Sustainability Challenges in Peptide Synthesis and Purification: From R&D to Production

Advances in antimicrobial peptides: From mechanistic insights to chemical modifications

This review provides a comprehensive analysis of antimicrobial peptides (AMPs), exploring their diverse sources, secondary structures, and unique characteristics. The review explores into the mechanisms underlying the antibacterial, immunomodulatory effects, antiviral, antiparasitic and antitumour of AMPs. Furthermore, it discusses the three principal synthesis pathways for AMPs and assesses their current clinical applications and preclinical research status. The paper also addresses the limitations of AMPs, including issues related to stability, resistance, and toxicity, while offering insights into strategies for their enhancement. Recent advancements in AMP research, such as chemical modifications (including amino acid sequence optimisation, terminal and side-chain modifications, PEGylation, conjugation with small molecules, conjugation with photosensitisers, metal ligands, polymerisation, cyclisation and specifically targeted antimicrobial peptides) are highlighted. The goal is to provide a foundation for the future design and optimisation of AMPs.

N- to C-Peptide Synthesis, Arguably the Future for Sustainable Production

A revolution in peptide production arrived from the innovation of carboxylate to amine C- to N-direction solid-phase synthesis. This cornerstone of modern peptide science has enabled multiple academic and industrial applications; however, the process of C- to N-solid phase peptide synthesis (C-N-SPPS) has extreme process mass intensity and poor atom economy. Notably, C-N-SPPS relies upon the use of atom-intensive protecting groups, such as the fluorenylmethyloxycarbonyl (Fmoc) protection and wasteful excess of protected amino acids and coupling agents. On the other hand, peptide synthesis in the amine to carboxylate N- to C-direction offers potential to minimize protection and may arguably enable more efficient means for manufacturing peptides. For example, efficient amide bond formation in the N- to C-direction has been accomplished using methods employing thioesters, vinyl esters, and transamidation to achieve peptide synthesis with minimal epimerization. This review aims to provide an overview of N- to C-peptide synthesis indicating advantages in taking this avenue for sustainable peptide production.

"Actual" peptide properties required for nanoparticle development in precision cancer therapeutic delivery

Functionalizing nanoparticles with peptides (3-30 amino acids) reduces premature clearance and increases colloidal stability and targeting capacity of cancer therapeutics. Glutamate/lysine-rich zwitterionic and hydrophilic/neutral peptides minimize reticuloendothelial digestion of nanomedicine through reducing particle hydrophobicity and depressing plasma anti-PEG immunoglobulin that disrupts the PEG-based particle stealth. Anionic peptides negate protein corona formation and subsequent particle aggregation in vivo enabling efficient nanoparticles biodistribution and drug targeting by facilitating their endothelial/extracellular matrix pore diffusion. Cationic and hydrophobic peptides display a strong affinity for anionic cancer cell membrane and mediate membrane porosification or receptor binding leading to particle uptake and endocytosis. The peptide ionic and hydrophobicity/hydrophilicity attributes collectively facilitate endosomal escape, and nuclear and mitochondria targeting of nanoparticles. Peptides are required to present with different physicochemical attributes from administration site, through blood and extracellular matrix, to cancer site of action. Charge/hydrophilicity-hydrophobicity switching and projection of receptor-specific domain of peptides are attainable through pH-pKa interplay and labile bond hydrolysis of "unwanted" domain to give rise to new functional domains in response to pH, thermal and enzymatic stimuli. Co-introducing all functional attributes on a single peptide is challenging. Use of peptide blends risks leaching during nanoparticles production. Peptides-nanoparticles conjugation risks peptide conformational alterations and loss of acidic/basic termini affecting their roles in nanoparticle stabilization, targeting, membrane permeabilization and subcellular delivery.

Tag-Assisted Liquid-Phase Oligonucleotide Synthesis: Toward a Convergent Approach

Although soluble support (tag)-assisted liquid-phase methods have found practical applications in peptide synthesis, they are still in their infancy for oligonucleotide synthesis. The development of techniques for selective tag cleavage with protective groups remaining is particularly important because such techniques are necessary to realize a convergent approach. Herein, we report an effective soluble support-assisted liquid-phase oligonucleotide synthesis using a novel tag that can be prepared from commercially available methyl gallate without column chromatography. Selective tag cleavages with protective groups remaining are made possible under mild reducing conditions to prepare protected fragments, which is necessary to realize a convergent approach.

Impact of counterion and salt form on the properties of long-acting injectable peptide hydrogels for drug delivery

Modifying the salt form of active pharmaceutical ingredients is a common method to enhance their physicochemical and biological properties, whilst improving their ability to be formulated into medicines that can be effectively delivered to patients. Salts and counterions are especially relevant to peptide therapies, given that the majority of low molecular weight peptides synthesised by solid-phase protocols form a trifluoroacetate (TFA) salt due to the use of trifluoroacetic acid in resin cleaving and follow-on purification methods. TFA salts are not viewed as favourably by medicine regulators and can be defined as a new chemical entity entirely due to their different biological and physicochemical properties. Despite some exceptions, the vast majority of therapeutic peptides are marketed as hydrochloride (HCl) or acetate salts, even though most early research and development is centred on TFA salts. The aim of the study was to compare the impact of salt form (TFA vs. HCl) on the biostability, cell cytotoxicity, drug release and rheological properties of a Napffky(p)G-OH peptide hydrogel platform that demonstrates promise as a long-acting drug delivery system. This study demonstrated no significant difference between the salt forms for properties important to its intended use. This paper also raises important points for discussion relating to the environmental and regulatory status of peptide salts and their use as pharmaceuticals.

Flow-to-Flow Technology: Amide Formation in the Absence of Traditional Coupling Reagents Using DPDTC

Reported herein is the use of a recyclable coupling agent, 2,2'-dipyridyldithiocarbonate (DPDTC), that generates isolable thioesters in a plug flow reactor (PFR). If not isolated, thioesters can be reintroduced directly into the PFR, along with amines, to generate amides in a "flow-to-flow" sense. Both electron-rich and -poor aromatic acids, as well as sterically hindered aliphatic acids, are efficiently coupled with a variety of amines, including the formation of Weinreb amides and peptides, in high yields.

Fundamental Aspects of SPPS and Green Chemical Peptide Synthesis

This perspective essay will briefly recount fundamental physicochemical properties of the peptide-resin that have led to the almost universal use of stepwise solid phase peptide synthesis (SPPS) for the chemical synthesis of peptides. The essay discusses multiple aspects that must be addressed if we are to develop truly green chemical peptide synthesis. An optimal SPPS approach that retains the advantages inherent to polymer-supported chemical synthesis, combined with convergent synthesis based on modern chemical ligation methods for the condensation of unprotected peptide segments, will be described as a path to green synthesis of peptides and their efficient manufacture. Only the most pertinent primary literature is cited.

