Neurobehavioral and molecular changes in a rodent model of ACTH-induced HPA axis dysfunction

Hypothalamic-pituitary-adrenal (HPA) axis dysregulation is linked to the pathophysiology of depression. Although exogenous adrenocorticotropic hormone (ACTH) is associated with a depressive-like phenotype in rodents, comprehensive neurobehavioral and mechanistic evidence to support these findings are limited. Sprague-Dawley rats (male, n = 30; female, n = 10) were randomly assigned to the control (male, n = 10) or ACTH (male, n = 20; female n = 10) groups that received saline (0.1 ml, sc.) or ACTH (100 μg/day, sc.), respectively, for two weeks. Thereafter, rats in the ACTH group were subdivided to receive ACTH plus saline (ACTH_S; male, n = 10; female, n = 5; 0.2 ml, ip.) or ACTH plus imipramine (ACTH_I; male, n = 10; female, n = 5;10 mg/kg, ip.) for a further four weeks. Neurobehavioral changes were assessed using the forced swim test (FST), the sucrose preference test (SPT), and the open field test (OFT). Following termination, the brain regional mRNA expression of BDNF and CREB was determined using RT-PCR. After two-weeks, ACTH administration significantly increased immobility in the FST (p = 0.03), decreased interaction with the center of the OFT (p < 0.01), and increased sucrose consumption (p = 0.03) in male, but not female rats. ACTH administration significantly increased the expression of BDNF in the hippocampus and CREB in all brain regions in males (p < 0.05), but not in female rats. Imipramine treatment did not ameliorate these ACTH-induced neurobehavioral or molecular changes. In conclusion, ACTH administration resulted in a sex-specific onset of depressive-like symptoms and changes in brain regional expression of neurotrophic factors. These results suggest sex-specific mechanisms underlying the development of depressive-like behavior in a model of ACTH-induced HPA axis dysregulation.

Safety-Catch Linkers for Solid-Phase Peptide Synthesis

Solid-phase peptide synthesis (SPPS) is the preferred strategy for synthesizing most peptides for research purposes and on a multi-kilogram scale. One key to the success of SPPS is the continual evolution and improvement of the original method proposed by Merrifield. Over the years, this approach has been enhanced with the introduction of new solid supports, protecting groups for amino acids, coupling reagents, and other tools. One of these improvements is the use of the so-called "safety-catch" linkers/resins. The linker is understood as the moiety that links the peptide to the solid support and protects the C-terminal carboxylic group. The "safety-catch" concept relies on linkers that are totally stable under the conditions needed for both α-amino and side-chain deprotection that, at the end of synthesis, can be made labile to one of those conditions by a simple chemical reaction (e.g., an alkylation). This unique characteristic enables the simultaneous use of two primary protecting strategies: tert-butoxycarbonyl (Boc) and fluorenylmethoxycarbonyl (Fmoc). Ultimately, at the end of synthesis, either acids (which are incompatible with Boc) or bases (which are incompatible with Fmoc) can be employed to cleave the peptide from the resin. This review focuses on the most significant "safety-catch" linkers.

2023 FDA TIDES (Peptides and Oligonucleotides) Harvest

A total of nine TIDES (pepTIDES and oligonucleoTIDES) were approved by the FDA during 2023. The four approved oligonucleotides are indicated for various types of disorders, including amyotrophic lateral sclerosis, geographic atrophy, primary hyperoxaluria type 1, and polyneuropathy of hereditary transthyretin-mediated amyloidosis. All oligonucleotides show chemically modified structures to enhance their stability and therapeutic effectiveness as antisense or aptamer oligomers. Some of them demonstrate various types of conjugation to driving ligands. The approved peptides comprise various structures, including linear, cyclic, and lipopeptides, and have diverse applications. Interestingly, the FDA has granted its first orphan drug designation for a peptide-based drug as a highly selective chemokine antagonist. Furthermore, Rett syndrome has found its first-ever core symptoms treatment, which is also peptide-based. Here, we analyze the TIDES approved in 2023 on the basis of their chemical structure, medical target, mode of action, administration route, and common adverse effects.

