Disulfide bond replacement with non-reducible side chain to tail macrolactamization for the development of potent and selective CXCR4 peptide antagonists endowed with flanking binding sites

The present study describes a small library of peptides derived from a potent and selective CXCR4 antagonist (3), wherein the native disulfide bond is replaced using a side-chain to tail macrolactamization technique to vary ring size and amino acid composition. The peptides were preliminary assessed for their ability to interfere with the interaction between the receptor and anti-CXCR4 PE-conjugated antibody clone 12G5. Two promising candidates (13 and 17) were identified and further evaluated in a125I-CXCL12 competition binding assay, exhibiting IC50 in the low-nanomolar range. Furthermore, both candidates displayed high selectivity towards CXCR4 with respect to the cognate receptor CXCR7, ability to block CXCL12-dependent cancer cell migration, and receptor internalization, albeit at a higher concentration compared to 3. Molecular modeling studies on 13 and 17 produced a theoretical model that may serve as a guide for future modifications, aiding in the development of analogs with improved affinity. Finally, the study provides valuable insights into developing therapeutic agents targeting CXCR4-mediated processes, demonstrating the adaptability of our lead peptide 3 to alternative cyclization approaches and offering prospects for comprehensive investigations into the receptor region's interaction with its C-terminal region.

Growing Impact of Intramolecular Click Chemistry in Organic Synthesis

Click Chemistry, a modular, rapid, and one of the most reliable tool for the regioselective 1,2,3-triazole forming [3+2] reaction of organic azide and terimal alkyne is widely explored in various emerging domains of research ranging from chemical biology to catalysis and medicinal chemistry to material science. This regioselective reaction from a diverse range of azido-alkyne scaffolds has been well performed in both intermolecular as well as intramolecular fashions. In comparison to the intermolecular metal (Cu/Ru/Ni) variant of 'Click Chemistry', the intramolecular click tool is little addressed. The intramolecular click chemistry is exemplified as a mordern tool of cyclization which involves metal-catalyzed (CuAAC/RuAAC) cyclization, organo-catalyzed cyclization, and thermal-induced topochemical reaction. Thus, we report herein the recent approaches on intramolecular azide-alkyne cycloaddition 'Click Chemistry' with their wide-spread emerging applications in the developement of a diverse range of molecules including fused-heterocycles, well-defined peptidomemics, and macrocyclic architectures of various notable features.

Ultrasound-assisted Peptide Nucleic Acids synthesis (US-PNAS)

Herein, we developed an innovative and easily accessible solid-phase synthetic protocol for Peptide Nucleic Acid (PNA) oligomers by systematically investigating the ultrasonication effects in all steps of the PNA synthesis (US-PNAS). When compared with standard protocols, the application of the so-obtained US-PNAS approach succeeded in improving the crude product purities and the isolated yields of different PNA, including small or medium-sized oligomers (5-mer and 9-mer), complex purine-rich sequences (like a 5-mer Guanine homoligomer and the telomeric sequence TEL-13) and longer oligomers (such as the 18-mer anti-IVS2-654 PNA and the 23-mer anti-mRNA 155 PNA). Noteworthy, our ultrasound-assisted strategy is compatible with the commercially available PNA monomers and well-established coupling reagents and only requires the use of an ultrasonic bath, which is a simple equipment generally available in most synthetic laboratories.

Development of an o-aminoanilide-mediated native chemical ligation-assisted DADA strategy for the synthesis of disulfide surrogate peptides

The hydrazide-based native chemical ligation-assisted diaminodiacid (DADA) strategy is an efficient method for synthesizing large-span disulfide bridge surrogates. However, it is difficult to synthesize disulfide bond surrogates at Gln-Cys or Asn-Cys ligation sites using this strategy. Herein, we report a peptide o-aminoanilide-mediated NCL-assisted DADA strategy that enables the synthesis of large-span peptide disulfide bridge surrogates containing only Gln-Cys or Asn-Cys ligation sites. Through this strategy, we successfully synthesized disulfide bond surrogates of conotoxin vil14a and κ-hefutoxin 1. This strategy provides a new option to obtain large-span peptide disulfide bridge substitutes for native chemical ligation at Gln-Cys and Asn-Cys sites.

Recent Progress in Catalytic Synthesis of 1,2,3-Triazoles

1,2,3-triazoles represent a functional heterocyclic core that has been at the center of modern organic chemistry since the beginning of click chemistry. Being a versatile framework, such an aromatic ring can be observed in uncountable molecules useful in medicine and photochemistry, just to name a few. This review summarizes the progress achieved in their synthesis from 2015 to today, with particular emphasis on the development of new catalytic and eco-compatible approaches. In doing so, we subdivided the report based on their degree of functionalization and, for each subparagraph, we outlined the role of the catalyst employed.