Structural and functional analysis of a homotrimeric collagen peptide

Objective

This study aimed to chemically synthesize a homotrimeric collagen peptide, evaluate its safety, and assess its effectiveness in promoting collagen synthesis.

Methods

A homotrimeric collagen peptide was synthesized and structurally characterized using circular dichroism and infrared spectroscopy. Thermal stability was analyzed by TG-DSC, and molecular weight and amino acid composition were determined. In vitro cytotoxicity testing assessed safety, while UV-induced photoaging experiments evaluated its effects on collagen and elastin synthesis. In vivo studies in BALB/c mice examined its impact on collagen content, skin structure, and angiogenesis.

Results

The synthesized collagen peptide exhibited high purity (99.1%) and an amino acid composition of glycine, proline, and hydroxyproline in a balanced ratio (15:17:13). Structural analysis confirmed a stable triple-helical conformation similar to type I collagen with excellent thermal stability (Tm = 326.15°C). Cytotoxicity testing showed no adverse effects on cell viability. In vitro, the peptide significantly enhanced collagen and elastin synthesis in fibroblasts. In vivo, intradermal and subcutaneous injection increased collagen content, improved skin structure, and enhanced microvessel density.

Conclusion

This study presents a chemically synthesized homotrimeric collagen peptide with superior purity, structural stability, and biological efficacy in promoting collagen synthesis. Compared to previous studies, this biomimetic material exhibits exceptional thermal stability (Tm = 326.15°C) and a well-balanced amino acid composition, enabling applications in cosmetics and medical devices requiring heat sterilization (e.g., autoclaving), as validated by our patented method (China Patent No. ZL202410309842.9).

Preparation and Encapsulation of DPP-IV Inhibitory Peptides: Challenges and Strategies for Functional Food Development

Dipeptidyl peptidase IV (DPP-IV) inhibitory peptides have emerged as promising functional ingredients for managing type 2 diabetes due to their ability to enhance insulin secretion and improve glycemic control. This review provides a concise overview of current strategies for the preparation and encapsulation of DPP-IV inhibitory peptides, with a focus on food industry application, evaluating bioinformatics for substrate selection, and methods like mild enzymatic hydrolysis, cost-effective fermentation, and high-purity chemical synthesis for peptide production. Challenges associated with incorporating these peptides into food products are addressed, including impacts on sensory properties, stability during processing and digestion, and the need for effective delivery systems to enhance bioavailability. Potential solutions to improve peptide stability and targeted release, such as emulsions, liposomes, and nanoparticles, are explored. Future research directions are outlined, emphasizing the necessity for scalable production methods, co-encapsulation strategies, and consumer acceptance studies to facilitate the commercialization of DPP-IV inhibitory peptides as functional food ingredients. By addressing these key areas, this review aims to provide a theoretical foundation and practical guidance for the development of DPP-IV inhibitory peptides, paving the way for their broader application in the prevention and management of type 2 diabetes.

Twisted Amide-Mediated Synthesis and Rapid Structure-Activity Relationship Study of Medium-Sized Cyclic Peptides

Medium-sized cyclic peptides are expected to be ideal drug leads because these peptides combine the advantages, while compensating for the disadvantages, of small molecules and antibodies. Although medium-sized peptides can be produced by chemical synthesis, two major problems, namely (i) Cα-epimerization during C-terminal modification and (ii) side reactions in the cyclization, remain to be solved. These issues have hampered the synthesis of pure materials for bioassays, making it difficult to accomplish accurate structure-activity relationship (SAR) studies. Herein, we report an efficient synthesis of medium-sized cyclic peptides based on the twisted amide-mediated amidation strategy. First, a variety of linear peptides were synthesized by the "inverse" peptide synthesis and fragment coupling. Second, the C-terminus of the linear peptides were converted to twisted amides, which were then reacted with a variety of α-amino acyl sulfonamides, realizing the rapid C-terminal diversification of peptides. Finally, the resulting linear peptides were cyclized by the intramolecular twisted amide-mediated amidation to afford stereochemically pure cyclic peptides. Using this strategy, total synthesis of acyl-surugamide A, the stereoselective synthesis of 13 non-natural analogs, and the discovery of potent antimicrobial/antifungal peptides beyond the natural product were also achieved.

Isolation, total synthesis and structure determination of antifungal macrocyclic depsipeptide, tetraselide

Macrocyclic peptides, including depsipeptides, are an emerging new modality in drug discovery research. Tetraselide, an antifungal cyclic peptide isolated from a marine-derived filamentous fungus, possesses a unique amphiphilic structural feature consisting of five consecutive β-hydroxy-amino acid residues and fatty acid moieties. Because the structure elucidation of the naturally occurring product left six stereocenters ambiguous, we implemented bioinformatic analyses, chemical degradation studies and chiral pool fragment synthesis to identify two of the undetermined stereocenters. Convergent total synthesis of the four remaining plausible isomers of tetraselide was accomplished via liquid-phase peptide synthesis (LPPS) using soluble hydrophobic tag auxiliaries. The key advances involve fragment coupling by the serine/threonine ligation (STL) reaction and head-to-tail macrolactamization of the carrier-supported precursors that enabled systematic elaboration of the amphiphilic cyclic peptides. Ultimately, we determined the absolute structure of this natural product.

Substrate recognition by a peptide-aminoacyl-tRNA ligase

The continuing discovery of new peptide-aminoacyl-tRNA ligases (PEARLs) has unveiled a diverse array of enzymes with the unique potential to append amino acids to the C terminus of substrate peptides in an aminoacyl-tRNA-dependent manner. To date, PEARLs have been reported that can conjugate Cys, Ala, Trp, Gly, Leu, Asn, and Thr residues, but the basis of peptide substrate and aminoacyl-tRNA recognition is not known. Cell-free expression (CFE) has emerged as a powerful tool to rapidly assay activity of substrate variants, and we used the technique in this study to investigate the peptide substrate specificity of the PEARL [Formula: see text]. This enzyme that adds Trp was discovered previously during genome mining for ribosomally synthesized and posttranslational modified peptides (RiPPs). The enzyme is remarkably tolerant of changes to the C-terminal amino acid of the peptide substrate, and truncation and replacement experiments suggest a minimal sequence requirement. An AlphaFold3 model provided insights into binding interactions of the substrate peptide BhaA-Ala to [Formula: see text] and also generated predictions for tRNA, ATP, and Mg2+ binding modes that were tested by site-directed mutagenesis. The data suggest that several highly conserved residues in PEARLs recognize the 3'-CCA sequence present in all tRNAs. The minimal sequence required for Trp incorporation by [Formula: see text] was employed as a protein tag for C-terminal labeling of eGFP, lysozyme, and MBP with Trp and 5-Br-Trp.

