Solid-Phase Synthesis of β-Amino Ketones Via DNA-Compatible Organocatalytic Mannich Reactions

One-bead-one-compound (OBOC) libraries constructed by solid-phase split-and-pool synthesis are a valuable source of protein ligands. Most OBOC libraries are comprised of oligoamides, particularly peptides, peptoids, and peptoid-inspired molecules. Further diversification of the chemical space covered by OBOC libraries is desirable. Toward this end, we report here the efficient proline-catalyzed asymmetric Mannich reaction between immobilized aldehydes and soluble ketones and anilines. The reaction conditions do not compromise the amplification of DNA by the PCR. Thus, this chemistry will likely be useful for the construction of novel DNA-encoded libraries by solid-phase synthesis.

ADPr-Peptide Synthesis

Synthetic mono-ADPr-peptides are useful for structural, biochemical, and proteomics studies. We describe here a protocol for the preparation of mono-ADPr-peptides based on a fairly standard Fmoc-based solid-phase synthesis. Phosphoribosylated precursor building blocks are introduced into the peptide chain on solid-phase and subsequently converted to ADPr-sites by chemical phosphorylation with adenosine phosphoramidite. Suitably protected phosphoribosylated glutamine, asparagine, and citrulline building blocks described in this protocol allow introduction of ADP-Gln, ADPr-Asn, and ADPr-Cit into peptide chains as demonstrated for three peptides. Trifunctional amino acids, for which base-sensitive side-chain protection is available, can be accommodated in the sequences flanking the ADPr-cites.

Solid-phase supported design of carriers for therapeutic nucleic acid delivery

Nucleic acid molecules are important therapeutic agents in the field of antisense oligonucleotide, RNA interference, and gene therapies. Since nucleic acids are not able to cross cell membranes and enter efficiently into cells on their own, the development of efficient, safe, and precise delivery systems is the crucial challenge for development of nucleic acid therapeutics. For the delivery of nucleic acids to their intracellular site of action, either the cytosol or the nucleus, several extracellular and intracellular barriers have to be overcome. Multifunctional carriers may handle the different special requirements of each barrier. The complexity of such macromolecules however poses a new hurdle in medical translation, which is the chemical production in reproducible and well-defined form. Solid-phase assisted synthesis (SPS) presents a solution for this challenge. The current review provides an overview on the design and SPS of precise sequence-defined synthetic carriers for nucleic acid cargos.

Removable Backbone Modification Method for the Chemical Synthesis of Membrane Proteins

Chemical synthesis can produce water-soluble globular proteins bearing specifically designed modifications. These synthetic molecules have been used to study the biological functions of proteins and to improve the pharmacological properties of protein drugs. However, the above advances notwithstanding, membrane proteins (MPs), which comprise 20-30% of all proteins in the proteomes of most eukaryotic cells, remain elusive with regard to chemical synthesis. This difficulty stems from the strong hydrophobic character of MPs, which can cause considerable handling issues during ligation, purification, and characterization steps. Considerable efforts have been made to improve the solubility of transmembrane peptides for chemical ligation. These methods can be classified into two main categories: the manipulation of external factors and chemical modification of the peptide. This Account summarizes our research advances in the development of chemical modification especially the two generations of removable backbone modification (RBM) strategy for the chemical synthesis of MPs. In the first RBM generation, we install a removable modification group at the backbone amide of Gly within the transmembrane peptides. In the second RBM generation, the RBM group can be installed into all primary amino acid residues. The second RBM strategy combines the activated intramolecular O-to-N acyl transfer reaction, in which a phenyl group remains unprotected during the coupling process, which can play a catalytic role to generate the activated phenyl ester to assist in the formation of amide. The key feature of the RBM group is its switchable stability in trifluoroacetic acid. The stability of these backbone amide N-modifications toward TFA can be modified by regulating the electronic effects of phenol groups. The free phenol group is acylated to survive the TFA deprotection step, while the acyl phenyl ester will be quantitatively hydrolyzed in a neutral aqueous solution, and the free phenol group increases the electron density of the benzene ring to make the RBM labile to TFA. The transmembrane peptide segment bearing RBM groups behaves like a water-soluble peptide during fluorenylmethyloxycarbonyl based solid-phase peptide synthesis (Fmoc SPPS), ligation, purification, and characterization. The quantitative removal of the RBM group can be performed to obtain full-length MPs. The RBM strategy was used to prepare the core transmembrane domain Kir5.1[64-179] not readily accessible by recombinant protein expression, the influenza A virus M2 proton channel with phosphorylation, the cation-specific ion channel p7 from the hepatitis C virus with site-specific NMR isotope labels, and so on. The RBM method enables the practical engineering of small- to medium-sized MPs or membrane protein domains to address fundamental questions in the biochemical, biophysical, and pharmaceutical sciences.