Morpholine, a strong contender for Fmoc removal in solid-phase peptide synthesis

Morpholine, which scores 7.5 in terms of greenness and is not a regulated substance, could be considered a strong contender for Fmoc removal in solid-phase peptide synthesis (SPPS). Morpholine in dimethylformamide (DMF) (50%-60%) efficiently removes Fmoc in SPPS, minimizes the formation of diketopiperazine, and almost avoids the aspartimide formation. As a proof of concept, somatostatin has been synthesized using 50% morpholine in DMF with the same purity as when using 20% piperidine-DMF.

The Pharmaceutical Industry in 2023: An Analysis of FDA Drug Approvals from the Perspective of Molecules

With the COVID-19 pandemic behind us, the U.S. Food and Drug Administration (FDA) has approved 55 new drugs in 2023, a figure consistent with the number authorized in the last five years (53 per year on average). Thus, 2023 marks the second-best yearly FDA harvest after 2018 (59 approvals) in all the series. Monoclonal antibodies (mAbs) continue to be the class of drugs with the most approvals, with an exceptional 12, a number that makes it the most outstanding year for this class. As in 2022, five proteins/enzymes have been approved in 2023. However, no antibody-drug conjugates (ADCs) have been released onto the market. With respect to TIDES (peptides and oligonucleotides), 2023 has proved a spectacular year, with a total of nine approvals, corresponding to five peptides and four oligonucleotides. Natural products continue to be the best source of inspiration for drug development, with 10 new products on the market. Three drugs in this year's harvest are pegylated, which may indicate the return of pegylation as a method to increase the half-lives of drugs after the withdrawal of peginesatide from the market in 2013. Following the trends in recent years, two bispecific drugs have been authorized in 2023. As in the preceding years, fluorine and/or N-aromatic heterocycles are present in most of the drugs. Herein, the 55 new drugs approved by the FDA in 2023 are analyzed exclusively on the basis of their chemical structure. They are classified as the following: biologics (antibodies, proteins/enzymes); TIDES (peptide and oligonucleotides); combined drugs; pegylated drugs; natural products; nitrogen aromatic heterocycles; fluorine-containing molecules; and other small molecules.

Self-assembly of NrTP6 cell-penetrating lipo-peptide with variable number of lipid chains: Impact of phosphate ions on lipid association

HYPOTHESIS

Lipopeptides synthesized from the Nucleolar Targeting Peptide (NrTP6) with one, two or four dodecanoic fatty acid (FA) chains, display large head to tail volumes, which together with the number of lipid chains per molecule, impacts their self-assembly behavior. In phosphate buffer (PB), peptide to peptide interactions are triggered by the presence of phosphate ions that act as ionic crosslinkers, affecting the organization of the lipid assemblies.

EXPERIMENTAL

The NrTP6 lipopeptides were synthesized by the solid phase peptide synthesis technique. The critical micellar concentration (CMC) of the lipopeptides was determined in water and PB by pyrene fluorescence. The size and morphology of lipopeptide assemblies were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Circular dichroism (CD) was used to study the secondary structures of the lipopeptide assemblies.

RESULTS

For NrTP6 lipopeptides with two and four lipid chains, CMCs in water are larger than in PB. TEM images of the lipopeptide assemblies show different morphologies including fibers, rods, and spheres depending on the number of lipid chains, concentration and whether they are assembled in water or PB. CD spectroscopy shows that the peptide conformation, either random or beta, correlates with the morphology of the assemblies.

N,N-Dimethyl Formamide European Restriction Demands Solvent Substitution in Research and Development

As of December 2023, the use of common solvent N,N-dimethyl formamide (DMF) will be restricted in the European Union because of its reproductive health hazard. Industrial facilities must comply with stricter exposure limits, and researchers are recommended to find alternative solvents. Here we explain the restrictions on DMF, which disciplines are affected, and how to substitute DMF to keep research and development commercially relevant.