Harnessing bacterial antimicrobial peptides: a comprehensive review on properties, mechanisms, applications, and challenges in combating antimicrobial resistance

Antimicrobial resistance (AMR) is a significant global health concern due to the persistence of pathogens and the emergence of resistance in bacterial infections. Bacterial-derived antimicrobial peptides (BAMPs) have emerged as a promising strategy to combat these challenges. Known for their diversity and multifaceted nature, BAMPs are notable bioactive agents that exhibit potent antimicrobial activities against various pathogens. This review explores the intricate properties and underlying mechanisms of BAMPs, emphasizing their diverse applications in addressing AMR. Additionally, the review investigates the mechanisms, analyses the challenges in utilizing BAMPs effectively, and examines their potential applications and associated deployment challenges providing comprehensive insights into how BAMPs can be harnessed to combat AMR across different domains. The significance of this review lies in highlighting the potential of BAMPs as transformative agents in combating AMR, offering sustainable and eco-friendly solutions to this pressing global health challenge.

Sustainable Ultrasound-Assisted Solid-Phase peptide synthesis (SUS-SPPS): Less Waste, more efficiency

The integration of low-frequency ultrasound with Solid-Phase Peptide Synthesis (SPPS) was explored to establish a Sustainable Ultrasound-assisted Solid-Phase Peptide Synthesis (SUS-SPPS) method. This innovative approach significantly reduces solvent consumption, washing steps, time, and reagent usage compared to conventional manual SPPS protocols. The SUS-SPPS method exploits ultrasound at every stage of synthesis and work-up, reducing the process to just two steps. The first step sequentially combines Fmoc-amino acid coupling, capping of unreacted amino groups, and Fmoc deprotection into a single operation, while the second one consists of a single washing procedure. Moreover, we demonstrated that the method is compatible with various resin types, including Rink-amide, Wang, and Cl-Trt resins, and facilitates the efficient synthesis of peptides of varying lengths (up to 20-mers) and compositions, including those traditionally considered "difficult sequences", with excellent yields and purity. Notably, SUS-SPPS reduces solvent usage per coupling cycle by 83-88%, marking a significant breakthrough in sustainable peptide synthesis.

An Electrochemical Design for a General Catalytic Carboxylic Acid Substitution Platform via Anhydrides at Room Temperature: Amidation, Esterification, and Thioesterification

An original concept for catalytic electrochemical dehydration has enabled a suite of acid substitutions, including amidation, esterification, and thioesterification, through a linchpin anhydride formed in situ. By avoiding stoichiometric dehydrating agents, this method addresses a leading challenge in organic synthesis and green chemistry. It also proceeds without acid additives at room temperature, accesses a diverse range of product structures, is easily scaled, and enabled the first example of catalytic peptide coupling at room temperature.

Base-Labile Safety-Catch Linker: Synthesis and Applications in Solid-Phase Peptide Synthesis

The safety-catch concept involves a protecting group that remains stable under a range of chemical conditions and subsequently becomes labile under one of those conditions upon a chemical modification of the protecting group. The safety-catch approach introduces flexibility into the scheme, enabling the use of the same reagent in two distinct steps of the chemical process. For example, it facilitates α-amino deprotection and final cleavage in a solid-phase peptide synthesis scheme. Herein, we developed a safety-catch linker based on sulfinyl designed to enable peptide elongation via fluorenylmethoxycarbonyl (Fmoc) chemistry. Subsequently, upon chemical modification (oxidation of the sulfinyl group into the corresponding sulfone), the peptide is released using a secondary amine via a β-elimination reaction, which also serves to remove the Fmoc group in each step. The optimization of both key reactions, oxidation of the linker, and peptide release were achieved using a multi-detachable system, which allows specific control of both reactions. The use of this linker opens the possibility of cleaving peptides from the solid support without trifluoroacetic acid.

From lead to market: chemical approaches to transform peptides into therapeutics

Peptides are a powerful drug modality with potential to access difficult targets. This recognition underlies their growth in the global pharmaceutical market, with peptides representing ~8% of drugs approved by the FDA over the past decade. Currently, the peptide therapeutic landscape is evolving, with high-throughput display technologies driving the identification of peptide leads with enhanced diversity. Yet, chemical modifications remain essential for improving the 'drug-like' properties of peptides and ultimately translating leads to market. In this review, we explore two recent therapeutic candidates (semaglutide, a peptide hormone analogue, and MK-0616, an mRNA display-derived candidate) as case studies that highlight general approaches to improving pharmacokinetics (PK) and potency. We also emphasize the critical link between advances in medicinal chemistry and the optimisation of highly efficacious peptide therapeutics.

Introducing Regioselective Disulfide Linkages in Peptides under Pseudodilute Conditions by Harnessing Bro̷nsted Acid-Activated N-Chlorosuccinimide

Methods that assemble multiple peptide disulfide bonds in the solid phase (pseudodilute conditions) are in high demand for synthesizing disulfide-rich peptides. Yet, the existing repertoire of disulfide-forming orthogonal chemistries in the solid phase is often hindered by additional steps for protecting group removals as well as the absolute necessity of rare, customized orthogonal cysteine (Cys) building blocks. We now describe a conceptually new while operationally simple on-resin method for disulfide assembly with widely accessible Cys protecting groups (Trt, Acm, and t Bu) using acid-activated N-chlorosuccinimide (NCS) in a single step. In the process, S- t Bu Cys emerged as a new orthogonal building block for the single-step assembly of the peptide disulfide. In our investigations, 2% TFA-activated NCS offered rapid (∼15 min) and a clean disulfide product in various peptides. Eventually, this novel strategy (2% TFA-NCS) was strategically merged in stepwise cross-linking with our previously described I2/S2O8 2--mediated disulfide assembly protocol to leverage two regioselective disulfide bonds into conotoxin, gomesin, and a de novo sequence within ∼30 min. Invariably, this new method proved highly productive and operationally simple. DFT calculations also support the hypothesis of NCS activation that assists efficient disulfide assembly in crossing a low-lying energy barrier via sulfonium intermediates. This newly developed method for t Bu deprotection and concomitant disulfide assembly in the solid phase should find wide applications in de novo peptide disulfide synthesis.

Rapid peptide synthesis using a methylimidazolium sulfinyl fluoride salt

Peptide couplings have been a subject of investigation for over a century, with modern research seeking to discover new methodologies that minimize purification steps, minimize reagent expense, and/or decrease reaction times. Of the numerous coupling reagents available, sulfur(IV) fluorides have potential as they can effectively transform carboxylic acids to reactive intermediates, and the sulfite by-products can be removed through aqueous washes. Here we demonstrate the formation and capture of key acyl fluorosulfite intermediates for peptide couplings in 15 min total, without epimerization or column chromatography for purification. Dipeptides were obtained in 40-94% yields. This approach was expanded to longer chains through iterative couplings, with oligopeptides obtained in 24-57% yields, each within 2 days. Mechanistic studies indicate the reaction does not proceed through acyl fluoride intermediates, and instead involves nucleophilic catalysis. The mild conditions are tolerant of a wide range of protecting groups of canonical and non-canonical amino acids.

