Total chemical synthesis of a heterodimeric interchain bis-lactam-linked Peptide: application to an analogue of human insulin-like Peptide 3

Systemic administration of a novel Beclin 1-derived peptide significantly upregulates autophagy in the spinal motor neurons of autophagy reporter mice

Autophagy, an intracellular degradation system, plays a vital role in protecting cells by clearing damaged organelles, pathogens, and protein aggregates. Autophagy upregulation through pharmacological interventions has gained significant attention as a potential therapeutic avenue for proteinopathies. Here, we report the development of an autophagy-inducing peptide (BCN4) derived from the Beclin 1 protein, the master regulator of autophagy. To deliver the BCN4 into cells and the central nervous system (CNS), it was conjugated to our previously developed cell and blood-brain barrier-penetrating peptide (CPP). CPP-BCN4 significantly upregulated autophagy and reduced protein aggregates in motor neuron (MN)-like cells. Moreover, its systemic administration in a reporter mouse model of autophagy resulted in a significant increase in autophagy activity in the spinal MNs. Therefore, this novel autophagy-inducing peptide with a demonstrated ability to upregulate autophagy in the CNS has significant potential for the treatment of various neurodegenerative diseases with protein aggregates as a characteristic feature.

Semisynthesis of A6-A11 lactam insulin

Insulin replacement therapy is essential for the management of diabetes. However, despite the relative success of this therapeutic strategy, there is still a need to improve glycaemic control and the overall quality of life of patients. This need has driven research into orally available, glucose-responsive and rapid-acting insulins. A key consideration during analogue development is formulation stability, which can be improved via the replacement of insulin's A6-A11 disulfide bond with stable mimetics. Unfortunately, analogues such as these require extensive chemical synthesis to incorporate the nonnative cross-links, which is not a scalable synthetic approach. To address this issue, we demonstrate proof of principle for the semisynthesis of insulin analogues bearing nonnative A6-A11 cystine isosteres. The key feature of our synthetic strategy involves the use of several biosynthetically derived peptide precursors which can be produced at scale cost-effectively and a small, chemically synthesised A6-A11 macrocyclic lactam fragment. Although the assembled A6-A11 lactam insulin possesses poor biological activity in vitro, our synthetic strategy can be applied to other disulfide mimetics that have been shown to improve thermal stability without significantly affecting activity and structure. Moreover, we envisage that this new semisynthetic approach will underpin a new generation of hyperstable proteomimetics.

Nature-inspired dimerization as a strategy to modulate neuropeptide pharmacology exemplified with vasopressin and oxytocin

Vasopressin (VP) and oxytocin (OT) are cyclic neuropeptides that regulate fundamental physiological functions via four G protein-coupled receptors, V_1aR, V_1bR, V₂R, and OTR. Ligand development remains challenging for these receptors due to complex structure–activity relationships. Here, we investigated dimerization as a strategy for developing ligands with novel pharmacology. We regioselectively synthesised and systematically studied parallel, antiparallel and N- to C-terminal cyclized homo- and heterodimer constructs of VP, OT and dVDAVP (1-deamino-4-valine-8-d-arginine-VP). All disulfide-linked dimers, except for the head-to-tail cyclized constructs, retained nanomolar potency despite the structural implications of dimerization. Our results support a single chain interaction for receptor activation. Dimer orientation had little impact on activity, except for the dVDAVP homodimers, where an antagonist to agonist switch was observed at the V_1aR. This study provides novel insights into the structural requirements of VP/OT receptor activation and spotlights dimerization as a strategy to modulate pharmacology, a concept also frequently observed in nature.

Structural and pharmacological study of parallel, antiparallel and N- to C-terminal cyclized homo- and heterodimers of vasopressin and oxytocin. This study spotlights dimerization as a strategy to modulate the pharmacology of neuropeptides.

Automated Solid-Phase Peptide Synthesis

The development of solid-phase peptide synthesis by Bruce Merrifield paved the way for a synthesis carried out by machines. Automated peptide synthesis is a fast and convenient way of synthesizing many peptides simultaneously. This chapter tries to give a general guidance for the development of synthesis protocols for the peptide synthesizer. It also provides some suggestions for the modification of the synthesized peptides. Additionally, many examples of possible challenges during and after the synthesis are given in order to support the reader in finding the best synthesis strategy. Numerous references are given to many of the described matters.

Synthesis and Characterization of an A6-A11 Methylene Thioacetal Human Insulin Analogue with Enhanced Stability

Insulin has been a life-saving drug for millions of people with diabetes. However, several challenges exist which limit therapeutic benefits and reduce patient convenience. One key challenge is the fibrillation propensity, which necessitates refrigeration for storage. To address this limitation, we chemically synthesized and evaluated a methylene thioacetal human insulin analogue (SCS-Ins). The synthesized SCS-Ins showed enhanced serum stability and aggregation resistance while retaining bioactivity compared with native insulin.

A Strategy To Prepare Peptide Heterodimers in the Solid Phase with an Acid-Labile Linker

The currently synthetic methods of peptide heterodimer involve tedious synthesis and purification steps. An acid-labile traceless linker was prepared, which is highly compatible with the Fmoc strategy and could be used to prepare peptide heterodimer on resin. The linker could be cleaved concomitantly with peptide cleavage, and two model heterodimers were synthesized. The proposed synthesis procedure is simple, straightforward, and provides great convenience for preparing disulfide-linked peptide heterodimers.