Protocol for Facile Synthesis of Fmoc-N-Me-AA-OH Using 2-CTC Resin as Temporary and Reusable Protecting Group

One approach to enhance the bioavailability and half-life of peptides in vivo is through N-methylation of one or more of the amino acids within the peptide sequence. However, commercially available Fmoc-N-Me-AA-OHs are limited and often expensive. In this study, a solid-phase synthesis method for Fmoc-N-Me-AA-OH was developed using a 2-chlorotrityl chloride (2-CTC) resin as a temporary protective group for the carboxylic acid strategy. Two strategies for the alkylation step were compared, employing either dimethyl sulfate or methyl iodide in the Biron-Kessler method. In this work we tested the protocol with two amino acids: Fmoc-Thr(tBu)-OH and Fmoc-βAla-OH. The first one is an alpha amino acid, very hindered and with the amine group directly influenced by the electronic effects of the carboxy group, whereas in Fmoc-βAla-OH, the presence of a methylene group weakens this influence due to the intervening carbon atoms. The desired amino acids, Fmoc-N-Me-Thr(tBu)-OH and Fmoc-N-Me-βAla-OH, were synthesized by both strategies with high yield and purity.

A safety-catch protecting group strategy compatible with Boc-chemistry for the synthesis of peptide nucleic acids (PNAs)

Peptide Nucleic Acids (PNAs) are an intriguing class of synthetic biomolecules with great potential in medicine. Although PNAs could be considered analogs of oligonucleotides, their synthesis is more like that of peptides. In both cases, a Solid-Phase Synthesis (SPS) approach is used. Herein, the advantage using Boc as a temporal protecting group has been demonstrated to be more favored than Fmoc. In this context, a new PNA SPS strategy has been developed based on a safety-catch protecting group scheme for the exocyclic nitrogen of the side-chain bases and the linker. Sulfinyl (sulfoxide)-containing moieties are fully stable to the trifluoroacetic acid (TFA) used to remove the Boc group, but they can be reduced to the corresponding sulfide derivatives, which are labile in the presence of TFA. The efficiency of this novel synthetic strategy has been demonstrated in the synthesis of the PNA pentamer H-PNA(TATCT)-βAla-OH.

Improving 2-Chlorotrityl Chloride (2-CTC) Resin Activation

Used in solid-phase peptide synthesis (SPPS) for peptides with an acid termination, the 2-chlorotrityl chloride (2-CTC) resin is highly susceptible to moisture, leading to reduced resin loading and lower synthetic yields. It is therefore recommended that the resin be activated with thionyl chloride (SOCl2) before peptide assembly. Here we present an optimized procedure for resin activation that minimizes the use of SOCl2 as the activation reagent and reduces the activation time. Additionally, we demonstrate the feasibility of reusing the 2-CTC resin when following the activation protocol, achieving comparable results to the first usage of the resin. Moreover, we achieved different degrees of resin activation by varying the amount of SOCl2. For instance, the use of 2% SOCl2 in anhydrous dichloromethane (DCM) allowed up to 44% activation of the resin, thereby making it suitable for the synthesis of longer peptides. Alternatively, employing 25% SOCl2 in anhydrous DCM resulted in up to 80% activation with a reaction time of only 5 min in both cases.

Antimicrobial Peptide Synergies for Fighting Infectious Diseases

Antimicrobial peptides (AMPs) are essential elements of thehost defense system. Characterized by heterogenous structures and broad-spectrumaction, they are promising candidates for combating multidrug resistance. Thecombined use of AMPs with other antimicrobial agents provides a new arsenal ofdrugs with synergistic action, thereby overcoming the drawback of monotherapiesduring infections. AMPs kill microbes via pore formation, thus inhibitingintracellular functions. This mechanism of action by AMPs is an advantage overantibiotics as it hinders the development of drug resistance. The synergisticeffect of AMPs will allow the repurposing of conventional antimicrobials andenhance their clinical outcomes, reduce toxicity, and, most significantly,prevent the development of resistance. In this review, various synergies ofAMPs with antimicrobials and miscellaneous agents are discussed. The effect ofstructural diversity and chemical modification on AMP properties is firstaddressed and then different combinations that can lead to synergistic action,whether this combination is between AMPs and antimicrobials, or AMPs andmiscellaneous compounds, are attended. This review can serve as guidance whenredesigning and repurposing the use of AMPs in combination with other antimicrobialagents for enhanced clinical outcomes.