Recombinant Production of The Cyclotide Kalata B1 by Conditional Split Inteins

This study describes the design, production, and characterization of a novel conditional intein system for the recombinant production of cyclic peptides. The system is based on two key features: (1) a promiscuous extein recognition site allowing cyclization of virtually any peptide, and (2) a secondary split site within the intein itself enabling triggered splicing at will. Two intein precursors were recombinantly expressed, purified, and then self-assembled in vitro to cyclize the model peptide kalata B1 (kB1). Cyclized kB1 was successfully purified, refolded, and characterized by mass spectrometry and NMR, demonstrating correct disulfide bond formation and identical structure to synthetic kB1. Importantly, the intein-derived kB1 retained full biological activity as evidenced by insect cell toxicity assays. This work establishes a versatile and efficient approach for intein-mediated protein cyclization with potential applications in bioengineering and peptide discovery.

Evolution of branched peptides as novel biomaterials

Branched peptide-based materials draw inspiration from dendritic structures to emulate the complex architecture of native tissues, aiming to enhance the performance of biomaterials in medical applications. These innovative materials benefit from several key features: they exhibit slower degradation rates, greater stiffness, and the ability to self-assemble. These properties are crucial for maintaining the structural integrity and functionality of the materials over time. By integrating bioactive peptides and natural polymers within their branched frameworks, these materials offer modularity and tunability and can accommodate a range of mechanical properties, degradation rates, and biological functions making them suitable for biomedical applications, including drug delivery systems, wound healing scaffolds, and tissue engineering constructs. In drug delivery, these materials can be engineered to release therapeutic agents in a controlled manner, enhancing the efficacy and safety of treatments. In wound healing, they provide a supportive environment which promotes rapid and efficient tissue repair. The combination of biomimetic design and functional adaptability makes branched peptide-based materials a promising candidate for the development of next-generation biomaterials, paving the way for significant advancements in healthcare.

Integrating synthetic polypeptides with innovative material forming techniques for advanced biomedical applications

Polypeptides are highly valued in biomedical science for their biocompatibility and biodegradability, making them valuable in drug delivery, tissue engineering, and antibacterial dressing. The diverse design of polymer chains and self-assembly techniques allow different side chains and secondary structures, enhancing their biomedical potential. However, the traditional solid powder form of polypeptides presents challenges in skin applications, shipping, and recycling, limiting their practical utility. Recent advancements in material forming methods and polypeptide synthesis have produced biomaterials with uniform, distinct shapes, improving usability. This review outlines the progress in polypeptide synthesis and material-forming methods over the past decade. The main synthesis techniques include solid-phase synthesis and ring-opening polymerization of N-carboxyanhydrides while forming methods like electrospinning, 3D printing, and coating are explored. Integrating structural design with these methods is emphasized, leading to diverse polypeptide materials with unique shapes. The review also identifies research hotspots using VOSviewer software, which are visually presented in circular packing images. It further discusses emerging applications such as drug delivery, wound healing, and tissue engineering, emphasizing the crucial role of material shape in enhancing performance. The review concludes by exploring future trends in developing distinct polypeptide shapes for advanced biomedical applications, encouraging further research.

Dioxazolones as electrophilic amide sources in copper-catalyzed and -mediated transformations

Over the past decade, dioxazolones have been widely used as N-acylamide sources in amidation processes of challenging substrates, typically employing precious transition metals. However, these catalytic systems often present several challenges associated with cost, toxicity, stability, and recyclability. Among the 3d transition metals, copper catalysts have been gaining increasing attention owing to their abundance, cost-effectiveness, and sustainability. Recently, these catalytic systems have been applied to the chemical transformation of dioxazolones, conferring a convenient protocol towards amidated products. This review highlights recent advancements in the synthetic transformations of dioxazolones, with particular examples of copper salts.

Natural Cyclic Peptides: Synthetic Strategies and Biomedical Applications

Natural cyclic peptides, a diverse class of bioactive compounds, have been isolated from various natural sources and are renowned for their extensive structural variability and broad spectrum of medicinal properties. Over 40 cyclic peptides or their derivatives are currently approved as medicines, underscoring their significant therapeutic potential. These compounds are employed in diverse roles, including antibiotics, antifungals, antiparasitics, immune modulators, and anti-inflammatory agents. Their unique ability to combine high specificity with desirable pharmacokinetic properties makes them valuable tools in addressing unmet medical needs, such as combating drug-resistant pathogens and targeting challenging biological pathways. Due to the typically low concentrations of cyclic peptides in nature, effective synthetic strategies are indispensable for their acquisition, characterization, and biological evaluation. Cyclization, a critical step in their synthesis, enhances metabolic stability, bioavailability, and receptor binding affinity. Advances in synthetic methodologies-such as solid-phase peptide synthesis (SPPS), chemoenzymatic approaches, and orthogonal protection strategies-have transformed cyclic peptide production, enabling greater structural complexity and precision. This review compiles recent progress in the total synthesis and biological evaluation of natural cyclic peptides from 2017 onward, categorized by cyclization strategies: head-to-tail; head-to-side-chain; tail-to-side-chain; and side-chain-to-side-chain strategies. Each account includes retrosynthetic analyses, synthetic advancements, and biological data to illustrate their therapeutic relevance and innovative methodologies. Looking ahead, the future of cyclic peptides in drug discovery is bright. Emerging trends, including integrating computational tools for rational design, novel cyclization techniques to improve pharmacokinetic profiles, and interdisciplinary collaboration among chemists, biologists, and computational scientists, promise to expand the scope of cyclic peptide-based therapeutics. These advancements can potentially address complex diseases and advance the broader field of biological drug development.

Molecular Dynamics of Peptide Sequencing through MoS2 Solid-State Nanopores for Binary Encoding Applications

Biological peptides have emerged as promising candidates for data storage applications due to their versatility and programmability. Recent advances in peptide synthesis and sequencing technologies have enabled the development of peptide-based data storage systems for realizing novel information storage technologies with enhanced capacity, durability, and data access speeds. In this study, we performed coarse-grained peptide sequencing of 12 distinct sequences through single-layer MoS2 solid-state nanopores (SSNs) using molecular dynamics (MD). Peptide sequences were composed of 1 positively charged, 1 negatively charged, and 4 neutral amino acids, with the position of amino acids in the sequence being shuffled to generate all possible configurations. From MD, the goal was to evaluate the efficiency of these peptide sequences to encode binary information based on ionic current traces monitored during their passage through the SSNs. Classification approaches using LightGBM were trained and tested to analyze different sequence factors such as the position of amino acids or the spacing between charged amino acids in the sequences. Our findings reveal the presence of two distinct groups of sequences determined by the relative position of the positively charged amino acid compared to the negatively charged amino acid. Furthermore, we observe a strong correlation between discrimination accuracy and the separation in the sequence between charged amino acids, depending on the number of adjacent neutral amino acids between them. Finally, MD allowed us to establish the nonlinear relationship between amino acid positions inside the pore (called sequence motifs) and fluctuations in ionic current traces to discriminate false positives and to enable effective training of machine learning classification algorithms. These very promising results emphasized the best approaches to design peptide sequences as building blocks for molecular data storage. Finally, this study highlights the potential of the proposed approach for designing peptide sequence combinations that could help the development of efficient, scalable, and reliable molecular data storage solutions, with future research focused on encoding longer binary chains to enhance storage capacity and support the goal of stable, energy-free biological systems.

