Biomimetic synthesis of gramicidin s and analogues by enzymatic cyclization of linear precursors on solid support

[reaction: see text] Gramicidin S is a potent decapeptide antibiotic with high hemolytic activity but is unlikely to provoke microbial resistance. Here we demonstrate that gramicidin thioesterase (GrsB TE) correctly cyclizes immobilized linear decapeptide precursors into head-to-tail products, indicating its suitability for parallel solid-phase synthesis of gramicidin analogues from linear precursors on solid support. This chemoenzymatic method will enable the optimization of the therapeutic index of the natural product to fight microbial resistance.     

Green solid-phase peptide synthesis 4. γ-Valerolactone and N-formylmorpholine as green solvents for solid phase peptide synthesis

Herein, we report the use of γ-valerolactone (GVL) and N-formylmorpholine (NFM) as DMF substitutes in polystyrene based SPPS. The solubility of selected amino acids and coupling reagents were studied in GVL and NFM, followed by their use in the successful synthesis of Aib-enkephalin pentapeptide (H-Tyr-Aib-Aib-Phe-Leu-NH₂) and Aib-ACP decapeptide (H-Val-Gln-Aib-Aib-Ile-Asp-Tyr-Ile-Asn-Gly-NH₂).     

High-pressure-promoted Fmoc-aminoacylation of N-ethylcysteine: preparation of key devices for the solid-phase synthesis of peptide thioesters

In this study synthesis of Fmoc-aminoacyl-N-ethyl-S-triphenylmethylcysteine, a new N→S acyl migratory device for the preparation of peptide thioesters by Fmoc solid-phase peptide synthesis (SPPS) is described. Condensation of Fmoc-aminoacyl fluoride and N-ethyl-S-triphenylmethylcysteine allyl ester, readily prepared from known S-triphenylmethylcysteine allyl ester, was efficiently promoted in CH₂Cl₂ under high-pressure (800 MPa). When the reaction was performed with the additive DIEA, considerable epimerization at the chiral centers occurred, affording a mixture of diastereomers. When the preparation procedure for N-ethyl-S-triphenylmethylcysteine allyl ester was changed and the additive DIEA in the high-pressure reaction was excluded, Fmoc-aminoacyl-N-ethyl-S-triphenylmethylcysteines was obtained as a single stereoisomer without epimerization. The Fmoc-l-leucine adduct thus prepared was deallylated and used for the SPPS of a known decapeptide. A remarkable increase (44%) in the overall yield of the decapeptidethioester was achieved, compared to the 7% obtained by the stepwise on-resin Leu-Cys condensation method.     

Sunflower trypsin inhibitor (SFTI-1) analogues of synthetic and biological origin via N→S acyl transfer: potential inhibitors of human Kallikrein-5 (KLK5)

Sunflower Trypsin Inhibitor (SFTI-1) analogues have been prepared from simple linear precursors produced either by chemical synthesis or following purification from Escherichia coli. We have shown, for the first time that these linear SFTI-1 derived peptide sequences can be converted to circular peptides via selective consecutive acyl transfer reactions, and that the products derived from synthetic and bacterial origin are identical. Preliminary analysis of the semi-synthetic SFTI-1 analogues confirmed SFTI-I10H as an inhibitor of Kallikrein-5 (KLK5) protease that could also mediate its action on human keratinocytes. The preliminary results obtained serve as a useful starting point for the biological production of SFTI-1 based, selective KLK5 inhibitors for the treatment of atopic dermatitis.     

Synthesis of the repeating decapeptide unit of Mefp1 in orthogonally protected form

Mefp1 is a protein produced by the marine mussel, Mytilus edulis, which helps the organism to adhere to surfaces in turbulent waters. To better understand the nature of the adhesion process, we sought to synthesize homogeneous oligopeptides based on the repeating decapeptide unit of the protein. The fully protected decapeptide 10 has been synthesized from appropriately protected amino acid building blocks using a fragment condensation strategy. A key feature of the strategy is the late incorporation of the synthetically valuable dihydroxyproline residue. This synthesis of the orthogonally protected repeating decapeptide unit of Mefp1 represents an important first step toward producing useful quantities of homogeneous oligopeptides related to the protein.     