Effect of tacticity-derived topological constraints in bactericidal peptides

Topology is a key element in structure-activity relationship estimation while designing physiologically-active molecular constructs. Peptides may be a preferred choice for therapeutics, principally due to their biocompatibility, low toxicity and predictable metabolism. Peptide design only guarantees functional group constitution by opting specific amino acid sequence, and not their spatial orientation to bind and incite physiological response on chosen targets. This is principally because peptide conformation is subject to external flux, due to the isotactic stereochemistry of the peptide chain. Stereochemical engineering of the peptide main chain offers the possibility of multiplying the structural space of a typical sequence to many orders of magnitude, and limiting the otherwise fluxional non-specific functional group dispensation in space by offering greater conformational rigidity. We put to test, this conceptual possibility already established in theoretical models, by designing amphipathic peptide systems and experimenting with them on Gram-positive, Gram-negative and antibiotic-resistant bacteria. The unusual conformational rigidity and stability of syndiotactic peptides enable them to retain the designed electrostatic environment, while they encounter the membrane surface. All the six designed systems exhibited bactericidal activity, pointing to the utility and specificity of stereo-engineered peptide systems for therapeutic applications. Overall, we hope that this work provides important insights and useful directives in designing novel peptide systems with antimicrobial activity, by expanding the design space, incorporating D-amino acid as an additional design variable.

Solid-phase synthesis and fluorine-18 radiolabeling of cycloRGDyK

Solid-phase peptide synthesis, head-to-tail cyclization, and subsequent radiolabeling provided a reproducible, simple, rapid synthetic method to generate the cyclic peptide radiotracer cRGDyK([18F]FBA). Herein is reported the first on-resin cyclization and 18F-radiolabeling of a cyclic peptide (cRGDyK) in an overall peptide synthesis yield of 88% (cRGDyK(NH2)) and subsequent radiolabeling yield of 14 ± 2% (decay corrected, n = 4). This approach is generally applicable to the development of an automated process for the synthesis of cyclic radiolabeled peptides for positron emission tomography (PET).

Multifunctional Oligoaminoamides for the Receptor-Specific Delivery of Therapeutic RNA

Drugs with novel and versatile modes of action, such as therapeutic nucleic acids or proteins, open new possibilities for the precise therapy of different diseases. The most crucial limitation during the development of a therapeutic drug remains the safe and efficient intracellular delivery.To overcome the hurdles and to realize the successful delivery of such new biopharmaceuticals, our laboratory has recently developed a sequence-defined, cationic oligomer platform based on solid-phase synthesis. These multifunctional oligomers have displayed efficient delivery of therapeutic RNA in vitro and in vivo. In this chapter, we provide a brief background on the special features and applications of these carrier systems as well as detailed protocols for the oligomer and polyplex synthesis and their evaluation.

Advances in Fmoc solid-phase peptide synthesis

Today, Fmoc SPPS is the method of choice for peptide synthesis. Very-high-quality Fmoc building blocks are available at low cost because of the economies of scale arising from current multiton production of therapeutic peptides by Fmoc SPPS. Many modified derivatives are commercially available as Fmoc building blocks, making synthetic access to a broad range of peptide derivatives straightforward. The number of synthetic peptides entering clinical trials has grown continuously over the last decade, and recent advances in the Fmoc SPPS technology are a response to the growing demand from medicinal chemistry and pharmacology. Improvements are being continually reported for peptide quality, synthesis time and novel synthetic targets. Topical peptide research has contributed to a continuous improvement and expansion of Fmoc SPPS applications.