Catalytic peptide/hemin complex from ester-amide exchange reaction mediated by deep eutectic solvents

The functions of peptides often emerge upon their self-assembly or binding with other co-factors. However, the synthetic complexity makes these functional peptides intractable. Here, we utilize the ester-amide exchange reaction in deep eutectic solvents to generate peptide libraries from unactivated amino acids. This strategy leads to peptide mixtures that exhibit hemin-binding capability and peroxidase-like activity.

How Useful are Antimicrobial Peptide Properties for Predicting Activity, Selectivity, and Potency?

Antimicrobial peptides (AMPs) are recognized for their potential application as new generation antibiotics, however, up to date, they have not been widely commercialized as expected. Although current bioinformatics tools can predict antimicrobial activity based on only amino acid sequences with astounding accuracy, peptide selectivity and potency are not foreseeable. This, in turn, creates a bottleneck not only in the discovery and isolation of promising candidates but, most importantly, in the design and development of novel synthetic peptides. In this paper, we discuss the challenges faced when trying to predict peptide selectivity and potency, based on peptide sequence, structure and relevant biophysical properties such as length, net charge and hydrophobicity. Here, pore-forming alpha-helical antimicrobial peptides family isolated from anurans was used as the case study. Our findings revealed no congruent relationship between the predicted peptide properties and reported microbial assay data, such as minimum inhibitory concentrations against microorganisms and hemolysis. In many instances, the peptides with the best physicochemical properties performed poorly against microbial strains. In some cases, the predicted properties were so similar that differences in activity amongst peptides of the same family could not be projected. Our general conclusion is that antimicrobial peptides of interest must be carefully examined since there is no universal strategy for accurately predicting their behavior.

Insight into Protein Engineering: From In silico Modelling to In vitro Synthesis

Protein engineering alters the polypeptide chain to obtain a novel protein with improved functional properties. This field constantly evolves with advanced in silico tools and techniques to design novel proteins and peptides. Rational incorporating mutations, unnatural amino acids, and post-translational modifications increases the applications of engineered proteins and peptides. It aids in developing drugs with maximum efficacy and minimum side effects. Currently, the engineering of peptides is gaining attention due to their high stability, binding specificity, less immunogenic, and reduced toxicity properties. Engineered peptides are potent candidates for drug development due to their high specificity and low cost of production compared with other biologics, including proteins and antibodies. Therefore, understanding the current perception of designing and engineering peptides with the help of currently available in silico tools is crucial. This review extensively studies various in silico tools available for protein engineering in the prospect of designing peptides as therapeutics, followed by in vitro aspects. Moreover, a discussion on the chemical synthesis and purification of peptides, a case study, and challenges are also incorporated.

Towards green, scalable peptide synthesis: leveraging DEG-crosslinked polystyrene resins to overcome hydrophobicity challenges

Diethylene glycol dimethacrylate (DEG)-crosslinked polystyrene (PS) resin offers a promising alternative to traditional divinyl benzene (DVB)-PS resin for solid-phase peptide synthesis (SPPS), particularly for challenging sequences with hydrophobic or bulky amino acids. DEG-PS resin's reduced hydrophobicity and enhanced flexibility improve synthesis efficiency, yielding peptides up to 28 residues with higher purities and yields compared to DVB-PS. In various syntheses, DEG-PS outperformed DVB-PS resin, with higher purities and yields for challenging peptides such as ABC analogue (73.2%, 58.3% vs. 72.5%, 46.3%) and Thymosin (58.4%, 48.6% vs. 54.0%, 39.2%). In addition, DEG-PS resin effectively suppressed common side reactions, such as dipeptide formation, typically encountered with Wang PS-based resins. Incorporating green chemistry principles, DEG-PS enabled the synthesis of complex peptides with satisfactory results using environmentally friendly solvents and reagents. Three challenging peptides; β (34-42), Jung and Redemann (JR), and ABRF 1992 - were synthesized on DEG-PS resin, achieving purities of 41.4%, 41.0%, and 68.0%, and yields of 50.5%, 52.6%, and 56.2%, respectively. These findings highlight DEG-PS resin's advantages for classical, green, and automated SPPS, offering superior performance and scalability for industrial applications.

Therapeutic peptide development revolutionized: Harnessing the power of artificial intelligence for drug discovery

Due to the spread of antibiotic resistance, global attention is focused on its inhibition and the expansion of effective medicinal compounds. The novel functional properties of peptides have opened up new horizons in personalized medicine. With artificial intelligence methods combined with therapeutic peptide products, pharmaceuticals and biotechnology advance drug development rapidly and reduce costs. Short-chain peptides inhibit a wide range of pathogens and have great potential for targeting diseases. To address the challenges of synthesis and sustainability, artificial intelligence methods, namely machine learning, must be integrated into their production. Learning methods can use complicated computations to select the active and toxic compounds of the drug and its metabolic activity. Through this comprehensive review, we investigated the artificial intelligence method as a potential tool for finding peptide-based drugs and providing a more accurate analysis of peptides through the introduction of predictable databases for effective selection and development.

Unraveling the complexity of amorphous solid as direct ingredient for conventional oral solid dosage form: The story of Elagolix Sodium

Conventional solid oral dosage form development is not typically challenged by reliance on an amorphous drug substance as a direct ingredient in the drug product, as this may result in product development hurdles arising from process design and scale-up, control of physical quality attributes, drug product processability and stability. Here, we present the Chemistry, Manufacturing and Controls development journey behind the successful commercialization of an amorphous drug substance, Elagolix Sodium, a first-in-class, orally active gonadotropin-releasing hormone antagonist. The reason behind the lack of crystalline state was assessed via Molecular Dynamics (MD) at the molecular and inter-molecular level, revealing barriers for nucleation due to prevalence of intra-molecular hydrogen bond, repulsive interactions between active pharmaceutical ingredient (API) molecules and strong solvation effects. To provide a foundational basis for the design of the API manufacturing process, we modeled the solvent-induced plasticization behavior experimentally and computationally via MD for insights into molecular mobility. In addition, we applied material science tetrahedron concepts to link API porosity to drug product tablet compressibility. Finally, we designed the API isolation process, incorporating computational fluid dynamics modeling in the design of an impinging jet mixer for precipitation and solvent-dependent glass transition relationships in the cake wash, blow-down and drying process, to enable the consistent manufacture of a porous, non-sintered amorphous API powder that is suitable for robust drug product manufacturing.

