Macrocyclic Antibiotics Research Articles

Characterization of a LAL-type regulator NemR in nemadectin biosynthesis and its application for increasing nemadectin production in Streptomyces cyaneogriseus.

Nemadectin, a macrocyclic lactone antibiotic, is produced by Streptomyces cyaneogriseus ssp. noncyanogenus. A methoxime derivative of nemadectin, moxdectin, has been widely used to control insect and helminth in animal health. Despite the importance of nemadectin, little attention has been paid to the regulation of nemadectin biosynthesis, which has hindered efforts to improve nemadectin production via genetic manipulation of regulatory genes. Here, we characterize the function of nemR, the cluster-situated regulatory gene encoding a LAL-family transcriptional regulator, in the nemadectin biosynthesis gene cluster of S. cyaneogriseus ssp. noncyanogenus NMWT1. NemR is shown to be essential for nemadectin production and found to directly activate the transcription of nemA1-1/A1-2/A2, nemC and nemA4/A3/E/D operons, but indirectly activate that of nemG and nemF. A highly conserved sequence 5'-TGGGGTGKATAGGGGGTA-3' (K=T/G) is verified to be essential for NemR binding. Moreover, four novel targets of NemR, including genes encoding an SsgA-like protein (TU94_12730), a methylmalonyl-CoA mutase (TU94_19950), a thioesterase of oligomycin biosynthesis (TU94_22425) and a MFS family transporter (TU94_24835) are identified. Overexpression of nemR significantly increased nemadectin production by 79.9%, in comparison with NMWT1, suggesting that nemR plays an important role in the nemadectin biosynthesis.

Flexizyme-Enabled Benchtop Biosynthesis of Thiopeptides.

Thiopeptides are natural antibiotics that are fashioned from short peptides by multiple layers of post-translational modification. Their biosynthesis, in particular the pyridine synthases that form the macrocyclic antibiotic core, has attracted intensive research but is complicated by the challenges of reconstituting multiple-pathway enzymes. By combining select RiPP enzymes with cell free expression and flexizyme-based codon reprogramming, we have developed a benchtop biosynthesis of thiopeptide scaffolds. This strategy side-steps several challenges related to the investigation of thiopeptide enzymes and allows access to analytical quantities of new thiopeptide analogs. We further demonstrate that this strategy can be used to validate the activity of new pyridine synthases without the need to reconstitute the cognate prior pathway enzymes.

Chiral Mobile-Phase Additives in HPLC Enantioseparations.

High-performance liquid chromatography (HPLC) is one of the main separation techniques for chiral drugs. Among the chiral HPLC techniques available, the chiral mobile-phase additive (CMPA) technique is a valuable method for the direct enantioseparation of chiral chemical entities. In the CMPA method, the chiral selector is dissolved in the mobile phase while the stationary phase is achiral. Interaction with the analyte enantiomers results in the formation of transient diastereomeric complexes. These complexes differ in their formation constants and/or distribution between the (achiral) stationary phase and the mobile phase resulting in an enantioseparation. This chapter describes the HPLC separation applying CMPA methods by several most useful types of chiral selectors including chiral ligand exchangers, macrocyclic antibiotics, and cyclodextrins.

Preparation of macrocycle antibiotic chiral stationary phases by wrapping with a net in high performance liquid chromatography

Vancomycin and teicoplanin are glycopeptide macrocyclic antibiotics with three-dimensional ring structures and multiple chiral centers. They are commonly used chiral recognition materials in enantioseparation by high-performance liquid chromatography. In this study, six chiral stationary phases wrapped with a net on silica gels were prepared by interfacial polymerization using vancomycin and teicoplanin as chiral selectors, piperazine as a monomer, 4,4'-diphenylmethane diisocyanate (MDI), 1,6-hexamethylene diisocyanate (HDI), and 2,4-toluene diisocyanate (TDI) as crosslinker. The fabricated chiral columns were used for enantioseparations. Compared to the crosslinked and commercial columns composed of vancomycin and teicoplanin, the columns wrapped with a net exhibited complementarity for the optical resolutions.

