Convergent synthesis of aminomethylene peptidomimetics

This protocol describes a convergent synthesis of reduced amide bond peptidomimetics using thioacid-terminated peptides and aziridine-containing peptide conjugates. This approach could be used to produce peptides and proteins with modified backbones. The peptide conjugates are made using readily available aziridine aldehydes. The convergent synthesis of peptidomimetics is demonstrated through the preparation of long and short peptide fragments with an aminomethylene group incorporated within them. This transformation is amenable to the synthesis of peptides with reduced amide bonds at cysteine and alanine. The procedure describes the preparation of each component used and highlights the ease of synthesis of aminomethylene peptidomimetics, and takes about 3 d to complete.     

Aziridinyl peptides as inhibitors of cysteine proteases: effect of a free carboxylic acid function on inhibition

Peptides containing aziridine-2,3-dicarboxylate (Azi) as electrophilic building block are evaluated as inhibitors of the cysteine proteases papain, cathepsin B, cathepsin L and clostripain. The influence of a free carboxylic acid as functional group at different positions of the inhibitor molecule on inhibition is analyzed. Structure-activity relationships and binding mode hypotheses are discussed. In contrast to the bacterial enzyme clostripain, the papain like mammalian proteases (cathepsins) are irreversibly inactivated by aziridinyl peptides. N-Unsubstituted aziridines are much more potent inhibitors of papain and cathepsins if they contain the free carboxylic acid attached to the aziridine ring (HOAzi-Leu-ProOBzl). Two free carboxylic acid functions at the aziridine ring are necessary for good inhibition of these enzymes by N-acylated aziridinyl peptides (BOC-Phe-Azi(OH)2). Chimeric bispeptidyl derivatives are selective CB inhibitors if the free acid is located at the C-terminus of the peptide (BOC-Phe-(EtO)Azi-Leu-ProOH). Clostripain is only inhibited by aziridinyl peptide esters.     

Aziridine-2-carboxylic acid. A reactive amino acid unit for a new class of cysteine proteinase inhibitors.

The three-membered ring of aziridine-2-carboxylic acid, which is susceptible to opening by nucleophiles, has been analyzed as a potential useful handle for the design of specific irreversible inhibitors of cysteine proteinases. For this thiol-reactive amino acid, an imino analogue of proline, a second-order rate constant of 17.07 M-1.s-1 for inactivation of papain was determined. Thus, the aziridine moiety proved to be remarkably more reactive than activated double bonds, e.g. N-ethylmaleimide, or halides such as alpha-iodopropionic acid or chloroacetic acid. Since it does not alkylate histidine under conditions in which quantitative alkylation occurs with N-ethyl-maleimide, it could represent an interesting reactive amino acid unit for the synthesis of a new class of irreversible inhibitors, at least in terms of specificity of the chemical reaction involved in the inactivation process.     

Dehydroalanine-containing peptides: preparation from phenylselenocysteine and utility in convergent ligation strategies

This protocol describes the methodology for the synthesis of dehydroalanine (Dha)-containing peptides and illustrates their use in convergent ligation strategies for the preparation of peptide conjugates. A nonproteinogenic amino acid, Fmoc-Se-phenylselenocysteine (SecPh), can be prepared in high yield over four synthetic steps and be conveniently incorporated into peptides by standard solid-phase peptide synthesis techniques. Globally deprotected peptides containing phenylselenocysteine can be converted to dehydrated peptides following a chemoselective, mild oxidation with hydrogen peroxide or sodium periodate (i.e., the phenylselenocysteine side chain is converted to that of Dha). Dha residues are electrophilic handles for the preparation of glycopeptides, lipopeptides or other peptide conjugates; one such transformation will be outlined here. The preparation of Dha-containing peptides, including the synthesis of SecPh, peptide elongation and oxidative treatment of phenylselenocysteine-containing peptides can be completed by one person in approximately 3-5 weeks. However, once SecPh is in hand, the time required for the preparation of peptides is significantly shorter and comparable to that for any peptide synthesis.     