Aspects of complexity in quality and safety assessment of peptide therapeutics and peptide-related impurities. A regulatory perspective

In recent years, a number of therapeutic peptides have been authorized in the EU market, and several others are in the clinical development phase or under assessment for full dossier or generic applications. Quality and safety guidelines specific to peptides are limited, and some aspects have to be considered. In particular, concerns relate to the analytical investigation for impurities and the toxicological assessment of these substances. The guidelines and the compendial pharmacopoeias provide certain references but that may be questionable if interpreted according to whether therapeutic peptides are considered chemical or biological entities, large or small. The characterization of peptide-related impurities cannot follow the small molecule approach but should consider aspects closely linked to the complex mechanisms of action that these large molecules can exert in the human body. Although direct genotoxic mechanisms cannot be excluded, hazardous interactions on biological systems cannot be ruled out, as in the case of natural peptide toxins and their specific interactions with cellular or membrane targets. From a regulatory perspective, only after specific risk identification and characterization should an equally specific safety threshold in relation to potential toxicity be defined.

Preparation, design, identification and application of self-assembly peptides from seafood: A review

Hydrogels formed by self-assembling peptides with low toxicity and high biocompatibility have been widely used in food and biomedical fields. Seafood contains rich protein resources and is also one of the important sources of natural bioactive peptides. The self-assembled peptides in seafood have good functional activity and are very beneficial to human health. In this review, the sequence of seafood self-assembly peptide was introduced, and the preparation, screening, identification and characterization. The rule of self-assembled peptides was elucidated from amino acid sequence composition, amino acid properties (hydrophilic, hydrophobic and electric), secondary structure, interaction and peptide properties (hydrophilic and hydrophobic). It was introduced that the application of hydrogels formed by self-assembled peptides, which lays a theoretical foundation for the development of seafood self-assembled peptides in functional foods and the application of biological materials.

Mechanism Insight into Direct Amidation Catalyzed by Zr Salts: Evidence of Zr Oxo Clusters as Active Species

The capricious reactivity and speciation of earth-abundant metals (EAM) hinder the mechanistic understanding essential to boost their efficiency and versatility in catalysis. Moreover, metal's solution chemistry and reactivity are conventionally controlled using organic ligands, while their fundamental chemistry in operando conditions is often overlooked. However, in this study, we showcase how a better understanding of in operando conditions may result in improved catalytic reactions. By assessing the composition and structure of active species for Zr-catalyzed direct amide bond formations under operating conditions, we discovered zirconium oxo clusters form quickly and are likely active species in the reactions. Formation of these clusters dismisses the use of additional organic ligands, inert atmosphere, anhydrous solvents, or even water scavenging to provide amides in good to excellent yields. More specifically, dodeca- and hexazirconium oxo clusters (Zr12 and Zr6, respectively) rapidly form from commercial, readily available Zr salts under reaction conditions known to afford amides directly from nonactivated carboxylic acid and amine substrates. Extended X-ray absorption fine structure (EXAFS) experiments confirm the presence of oxo clusters in solution throughout the reaction, while their key role in the mechanism is supported by an in-depth computational study employing density functional theory (DFT) and molecular dynamics (MD) methods. These results underline the value of (earth-abundant) metals' intrinsic solution chemistry to transformative mechanistic understanding and to enhance the sustainability of organic transformations.

A sustainable protocol for the synthesis of N-acyl tryptamines, a class of potential gut microbiota-derived endocannabinoid-like mediators

A simple and sustainable propylphosphonic anhydride (T3P)-assisted methodology for the synthesis of N-acyl tryptamines, an interesting class of gut microbiota-derived endocannabinoid-like lipid mediators, was proposed. This protocol is characterized by great operational simplicity, and all products were obtained at room temperature, without the use of an inert atmosphere and by using limited amounts of non-halogenated solvents. Finally, the possibility to realize the reaction under mechanochemical conditions was explored with interesting results.

Improved Electrochemical Peptide Synthesis Enabled by Electron-Rich Triaryl Phosphines

While remarkable progress has been made in the development of peptide medicines, many problems related to peptide synthesis remain unresolved. Previously, we reported electrochemical peptide synthesis using a phosphine as a potentially recyclable coupling reagent. However, there was room for improvement from the point of view of reaction efficiency, especially in the carboxylic acid activation step and the peptide bond formation step. To overcome these challenges, we searched for the optimal phosphine. Among phosphines with various electronic properties, we found that electron-rich triaryl phosphines improved the reaction efficiency. Consequently, we successfully performed electrochemical peptide synthesis on sterically hindered and valuable amino acids. We also synthesized oligopeptides that were challenging with our previous method. Finally, we examined the effect of substituents on the phosphine cations, and gained some insights into reactivity, which will aid researchers designing reactions involving phosphine cations.

Purification of recombinantly produced somatostatin-28 comparing hydrochloric acid and polyethyleneimine as E. coli extraction aids

Peptides are used for diagnostics, therapeutics, and as antimicrobial agents. Most peptides are produced by chemical synthesis, but recombinant production has recently become an attractive alternative due to the advantages of high titers, less toxic waste and correct folding of tertiary structure. Somatostatin-28 is a peptide hormone that regulates the endocrine system, cell proliferation and inhibits the release of numerous secondary hormones in human body. It is composed of 28 amino acids and has one disulfide bond, which makes it to an optimal model peptide for a whole downstream purification process. We produced the peptide in the periplasm of E. coli using the CASPON™ technology, an affinity fusion technology system that enables high soluble expression of recombinant proteins and cleaves the fusion tag with a circularly permuted human caspase-2. Furthermore, purification of the products is straight forward using an established platform process. Two different case studies for downstream purification are presented, starting with either hydrochloric acid or polyethyleneimine as an extraction aid. After release of affinity-tagged somatostatin-28 out of E. coli's periplasm, several purification steps were performed, delivering a pure peptide solution after the final polishing step. The process was monitored by reversed-phase high-performance liquid chromatography as well as mass spectrometry to determine the yield and correct disulfide bond formation. Monitoring of impurities like host cell proteins, DNA and endotoxins after each downstream unit confirmed effective removal for both purification pathways.

