Microwave-assisted Solid-phase Peptide Synthesis Research Articles

Exploring Tryptophan-based Short Peptides: Promising Candidate for Anticancer and Antimicrobial Therapies

Background: Ultra-short peptides are essential therapeutic agents due to their heightened selectivity and reduced toxicity. Scientific literature documents the utilization of dipeptides, tripeptides, and tetrapeptides as promising agents for combating cancer. We have created a range of tryptophan-based peptides derived from literature sources in order to assess their potential as anticancer drugs. Methods: We present the results of our study on the antibacterial and anticancer effectiveness of 10 ultra-short peptides that were produced utilizing microwave-assisted solid phase peptide synthesis. The synthesized peptides underwent screening for in vitro antibacterial activity using the agar dilution method. Results: HPLC, LC-MS, 1H NMR, and 13C NMR spectroscopy were used to analyze the synthesized peptides. In tests using the HeLa and MCF-7 cell lines, the synthesized peptides' anticancer efficacy was assessed. The study found that two peptides showed potential median inhibitory concentration (IC50) values of 3.9±0.13 μM and 1.8±0.09 μM, respectively, and showed more activity than the reference medication doxorubicin. Conclusion: The antibacterial activity of synthesized peptides 3b and 4b was found to be better than the other synthetic peptides. MIC value of roughly 5–50 μg/mL for peptides 3a, 4c, and 4d showed strong antifungal activity against Candida albicans. The synthesized peptides were also evaluated for their anticancer activity against HeLa and MCF-7 cell lines, and found that peptides 3e and 4e were more potent than other peptides against doxorubicin.

Synthesis, antimicrobial activity, and mechanistic studies of enterocin DD14, a leaderless two-peptide bacteriocin

Bacteriocins are promising alternatives to antibiotics in the food, veterinary and medical sectors, but their study and use is often hampered by the low yields and high costs associated with their purification from naturally occurring bacteria. Chemical synthesis has emerged as a means to overcome this limitation and design more active variants. In this study, microwave-assisted solid-phase peptide synthesis was used to produce the leaderless two-peptide bacteriocin enterocin DD14 (EntDD14), composed of EntDD14A (44 amino acids) and EntDD14B (43 amino acids). The resulting synthetic peptides, syn-EntDD14A and syn-EntDD14B, were tested against Gram-positive bacteria including Listeria, Staphylococcus and Enterococcus strains. Both peptides were found to be necessary for optimal, but not synergistic, antibacterial activity and to act through a pore-forming mechanism. Both peptides exhibited moderate cytotoxicity against eukaryotic cells.

Novel Polypeptide Automated Synthesis Devices: A Review

Peptides are a unique class of proteins and one-dimensional biological nanomaterials that play an exceptionally important role in life science and industrial applications. At present, peptide synthesis equipment encounters issues like low synthetic efficiency, challenges in scaling up, and limited automation. This article provides an overview of the key technologies in peptide synthesis equipment, covering aspects such as peptide information screening, peptide synthesis, and detection. It analyzes and summarizes the principles, methods, and critical challenges of traditional solid-phase peptide synthesis technology, microwave-assisted solid-phase peptide synthesis technology, and continuous-flow solid-phase peptide synthesis technology. It also discusses microfluidic solid-phase peptide synthesis technology and future research trends, offering insights into the search for an efficient, high-yield, high-purity, scalable, and intelligent peptide synthesis method, which holds significant research significance.

Microwave-Assisted Solid Phase Synthesis of Different Peptide Bonds: Recent Advancements

Abstract: Peptides are important as drugs and biologically active molecules. The synthesis of pep-tides has gathered considerable attention in recent years due to their various attractive properties. Conventional peptide synthesis is tedious and requires hazardous reagents and solvents. Micro-wave-assisted solid-phase peptide synthesis has several advantages compared with conventional batch synthesis. Herein, we have discussed various microwave-assisted solid-phase peptide bond synthesis methods developed over the last five years. Peptides are categorized into four groups - small, medium, large, and cyclic based on their length and structural characteristics to make it easier to understand. This review article also discusses the scope and limitations of microwave-assisted solid-phase peptide synthesis.

Chemical Synthesis of Alpha-Synuclein Proteins via Solid-Phase Peptide Synthesis and Native Chemical Ligation.