A Facile and Sensitive Electrochemical Analysis Based on Flower-Like Nanocomposite Supported Teicoplanin as the Recognition Element for Tyrosine Enantiomers

A facile and sensitive chiral analysis for the recognition of tyrosine (Tyr) enantiomers has been designed based on teicoplanin (Tei) and a flower-like nanocomposite which consisted of copper-platinum core-shell microspheres and single-walled carbon nanotubes-molybdenum disulfide (Cu@Pt/SWCTNs-MoS2). The flower-like nanocomposite was employed to improve the immobilization of the chiral selector Tei and the electrochemical performance. The nanocomposite was characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), Raman spectrum, fourier transform infrared spectroscopy (FTIR), water contact angles and electrochemical methods. The interaction between Tyr enantiomers and the Tei/Cu@Pt/SWCTNs-MoS2 chiral interface was determined via differential pulse voltammetry (DPV). The results exhibited enantioselective interaction between the modified electrodes and Tyr enantiomers, and a stronger interaction was obtained from L-Tyr than D-Tyr. The DPV responses were linearly dependent with concentration in the range of 10.0 μmol·L−1 to 5.0 mmol·L−1, and the limits of detection were 3.2 μmol·L−1 and 4.7 μmol·L−1 for L-Try and D-Tyr (at S/N = 3), respectively. The simple and cost-effective method opens up a new channel for the application of macrocyclic antibiotics.

LB12. Safety and Efficacy of Fidaxomicin and Vancomycin in Pediatric Patients with Clostridium difficile Infection: Phase III, Multicenter, Investigator-blind, Randomized, Parallel Group (SUNSHINE) Study

Background Clostridium difficile infection (CDI), a common cause of antibiotic-associated diarrhea, leads to substantial healthcare burden. In children and young adults, the incidence of CDI is increasing. Fidaxomicin (FDX) is a narrow-spectrum macrocyclic antibiotic treatment for CDI in adults, but pediatric data are limited. The primary objective of our study was to investigate safety and efficacy of FDX and vancomycin (VAN) in children.MethodsPatients aged <18 years with new laboratory-confirmed CDI and diarrhea (watery diarrhea for patients aged <2 years, and ≥3 unformed bowel movements in 24 hours for patients aged ≥2 years) were enrolled in a randomized, investigator-blinded study. Participants were randomized (2:1) to 10 days of treatment with either FDX (oral suspension 32 mg/kg/day or tablets 200 mg BID) or VAN (oral liquid 40 mg/kg/day or capsules 125 mg QID). Concurrent use of other antibiotic treatment for CDI was not permitted. Randomization was stratified by age group. The primary efficacy endpoint was confirmed clinical response (CCR) at Day 12 (absence of diarrhea for 2 consecutive days on treatment and remaining well until treatment discontinuation). Other efficacy endpoints were also evaluated.ResultsOf 142 patients in the full analysis set (FDX n = 98; VAN n = 44), 30 were aged <2 years, 48 were aged 2 to <6 years, 36 were aged 6 to <12 years and 28 were aged 12 to <18 years. At baseline, 28.6% of the FDX arm and 22.7% of the VAN arm had prior confirmed CDI. Overall, 73.5% of the FDX arm and 75.0% of the VAN arm had ≥1 treatment-emergent adverse event. There were three deaths in the FDX arm during the study and two deaths in the VAN arm after end of study (post-Day 40); none were related to treatment. There was a trend to improved CCR and other efficacy outcomes for FDX (figure) and this was statistically significant for global cure (adjusted difference 18.8%; 95% CI 1.5%, 35.3%).ConclusionsThere was a consistent trend for improved efficacy outcomes with FDX compared with VAN, as shown by the adjusted treatment differences, although the small sample size precluded conclusions on most outcome differences.Figure. Disclosures J. Wolf, Astellas Pharma: Consultant and Non-Financial Support, Consulting fee and This study was initiated and sponsored by Astellas. Medical writing support was provided by Cello Health MedErgy and funded by Astellas. . K. Kalocsai, Astellas Pharma: Non-Financial Support, This study was initiated and sponsored by Astellas. Medical writing support was provided by Cello Health MedErgy and funded by Astellas. . C. Fortuny, Astellas Pharma: Non-Financial Support, This study was initiated and sponsored by Astellas. Medical writing support was provided by Cello Health MedErgy and funded by Astellas. . S. Lazar, Astellas Pharma: Non-Financial Support, This study was initiated and sponsored by Astellas. Medical writing support was provided by Cello Health MedErgy and funded by Astellas. . S. Bosis, Astellas Pharma: Non-Financial Support, This study was initiated and sponsored by Astellas. Medical writing support was provided by Cello Health MedErgy and funded by Astellas. . B. Korczowski, Astellas Pharma: Non-Financial Support, This study was initiated and sponsored by Astellas. Medical writing support was provided by Cello Health MedErgy and funded by Astellas. . A. Petit, Astellas Pharma: Non-Financial Support, This study was initiated and sponsored by Astellas. Medical writing support was provided by Cello Health MedErgy and funded by Astellas. . D. Bradford, Astellas Pharma: Employee and Non-Financial Support, Medical writing support was provided by Cello Health MedErgy and funded by Astellas. and Salary. E. Incera, Astellas Pharma: Employee of Iqvia, a CRO contracted by Astellas, Medical writing support was provided by Cello Health MedErgy and funded by Astellas. . J. Melis, Astellas Pharma: Employee and Non-Financial Support, Medical writing support was provided by Cello Health MedErgy and funded by Astellas. and Salary. R. Van Maanen, Astellas Pharma: Employee and Non-Financial Support, Medical writing support was provided by Cello Health MedErgy and funded by Astellas. and Salary.