The Use of Microwave-Assisted Solid-Phase Peptide Synthesis and Click Chemistry for the Synthesis of Vaccine Candidates Against Hookworm Infection

A protein-based vaccine approach against hookworm infection has failed to deliver the expected outcome, due to a problem with an allergic response in the patient or difficulties in the proteins' production. This implication could be overcome by using a chemically synthesized peptide-based vaccine approach. This approach utilizes minimal pathogenic components that are necessary for the stimulation of the immune response without triggering adverse side effects. To boost the peptide's immunogenicity, a lipid core peptide (LCP) system can be utilized as a carrier molecule/immunostimulant. This chapter describes in detail the synthesizing of protected lipoamino acid, the self-adjuvanting moiety (LCP core), the peptide epitope, and the final vaccine candidate. The subunit peptide and the LCP core were synthesized using microwave-assisted solid-phase peptide synthesis (SPPS). Then the final hookworm vaccine construct was assembled using the copper-catalyzed azide-alkyne cycloaddition, or "click," reaction.

Current covalent modification methods for detecting RNA in fixed and living cells

Labeling RNAs is of particular interest for elucidating localization, transport, and regulation of specific transcripts, ideally in living cells. Numerous methods have been developed ranging from hybridizing probes to genetically encoded reporters and chemo-enzymatic approaches. This review focuses on covalent labeling approaches that rely on the introduction of a small reactive group into the nascent or completed transcript followed by bioorthogonal click chemistry. State of the approaches for labeling RNA in fixed and living cells will be presented and emerging strategies with great potential for application in the complex cellular environment will be discussed.

TOMBU and COMBU as Novel Uronium-type peptide coupling reagents derived from Oxyma-B

Here we describe two novel uronium salts, TOMBU and COMBU, derived from the recently described Oxyma-B for use in peptide bond synthesis. These coupling reagents are more stable than COMU in DMF. Furthermore, using various peptide synthetic models in solution and solid-phase synthesis, we reveal that they show better performance than HBTU in terms of preserving chiral integrity and coupling yields, but slightly worse performance than COMU.

Efficient solid-phase synthesis of pppRNA by using product-specific labeling

A novel solid-phase synthesis and purification strategy for 5'-triphosphate oligonucleotides by using lipophilic tagging of the triphosphate moiety is reported. This is based on triphosphate synthesis with 5'-O-cyclotriphosphate intermediates, whereby a lipophilic tag, such as decylamine, is introduced during the ring-opening reaction to give a linear gamma-phosphate-tagged species. This method enables the highly efficient synthesis of 5'-triphosphorylated RNA derivatives and their gamma-phosphate-substituted analogues and will especially facilitate the advancement of therapeutic approaches that make use of 5'-triphosphate oligonucleotides as potent activators of the cytosolic immune sensor RIG-I.

Expedient total synthesis of small to medium-sized membrane proteins via Fmoc chemistry

Total chemical synthesis provides a unique approach for the access to uncontaminated, monodisperse, and more importantly, post-translationally modified membrane proteins. In the present study we report a practical procedure for expedient and cost-effective synthesis of small to medium-sized membrane proteins in multimilligram scale through the use of automated Fmoc chemistry. The key finding of our study is that after the attachment of a removable arginine-tagged backbone modification group, the membrane protein segments behave almost the same as ordinary water-soluble peptides in terms of Fmoc solid-phase synthesis, ligation, purification, and mass spectrometry characterization. The efficiency and practicality of the new method is demonstrated by the successful preparation of Ser64-phosphorylated M2 proton channel from influenza A virus and the membrane-embedded domain of an inward rectifier K(+) channel protein Kir5.1. Functional characterizations of these chemically synthesized membrane proteins indicate that they provide useful and otherwise-difficult-to-access materials for biochemistry and biophysics studies.