Serinol-Based Versatile Disulfide-Reducing Reagent

Here, we report the synthesis of disulfide-reducing agents 2-(dibenzylamino) propane-1,3-dithiol (DPDT) and 2-(dibenzylamino)-2-methylpropane-1,3-dithiol (DMPDT) from serinol and methyl serinol, respectively. DPDT was found to show greater stability than DMPDT. Hence, the effectiveness of DPDT as a reducing agent was evaluated in both liquid and solid phases. The reducing capacity of this agent was comparable to that of DTT.

FDA Approvals of Biologics in 2022

The year 2022 witnessed the control of the COVID-19 pandemic in most countries through social and hygiene measures and also vaccination campaigns. It also saw a decrease in total approvals by the U.S. Food and Drug Administration (FDA). Nevertheless, there was no fall in the Biologics class, which was boosted through the authorization of 15 novel molecules, thus maintaining the figures achieved in previous years. Indeed, the decrease in approvals was only for the category of small molecules. Monoclonal antibodies (mAbs) continued to be the drug class with the most approvals, and cancer remained the most targeted disease, followed by autoimmune conditions, as in previous years. Interestingly, the FDA gave the green light to a remarkable number of bispecific Biologics (four), the highest number in recent years. Indeed, 2022 was another year without the approval of an antimicrobial Biologic, although important advancements were made in targeting new diseases, which are discussed herein. In this work, we only analyze the Biologics authorized in 2022. Furthermore, we also consider the orphan drugs authorized. We not only apply a quantitative analysis to this year's harvest, but also compare the efficacy of the Biologics with those authorized in previous years. On the basis of their chemical structure, the Biologics addressed fall into the following classes: monoclonal antibodies; antibody-drug conjugates; and proteins/enzymes.

Methionine-Containing Peptides: Avoiding Secondary Reactions in the Final Global Deprotection

The solid-phase synthesis of Met-containing peptides using a fluorenylmethoxycarbonyl (Fmoc)/tert-butyl (tBu) protection scheme is inevitably accompanied by two stubborn side reactions, namely, oxidation and S-alkylation (tert-butylation), which result in the formation of Met(O) and sulfonium salt impurities of the target peptide, respectively. These two reactions are acid-catalyzed, and they occur during the final trifluoroacetic (TFA)-based acidolytic cleavage step. Herein, we developed two new cleavage solutions that eradicate the oxidation and reduce S-alkylation. TFA-anisole-trimethylsilyl chloride (TMSCl)-Me₂S-triisopropylsilane (TIS) containing 1 mg of triphenyl phosphine per mL of solution was the optimal mixture for Cys-containing peptides, while for the remaining peptides, TIS was not required. Both cleavage solutions proved to be excellent when sensitive amino acids such as Cys and Trp were involved. TMSCl did not affect either of these sensitive amino acids. Reversing the sulfonium salt to free Met-containing peptide was achieved by heating the peptide at 40 °C for 24 h using 5% acetic acid.

The challenge of peptide nucleic acid synthesis

Peptide nucleic acids (PNAs) are an important class of DNA/RNA mimics that can hybridize complementary chains of nucleic acids with high affinity and specificity. Because of this property and their metabolic stability, PNAs have broad potential applications in different fields. Consisting of a neutral polyamide backbone, PNAs are prepared following the method used for peptide synthesis. In this regard, they are prepared by the sequential coupling of the protected monomers on a solid support using a similar approach to solid-phase peptide synthesis (SPPS). However, PNA synthesis is a little more challenging due to issues of the difficulty on the preparation of monomers and their solubility. Furthermore, the PNA elongation is jeopardized by intra/inter chain aggregation and side reactions. These hurdles can be overcome using different protecting group strategies on the PNA monomer, which also dictate the approach followed to prepare the oligomers. Herein, the main synthetic strategies driven by the protecting group scheme are discussed. However, there is still ample scope for further enhancement of the overall process.