Peptide chemistry toolbox - Transforming natural peptides into peptide therapeutics

The development of solid phase peptide synthesis has released tremendous opportunities for using synthetic peptides in medicinal applications. In the last decades, peptide therapeutics became an emerging market in pharmaceutical industry. The need for synthetic strategies in order to improve peptidic properties, such as longer half-life, higher bioavailability, increased potency and efficiency is accordingly rising. In this mini-review, we present a toolbox of modifications in peptide chemistry for overcoming the main drawbacks during the transition from natural peptides to peptide therapeutics. Modifications at the level of the peptide backbone, amino acid side chains and higher orders of structures are described. Furthermore, we are discussing the future of peptide therapeutics development and their impact on the pharmaceutical market.

Novel Methods for the Chemical Synthesis of Insulin Superfamily Peptides and of Analogues Containing Disulfide Isosteres

The insulin superfamily of peptides is ubiquitous within vertebrates and invertebrates and is characterized by the presence of a set of three disulfide bonds in a unique disposition. With the exception of insulin-like growth factors I and II, which are single chain peptides, the remaining 8 members of the human insulin superfamily are two-chain peptides containing one intramolecular and two intermolecular disulfide bridges. These structural features have long made the chemical synthesis of the peptides a considerable challenge, in particular, including their correct disulfide bond pairing and formation. However, they have also afforded the opportunity to develop modern solid phase synthesis methods for the preparation of such peptides that incorporate novel or improved chemical methods for the controlled introduction of both disulfide bonds and their surrogates, both during and after peptide chain assembly. In turn, this has enabled a detailed probing of the structure and function relationship of this small but complex superfamily of peptides. After initially using and subsequently identifying significant limitations of the approach of simultaneous random chain combination and oxidative folding, our laboratory undertook to develop robust chemical synthesis strategies in concert with orthogonal cysteine S-protecting groups and corresponding regioselective disulfide bond formation. These have included the separate synthesis of each of the two chains or of the two chains linked by an artificial C-peptide that is removed following postoxidative folding. These, in turn, have enabled an increased ease of acquisition in a good yield of not only members of human insulin superfamily but other insulin-like peptides. Importantly, these successful methods have enabled, for the first time, a detailed analysis of the role that the disulfide bonds play in the structure and function of such peptides. This was achieved by selective removal of the disulfide bonds or by the judicious insertion of disulfide isosteres that possess structurally subtle variations in bond length, hydrophobicity, and angle. These include lactam, dicarba, and cystathionine, each of which has required modifications to the peptide synthesis protocols for their successful placement within the peptides. Together, these synthesis improvements and the novel chemical developments of cysteine/cystine analogues have greatly aided in the development of novel insulin-like peptide (INSL) analogues, principally with intra-A-chain disulfide isosteres, possessing not only improved functional properties such as increased receptor selectivity but also, with one important and unexpected exception, greater in vivo half-lives due to stability against disulfide reductases. Such analogues greatly will aid further biochemical and pharmacological analyses to delineate the structure-function relationships of INSLs and also future potential drug development.

Disulfide Bond Mimetics: Strategies and Challenges

The activity profile of many biologically relevant proteins and peptides often relies on a precise 3D structural organization. In this context, disulfide bonds are natural covalent constraints that play a key role in driving and stabilizing the folding pattern of these molecules. Despite its prominent significance as structural motif, the disulfide bond itself is inherently unstable under physiological conditions, posing a major limit to the use and development of disulfide-rich peptides and proteins as molecular tools and drug lead compounds. To tackle this restriction, disulfide engineering with stable functional analogues has arisen a considerable interest. Here, the most popular approaches to disulfide replacement are reviewed and discussed with particular emphasis on advantages and limitations under both functional and synthetic perspectives.

Total Chemical Synthesis of an Intra-A-Chain Cystathionine Human Insulin Analogue with Enhanced Thermal Stability

Despite recent advances in the treatment of diabetes mellitus, storage of insulin formulations at 4 °C is still necessary to minimize chemical degradation. This is problematic in tropical regions where reliable refrigeration is not ubiquitous. Some degradation byproducts are caused by disulfide shuffling of cystine that leads to covalently bonded oligomers. Consequently we examined the utility of the non-reducible cystine isostere, cystathionine, within the A-chain. Reported herein is an efficient method for forming this mimic using simple monomeric building blocks. The intra-A-chain cystathionine insulin analogue was obtained in good overall yield, chemically characterized and demonstrated to possess native binding affinity for the insulin receptor isoform B. It was also shown to possess significantly enhanced thermal stability indicating potential application to next-generation insulin analogues.

Chemical synthesis of peptides within the insulin superfamily

The synthesis of insulin has inspired fundamental advances in the art of peptide science while simultaneously revealing the structure-function relationship of this centrally important metabolic hormone. This review highlights milestones in the chemical synthesis of insulin that can be divided into two separate approaches: (i) disulfide bond formation driven by protein folding and (ii) chemical reactivity-directed sequential disulfide bond formation. Common to the two approaches are the persistent challenges presented by the hydrophobic nature of the individual A-chain and B-chain and the need for selective disulfide formation under mildly oxidative conditions. The extension and elaboration of these synthetic approaches have been ongoing within the broader insulin superfamily. These structurally similar peptides include the insulin-like growth factors and also the related peptides such as relaxin that signal through G-protein-coupled receptors. After a half-century of advances in insulin chemistry, we have reached a point where synthesis is no longer limiting structural and biological investigation within this family of peptide hormones. The future will increasingly focus on the refinement of structure to meet medicinal purposes that have long been pursued, such as the development of a glucose-sensitive insulin. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

A perfluoroaromatic abiotic analog of H2 relaxin enabled by rapid flow-based peptide synthesis

We report on the rapid-flow based synthesis and functional characterization of a H2 relaxin analog that takes advantage of perfluoroarylation-cysteine SNAr chemistry for a disulfide replacement strategy.