[Solid phase peptide synthesis: interest in the valorization of molecular substances from animal venoms]

Toxins from animal venoms are small peptide molecules able to interact with a wide range of specific cellular targets in order to modulate their activity, which enables them to act in many physiological and pathological processes. Recently, structuralandpharmacologicalstudieshaveshown the involvement of these biological agents in the pathogenesis of many diseases like diabetes, cancer paralysis, autoimmune diseases or neurological disorders. Nevertheless, the only punfication from scorpion venoms of theses peptides still doesn't offer sufficient quantities to allow conducting the pharmacological and structure-function studies. The solid phases peptide synthesis (SPPS) is a methodology that allows us to produce non-limited quantities of structural analogsfrom these peptides-toxins in. In this paper; we will try to highlight the importance of this methodology, and peptide engineering in general, in obtaining peptides of interest. We are also going to elucidate the problems encountered during the chemical synthesis of some betides and explain how to overcome them.

A comprehensive one-pot synthesis of protected cysteine and selenocysteine SPPS derivatives

A proof-of-principle methodology is presented in which all commercially-available cysteine (Cys) and selenocysteine (Sec) solid phase peptide synthesis (SPPS) derivatives are synthesized in high yield from easily prepared protected dichalcogenide precursors. A Zn-mediated biphasic reduction process applied to a series of four bis-N(α)-protected dichalcogenide compounds allows facile conversion to their corresponding thiol and selenol intermediates followed by insitu S- or Se-alkylation with various electrophiles to directly access twenty one known Cys and Sec SPPS derivatives. Most of these derivatives were able to be precipitated in crude form out of petroleum ether in sufficient purity for direct use as peptide building blocks. Subsequent incorporation of these derivatives into peptide models nicely illustrates their viability and applicability toward SPPS.

An automated Teflon microfluidic peptide synthesizer

We present a microfluidic synthesizer made entirely of Teflon material for solid phase peptide synthesis (SPPS). Solvent-resistant perfluoroalkoxy (PFA) was used to construct chip-sized devices featuring multiple tri-layer pneumatic microvalves. Using these devices, model peptides were automatically synthesized and cleaved in situ in a continuous-flow manner. The total coupling and cleavage time was significantly reduced compared to conventional bulk reactors. The synthesis of a decapeptide, for instance, took less than 6 h using our device while it usually takes more than three days using conventional reactors.

Preparation and evaluation at the delta opioid receptor of a series of linear leu-enkephalin analogues obtained by systematic replacement of the amides

Leu-enkephalin analogues, in which the amide bonds were sequentially and systematically replaced either by ester or N-methyl amide bonds, were prepared using classical organic chemistry as well as solid phase peptide synthesis (SPPS). The peptidomimetics were characterized using competition binding, ERK1/2 phosphorylation, receptor internalization, and contractility assays to evaluate their pharmacological profile over the delta opioid receptor (DOPr). The lipophilicity (LogD7.4) and plasma stability of the active analogues were also measured. Our results revealed that the last amide bond can be successfully replaced by either an ester or an N-methyl amide bond without significantly decreasing the biological activity of the corresponding analogues when compared to Leu-enkephalin. The peptidomimetics with an N-methyl amide function between residues Phe and Leu were found to be more lipophilic and more stable than Leu-enkephalin. Findings from the present study further revealed that the hydrogen-bond donor properties of the fourth amide of Leu-enkephalin are not important for its biological activity on DOPr. Our results show that the systematic replacement of amide bonds by isosteric functions represents an efficient way to design and synthesize novel peptide analogues with enhanced stability. Our findings further suggest that such a strategy can also be useful to study the biological roles of amide bonds.

Solid phase synthesis and biological evaluation of probestin as an angiogenesis inhibitor

Probestin is a potent aminopeptidase N (APN) inhibitor originally isolated from the bacterial culture broth. Here, we report probestin synthesis by solid phase peptide synthesis (SPPS) method and evaluated its activity to inhibit angiogenesis using a chicken embryo chorioallantoic membrane (CAM) assay and a CAM tumor xenograft model. Results from these studies demonstrate that probestin inhibits the angiogenic activity and tumor growth.