Cryptic enzymatic assembly of peptides armed with β-lactone warheads

Nature has evolved biosynthetic pathways to molecules possessing reactive warheads that inspired the development of many therapeutic agents, including penicillin antibiotics. Peptides armed with electrophilic warheads have proven to be particularly effective covalent inhibitors, providing essential antimicrobial, antiviral and anticancer agents. Here we provide a full characterization of the pathways that nature deploys to assemble peptides with β-lactone warheads, which are potent proteasome inhibitors with promising anticancer activity. Warhead assembly involves a three-step cryptic methylation sequence, which is likely required to reduce unfavorable electrostatic interactions during the sterically demanding β-lactonization. Amide-bond synthetase and adenosine triphosphate (ATP)-grasp enzymes couple amino acids to the β-lactone warhead, generating the bioactive peptide products. After reconstituting the entire pathway to β-lactone peptides in vitro, we go on to deliver a diverse range of analogs through enzymatic cascade reactions. Our approach is more efficient and cleaner than the synthetic methods currently used to produce clinically important warhead-containing peptides.

Phe-Phe-Based Macroscopic Supramolecular Hydrogel Construction Strategies and Biomedical Applications

Since the phenylalanine (Phe) dipeptide moiety is referred to as an essential structure for building amyloid-β peptide from Alzheimer's disease, its wonderful assembly ability to form nanofibers has been extensively studied. Cross-linked Phe-Phe-based peptide nanofibers can construct networks, thus encapsulating the drugs to form supramolecular hydrogels. Recently, scientists have proposed a variety of Phe-Phe-based macroscopic supramolecular hydrogels and used them in biomedical applications. Therefore, we summarize the construction strategies of Phe-Phe-based macroscopic supramolecular hydrogels and list their represented biomedical applications (e.g., wound healing, eye protection, cancer therapy, etc.) since the birth of Phe-Phe-based supramolecular hydrogels. In addition, we present the perspectives and challenges of Phe-Phe-based macroscopic peptide hydrogels.

Efficient Solution-Phase Dipeptide Synthesis Using Titanium Tetrachloride and Microwave Heating

Microwaves have been successfully employed in the Lewis acid titanium tetrachloride-assisted synthesis of peptide systems. Dipeptide systems with their amino function differently protected with urethane protecting groups have been synthesized in short periods of time and with high yields. The formation of the peptide bond between the two reacting amino acids was achieved in pyridine by using titanium tetrachloride as a condensing agent and heating the reaction mixture with a microwave reactor. The reaction conditions are compatible with amino acids featuring various side chains and different protecting groups on both the amino function and side chains. Additionally, the substrates retain their chiral integrity after reaction.

Optimization of peptide synthesis time and sustainability using novel eco-friendly binary solvent systems with induction heating on an automated peptide synthesizer

On December 12th, 2023, the European Commission took regulatory action to amend Annex XVII of REACH, imposing restrictions on the use of N,N-dimethylformamide (DMF) within the EU market owing to its high toxicity. Historically, DMF has been widely considered the gold standard for solid-phase peptide synthesis (SPPS). Being urgent to propose alternative solvents, we tested the suitability of non-hazardous neat and mixed solvents. Notably, binary solvent mixtures containing dimethyl sulfoxide as one of the solvent partners demonstrated high efficacy in solubilizing reagents while maintaining the desired swelling characteristics of common resins. A series of binary solvent mixtures were tested in automated SPPS, both at room temperature and high temperature, employing the PurePep® Chorus synthesizer, which enabled controlled induction heating between 25 and 90°C with oscillation mixing. The performances were assessed in challenging peptide sequences, i.e., ACP (65-74), and in longer and aggregating sequences like SARS-CoV-2 RBM (436-507) and β-amyloid (1-42). Furthermore, as part of the proposed sustainable approach to minimize the utilization of hazardous solvents, we coupled the novel PurePep EasyClean catch-and-release purification technology. This work, addressing regulatory compliance, emphasizes the crucial role of green chemistry in advancing safer and more environmentally friendly practices in SPPS.

Origami of KR-12 Designed Antimicrobial Peptides and Their Potential Applications

This review describes the discovery, structure, activity, engineered constructs, and applications of KR-12, the smallest antibacterial peptide of human cathelicidin LL-37, the production of which can be induced under sunlight or by vitamin D. It is a moonlighting peptide that shows both antimicrobial and immune-regulatory effects. Compared to LL-37, KR-12 is extremely appealing due to its small size, lack of toxicity, and narrow-spectrum antimicrobial activity. Consequently, various KR-12 peptides have been engineered to tune peptide activity and stability via amino acid substitution, end capping, hybridization, conjugation, sidechain stapling, and backbone macrocyclization. We also mention recently discovered peptides KR-8 and RIK-10 that are shorter than KR-12. Nano-formulation provides an avenue to targeted delivery, controlled release, and increased bioavailability. In addition, KR-12 has been covalently immobilized on biomaterials/medical implants to prevent biofilm formation. These constructs with enhanced potency and stability are demonstrated to eradicate drug-resistant pathogens, disrupt preformed biofilms, neutralize endotoxins, and regulate host immune responses. Also highlighted are the safety and efficacy of these peptides in various topical and systemic animal models. Finaly, we summarize the achievements and discuss future developments of KR-12 peptides as cosmetic preservatives, novel antibiotics, anti-inflammatory peptides, and microbiota-restoring agents.

Protein desulfurization and deselenization

Methods enabling the dechalcogenation of thiols or selenols have been investigated and developed for a long time in fields of research as diverse as the study of prebiotic chemistry, the engineering of fuel processing techniques, the study of biomolecule structures and function or the chemical synthesis of biomolecules. The dechalcogenation of thiol or selenol amino acids is nowadays a particularly flourishing area of research for being a pillar of modern chemical protein synthesis, when used in combination with thiol or selenol-based chemoselective peptide ligation chemistries. This review offers a comprehensive and scholarly overview of the field, emphasizing emerging trends and providing a detailed and critical mechanistic discussion of the dechalcogenation methods developed so far. Taking advantage of recently published reports, it also clarifies some unexpected desulfurization reactions that were observed in the past and for which no explanation was provided at the time. Additionally, the review includes a discussion on principal desulfurization methods within the framework of newly introduced green chemistry metrics and toolkits, providing a well-rounded exploration of the subject.

Bioproduction Platform to Generate Functionalized Disulfide-Constrained Peptide Analogues

Disulfide-constrained peptides (DCPs) have gained increased attention as a drug modality due to their exceptional stability and combined advantages of large biologics and small molecules. Chemical synthesis, although widely used to produce DCPs, is associated with high cost, both economically and environmentally. To reduce the dependence on solid phase peptide synthesis and the negative environmental footprint associated with it, we present a highly versatile, low-cost, and environmentally friendly bioproduction platform to generate DCPs and their conjugates as well as chemically modified or isotope-labeled DCPs. Using the DCP against the E3 ubiquitin ligase Zinc and Ring Finger 3, MK1-3.6.10, as a model peptide, we have demonstrated the use of bacterial expression, combined with Ser ligation or transglutaminase-mediated XTEN ligation, to produce multivalent MK1-3.6.10 and MK1-3.6.10 with N-terminal functional groups. We have also developed a bioproduction method for the site-specific incorporation of unnatural amino acids into recombinant DCPs by the amber codon suppression system. Lastly, we produced 15N/13C-labeled MK1-3.6.10 with high yield and assessed the performance of a semiautomated resonance assignment workflow that could be used to accelerate binding studies and structural characterization of DCPs. This study provides a proof of concept to generate functionalized DCPs using bioproduction, providing a potential solution to alleviate the reliance on hazardous chemicals, reduce the cost, and expedite the timeline for DCP discovery.