Biosynthetic studies of Nocathiacin-I

Nocathiacin-I is one of the newest members of thiazolyl peptide class of antibiotics. It is a potent inhibitor of bacterial protein synthesis and showed potent in vitro and in vivo Gram-positive antibacterial activity. Understanding of the biosynthesis of natural products is important for improvement of titer and precursor directed biosynthesis for new compounds. Biosynthesis of nocathiacin-I in Amycolatopsis fastidiosa using stable isotope precursor incorporation is described.     

Microbially induced separation of quartz from hematite using sulfate reducing bacteria

Cells and metabolic products of Desulfovibrio desulfuricans were successfully used to separate quartz from hematite through environmentally benign microbially induced flotation. Bacterial metabolic products such as extracellular proteins and polysaccharides were isolated from both unadapted and mineral-adapted bacterial metabolite and their basic characteristics were studied in order to get insight into the changes brought about on bioreagents during adaptation. Interaction between bacterial cells and metabolites with minerals like hematite and quartz brought about significant surface-chemical changes on both the minerals. Quartz was rendered more hydrophobic, while hematite became more hydrophilic after biotreatment. The predominance of bacterial polysaccharides on interacted hematite and of proteins on quartz was responsible for the above surface-chemical changes, as attested through adsorption studies. Surface-chemical changes were also observed on bacterial cells after adaptation to the above minerals. Selective separation of quartz from hematite was achieved through interaction with quartz-adapted bacterial cells and metabolite. Mineral-specific proteins secreted by quartz-adapted cells were responsible for conferment of hydrophobicity on quartz resulting in enhanced separation from hematite through flotation.     

Searching Hit Potential Antimicrobials in Natural Compounds Space against Biofilm Formation

Biofilms are communities of microorganisms that can colonize biotic and abiotic surfaces and thus play a significant role in the persistence of bacterial infection and resistance to antimicrobial. About 65% and 80% of microbial and chronic infections are associated with biofilm formation, respectively. The increase in infections by multi-resistant bacteria instigates the need for the discovery of novel natural-based drugs that act as inhibitory molecules. The inhibition of diguanylate cyclases (DGCs), the enzyme implicated in the synthesis of the second messenger, cyclic diguanylate (c-di-GMP), involved in the biofilm formation, represents a potential approach for preventing the biofilm development. It has been extensively studied using PleD protein as a model of DGC for in silico studies as virtual screening and as a model for in vitro studies in biofilms formation. This study aimed to search for natural products capable of inhibiting the Caulobacter crescentus enzyme PleD. For this purpose, 224,205 molecules from the natural products ZINC15 database, have been evaluated through molecular docking and molecular dynamic simulation. Our results suggest trans-Aconitic acid (TAA) as a possible starting point for hit-to-lead methodologies to obtain new inhibitors of the PleD protein and hence blocking the biofilm formation.     

Facile synthesis of Gramicidin S via cyclication of a linear pentapeptide

Azide and N-hydroxysuccinimide ester of five pentapeptides related to gramicidin S (cyclic decapeptide) were cyclized to determine the ratio of dimer to monomer in the cyclization product, the pentapeptide derivative with D-Phe as C-terminus giving the dimer in good yield.     

A task-specific ionic liquid [bmim]SCN for the conversion of alkyl halides to alkyl thiocyanates at room temperature

A new “task-specific” ionic liquid (TSIL), 1-n-butyl-3-methylimidazolium thiocyanate ([bmim]SCN), has been prepared and used for the first time as the medium as well as reactant for the synthesis of alkyl thiocyanates from the corresponding alkyl halides by thiocyanate-halide exchange at room temperature. The alkyl thiocyanate products can be easily isolated from the reaction mixture by simple extraction and the ionic liquid 1-n-butyl-3-methylimidazolium halide may be reused for the synthesis of the ionic liquid [bmim]SCN and recycled for further use.     