Proline editing: a general and practical approach to the synthesis of functionally and structurally diverse peptides. Analysis of steric versus stereoelectronic effects of 4-substituted prolines on conformation within peptides

Functionalized proline residues have diverse applications. Herein we describe a practical approach, proline editing, for the synthesis of peptides with stereospecifically modified proline residues. Peptides are synthesized by standard solid-phase peptide synthesis to incorporate Fmoc-hydroxyproline (4R-Hyp). In an automated manner, the Hyp hydroxyl is protected and the remainder of the peptide synthesized. After peptide synthesis, the Hyp protecting group is orthogonally removed and Hyp selectively modified to generate substituted proline amino acids, with the peptide main chain functioning to "protect" the proline amino and carboxyl groups. In a model tetrapeptide (Ac-TYPN-NH2), 4R-Hyp was stereospecifically converted to 122 different 4-substituted prolyl amino acids, with 4R or 4S stereochemistry, via Mitsunobu, oxidation, reduction, acylation, and substitution reactions. 4-Substituted prolines synthesized via proline editing include incorporated structured amino acid mimetics (Cys, Asp/Glu, Phe, Lys, Arg, pSer/pThr), recognition motifs (biotin, RGD), electron-withdrawing groups to induce stereoelectronic effects (fluoro, nitrobenzoate), handles for heteronuclear NMR ((19)F:fluoro; pentafluorophenyl or perfluoro-tert-butyl ether; 4,4-difluoro; (77)SePh) and other spectroscopies (fluorescence, IR: cyanophenyl ether), leaving groups (sulfonate, halide, NHS, bromoacetate), and other reactive handles (amine, thiol, thioester, ketone, hydroxylamine, maleimide, acrylate, azide, alkene, alkyne, aryl halide, tetrazine, 1,2-aminothiol). Proline editing provides access to these proline derivatives with no solution-phase synthesis. All peptides were analyzed by NMR to identify stereoelectronic and steric effects on conformation. Proline derivatives were synthesized to permit bioorthogonal conjugation reactions, including azide-alkyne, tetrazine-trans-cyclooctene, oxime, reductive amination, native chemical ligation, Suzuki, Sonogashira, cross-metathesis, and Diels-Alder reactions. These proline derivatives allowed three parallel bioorthogonal reactions to be conducted in one solution.

Synthesis of O-glycopeptides and construction of glycopeptide microarrays

O-glycosylation of proteins is an important modification which affects biological function and immunity. In this chapter, we provide protocols for efficient solid-phase O-glycopeptide synthesis (SPGPS) and protocols for the construction of glycopeptide microarray chips for screening applications. This will be exemplified for mucin-type glycopeptides and the construction of glycopeptide microarrays. To this end, the protocols provided are particularly suited for small-scale robotic parallel synthesis. N-Terminal amine capping of deletion peptides during synthesis stands out as vital to this strategy. It allows for direct on-slide enrichment of the full-length target product and thereby bypasses tedious isolation and purification procedures.

Synthesis of antimicrobial peptoids

Peptoids (N-substituted glycines) are mimics of α-peptides in which the side chains are attached to the backbone N (α) -amide nitrogen instead of the C (α) -atom. Peptoids hold promise as therapeutics since they often retain the biological activity of the parent peptide and are stable to proteases. In recent years, peptoids have attracted attention as new potential antibiotics against multiresistant bacteria. Here we describe the submonomer solid-phase synthesis of an antimicrobial peptoid, H-Nmbn-Nlys-Nlys-Nnap-Nbut-Nmbn-Nlys-NH2.

Microwave-assisted solid-phase peptide synthesis using the biotage Syro Wave™

Fast and precise heating by microwave irradiation during solid-phase peptide synthesis (SPPS) can reduce reaction times as well as provide better purities and greater yields for the synthesis of difficult peptides. Microwave- assisted SPPS has proven to be a useful and reliable tool for the synthesis of peptides as well as small proteins. It is particularly well suited for sequences with a high propensity to form β-sheet-type structures and for sterically difficult couplings. In this protocol, conditions and detailed procedures are described for performing microwave-assisted SPPS using the Syro Wave™. Here we describe the synthesis of two difficult peptide sequences: the first is derived from the C-terminus of the MuLV CTL epitope, the second is a de novo designed peptide with a C-terminal alkyne.