2022 FDA TIDES (Peptides and Oligonucleotides) Harvest

A total of 37 new drug entities were approved in 2022; although that year registered the lowest number of drug approvals since 2016, the TIDES class consolidated its presence with a total of five authorizations (four peptides and one oligonucleotide). Interestingly, 23 out of 37 drugs were first-in-class and thus received fast-track designation by the FDA in categories such as breakthrough therapy, priority review voucher, orphan drug, accelerated approval, and so on. Here, we analyze the TIDES approved in 2022 on the basis of their chemical structure, medical target, mode of action, administration route, and common adverse effects.

The Pharmaceutical Industry in 2022: An Analysis of FDA Drug Approvals from the Perspective of Molecules

While 2021 ended with the world engulfed in the COVID-19 Omicron wave, 2022 has ended in almost all countries, except China, with COVID-19 being likened to the flu. In this context, the U.S. Food and Drug Administration (FDA) has authorized only 37 new drugs this year compared to an average of 52 in the last four years. Thus 2022 is the second lowest harvest after 2016 in the last six years. This ranking may be transient and will be confirmed in the coming years. In this regard, the reduction in the number of drugs accepted by the FDA this year applies only to the so-called small molecules as there has been no variation in the respective numbers of biologics or TIDES (peptides and oligonucleotides). Monoclonal antibodies (mAbs) continue to be the class with the most drugs authorized (9), while proteins/enzymes (5) and an antibody-drug conjugate complete the biologics harvest. In 2022, five TIDES and seven drugs inspired by natural products have received the green light, thus showing the same tendency as in previous years. Finally, pharmaceutical agents with nitrogen aromatic heterocycles and/or fluorine atoms continue to be predominant among small molecules this year. Furthermore, three drugs have been approved for imaging, reinforcing the trend in recent years for this class of treatments. A keyword in 2022 is bispecificity since four drugs have this property (two mAbs, one protein, and one peptide). Herein, the 37 new drugs approved by the FDA in 2022 are analyzed. On the basis of chemical structure alone, these drugs are classified as the following: biologics (antibodies, antibody-drug conjugates, proteins/enzymes), TIDES (peptide and oligonucleotides), combined drugs, natural products; nitrogen aromatic heterocycles, fluorine-containing molecules, and other small molecules.

Studying Lipid Membrane Interactions of a Super-Cationic Peptide in Model Membranes and Living Bacteria

The super-cationic peptide dendrimers (SCPD) family is a valuable class of antimicrobial peptide candidates for the future development of antibacterial agents against multidrug-resistant gram-negative bacteria. The deep knowledge of their mechanism of action is a major challenge in research, since it may be the basis for future modifications/optimizations. In this work we have explored the interaction between SCPD and membranes through biophysical and microbiological approaches in the case of the G1OLO-L₂OL₂ peptide. Results support the idea that the peptide is not only adsorbed or close to the surface of the membrane but associated/absorbed to some extent to the hydrophobic-hydrophilic region of the phospholipids. The presence of low concentrations of the peptide at the surface level is concomitant with destabilization of the cell integrity and this may contribute to osmotic stress, although other mechanisms of action cannot be ruled out.

A Practical Peptide Synthesis Workflow Using Amino-Li-Resin

Herein we report a practical approach for peptide synthesis using second-generation fibrous polyacrylamide resin (Li-resin, “Li” is coming from the name of its inventor, Yongfu Li). This resin with the corresponding handle was used for solid phase peptide synthesis (SPPS) using a fluorenylmethoxycarbonyl (Fmoc) approach. We reveal that the most appropriate mixing and filtration strategy when using amino-Li-resin in SPPS is via shaking and gravity filtration, instead of mechanical stirring and suction filtration used with other resins. The strategy was demonstrated with the SPPS of H-Tyr-Ile-Ile-Phe-Leu-NH₂, which contains the difficult sequence Ile-Ile. The peptide was obtained with excellent purity and yield. We are confident that this strategy will be rapidly implemented by other peptide laboratories.