Synthesis,characterisation and antibacterial studies of carbon nanoparticle and carbon nanoparticle encapsulated in functionally modified β-cyclodextrin with {5-[4-(dimethylamino) benzylidene]-4-oxo-2-thioxo-1, 3-thiazolidin-3-yl} acetic acid

This paper describes the synthesis of carbon nanoparticle (CNP) from natural sources such as kitchen soot, synthesis of a chromophoric system {5-[4-(dimethylamino) benzylidene]-4-oxo-2-thioxo1, 3-thiazolidin-3-yl} acetic acid and its incorporation into β-cyclodextrin (β-CD) through the esterification of the hydroxyl group with the free carboxyl function of the chromophoric system by DCC coupling. Encapsulation of CNP into functionally modified β-CD system was achieved. Characterisation of the products was undertaken by UV–visible, FT-IR, NMR, fluorescence spectroscopic methods, SEM, TEM and X-ray diffraction methods. Their antibacterial activities were addressed. The antibacterial activity of CNP and functionally modified β-CD-CNP products were tested against various pathogenic bacterial strains such as Streptcoccus haemoliticus (+ve), Staphylococcus aureus (+ve), Klebsiella pneumonia (?ve) and E. coli (MTCC1687) (?ve) by disc diffusion method. The results showed that the CNPs and functionally modified products have good antibacterial activity against selected pathogenic bacterial strains.     

An intramolecular oxo Diels-Alder approach to 1-oxo-1,2,3,3a,4,7a-hexahydro-pyrano[3,4-c]pyrrole-4-carboxylic acid ethyl esters

The diastereoselective synthesis of a series of 1-oxo-1,2,3,3a,4,7a-hexahydro-pyrano[3,4-c]pyrrole-4-carboxylic acid ethyl esters via an oxo Diels-Alder reaction is described. Ab initio calculations predicted the products of the exo cycloaddition to be the thermodynamic products while the products resulting from the endo cycloaddition were predicted to be the kinetic products. The calculations were born out by experimental data.     

Vanchrobactin: absolute configuration and total synthesis

The stereochemistry of vanchrobactin, a siderophore produced by the bacterial fish pathogenVibrio anguillarum serotype O2, was elucidated by chiral capillary electrophoresis analysis and total synthesis as N-[N′-(2,3-dihydroxybenzoyl)-d-arginyl]-l-serine.     

Synthesis of novel benzopyrano[3,2-c]coumarins via tandem base promoted nucleophilic substitution and intramolecular electrophilic aromatic cyclization

Efficient and facile synthesis of 7H-benzopyrano[3,2-c]coumarins has been achieved by mild base promoted reaction of 4-chloro-3-formylcoumarin with diversely functionalized resorcinols. All the products were obtained as pure precipitates from the reaction mixture and the structure of the product was confirmed by X-ray analysis.     

Synthesis of a highly hydrophobic cyclic decapeptide by solid-phase synthesis of linear peptide and cyclization in solution

<正>A general method was described to synthesize a highly hydrophobic cyclic peptide,cyclo[LWLWLWLWLQ]where underlines indicate D-configuration of the amino acid,by a two-step solid-phase/solution synthesis strategy.The linear decapeptide was assembled by standard Boc chemistry on solid-phase and subsequently cyclized in solution with high efficiency and reproducibility. In subsequent purification by semi-preparative HPLC,50%(v/v) DMF/H_2O was employed as the solvent to overcome the difficulty of solubilization for the hydrophobic cyclic decapeptide and achieved a total yield of 30-35%with a purity of over 98%.     