A total solid-phase synthesis of DILP8

We have developed a cysteine anchoring method for the synthesis of DILP8 and its analogues. The first is to synthesis of DILP8A SS13-18, C14-MeOBzl, C24-Acm and activate it as DILP8A S13-18, C14-SSPyr C24-Acm. A next step is to synthesize the DILP8BC16-Acm. The desired peptide, DILP8 with Cys(Acm) at A-24 and B-16, was then dissolved in 75% HOAc by addition of Iodine in MeOH and 4M HCl in dioxane. The reaction mixture was monitored by HPLC and the excess iodine was reduced with ascorbic acid. Purification of the peptide was achieved by HPLC. Pure synthetic DILP8 showed a single peak on analytical HPLC with corrected molecular ion. By using the above methods, enough peptide and highly homogenous pure DLP8 were generated.

Peptide release, side-chain deprotection, work-up, and isolation

After having successfully synthesized a peptide, it has to be released from the solid support, unless it is being used for on-resin display. The linker and, in some cases, the cleavage mixture determine the C-terminal functionality of the released peptide. In most cases, the peptide is released with concomitant removal of side-chain protecting groups. However, some combinations of linkers and side-chain protecting groups enable a two-stage procedure, either using orthogonal chemistry or graduated labilities. Herein, we describe protocols for the release of peptides from the most commonly used linker types providing a variety of different C-terminal functionalities, including acids, amides, amines, and aldehydes. Moreover, suggestions for determination of peptide purity and for storage conditions are provided.

Preparation of C-terminally modified chemokines by expressed protein ligation

In order to link structural features on a molecular level to the function of chemokines, site-specific modification strategies are strongly required. These can be used to incorporate fluorescent dyes and/or physical probes to allow investigations in a wide range of biological and physical techniques, e.g., nuclear magnetic resonance (NMR) spectroscopy, fluorescence microscopy, fluorescence resonance energy transfer (FRET), or fluorescence correlation spectroscopy (FCS). Only a limited number of functional groups within the 20 canonical amino acids allow ligation strategies that can be helpful to introduce novel functionalities, which in turn expand the scope of chemoselective and orthogonal reactivity of (semi)synthetic chemokines. In the present chapter we mainly focus on the fabulous history of native chemical ligation (NCL) and provide a general protocol for the preparation of C-terminally modified SDF-1α including tips and tricks for practical work. We believe that this protocol can be easily adapted to other chemokines and many proteins in general.

Synthesis of N-methylated peptides: on-resin methylation and microwave-assisted couplings

N-methylation may positively influence the pharmacokinetic properties of peptides by improving oral availability and in vivo half-life. Additionally, target affinity and specificity may be improved. Here, we describe the solid-phase N-methylation of peptides using direct alkylation. This method allows a rapid N-methyl scan of synthetic, bioactive peptides. Additionally, a microwave-enhanced method for the difficult coupling onto the methylated N terminus is provided.

Solid-phase synthesis of phosphopeptides

Phosphopeptides are generally prepared by incorporation of suitable, protected phosphoamino acid derivatives during peptide synthesis using routine coupling protocols. The feasibility of chemical synthesis of phosphorylated peptides by Fmoc-SPPS was greatly enhanced by the introduction of the monobenzyl protecting group for the phosphate group. This minimized β-elimination of the phosphate group and made Fmoc-based synthesis of phosphopeptides the preferred synthesis strategy. Described here is our strategy for the synthesis of phosphopeptides attached to the solid support PEGA via a backbone amide linker type. This linker allows removal of side-chain protection groups without releasing the phosphopeptide from the solid support, thus enabling solid-phase-based pull-down reactions and peptide-protein interaction studies.

Synthesis of C-terminal peptide thioesters using Fmoc-based solid-phase peptide chemistry

This chapter provides two protocols for the solid-phase synthesis of peptide thioesters using N (α) -Fmoc-protected amino acids. The first protocol is based on a so-called safety-catch linker, while the second relies on a backbone amide linker.