Macrocyclic Antibiotics as Chiral Selectors in High-Performance Liquid Chromatography and Capillary Electrophoresis

Data on the use of macrocyclic antibiotics (vancomycin, teicoplanin, teicoplanin aglycone, and eremomycin) for the enantioseparation of amino acids, various amino acid derivatives, α-phenylcarboxylic acids, β-blockers, and some pharmaceutical preparations in reversed-phase and polar-organic HPLC modes are summarized. It is shown that mixed chiral selectors (eremomycin–vancomycin, eremomycin–bovine serum albumin) combine the properties of two selectors. Eremomycin and macrolides (azithromycin, erythromycin, and clarithromycin) are successfully used as chiral selectors in capillary electrophoresis. Aqueous and aqueous–organic supporting electrolytes (SEs) with the addition of eremomycin or nonaqueous supporting electrolytes with the addition of a macrolide are used for enantioseparation. The use of nonaqueous supporting electrolytes decreases the adsorption of the selectors on the quartz capillary surface and enables the separation of enantiomers at a low concentration of a chiral selector. Additions of boric acid into the supporting electrolyte improve the selectivity of separation.

Смешанные хиральные неподвижные фазы в хроматографии (обзор)

Обсуждается использование смешанных селекторов в газовой и высокоэффективной жидкостной хроматографии для разделения оптических изомеров. Они позволяют повысить универсальность хиральной фазы. В газовой хроматографии широко и успешно используются смеси модифицированного β-циклодекстрина. В ВЭЖХ наиболее изучены смешанные хиральные селекторы на основенизкомолекулярных селекторов и производных полисахаридов, в меньшей степени ̶ белков и макроциклических антибиотиков.

Combination of field amplified sample injection and hydrophobic interaction electrokinetic chromatography (FASI-HIEKC) as a signal amplification method for the determination of selected macrocyclic antibiotics

In this study, a field amplified sample injection (FASI) and hydrophobic interaction electrokinetic chromatography (HIEKC) method has been developed for the separation of five macrolide antibiotics: spiramycin, ivermectin, tylosin, josamycin, rapamycin, and one ansamycin drug – rifamycin. By the manipulation of both the sample and separation buffer compositions, their pH values and molarity, a systematic approach has been achieved to maximize analyte differential electrophoretic mobility and signal amplification. The impact of the sample solution composition and the injection mode on the signal amplification effect of the six tested antibiotics was also investigated. Moreover, the influence of the injection of the sample and the water plug on the quantity, symmetry and height of the analyte signal was demonstrated. All the analytes were completely resolved in less than 8 min in an uncoated fused-silica capillary of 75 μm internal diameter (I.D.) x 50 cm length. The electrophoretic separations were performed in a 60% (v/v) acetonitrile and 20 mM phosphate electrolyte system (pH 7.1) with an applied voltage of 25 kV. The established method was validated and confirmed to be applicable for the determination of the active ingredients in a quality control analysis.