Solid-phase route to Fmoc-protected cationic amino acid building blocks

Diamino acids are commonly found in bioactive compounds, yet only few are commercially available as building blocks for solid-phase peptide synthesis. In the present work a convenient, inexpensive route to multiple-charged amino acid building blocks with varying degree of hydrophobicity was developed. A versatile solid-phase protocol leading to selectively protected amino alcohol intermediates was followed by oxidation to yield the desired di- or polycationic amino acid building blocks in gram-scale amounts. The synthetic sequence comprises loading of (S)-1-(p-nosyl)aziridine-2-methanol onto a freshly prepared trityl bromide resin, followed by ring opening with an appropriate primary amine, on-resin N(β)-Boc protection of the resulting secondary amine, exchange of the N(α)-protecting group, cleavage from the resin, and finally oxidation in solution to yield the target γ-aza substituted building blocks having an Fmoc/Boc protection scheme. This strategy facilitates incorporation of multiple positive charges into the building blocks provided that the corresponding partially protected di- or polyamines are available. An array of compounds covering a wide variety of γ-aza substituted analogs of simple neutral amino acids as well as analogs displaying high bulkiness or polycationic side chains was prepared. Two building blocks were incorporated into peptide sequences using microwave-assisted solid-phase peptide synthesis confirming their general utility.     

AlCl3 induced (hetero)arylation of 2,3-dichloroquinoxaline: a one-pot synthesis of mono/disubstituted quinoxalines as potential antitubercular agents

A direct and single-step method has been developed for the synthesis of mono and 2,3-disubstituted quinoxalines by using a AlCl(3) induced (hetero)arylation of 2,3-dichloroquinoxaline. Both symmetrical and unsymmetrical 2,3-disubstituted quinoxalines can be prepared conveniently by using this method under appropriate reaction conditions. The reaction proceeds via C-C bond formation and can be utilized for the preparation of a variety of quinoxaline derivatives from readily available starting materials and reagents. The molecular structure of a representative compound was confirmed by single crystal X-ray diffraction study. Some of the compounds synthesized were tested for chorismate mutase inhibitory properties in vitro and one compound showed promising activity representing one of the few examples of chorismate mutase inhibition by a heteroarene based small molecule.     

Selective synthesis of 3-hydroxy acids from Meldrum's acids using SmI2-H2O

The single-step synthesis of 3-hydroxy carboxylic acids from readily available Meldrum's acids involves a selective monoreduction using a SmI(2)-H(2)O complex to give products in high crude purity, and it represents a considerable advancement over other methods for the synthesis of 3-hydroxy acids. The protocol includes a detailed guide to the preparation of a single electron-reducing SmI(2)-H(2)O complex and describes two representative examples of the methodology: monoreduction of a fully saturated Meldrum's acid (5-(4-bromobenzyl)-2,2-dimethyl-1,3-dioxane-4,6-dione) and tandem conjugate reduction-selective monoreduction of α,β-unsaturated Meldrum's acid (5-(4-methoxybenzylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione). The protocol for selective monoreduction of Meldrum's acids takes ～6 h to complete.     

Complete synthesis of the bicyclic ring of a mutacin analog with orthogonally protected lanthionine via solid‐phase intracyclization

Mutacin 1140 (MU1140) is a naturally occurring lantibiotic derived from posttranslational modifications of a ribosomally synthesized peptide during the fermentation of a bacterium called Streptococcus mutans, the etiological agent of dental cavities. A practical approach for chemically synthesizing lantibiotics would be a valuable tool to expand the MU1140 library with additional semisynthetic analogs. In turn, an expanded library may prove useful to explore additional therapeutic indications for this pipeline of novel compounds. In this work, orthogonally protected lanthionine analogs were synthesized via an aziridine ring opening strategy. This lanthionine was utilized to synthesize a cysteamine (Cya) instead of the (S)‐aminovinyl‐D‐cysteine (AviCys) that is naturally found in MU1140. The Cya containing bicyclic C/D ring of MU1140 was synthesized by Fmoc solid‐phase peptide synthesis (SPPS). The linear peptides were synthesized using OPfp ester derivatives and using various common coupling reagents such as COMU and TCTU. The linear peptide was intracyclized with DEPBT to construct the so‐called bicyclic ring C/D. This is the first report on the complete chemical synthesis of the bicyclic C/D ring of a MU1140 analog using orthogonally protected lanthionines using SPPS.     

Synthesis of (±)-11-deoxy-15-ethynyl prostaglandins

This article describes the preparation of (±)-11-deoxy-15-ethynyl prostaglandins ( & ). The key step involves a conjugate addition of the substituted 1-lithio-1-oct-1-ene ( ) to the cyclopentenone ( & ) to furnish 11-deoxy-prostaglandin skeleton in a simple fashion. Of particular interest in this synthesis is the preparation of alkyl side chain ( ) which was achieved in an efficient three-step synthesis starting from the readily available β-iodo vinyl ketone ( ).     