Solid-phase peptide synthesis: an introduction

This chapter provides an introduction to and overview of peptide chemistry with a focus on solid-phase peptide synthesis. The background, the most common reagents, and some mechanisms are presented. This chapter also points to the different chapters and puts them into perspective.

Synthesis of cyclic disulfide-rich peptides

In this chapter we describe two SPPS approaches for producing cyclic disulfide-rich peptides in our laboratory, including cyclotides from plants, cyclic conotoxins from cone snail venoms, chlorotoxin from scorpion venom, and the sunflower trypsin inhibitor peptide, SFTI-1.

Synthesis of peptides using tert-butyloxycarbonyl (Boc) as the α-amino protection group

The use of the tert-butyloxycarbonyl (Boc) as the Nα-amino protecting group in peptide synthesis can be advantageous in several cases, such as synthesis of hydrophobic peptides and peptides containing ester and thioester moieties. The primary challenge of using Boc SPPS is the need for treatment of the resin-bound peptide with hazardous hydrogen fluoride (HF), which requires special equipment.

Direct production of cellulose laurate by mechanical activation-strengthened solid phase synthesis

This work reports that cellulose laurate could be directly produced by mechanical activation-strengthened solid phase synthesis (MASPS) in a customized stirring mill with using bagasse pulp and lauric acid as materials in an environmentally friendly way. Cellulose laurates with different degree of substitution were obtained under different synthesis conditions without the use of organic co-reagents and solvents. The characterization results showed that cellulose laurates had great changes in surface morphologies and crystal structures compared with bagasse pulp because of the intense milling and introduction of laurate groups, but still retained the cellulose I crystalline form of the native cellulose. MASPS could be considered as a simple, efficient and green method for the production of long chain cellulose esters.

Chemical synthesis and biological activity of analogues of the lantibiotic epilancin 15X

Lantibiotics are a large family of antibacterial peptide natural products containing multiple post-translational modifications, including the thioether structures lanthionine and methyllanthionine. Efforts to probe structure-activity relationships and engineer improved pharmacological properties have driven the development of new methods to produce non-natural analogues of these compounds. In this study, solid-supported chemical synthesis was used to produce analogues of the potent lantibiotic epilancin 15X, in order to assess the importance of several N-terminal post-translational modifications for biological activity. Surprisingly, substitution of these moieties, including the unusual N-terminal D-lactyl moiety, resulted in relatively small changes in the antimicrobial activity and pore-forming ability of the peptides.

Solid-phase parallel synthesis of drug-like artificial 2H-benzopyran libraries

This review covers the construction of drug-like 2H-benzopyrans and related libraries using solid-phase parallel synthesis. In this context, the preparation of substituted benzopyrans such as mono-, di- and trisubstituted benzopyran derivatives and additional ring-fused benzopyrans such as benzopyranoisoxazoles, benzopyranopyrazoles, six-membered ring-fused benzopyrans, and polycyclic benzopyrans are highlighted.

Novel protocol for the chemical synthesis of crustacean hyperglycemic hormone analogues--an efficient experimental tool for studying their functions

The crustacean Hyperglycemic Hormone (cHH) is present in many decapods in different isoforms, whose specific biological functions are still poorly understood. Here we report on the first chemical synthesis of three distinct isoforms of the cHH of Astacus leptodactylus carried out by solid phase peptide synthesis coupled to native chemical ligation. The synthetic 72 amino acid long peptide amides, containing L- or D-Phe³ and (Glp¹, D-Phe³) were tested for their biological activity by means of homologous in vivo bioassays. The hyperglycemic activity of the D-isoforms was significantly higher than that of the L-isoform, while the presence of the N-terminal Glp residue had no influence on the peptide activity. The results show that the presence of D-Phe³ modifies the cHH functionality, contributing to the diversification of the hormone pool.

