ferric-coprogen. This pathway also involves the FhuD periplasmic binding protein. Docking of the siderophores to the FhuE and FhuD receptor structures showed that binding of the hydroxamate trimer is energetically favorable corroborating the experimentally suggested uptake path. Therefore, this siderophore mimic, as well as its conjugate with PNA, is most probably internalized through the hydroxamate pathway.

Detection of Microorganisms Using Artificial Siderophore-FeIII Complex-Modified Substrates.

Four FeIII complexes of typical artificial siderophore ligands containing catecholate and/or hydroxamate groups of tricatecholate, biscatecholate-monohydroxamate, monocatecholate-bishydroxamate, and trihydroxamate type artificial siderophores (K3[FeIIILC3], K2[FeIIILC2H1], K[FeIIILC1H2], and [FeIIILH3]) were modified on Au substrate surfaces. Their abilities to adsorb microorganisms were investigated using scanning electron microscopy, quartz crystal microbalance, and AC impedance methods. The artificial siderophore-iron complexes modified on Au substrates (FeLC3/Au, FeLC2H1/Au, FeLC1H2/Au, and FeLH3/Au) showed the selective immobilization behavior for various microorganisms, depending on the structural features of the artificial siderophores (the number of catecholate and hydroxamate arms). Their specificities corresponded well with the structural characteristics of natural siderophores released by microorganisms and used for FeIII ion uptake. These findings suggest that they were generated via specific interactions between the artificial siderophore-FeIII complexes and the receptors on microorganism surfaces. Our observations revealed that the FeL/Au systems may be potentially used as effective microbe-capturing probes that can enable rapid and simple detection and identification of various microorganisms.

Inactivation of siderophore iron-chelating moieties by the fungal wheat root symbiont Pyrenophora biseptata.

We investigated the ability of four plant and soil-associated fungi to modify or degrade siderophore structures leading to reduced siderophore iron-affinity in iron-limited and iron-replete cultures. Pyrenophora biseptata, a melanized fungus from wheat roots, was effective in inactivating siderophore iron-chelating moieties. In the supernatant solution, the tris-hydroxamate siderophore desferrioxamine B (DFOB) underwent a stepwise reduction of the three hydroxamate groups in DFOB to amides leading to a progressive loss in iron affinity. A mechanism is suggested based on the formation of transient ferrous iron followed by reduction of the siderophore hydroxamate groups during fungal high-affinity reductive iron uptake. P. biseptata also produced its own tris-hydroxamate siderophores (neocoprogen I and II, coprogen and dimerum acid) in iron-limited media and we observed loss of hydroxamate chelating groups during incubation in a manner analogous to DFOB. A redox-based reaction was also involved with the tris-catecholate siderophore protochelin in which oxidation of the catechol groups to quinones was observed. The new siderophore inactivating activity of the wheat symbiont P. biseptata is potentially widespread among fungi with implications for the availability of iron to plants and the surrounding microbiome in siderophore-rich environments.