Solid-Phase Synthesis of an "Inaccessible" hGH-Derived Peptide Using a Pseudoproline Monomer and SIT-Protection for Cysteine

The solid-phase peptide synthesis (SPPS) of the C-terminal sequence of hGH with one extra Tyr attached to its N-terminus (total of 16 residues with a disulfide bridge) has been accomplished for the first time by optimizing several synthetic parameters. First of all, the two Ser residues (positions 9 and 13 of the molecule) have been introduced as a single amino acid, Fmoc-Ser(ψ^Me,Mepro)-OH, demonstrating that the acylation of these hindered moieties is possible. This allows us to avoid the use of the corresponding dipeptides, Fmoc-AA-Ser(ψ^Me,Mepro)-OH, which are very often not commercially available or very costly. The second part of the sequence has been elongated via a double coupling approach using two of the most effective coupling methods (DIC-OxymaPure and HATU-DIEA). Finally, the disulfide bridging has been carried out very smoothly by a chemoselective thiol-disulfide interchange reaction between a SIT (sec-isoamyl mercaptan)-protected Cys residue and the free thiol of the second Cys. The synthesis of this short peptide has evidenced that SPPS is a multifactorial process which should be optimized in each case.

Novel CA(1-7)M(2-9) Analogs: Synthesis, Characterization, and Antibacterial Evaluation

Hybrid peptides from cecropin A and melittin have attracted the interest of the research community for decades. Here we synthesized several new analogs of the pentadecapeptide CA(1-7)M(2-9) and studied their antibacterial and hemolytic activity and tryptic stability. Single substitution of the Lys residues by Arg did not have a significant impact on the antibacterial activity of these analogs, but the substitution of the five Lys residues by Arg resulted in an increment in hemolytic activity. In contrast, the substitution of Lys residues by Orn conserved the antibacterial activity, with even lower hemolysis, and improved the enzymatic stability. The disulfide cyclic version of CA(1-7)M(2-9) was obtained by adding a Cys residue to each end of the peptide and carrying out a chemoselective thiol-disulfide interchange using sec-isoamylmecaptan as protecting group of one of these residues. This cyclic peptide showed good antibacterial activity with low hemolysis and improved enzymatic stability.

Acetic Acid Mediated for One-Pot Synthesis of Novel Pyrazolyl s-Triazine Derivatives for the Targeted Therapy of Triple-Negative Breast Tumor Cells (MDA-MB-231) via EGFR/PI3K/AKT/mTOR Signaling Cascades

Here, we described the synthesis of novel pyrazole-s-triazine derivatives via an easy one-pot procedure for the reaction of β-dicarbonyl compounds (ethylacetoacetate, 5,5-dimethyl-1,3-cyclohexadione or 1,3-cyclohexadionone) with N,N-dimethylformamide dimethylacetal, followed by addition of 2-hydrazinyl-4,6-disubstituted-s-triazine either in ethanol-acetic acid or neat acetic acid to afford a novel pyrazole and pyrazole-fused cycloalkanone systems. The synthetic protocol proved to be efficient, with a shorter reaction time and high chemical yield with broad substrates. The new pyrazolyl-s-triazine derivatives were tested against the following cell lines: MCF-7 (breast cancer); MDA-MB-231 (triple-negative breast cancer); U-87 MG (glioblastoma); A549 (non-small cell lung cancer); PANC-1 (pancreatic cancer); and human dermal fibroblasts (HDFs). The cell viability assay revealed that most of the s-triazine compounds induced cytotoxicity in all the cell lines tested. However, compounds 7d, 7f and 7c, which all have a piperidine or morpholine moiety with one aniline ring or two aniline rings in their structures, were the most effective. Compounds 7f and 7d showed potent EGFR inhibitory activity with IC₅₀ values of 59.24 and 70.3 nM, respectively, compared to Tamoxifen (IC₅₀ value of 69.1 nM). Compound 7c exhibited moderate activity, with IC₅₀ values of 81.6 nM. Interestingly, hybrids 7d and 7f exerted remarkable PI3K/AKT/mTOR inhibitory activity with 0.66/0.82/0.80 and 0.35/0.56/0.66-fold, respectively, by inhibiting their concentrations to 4.39, 37.3, and 69.3 ng/mL in the 7d-treatment, and to 2.39, 25.34 and 57.6 ng/mL in the 7f-treatment compared to the untreated control.