Direct analysis of chiral active pharmaceutical ingredients and their counterions by ultra high performance liquid chromatography with macrocyclic glycopeptide-based chiral stationary phases

In this work the simultaneous separation of chiral active pharmaceutical ingredients (API) in salt form from their counterions has been performed by using different high-efficiency macrocyclic glycopeptide-based chiral stationary phases (CSPs). Not only a new zwitterionic vancomycin-based CSP has been prepared (similarly to what was done for teicoplanin) but macrocyclic selectors have also been bonded to sub-2 μm fully porous silica particles through traditional ureidic linkage to obtain versions of CSPs suitable for ultra-high performance applications. The direct separation of chiral APIs and counterions is particularly attracting since it simplifies the workflow traditionally used with reduction of analysis time and costs. The wide selection of macrocyclic antibiotics CSPs now available has allowed to manage different cases that can happen in the simultaneous separation of APIs and their counterions (either cations or anions). Indeed, while inorganic cations are retained on traditional vancomycin- and teicoplanin-based CSPs, inorganic anions are almost unretained (due to Donnan’s effect). On the other hand, cations and anions can be both retained on the zwitterionic versions of these CSPs. Afterwards, zwitterionic CSPs allowed the separation of other compounds including N-derivative amino-acids, profens, polyols, sugar anomers, oligosaccharides and inorganic anions/cations opening new perspectives in the use of this family of CSPs.

Macrocyclic Compounds from Ansamycin Antibiotic Class as Inhibitors of PD1-PDL1 Protein-Protein Interaction.

The ability of tumors to escape from immune destruction is attributed to the protein-protein interaction between programmed cell death protein 1 (PD1) and programmed cell death ligand 1 (PDL1) proteins expressed by immune T cells and cancer cells, respectively. Therefore, pharmacological inhibition of the PD1-PDL1 interaction presents an important therapeutic target against a variety of tumors expressing PDL1 on their cell surface. Recently, five antibodies have been approved and several are in clinical trials against the PD1-PDL1 protein-protein interaction target. In contrast, there are very few reports of small-molecule inhibitors of PD1-PDL1 interaction, and most of them have relatively modest or weak inhibition activities, emphasizing the difficulty in designing small-molecule inhibitors against this challenging target. Therefore, we focused our attention on macrocycles that are known to exhibit target activity comparable to large macromolecules despite having molecular weights closer to small, drug-like molecules. In this context, our present study led to the identification of several macrocyclic compounds from the ansamycin antibiotics class to be inhibitors of PD1-PDL1 interaction. Importantly, one of these macrocyclic antibiotics, Rifabutin, showed an IC50 value of ca. 25 µM. This is remarkable considering it has a relatively low molecular weight and still is capable of inhibiting PD1-PDL1 protein-protein interaction whose binding interface spans over ca. 1970 Å2. Thus, these macrocycles may serve as guiding points for discovery and optimization of more potent, selective small-molecule inhibitors of PD1-PDL1 interaction, one of the most promising therapeutic targets against cancer.

Total Synthesis and Biological Evaluation of the Glycosylated Macrocyclic Antibiotic Mangrolide A.

The macrocyclic antibiotic mangrolide A has been described to exhibit potent activity against a number of clinically important Gram-negative pathogens. Reported is the first enantioselective total synthesis of mangrolide A and derivatives. Salient features of this synthesis include a highly convergent macrocycle preparation, stereoselective synthesis of the disaccharide moiety, and two β-selective glycosylations. The synthesis of mangrolide A and its analogues enabled the re-examination of its activity against bacterial pathogens, and only minimal activity was observed.

Screening of macrocycles retention for microplanar analytical devices involving host-guest interactions and silica or octadecylsilica adsorbents

ABSTRACTThis paper reports planar chromatographic behavior and multivariate characterization of three types of macrocyclic compounds: cyclodextrins, calixarenes and macrocyclic antibiotics. Additionally two non-macrocyclic chemicals (estriol and pyrene) were analyzed as the reference retention markers. Target compounds were chromatographed using normal and reversed-phase systems and involving mono as well as binary water-organic liquids mobile phases based on methanol, ethanol and acetonitrile. Non-forced flow TLC/HPTLC elution was performed under isothermal (elevated temperature = 303 K) and mobile phase vapor saturated conditions using 10 cm long glass plates positioned vertically inside temperature controlled Dewar type chambers. It is hoped that presented retention data, which were collected for the whole range of binary mobile phases compositions (0–100%) may be useful for designing of hybrid active layers for extraction, separation and detection systems involving host-guest interactions. Retention profiles were inspected using multivariate statistics (principal component analysis, PCA). Based on reported data various extraction and separation systems can be created where weak or strong interactions of macrocycles with chromatographic stationary phases or given micro device active supports should be expected. Particularly, studied macrocycles can be applied as selective additives for solid phase adsorption (SPE, SPME), microfluidic paper devices (μPAD) as well as micro-total analytical systems (μTAS), where bars formed active layers are fabricated.