Structure-activity relationships of a snake cathelicidin-related peptide, BF-15

Cathelicidin-BF15 (BF-15) is a 15-mer peptide derived from Cathelicidin-BF (BF-30), which is found in the venom of the snake Bungarus fasciatus and exhibits broad antimicrobial activity. Since BF-15 retains most part of the antimicrobial activity of BF-30 but has significantly reduced haemolytic activity and a much shorter sequence length (and less cost), it is a particularly attractive template around which to design novel antimicrobial peptides. However, the structure-activity relationship of it is still unknown. We designed and synthesized a series of C-terminal amidated analogs of BF-15 based on its amphipathic α-helix structure. And we characterized their antimicrobial potency and haemolytic activity. We identified the amidated BF-15 (analog B1) with potent antimicrobial activity against several antibiotic-resistant bacteria (MICs between 1 and 64 μg/mL, 2-16-folds higher than BF-30) and much lower haemolytic activity. The subsequent circular dichroism study results showed a typical α-helix pattern of analog B1 and the content of the α-helix structure of it increased significantly comparing with BF-30, which indicates the peptide sequence of BF-15 may provide a major contribution to the α-helix content of the whole BF-30 sequence. The peptide induced chaotic membrane morphology and cell debris as determined by electron microscopy. This suggests that the antimicrobial activity of B1 is based on cytoplasmic membrane permeability. Taken together, our results suggested that peptide B1 should be considered as an excellent candidate for developing therapeutic drugs.

A sucrose-derived scaffold for multimerization of bioactive peptides

A spherical molecular scaffold bearing eight terminal alkyne groups was synthesized in one step from sucrose. One or more copies of a tetrapeptide azide, either N(3)(CH(2))(5)(CO)-His-DPhe-Arg-Trp-NH(2) (MSH4) or N(3)(CH(2))(5)(CO)-Trp-Met-Asp-Phe-NH(2) (CCK4), were attached to the scaffold via the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Competitive binding assays using Eu-labeled probes based on the superpotent ligands Ser-Tyr-Ser-Nle-Glu-His-DPhe-Arg-Trp-Gly-Lys-Pro-Val-NH(2) (NDP-α-MSH) and Asp-Tyr-Met-Gly-Trp-Met-Asp-Phe-NH(2) (CCK8) were used to study the interactions of monovalent and multivalent MSH4 and CCK4 constructs with Hek293 cells engineered to overexpress MC4R and CCK2R. All of the monovalent and multivalent MSH4 constructs exhibited binding comparable to that of the parental ligand, suggesting that either the ligand spacing was inappropriate for multivalent binding, or MSH4 is too weak a binder for a second 'anchoring' binding event to occur before the monovalently-bound construct is released from the cell surface. In contrast with this behavior, monovalent CCK4 constructs were significantly less potent than the parental ligand, while multivalent CCK4 constructs were as or more potent than the parental ligand. These results are suggestive of multivalent binding, which may be due to increased residence times for monovalently bound CCK4 constructs on the cell surface relative to MSH4 constructs, the greater residence time being necessary for the establishment of multivalent binding.

[Synthesis and biological activities of beta-chain fragments of hemoglobin]

To investigate the angiotensin I-converting enzyme (ACE) inhibitory activity of beta-chain hemoglobin fragments, 17 fragments were synthesized by microwave-assisted solid-phase synthesis method. Wang resin or Trt(2-Cl) resin, Fmoc and HBTU-HOBt were used as solid carrier, N-terminal amino acid protecting groups and coupling reagents, respectively. The ACE inhibitory, alpha-glucosidase inhibitory, antibacterial and antitumor activities of the synthesized fragments were assayed. In vitro, Val-Val-Tyr-Pro-Trp-Thr showed high ACE inhibitory activity (IC50 = 7.42 micromol x L(-1)). The results indicate that there are two active sites in Val-Val-Tyr-Pro-Trp-Thr-Gln-Arg-Phe, one consists of Val-Val-, and the other -Gln-Arg-Phe. Peptides showed high ACE inhibitory activity when the N-terminal was hydrophobic amino acid such as Val and C-terminal tripeptide contained Phe, Trp or Arg. Some of the fragments showed low a-glucosidase inhibitory activity. No antibacterial activity or antitumor activity was detected in vitro. The results indicate that these peptides have a potential antihypertensive effect and possible application in the treatment of hypertension.