Synthesis and Antiproliferative Activity of a New Series of Mono- and Bis(dimethylpyrazolyl)-s-triazine Derivatives Targeting EGFR/PI3K/AKT/mTOR Signaling Cascades

Here, we synthesized a newseries of mono- and bis(dimethylpyrazolyl)-s-triazine derivatives. The synthetic methodology involved the reaction of different mono- and dihydrazinyl-s-triazine derivatives with acetylacetone in the presence of triethylamine to produce the corresponding target products in high yield and purity. The antiproliferative activity of the novel mono- and bis(dimethylpyrazolyl)-s-triazine derivatives was studied against three cancer cell lines, namely, MCF-7, HCT-116, and HepG2. N-(4-Bromophenyl)-4-(3,5-dimethyl-1H-pyrazol-1-yl)-6-morpholino-1,3,5-triazin-2-amine 4f, N-(4-chlorophenyl)-4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazin-2-amine 5c, and 4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-N-(4-methoxyphenyl)-1,3,5-triazin-2-amine 5d showed promising activity against these cancer cells: 4f [(IC₅₀ = 4.53 ± 0.30 μM (MCF-7); 0.50 ± 0.080 μM (HCT-116); and 3.01 ± 0.49 μM (HepG2)]; 5d [(IC₅₀ = 3.66 ± 0.96 μM (HCT-116); and 5.42 ± 0.82 μM (HepG2)]; and 5c [(IC₅₀ = 2.29 ± 0.92 μM (MCF-7)]. Molecular docking studies revealed good binding affinity with the receptor targeting EGFR/PI3K/AKT/mTOR signaling cascades. Compound 4f exhibited potent EGFR inhibitory activity with an IC₅₀ value of 61 nM compared to that of Tamoxifen (IC₅₀ value of 69 nM), with EGFR inhibition of 83 and 84%, respectively, at a concentration of 10 μM. Interestingly, 4f showed remarkable PI3K/AKT/mTOR inhibitory activity with 0.18-, 0.27-, and 0.39-fold decrease in their concentration (reduction in controls from 6.64, 45.39, and 86.39 ng/mL to 1.24, 12.35, and 34.36 ng/mL, respectively). Hence, the synthetic 1,3,5-triazine derivative 4f exhibited promising antiproliferative activity in HCT-116 cells through apoptosis induction by targeting the EGFR and its downstream pathway.

Solid-Phase Peptide Synthesis Using a Four-Dimensional (Safety-Catch) Protecting Group Scheme

Peptides of importance to both academia and industry are mostly synthesized in the solid-phase mode using a two-dimensional scheme. The so-called Fmoc/tBu strategy, where the groups are removed by piperidine and TFA, respectively, is currently the method of choice for peptide synthesis. However, as the molecular diversity of cyclic and branched peptides becomes a challenging interest, a high level of orthogonal dimensionality is required, such as through triorthogonal protection schemes. Here we present a fourth category of orthogonal protecting groups that are stable under cleavage conditions, including the TFA treatment that removes the tBu-based groups. At the end of the synthetic process and upon some chemical manipulation, the groups in this fourth category were removed with TFA. This new concept of protecting groups could facilitate the synthesis and manipulation of difficult peptides.