Organic solute transporter OSTα/β is overexpressed in nonalcoholic steatohepatitis and modulated by drugs associated with liver injury.

The heteromeric steroid transporter organic solute transporter α/β (OSTα/β, SLC51A/B) was discovered over a decade ago, but its physiological significance in the liver remains uncertain. A major challenge has been the lack of suitable models expressing OSTα/β. Based on observations first reported here that hepatic OSTα/β is upregulated in nonalcoholic steatohepatitis, the aim of this research was to develop an in vitro model to evaluate OSTα/β function and interaction with drugs and bile acids. OSTα/β expression in human liver tissue was analyzed by quantitative RT-PCR, Western blotting, and immunofluorescence. Radiolabeled compounds were used to determine OSTα/β-mediated transport in the established in vitro model. The effect of bile acids and drugs, including those associated with cholestatic drug-induced liver injury, on OSTα/β-mediated transport was evaluated. Expression of OSTα/β was elevated in the liver of patients with nonalcoholic steatohepatitis and primary biliary cholangitis, whereas hepatocyte expression of OSTα/β was low in control liver tissue. Studies in the novel cell-based system showed rapid and linear OSTα/β-mediated transport for all tested compounds: dehydroepiandrosterone sulfate, digoxin, estrone sulfate, and taurocholate. The interaction study with 26 compounds revealed novel OSTα/β inhibitors: a biomarker for cholestasis, glycochenodeoxycholic acid; the major metabolite of troglitazone, troglitazone sulfate; and a macrocyclic antibiotic, fidaxomicin. Additionally, some drugs (e.g., digoxin) consistently stimulated taurocholate uptake in OSTα/β-overexpressing cells. Our findings demonstrate that OSTα/β is an important transporter in liver disease and imply a role for this transporter in bile acid-bile acid and drug-bile acid interactions, as well as cholestatic drug-induced liver injury. NEW & NOTEWORTHY The organic solute transporter OSTα/β is highly expressed in hepatocytes of liver tissue obtained from patients with nonalcoholic steatohepatitis and primary biliary cholangitis. OSTα/β substrates exhibit rapid, linear, and concentration-driven transport in an OSTα/β-overexpressing cell line. Drugs associated with hepatotoxicity modulate OSTα/β-mediated taurocholate transport. These data suggest that hepatic OSTα/β plays an essential role in patients with cholestasis and may have important clinical implications for bile acid and drug disposition.

Safety and clinical efficacy of tenvermectin, a novel antiparasitic 16-membered macrocyclic lactone antibiotics

Tenvermectin (TVM) is a novel 16-membered macrocyclic lactone antibiotics, which contains component TVM A and TVM B. However there is not any report on safety and clinical efficacy of TVM for developing as a potential drug. In order to understand the part of safety and clinical efficacy of TVM, we conducted the acute toxicity test, the standard bacterial reverse mutation (Ames) test and the clinical deworming test. In the acute toxicity studies, TVM, TVM A and ivermectin (IVM) were administrated once by oral gavage to mice and rats. Results showed that the oral LD50 values of TVM, TVM A and IVM in mice were 74.41, 106.95 and 53.06 mg/kg respectively. The oral LD50 values of TVM and TVM A in rats were determined to be 164.22 and 749.34 mg/kg respectively. TVM and IVM are moderately toxic substances, meanwhile the TVM A belongs to low toxic compounds, implying that the acute toxicity is highly related to the length of side chain of TVM at position C25. In the Ames test, results showed that TVM did not induce mutagenicity in Salmonella typhimurium TA97a, TA98, TA100, TA102 and TA1535 with and without metabolic activation system, speculating that the mutagenicity is probably not related to the side chain at position C25 of 16-membered macrocyclic lactone antibiotics. In the efficacy trail of TVM against swine nematodes, growing pigs natural infection of Ascaris suum and Trichuris suis were treated with a single subcutaneous injection 0.3 mg/kg b.w.. Results showed that TVM and IVM had excellent effect in expelling Ascaris suum, and TVM had potential efficacy against Trichuris suis, however IVM had no effect on Trichuris suis. This study suggests that the side chain of TVM at position C25 may have important biological functions, which is one of the key sites of the studies on structure-activity relationship of 16-membered macrocyclic lactone compounds. TVM is a new compound exhibited some advantages worthy of developing.