Alpha-Synuclein (α-Synuclein) is a 140 amino acid protein implicated in neurodegenerative disorders known as synucleino-pathies, where it accumulates in proteinaceous inclusions in the brain. The normal physiological function of α-Synuclein remains obscure, as it exists in several non-neuronal cells in which its function has not been studied. Given the tremendous interest in studying α-Synuclein, and the existing limitations in the production of modified forms of the protein, we developed a method for the chemical synthesis of α-Synuclein by combining peptide fragment synthesis via automated microwave-assisted solid-phase peptide synthesis and ligation strategies. Our synthetic pathway enables the synthesis of protein variants of interest, carrying either mutations or posttranslational modifications, for further investigations of the effects on the structure and aggregation behavior of the protein. Ultimately, our study forms the foundation for future syntheses and studies of other custom-made α-Synuclein variants with a single or several modifications, as necessary.

Solid-phase synthesis and pathological evaluation of pyroglutamate amyloid-β3-42 peptide

Pyroglutamate amyloid-β3-42 (AβpE3-42) is an N-terminally truncated and pyroglutamate-modified Aβ peptide retaining highly hydrophobic, amyloidogenic, and neurotoxic properties. In Alzheimer’s disease (AD) patients, AβpE3-42 peptides accumulate into oligomers and induce cellular toxicity and synaptic dysfunction. AβpE3-42 aggregates further seed the formation of amyloid plaques, which are the pathological hallmarks of AD. Given that AβpE3-42 peptides play critical roles in the development of neurodegeneration, a reliable and reproducible synthetic access to these peptides may support pathological and medicinal studies of AD. Here, we synthesized AβpE3-42 peptides through the microwave-assisted solid-phase peptide synthesis (SPPS). Utilizing thioflavin T fluorescence assay and dot blotting analysis with anti-amyloid oligomer antibody, the amyloidogenic activity of synthesized AβpE3-42 peptides was confirmed. We further observed the cytotoxicity of AβpE3-42 aggregates in cell viability test. To examine the cognitive deficits induced by synthetic AβpE3-42 peptides, AβpE3-42 oligomers were intracerebroventricularly injected into imprinting control region mice and Y-maze and Morris water maze tests were performed. We found that AβpE3-42 aggregates altered the expression level of postsynaptic density protein 95 in cortical lysates. Collectively, we produced AβpE3-42 peptides in the microwave-assisted SPPS and evaluated the amyloidogenic and pathological function of the synthesized peptides.

An Optimized Scalable Fully Automated Solid-Phase Microwave-Assisted cGMP-Ready Process for the Preparation of Eptifibatide

We investigated several strategies, based on the use of microwave-assisted solid-phase peptide synthesis (MW-SPPS) and scalable to kilogram-scale manufacturing, for the preparation of Eptifibatide,...

Improved Fmoc‐solid‐phase peptide synthesis of an extracellular loop of CFTR for antibody selection by the phage display technology

Cystic fibrosis (CF), a life-shortening genetic disease, is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene that codes for the CFTR protein, the major chloride channel expressed at the apical membrane of epithelial cells. The development of an imaging probe capable of non-invasively detect CFTR at the cell surface could be of great advantage for the management of CF. With that purpose, we synthesized the first extracellular loop of CFTR protein (ECL1) through fluorenylmethyloxycarbonyl (Fmoc)-based microwave-assisted solid-phase peptide synthesis (SPPS), according to a reported methodology. However, aspartimide formation, a well-characterized side reaction in Fmoc-SPPS, prompted us to adopt a different side-chain protection strategy for aspartic acid residues present in ECL1 sequence. The peptide was subsequently modified via PEGylation and biotinylation, and cyclized through disulfide bridge formation, mimicking the native loop conformation in CFTR protein. Herein, we report improvements in the synthesis of the first extracellular loop of CFTR, including peptide modifications that can be used to improve antigen presentation in phage display for selection of novel antibodies against plasma membrane CFTR.

New Developments in Microwave-Assisted Solid Phase Peptide Synthesis.

The unique combination of microwave heating with optimized carbodiimide activation has proven to be an indispensable technique for high-throughput peptide production. Here, we describe new methods in microwave-assisted solid phase peptide synthesis and optimized post-synthesis modifications that have been recently developed. These methods have drastically reduced synthesis time and solvent requirement while delivering peptides in high crude purities.

Synthetic Evaluation of Standard and Microwave-Assisted Solid Phase Peptide Synthesis of a Long Chimeric Peptide Derived from Four Plasmodium falciparum Proteins.

An 82-residue-long chimeric peptide was synthesised by solid phase peptide synthesis (SPPS), following the Fmoc protocol. Microwave (MW) radiation-assisted synthesis was compared to standard synthesis using low loading (0.20 mmol/g) of polyethylene glycol (PEG) resin. Similar synthetic difficulties were found when the chimeric peptide was obtained via these two reaction conditions, indicating that such difficulties were inherent to the sequence and could not be resolved using MW; by contrast, the number of coupling cycles and total reaction time became reduced whilst crude yield and percentage recovery after purification were higher for MW radiation-assisted synthesis.

Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide sequences. Synthesis of some unnatural amino acids often includes the use of a precursor consisting of a Schiff-base stabilized by a nickel cation. Unnatural side-chains can be installed on an amino acid backbone found in this Schiff-base complex. The resulting unnatural amino acid can then be isolated from this complex using hydrolysis of the Schiff-base, typically by employing reflux in strongly acidic solution. These highly acidic conditions may remove acid-labile side-chain protecting groups necessary for the unnatural amino acids to be used in microwave-assisted solid-phase peptide synthesis. In this work, we present an efficient hydrolysis and subsequent Fmoc protection of an amino acid isolated from a Ni-Schiff base complex. Hydrolysis conditions presented in this work are suitable for retention of acid-labile side-chain protecting groups and may be adaptable to a variety of unnatural amino acid substrates.

Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups.

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide sequences. Synthesis of some unnatural amino acids often includes the use of a precursor consisting of a Schiff-base stabilized by a nickel cation. Unnatural side-chains can be installed on an amino acid backbone found in this Schiff-base complex. The resulting unnatural amino acid can then be isolated from this complex using hydrolysis of the Schiff-base, typically by employing reflux in strongly acidic solution. These highly acidic conditions may remove acid-labile side-chain protecting groups necessary for the unnatural amino acids to be used in microwave-assisted solid-phase peptide synthesis. In this work, we present an efficient hydrolysis and subsequent Fmoc protection of an amino acid isolated from a Ni-Schiff base complex. Hydrolysis conditions presented in this work are suitable for retention of acid-labile side-chain protecting groups and may be adaptable to a variety of unnatural amino acid substrates.

Linear Multiepitope (Glyco)peptides for Type-Specific Serology of Herpes Simplex Virus (HSV) Infections.

Detection of type-specific antibodies is an important and essential part of accurate diagnosis, even in silent carriers of herpes simplex virus (HSV)-1 (oral) and HSV-2 (genital) infections. Serologic assays that identify HSV-1 and HSV-2 type-specific antibodies have been commercially available for more than a decade but often face problems related to cross-reactivity and similar issues. Attempts to identify type-specific peptide epitopes for use in serology for both HSV-1 and HSV-2 have been limited. We recently demonstrated epitope mapping of envelope glycoprotein G2 and identified a type-specific glycopeptide epitope that broadly recognized HSV-2 infected individuals. In the present work we have performed a comprehensive glycopeptide synthesis and microarray epitope mapping of 14 envelope proteins from HSV-1 and HSV-2, namely, gB, gC, gD, gE, gG, gH, and gI, using sera from HSV-1- and HSV-2-infected individuals and control sera. Several unique type-specific peptide epitopes with high sensitivity were identified and synthesized as one large linear multiepitope sequence using microwave-assisted solid-phase (glyco)peptide synthesis. Microarray validation with clinically defined HSV and Varicella Zoster (VZV) sera confirmed excellent cumulative specificities and sensitivities.

Short communication: Measuring the angiotensin-converting enzyme inhibitory activity of an 8-amino acid (8mer) fragment of the C12 antihypertensive peptide

An 8-AA (8mer) fragment (PFPEVFGK) of a known antihypertensive peptide derived from bovine αS1-casein (C12 antihypertensive peptide) was synthesized by microwave-assisted solid-phase peptide synthesis and purified by reverse phase HPLC. Its ability to inhibit angiotensin-converting enzyme (ACE) was assessed and compared with that of the parent 12mer peptide (FFVAPFPEVFGK) to determine the effect of truncating the sequence on overall hypotensive activity. The activity of the truncated 8mer peptide was found to be almost 1.5 times less active than that of the 12mer, with ACE-inhibiting IC50 (half-maximal inhibitory concentration) values of 108 and 69μM, for the 8mer and 12mer, respectively. Although the 8mer peptide is less active than the original 12mer peptide, its overall activity is comparable to activities reported for other small proteins that elicit physiological responses within humans. These results suggest that microbial degradation of the 12mer peptide would not result in a complete loss of antihypertensive activity if used to supplement fermented foods and that the stable 8mer peptide could have potential as a blood pressure–lowering agent for use in functional foods.