Targeting Leishmania Promastigotes and Amastigotes Forms through Amino Acids and Peptides: A Promising Therapeutic Strategy

Millions of people worldwide are affected by leishmaniasis, caused by the Leishmania parasite. Effective treatment is challenging due to the biological complexity of the parasite, drug toxicity, and increasing resistance to conventional drugs. To combat this disease, the development of specific strategies to target and selectively eliminate the parasite is crucial. This Review highlights the importance of amino acids in the developmental stages of Leishmania as a factor determining whether the infection progresses or is suppressed. It also explores the use of peptides as alternatives in parasite control and the development of novel targeted treatments. While these strategies show promise for more effective and targeted treatment, further studies to address the remaining challenges are imperative.

Solvent-Free Mechanosynthesis of Oligopeptides by Coupling Peptide Segments of Different Lengths - Elucidating the Role of Cesium Carbonate in Ball Mill Processes

We report an idea for the synthesis of oligopeptides using a solvent-free ball milling approach. Our concept is inspired by block play, in which it is possible to construct different objects using segments (blocks) of different sizes and lengths. We prove that by having a library of short peptides and employing the ball mill mechanosynthesis (BMMS) method, peptides can be easily coupled to form different oligopeptides with the desired functional and biological properties. Optimizing the BMMS process we found that the best yields we obtained when TBTU and cesium carbonate were used as reagents. The role of Cs2CO3 in the coupling mechanism was followed on each stage of synthesis by 1H, 13C and 133Cs NMR employing Magic Angle Spinning (MAS) techniques. It was found that cesium carbonate acts not only as a base but is also responsible for the activation of substrates and intermediates. The unique information about the BMMS mechanism is based on the analysis of 2D NMR data. The power of BMMS is proved by the example of different peptide combinations, 2+2, 3+2, 4+2, 5+2 and 4+4. The tetra-, penta-, hexa-, hepta- and octapeptides obtained under this project were fully characterized by MS and NMR techniques.

Molecular farming for sustainable production of clinical-grade antimicrobial peptides

Antimicrobial peptides (AMPs) are emerging as next-generation therapeutics due to their broad-spectrum activity against drug-resistant bacterial strains and their ability to eradicate biofilms, modulate immune responses, exert anti-inflammatory effects and improve disease management. They are produced through solid-phase peptide synthesis or in bacterial or yeast cells. Molecular farming, i.e. the production of biologics in plants, offers a low-cost, non-toxic, scalable and simple alternative platform to produce AMPs at a sustainable cost. In this review, we discuss the advantages of molecular farming for producing clinical-grade AMPs, advances in expression and purification systems and the cost advantage for industrial-scale production. We further review how 'green' production is filling the sustainability gap, streamlining patent and regulatory approvals and enabling successful clinical translations that demonstrate the future potential of AMPs produced by molecular farming. Finally, we discuss the regulatory challenges that need to be addressed to fully realize the potential of molecular farming-based AMP production for therapeutics.

A production platform for disulfide-bonded peptides in the periplasm of Escherichia coli

BACKGROUND

Recombinant peptide production in Escherichia coli provides a sustainable alternative to environmentally harmful and size-limited chemical synthesis. However, in-vivo production of disulfide-bonded peptides at high yields remains challenging, due to degradation by host proteases/peptidases and the necessity of translocation into the periplasmic space for disulfide bond formation.

RESULTS

In this study, we established an expression system for efficient and soluble production of disulfide-bonded peptides in the periplasm of E. coli. We chose model peptides with varying complexity (size, structure, number of disulfide bonds), namely parathyroid hormone 1-84, somatostatin 1-28, plectasin, and bovine pancreatic trypsin inhibitor (aprotinin). All peptides were expressed without and with the N-terminal, low molecular weight CASPON™ tag (4.1 kDa), with the expression cassette being integrated into the host genome. During BioLector™ cultivations at microliter scale, we found that most of our model peptides can only be sufficiently expressed in combination with the CASPON™ tag, otherwise expression was only weak or undetectable on SDS-PAGE. Undesired degradation by host proteases/peptidases was evident even with the CASPON™ tag. Therefore, we investigated whether degradation happened before or after translocation by expressing the peptides in combination with either a co- or post-translational signal sequence. Our results suggest that degradation predominantly happened after the translocation, as degradation fragments appeared to be identical independent of the signal sequence, and expression was not enhanced with the co-translational signal sequence. Lastly, we expressed all CASPON™-tagged peptides in two industry-relevant host strains during C-limited fed-batch cultivations in bioreactors. We found that the process performance was highly dependent on the peptide-host-combination. The titers that were reached varied between 0.6-2.6 g L-1, and exceeded previously published data in E. coli. Moreover, all peptides were shown by mass spectrometry to be expressed to completion, including full formation of disulfide bonds.

CONCLUSION

In this work, we demonstrated the potential of the CASPON™ technology as a highly efficient platform for the production of soluble peptides in the periplasm of E. coli. The titers we show here are unprecedented whenever parathyroid hormone, somatostatin, plectasin or bovine pancreatic trypsin inhibitor were produced in E. coli, thus making our proposed upstream platform favorable over previously published approaches and chemical synthesis.

From Zero to Hero: The Cyanide-Free Formation of Amino Acids and Amides from Acetylene, Ammonia and Carbon Monoxide in Aqueous Environments in a Simulated Hadean Scenario

Amino acids are one of the most important building blocks of life. During the biochemical process of translation, cells sequentially connect amino acids via amide bonds to synthesize proteins, using the genetic information in messenger RNA (mRNA) as a template. From a prebiotic perspective (i.e., without enzymatic catalysis), joining amino acids to peptides via amide bonds is difficult due to the highly endergonic nature of the condensation reaction. We show here that amides can be formed in reactions catalyzed by the transition metal sulfides from acetylene, carbon monoxide and ammonia under aqueous conditions. Some α- and β-amino acids were also formed under the same conditions, demonstrating an alternative cyanide-free path for the formation of amino acids in prebiotic environments. Experiments performed with stable isotope labeled precursors, like 15NH4Cl and 13C-acetylene, enabled the accurate mass spectroscopic identification of the products formed from the starting materials and their composition. Reactions catalyzed using the transition metal sulfides seem to offer a promising alternative pathway for the formation of amides and amino acids in prebiotic environments, bypassing the challenges posed by the highly endergonic condensation reaction. These findings shed light on the potential mechanisms by which the building blocks of life could have originated on early Earth.