Comparison of Fidaxomicin and Vancomycin for Recurrent Clostridium difficile Colitis

BackgroundFidaxomicin is a narrow spectrum macrocyclic antibiotic used for the treatment of Clostridium difficileinfection (CDI). The objective of this study is to compare the recurrence and mortality rates of patients with CDI who received either vancomycin or fidaxomicin at Stony Brook University Hospital.MethodsA retrospective chart review was performed to identify all hospitalized patients who received fidaxomicin and vancomycin for CDI for the period 2011–2015. Inclusion criteria included patient age ≥18 years, stool positive PCR test for C. difficile and being treated ≥10 days of either fidaxomicin or vancomycin orally. Clinical recurrence was defined as a return of diarrhea, a positive test for C. difficiletoxin B and a need for retreatment for CDI within 90 days of cessation of therapy.ResultsA total of 55 (52.7% male) and 74 (51.4% male) cases met inclusion criteria in the fidaxomicin (F) and vancomycin (V) groups, respectively. The mean age was 65.9 ± 1.88 and 63.7 ± 1.86 years in group F and V respectively (P = 0.4). Median length of hospitalization was 14 and 9 days for F and V respectively (P = 0.6). Both groups had similar proportions on the following variables: immunosuppression (V 36.5% vs. F 36.4%; P = 0.9), ≥ 1 prior episode of CDI (V 59.5% vs. F 61.8%; P = 0.8), sepsis on admission (V 29.7%, F 36.4%; P = 0.4), the use of any antibiotic during the last 30 days (V 74.3%, 71%, P = 0.7), and treatment with additional anti-CDI therapy (V 24.3%, F 29.1%; P = 0.5). CDI recurrence rate was 24% (V) and 40% (F, P = 0.057). The 90-day mortality rate was 4.1% in the vancomycin group and 10.9% in the fidaxomicin group (P = 0.13).ConclusionFidaxomicin had a higher recurrent CDI than vancomycin in this tertiary medical center.Disclosures All authors: No reported disclosures.

Fidaxomicin reduces early toxin A and B production and sporulation in Clostridium difficilein vitro.

Fidaxomicin, a macrocyclic antibiotic, has been approved for the treatment of Clostridium difficile infection (CDI). Previous work by our group has demonstrated that some antibiotics at sub-inhibitory concentrations stimulate early toxin production and sporulation by C. difficile. Prior studies revealed that fidaxomicin, when added to late stationary-phase organisms, reduced exotoxin production and spore formation by C. difficile. However, the ability of fidaxomicin to trigger early virulence factor production and spore formation has never been investigated. Sub-inhibitory concentrations of the RNA synthesis inhibitor fidaxomicin (1/4×, 1/8×, 1/16× MIC) were added immediately to lag-phase cultures of historical (strain 9689) and epidemic BI/NAP1/027 (strain 5325) strains of C. difficile, and their effects on sporulation and toxin A (TcdA) and toxin B (TcdB) production were compared.Results/Key findings. Even at sub-inhibitory concentrations, all doses of fidaxomicin reduced both TcdA and TcdB gene expression and protein production in the historical and epidemic C. difficile strains. Fidaxomicin also dose-dependently reduced viable spore production by the 9689 and 5325 strains. Reductions in spore formation were also observed in both strains treated with tigecycline and vancomycin. However, all concentrations of metronidazole stimulated a ~2 log increase in spore production by the 5325 isolate. The ability of fidaxomicin to suppress early exotoxin production and endospore formation by historical and epidemic strains of C. difficile may explain its clinical success in treating severe and recurrent cases of CDI disease.