Macrocyclization strategies for cyclic peptides and peptidomimetics

Peptides are a growing therapeutic class due to their unique spatial characteristics that can target traditionally "undruggable" protein-protein interactions and surfaces. Despite their advantages, peptides must overcome several key shortcomings to be considered as drug leads, including their high conformational flexibility and susceptibility to proteolytic cleavage. As a general approach for overcoming these challenges, macrocyclization of a linear peptide can usually improve these characteristics. Their synthetic accessibility makes peptide macrocycles very attractive, though traditional synthetic methods for macrocyclization can be challenging for peptides, especially for head-to-tail cyclization. This review provides an updated summary of the available macrocyclization chemistries, such as traditional lactam formation, azide-alkyne cycloadditions, ring-closing metathesis as well as unconventional cyclization reactions, and it is structured according to the obtained functional groups. Keeping peptide chemistry and screening in mind, the focus is given to reactions applicable in solution, on solid supports, and compatible with contemporary screening methods.

First-in-Class Cyclic Temporin L Analogue: Design, Synthesis, and Antimicrobial Assessment

The pharmacodynamic and pharmacokinetic properties of bioactive peptides can be modulated by introducing conformational constraints such as intramolecular macrocyclizations, which can involve either the backbone and/or side chains. Herein, we aimed at increasing the α-helicity content of temporin L, an isoform of an intriguing class of linear antimicrobial peptides (AMPs), endowed with a wide antimicrobial spectrum, by the employment of diverse side-chain tethering strategies, including lactam, 1,4-substituted [1,2,3]-triazole, hydrocarbon, and disulfide linkers. Our approach resulted in a library of cyclic temporin L analogues that were biologically assessed for their antimicrobial, cytotoxic, and antibiofilm activities, leading to the development of the first-in-class cyclic peptide related to this AMP family. Our results allowed us to expand the knowledge regarding the relationship between the α-helical character of temporin derivatives and their biological activity, paving the way for the development of improved antibiotic cyclic AMP analogues.

Metabolic and conformational stabilization of a VEGF-mimetic beta-hairpin peptide by click-chemistry

HPLW is a Vascular Endothelial Growth Factor (VEGF)-mimicking beta-hairpin peptide endowed of proangiogenic effect and showing valuable biomedical application in the proangiogenic therapy. However, the translational potential of HPLW is limited by its low metabolic stability, which would shorten the in vivo efficacy of the molecule. Here, we developed a peptide analog of HPLW, named HPLW2, that retains the structural and biological properties of the original peptide but features an impressive resistance to degradation by human serum proteases. HPLW2 was obtained by covalently modifying the chemical structure of the peptide with molecular tools known to impart protease resistance. Notably, the peptide was cyclized by installing an interstrand triazole bridge through Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reaction. HPLW2 appears as a novel and promising drug candidate with potential biomedical application in the proangiogenic therapy as a low molecular weight drug, alternative to the use of VEGF. Our work points out the utility of the interstrand triazole bridge as effective chemical platform for the conformational and metabolic stabilization of beta-hairpin bioactive peptides.

Cysteine [2,4] Disulfide Bond as a New Modifiable Site of α-Conotoxin TxIB

α-Conotoxin TxIB, a selective antagonist of α6/α3β2β3 nicotinic acetylcholine receptor, could be a potential therapeutic agent for addiction and Parkinson's disease. As a peptide with a complex pharmacophoric conformation, it is important and difficult to find a modifiable site which can be modified effectively and efficiently without activity loss. In this study, three xylene scaffolds were individually reacted with one pair of the cysteine residues ([1,3] or [2,4]), and iodine oxidation was used to form a disulfide bond between the other pair. Overall, six analogs were synthesized with moderate isolated yields from 55% to 65%, which is four times higher than the traditional two-step oxidation with orthogonal protection on cysteines. The cysteine [2,4] modified analogs, with higher stability in human serum than native TxIB, showed obvious inhibitory effect and selectivity on α6/α3β2β3 nicotinic acetylcholine receptors (nAChRs), which was 100 times more than the cysteine [1,3] modified ones. This result demonstrated that the cysteine [2,4] disulfide bond is a new modifiable site of TxIB, and further modification can be a simple and feasible strategy for the exploitation and utilization of α-Conotoxin TxIB in drug discovery.