Facile synthesis of Ag nanocubes and Au nanocages

This protocol describes a method for the synthesis of Ag nanocubes and their subsequent conversion into Au nanocages via the galvanic replacement reaction. The Ag nanocubes are prepared by a rapid (reaction time < 15 min), sulfide-mediated polyol method in which Ag(I) is reduced to Ag(0) by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) and a trace amount of Na(2)S. When the concentration of Ag atoms reaches supersaturation, they agglomerate to form seeds that then grow into Ag nanostructures. The presence of both PVP and Na(2)S facilitate the formation of nanocubes. With this method, Ag nanocubes can be prepared and isolated for use within approximately 3 h. The Ag nanocubes can then serve as sacrificial templates for the preparation of Au nanocages, with a method for their preparation also described herein. The procedure for Au nanocage preparation and isolation requires approximately 5 h.     

Parallel synthesis of peptide libraries using microwave irradiation

The application of microwave irradiation to solid-phase peptide synthesis increases product purity and reduces reaction time. Parallel synthesis in 96-well polypropylene filter plates with microwave irradiation is an efficient method for the rapid generation of combinatorial peptide libraries in sufficient purity to assay the products directly for biological activity without HPLC purification. In this protocol, the solid-phase support is arrayed into each well of a 96-well plate, reagents are delivered using a multichannel pipette and a microwave reactor is used to complete peptide coupling reactions in 6 min and Fmoc-removal reactions in 4 min under temperature-controlled conditions. The microwave-assisted parallel peptide synthesis protocol has been used to generate a library of difficult hexa-beta-peptides in 61% average initial purity (50% yield) and has been applied to the preparation of longer alpha- and beta-peptides. Using this protocol, a library of 96 different hexapeptides can be synthesized in 24 h (excluding characterization).     

Stereoselective synthesis of novel cyclopropyl analogues of known cysteine protease inhibitors

Efficient synthesis of two novel analogues of some known protease inhibitors, via the isosteric replacement of oxirane/aziridine moiety of the parent compounds by cyclopropane ring, is described.     

Solid-phase total synthesis of polymyxin B1.

The total solid-phase synthesis of polymyxin B1 (PMB1) has been achieved in 20% yield using the orthogonal protecting group N-1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl-(Dde). This report demonstrates that a complex peptide macrocycle can be synthesized in high yields using solid-phase synthesis. According to MS and HPLC, the synthetic peptide was identical to the naturally occurring antibiotic.     

Synthesis of optically active 1-acyl-2-O-alkyl-sn-glycero-3-phosphocholine via 1-O-benzyl-sn-glycerol 3-arenesulfonate

A stereocontrolled route to 1-palmitoyl-2-O-hexadecyl-sn-glycero-3-phosphocholine from (R)-glycidyl tosylate is described. This method gives very high enantioselectivity (93-96% enantiomeric excess) and can be used to prepare 3-acyl-2-O-alkyl-sn-glycero-1-phosphocholines from (S)-glycidyl tosylate. The key step is the preparation of 1-O-benzyl-sn-glycerol 3-tosylate by the boron trifluoride etherate catalyzed regio- and stereo-specific opening of the epoxide ring with excess benzyl alcohol. The alkyl group is introduced using alkyl trifluoromethanesulfonate in the presence of excess 2,6-di-tert-butyl-4-methylpyridine. Debenzylation gives 2-O-alkyl-sn-glycerol 3-arenesulfonate, which is acylated and then converted into the phosphocholine. The use of chiral glycidyl derivatives as starting materials for the synthesis of glycerophospholipids is discussed.     

Design, synthesis, and conformational analysis of azacycloalkane amino acids as conformationally constrained probes for mimicry of peptide secondary structures

Conformationally constrained amino acid and dipeptide units can serve in mimics of specific secondary structures for studying relationships between peptide conformation and biological activity. A variety of mimics are required to study systematically the structure-activity relationships in biologically relevant peptides. We present our efforts on the design, synthesis, and conformational analysis of a series of rigid surrogates of amino acid and dipeptide units for application within constrained peptide analogues, and for employment as inputs for combinatorial science. Conceived to be general and versatile, our methodology has delivered a variety of azacycloalkane and azabicycloalkane amino acids in enantiomerically pure form, via practical methods, from readily available and inexpensive starting materials.     