A Practical,efficient, and atom economic alternative to the Wittig and Horner–Wadsworth–Emmons reactions for the synthesis of (E)-α,β-unsaturated esters from aldehydes

We describe a highly efficient new methodology for the synthesis of (E)-α,β-unsaturated esters from aldehydes. In our DMAP-catalyzed reaction, both aromatic as well as aliphatic aldehydes furnish the desired products highly regio- and stereoselectively if treated with commercially available or synthetically easily accessible malonic acid half ester. A large scale application in the synthesis of p-methoxycinnamates, which are of use as sunscreen ingredients, is described.     

Gas chromatography—mass spectrometry studies on the occurrence of acetamide,propionamide, and furfuryl alcohol in pyrolyzates of bacteria,bacterial fractions,and model compounds

Fused-silica capillary gas chromatography—mass spectrometry was employed to investigate the production of several bacterial pyrolysis products, including acetamide, propionamide, and furfuryl alcohol. A variety of model compounds, selected for their similarity with bacterial structures, were pyrolyzed and amounts of these pyrolysis products were quantitatively determined. Model compounds included several analogues of muramyl dipeptide differing in chain length at the lactyl—peptide bridge as well as several neutral and amino sugars, amino acids, and nucleic acids. Bacterial cell walls and whole microbial cells were also analyzed. Measurement of the amounts of a few chemically identified pyrolysis products provides some chemotaxonomic differentiation of microorganisms, as demonstrated by the pyrolysis of a group of Gram-positive and Gram-negative bacteria (including samples of Legionella pneumophila), and fungi.     

One-pot approach for the synthesis of 2-aryl benzothiazoles via a two-component coupling of gem-dibromomethylarenes and o-aminothiophenols

One-pot synthesis of 2-aryl benzothiazoles from gem-dibromomethylarenes using 2-aminoarylthiols is described. Benzothiazoles were obtained in high chemical yields under mild conditions. This transformation would facilitate synthesis by short reaction times, large-scale synthesis, easy and quick isolation of the products, which are the main advantages of this procedure.     

Fleetamine (3-O-α-d-glucopyranosyl-swainsonine): the synthesis of a hypothetical inhibitor of endo-α-mannosidase

3-O-α-d-Glucopyranosyl-swainsonine was originally proposed¹⁷ as a potential inhibitor of the mammalian enzyme endo-α-mannosidase, but its synthesis has not been reported. Herein we report the total synthesis of this enigmatic compound, utilizing a halide-ion catalysed glycosylation of a swainsonine lactam with a glucosyl iodide donor as the key step. The resulting inhibitor was evaluated as an inhibitor of human endo-α-mannosidase, and as a ligand for bacterial orthologs from Bacteroides thetaiotaomicron and Bacteroides xylanisolvens, including active-centre variants, although no evidence for binding or inhibition was observed. The surprising lack of binding was rationalized by using structural alignment with an endo-α-mannosidase inhibitor complex, which identified deleterious interactions with the swainsonine piperidine ring and an essential active site residue.     

Stereoselective allylation of acyclic and chiral α-amino-β-Hydroxy aldehydes part 2: Application to the formal synthesis of the polyhydroxylated γ-amino acid (+)-Detoxinine

Stereoselective allylations of acyclic, chiral α-amino-β-hydroxy aldehydes mediated by BF₃·OEt₂ and its application to the formal synthesis of the polyhydroxylated γ-amino acid (+)-detoxinine are described. The reactions of syn-α-NHCbz-β-OTBS substrates mediated by BF₃·OEt₂ afforded syn-selective products. The same reaction conditions gave anti-selective products from syn-α-NCbzBn-β-OTBS substrates. A hydrogen-bonded transition state and Felkin-Anh model have been suggested to account for the stereochemical outcomes of the two reactions, respectively. One of the allylation products was used for the formal synthesis of the polyhydroxylated γ-amino acid (+)-detoxinine.