Synthesis and immunological evaluation of peptide-based vaccine candidates against malaria

Background: Malaria, caused by the protozoan parasite Plasmodium, is one of the main causes of morbidity and mortality of the whole human population.Intensive, ongoing research aims to develop an effective vaccine against malaria; however, it has been unsuccessful for over a century. The circumsporozoite protein (CSP) plays crucial a role in the parasite life cycle. CSP is the most dominant surface antigen of the initial pre-erythrocytic stage. We designed vaccine constructs using four different CD4+ and CD8+ T cell epitopes derived from the CSP and used the lipid core peptide (LCP) as a self-adjuvanting delivery system. Methods: All the constructs were synthesized using microwave-assisted solid phase peptide synthesis (SPPS). Immunological evaluation was carried out following subcutaneous administration of LCP-based vaccine candidates in a BALB/c mouse model. Interferon gamma (IFN-γ) production was used to measure the induction of epitope-specific cellular immune responses after vaccination. Results: Self-adjuvanting LCP malaria vaccines composed of different epitopes were synthesized.To determine whether the vaccine candidates were able to induce cellular immunity, mice were immunized with LCP constructs or peptide epitopes adjuvanted with cholera toxin.Two of the tested constructs induced a high level of INF-γ in mice after subcutaneous immunization. Conclusions: We have demonstrated here for the first time that the LCP delivery system induced epitopespecific cellular immune responses against an antigen derived from Plasmodium.

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.

Chemical Synthesis of a Glycopeptide Derived from Skp1 for Probing Protein Specific Glycosylation.

Skp1 is a cytoplasmic and nuclear protein, best known as an adaptor of the SCF family of E3-ubiquitin ligases that label proteins for their degradation. Skp1 in Dictyostelium is posttranslationally modified on a specific hydroxyproline (Hyp) residue by a pentasaccharide, which consists of a Fucα1,2-Galβ-1,3-GlcNAcα core, decorated with two α-linked Gal residues. A glycopeptide derived form Skp1 was prepared to characterize the α-galactosyltransferase (AgtA) that mediates the addition of the α-Gal moieties, and to develop antibodies suitable for tracking the trisaccharide isoform of Skp1 in cells. A strategy was developed for the synthesis of the core trisaccharide-Hyp based on the use of 2-naphthylmethyl (Nap) ethers as permanent protecting groups to allow late stage installation of the Hyp moiety. Tuning of glycosyl donor and acceptor reactivities was critical for achieving high yields and anomeric selectivities of glycosylations. The trisaccharide-Hyp moiety was employed for the preparation of the glycopeptide using microwave-assisted solid phase peptide synthesis. Enzyme kinetic studies revealed that trisaccharide-Hyp and trisaccharide-peptide are poorly recognized by AgtA, indicating the importance of context provided by the native Skp1 protein for engagement with the active site. The trisaccharide-peptide was a potent immunogen capable of generating a rabbit antiserum that was highly selective toward the trisaccharide isoform of full-length Skp1.

ChemInform Abstract: Microwave‐Assisted Solid‐Phase Peptide Synthesis Using the Biotage Syro Wave

AbstractReview: 21 refs.

Microwave-assisted solid-phase peptide synthesis of neurosecretory protein GL composed of 80 amino acid residues.

We recently identified a novel cDNA encoding a small secretory protein of 80 amino acid residues, termed neurosecretory protein GL (NPGL), from the chicken hypothalamus. Homologs of NPGL have been reported to be present in mammals, such as human and rat. NPGL is amidated at its C-terminus, contains an intramolecular disulfide bond, and is hydrophobic in nature. In this study, we have optimized the synthesis of the entire 80-amino acid peptide sequence of rat NPGL by microwave-assisted solid-phase peptide synthesis. NPGL was obtained with a 10% yield when the coupling reactions were performed using 1-[Bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium-3-oxid hexafluorophosphate (HATU) at 50 °C for 5 min, and Fmoc deprotections were performed using 40% piperidine containing 0.1 M HOBt. Furthermore, the disulfide bond of NPGL was formed with 20% yield with the use of glutathione-containing redox buffer and 50% acetonitrile.

Synthesis and characterisation of self-assembled and self-adjuvanting asymmetric multi-epitope lipopeptides of ovalbumin.

Designing a lipopeptide (LP) vaccine with a specific asymmetric arrangement of epitopes may result in an improved display of antigens, increasing host-cell recognition and immunogenicity. This study aimed to synthesise and characterise the physicochemical properties of a library of asymmetric LP-based vaccine candidates that contained multiple CD4(+) and CD8(+) T-cell epitopes from the model protein antigen, ovalbumin. These fully synthetic vaccine candidates were prepared by microwave-assisted solid phase peptide synthesis. The C12 or C16 lipoamino acids were coupled to the N or C terminus of the OVA CD4 peptide epitope. The OVA CD4 LPs and OVA CD8 peptide constructs were then conjugated using azide-alkyne Huisgen cycloaddition to give multivalent synthetic vaccines. Physiochemical characterisation of these vaccines showed a tendency to self-assemble in aqueous media. Changes in lipid length and position induced self-assembly with significant changes to their morphology and secondary structure as shown by transmission electron microscopy and circular dichroism.