Synthesis of peptide aldehydes.

The functionalization of peptides and proteins by aldehyde groups has become the subject of intensive research since the discovery of the inhibition properties of peptide aldehydes towards various enzymes. Furthermore, peptide aldehydes are of great interest for peptide backbone modification or ligation reactions. This review focuses upon their synthesis, which has been developed following two main strategies. The first strategy consists of prior synthesis of the peptide, followed by the introduction of the aldehyde function. The second possible strategy uses alpha-amino aldehydes as starting materials. After protection of the aldehyde, peptide elongation occurs. At the end of the synthesis, the aldehyde function can be unmasked.     

Synthesis,Characterization, and Antimicrobial Activity of Some New Thiophene Derivatives and Crystal Structure of Ethyl [4-(2-Thienylmethylene)Aminophenoxy]Acetate

Russian Journal of Bioorganic Chemistry - This work describes facile routes towards the synthesis of some novel thiophene derivatives. Thus, condensation of thiophene-2-carboxaldehyde with...     

The five bromotryptophans

Summary. The five regioisomeric bromotryptophans (BrTrps) play an important role in the life of sponges and lower marine invertebrates. These bromo-amino acids, which are formed by post-translational modifications, are not found in nature in their free state, but rather are involved in more complex structures. Any of the BrTrps can be part of a peptide, a cyclic peptide, an indole alkaloid, an ergot alkaloid, a macrocycle and others. The present review covers the synthesis, physical and spectroscopic properties of the five BrTrps. It also describes the many exiting pharmacological and biological activities played by the BrTrps and by various secondary metabolites containing brominated tryptophan moieties. Of special interest are cyclic peptides containing the 2-BrTrp unit, which were isolated from marine sponges e.g. konbamide, orbiculamide A, the various keramamides, jaspamide eusynstyelamide and more. Important families of non-cyclic peptides containing the 6-BrTrp, include the styelins, the conotoxins, the cathelicidins and several constrained macrocyclic peptides. Many marine secondary BrTrp-containing, non-peptidic metabolites also display a remarkable spectrum of bioactivities, which can be harnessed for therapeutic and other purposes. Examples are: barettin, bromotryptanthrin, tetraacetyl clionamide, cyclocinamide A, clavicipitic acid, various brominated β-carbolines. In this review we have presented the various synthetic routes leading to the preparation of the five BrTrps and many of its derivatives. Also, we have introduced the reader to many synthetic routes leading to BrTrp-containing non-peptidic natural products. Although the functional role of the various compounds in the human body is only poorly understood, its effects were extensively studied. Almost all of these compounds exhibit important therapeutic properties e.g. antifungal, antimicrobial, antihelmintic, insecticidal ichthyotoxic and anticancer activity. In the present review attempts have been made to provide synopsis, synthesis and symbiosis of chemical and biological actions, which may provide future guidance and facilitate further research in this area.     

Screening of electrophilic compounds yields an aziridinyl peptide as new active-site directed SARS-CoV main protease inhibitor

The coronavirus main protease, M^pro, is considered a major target for drugs suitable to combat coronavirus infections including the severe acute respiratory syndrome (SARS). In this study, comprehensive HPLC- and FRET-substrate-based screenings of various electrophilic compounds were performed to identify potential M^pro inhibitors. The data revealed that the coronaviral main protease is inhibited by aziridine- and oxirane-2-carboxylates. Among the trans-configured aziridine-2,3-dicarboxylates the Gly-Gly-containing peptide 2c was found to be the most potent inhibitor.     

Expanded-bed adsorption immobilized-metal affinity chromatography

The protocol describes a method for capture of secreted hexahistidine-tagged proteins using expanded-bed adsorption immobilized-metal affinity chromatography. The starting material for the procedure is any crude feedstock that contains a histidine (His)-tagged target protein. The protocol is exemplified using unclarified broth from Pichia pastoris fermentation as feedstock. The protocol can be used for laboratory studies or as part of a process for production of recombinant biotherapeutics to standards of good manufacturing practice. It takes approximately 5 h to purify proteins from 10 liters of feedstock and a further 5-6 h to sterilize and regenerate the column.