Hotspot, difficulty and progress in pediatric respiratory diseases

In recent years, with the continuous development of medical technology and progress, knowledge regarding respiratory disease become deepening, especially in lower respiratory tract infection bacterial resistance, application of macrocyclic ester antibiotics, severe and refractory mycoplasma pneumonia, refractory asthma, interstitial lung diseases, pediatric interventional bronchoscopy, and stem cell therapy which all have made great progress.In this review, the related hotspot, difficulty and research progress are summarized. Key words: Child; Respiratory diseases; Progress

Advances in macrocyclic peptide-based antibiotics

Macrocyclic peptide-based natural products have provided powerful new antibiotic drugs, drug candidates, and scaffolds for medicinal chemists as a source of inspiration to design novel antibiotics. While most of those natural products are active mainly against Gram-positive pathogens, novel macrocyclic peptide-based compounds have recently been described, which exhibit potent and specific activity against some of the most problematic Gram-negative ESKAPE pathogens. This mini-review gives an up-date on recent developments.

The incorporation and removal of &amp;Prime;auxiliary&amp;Prime; building blocks and their functions in the biosynthesis of polyketides and non-ribosomal polypeptides

Natural products that produced by animals, plants or microorganisms, especially polyketides (PKs), non-ribosomal peptides (NRPs) and their hybrids, exhibit an extremely wide range of biological activities, include antibacterial, antifungal, antitumor, antiviral and immunosuppressive activities, which underlie the critical roles of natural products in medical industry as various drugs. The biosynthetic pathways of PKs, NRPs and their hybrids share a templated multifunctional enzymology for skeleton assembly. Polyketide synthases (PKSs) usually catalyze C−C bond formation using short carboxylic acid as monomers, whereas non-ribosomal peptide synthetases (NRPSs) incorporate amino acids through C−N bond formation. Consistent with their catalytic cycles, both PKSs and NRPSs are often giant enzymes organized into modules, which each contains a common thiolation (T) domain for loading building blocks. A prototype of a PKS module consists of an acyltransferase (AT), a T domain and a β-ketoacyl synthase (KS) domain. A minimum NRPS module contains an adenylation (A) domain, a T domain and a condensation (C) domain. AT or A domain is responsible for recognition and activation of building blocks, while KS or C domain catalyzes the elongation of the growing skeleton. In general, modular PKSs or NRPSs appear to function as assembly lines, which program monomer polymerization/modification and chain tailoring/termination following a non-iteratively ″one domain, one function″ like co-linearity rule. Thus, the domain composition of each module and the number of modules can be used to predict the structure of skeleton. However, there are exceptions reported in recent years, as modules are now known to be both skipped and iterated during the normal biosynthetic processes. In addition, another origin for a lack of correlation between domain composition of the multienzyme complex and the final product structure has been identified recently. In this case, the missing building blocks are normally incorporated on the assembly lines, but they will be removed by the post-assembly modifications. These kind of building blocks which would not appear in the final products seem ″unnecessary″, but they are essential in the biosynthetic pathways exactly. In this review, we summarize these ″auxiliary″ building blocks, focus on the chemical mechanisms of the incorporation and removal of them and discuss their biological functions that have been reported since 2000. The related building blocks here include fatty acyls, amino acids, unnatural amino acids and fatty acyl-amino acids. Some of these ″auxiliary″ build blocks are involved in the biosynthesis of natural products with specific structures, such as 2,2′-bipyridine cores, tetrahydroisoquinoline alkaloids, β-lactam and macrocyclic lactam antibiotics. In this case, building blocks are incorporated by the PKSs, NRPSs or their hybrids assembly lines, but the chemical mechanisms are unusual. The biological functions of these kind of building blocks are considered to be strategies for protection of the reactive groups and mediation of molecular assembly and modifications. On the other hand, some of the ″auxiliary″ building blocks are present in biosynthesis of natural products which are structurally different from each other, however, the ″unnecessary″ building blocks are almost same and their chemical mechanisms of incorporation and removal are similar. These kind of building blocks are proposed to be very important for protection the chemical producers by prodrug generation. In summary, the molecules mentioned in this review could increase the knowledge regarding the ″auxiliary″ building blocks, add another layer of complexity to natural product biosynthesis, help to hypothesize biosynthetic pathways of other natural products with specific structures and assist the association of molecules and their gene clusters.