Active targeting of CD4+T lymphocytes by PEI-capped, peptide-functionalized gold nanoparticles

Active targeting is a promising approach for the treatment of viral infections. In particular, site-specific formulations for the treatment of HIV infection may overcome challenges associated with current ARV regimens. In this study we explored active targeting by synthesizing a gold nanoparticle construct decorated with an anti-CD4 cyclic peptide. The aim was to demonstrate selectivity of the system for the CD4 receptor and to deliver the RNA payload into T-lymphocytes. Colloidal gold nanoparticles functionalized withN-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) were formed by a one-pot synthesis method where thiol modified polyethyleneimine (PEI) was mixed with chloroauric acid. PEI-SPDP AuNPs (gold nanoparticles) were conjugated to an anti-CD4 peptide and loaded with RNA. We measured toxicity and uptake using TZM-bl and HeLa cells. Our findings show that the nanoparticles bind selectively to CD4 + cells. UV-vis characterisation of the nanoparticles revealed a surface plasmon resonance (SPR) peak at 527 nm, corresponding to a 6 nm diameter. HRTEM of the complete nanoparticles visualised circular shaped particles with average diameter of ∼7 nm. The polydispersity index was calculated to be 0.08, indicating monodispersity of complete NPS in solution. Through the pyridine-2-thione assay each nanoparticle was calculated to carry 1.37 × 10⁵SPDP molecules available for peptide binding. Flow cytometry showed that 13.6% of TZM-bl cells, and 0.14% of HeLa cells retained fluorescence after an overnight incubation, an indication of system binding. No internal RNA delivery was demonstrated. Further work is required to improve internalization.

Liquid-Phase Peptide Synthesis (LPPS): A Third Wave for the Preparation of Peptides

Since the last century, peptides have gained wide acceptance as drugs, with almost 100 already in the market and a large number in the pipeline. In this context, peptide synthesis has grown massively as a stringent field for pharmaceuticals around the globe. Three methodologies, namely, classical solution peptide synthesis (CSPS), solid-phase peptide synthesis (SPPS), and liquid-phase peptide synthesis (LPPS), have made significant contributions to the field. This review provides a comprehensive and integrated vision of LPPS as the third wave for peptide synthesis. LPPS combines the advantages of CSPS and SPPS, where peptide elongation is carried out in solution and the growing peptide chain is supported on a soluble tag, which confers characteristic properties. LPPS protocols allow the large-scale production of peptides and reduce the use of excess reagents and solvents, thus meeting the principles of green chemistry. In this review, tags associated with LPPS are broadly discussed under the following headings: polydisperse polyethylene glycol (PEG), membrane-enhanced peptide synthesis (MEPS), fluorous technology, ionic liquids (ILs), PolyCarbon, hydrophobic polymers, and group-assisted purification (GAP). It also highlights the signature accomplishments of LPPS tags and the limitations of the same.

2-Methoxy-4-methylsulfinylbenzyl Alcohol as a Safety-Catch Linker for the Fmoc/tBu Solid-Phase Peptide Synthesis Strategy

Fmoc and Boc group are the two main groups used to protect the α-amino function in Solid-Phase Peptide Synthesis (SPPS). In this regard, the use of the Mmsb linker allows the combination of these two groups. Peptide-O-Mmsb-Resin is stable to the piperidine and trifluoroacetic acid (TFA) treatment used to remove Fmoc and Boc, respectively. The peptide is detached in a two-step protocol, namely reduction of the sulfoxide to the sulfide with Me₃SiCl and Ph₃P, and then treatment with TFA. The advantage of this strategy has been demonstrated by the following: preparation of peptide with no diketopiperazine formation in sequences prone to this side reaction; on-resin cyclization without the concourse of common organic reagents such as Pd(0) but of difficult use in a biological laboratory; and on-resin disulfide formation in a total side-chain unprotected peptide. The use of Mmsb linker together with Msib (4-(methylsulfinyl)benzyl) and Msbh (4,4'-bis(methylsulfinyl)benzhydryl) described in the accompanying manuscript add a fourth dimension to the SPPS protecting group scheme.

Essential Role of Enzymatic Activity in the Leishmanicidal Mechanism of the Eosinophil Cationic Protein (RNase 3)

The recruitment of eosinophils into Leishmania lesions is frequently associated with a favorable evolution. A feasible effector for this process is eosinophil cationic protein (ECP, RNase 3), one of the main human eosinophil granule proteins, endowed with a broad spectrum of antimicrobial activity, including parasites. ECP was active on Leishmania promastigotes and axenic amastigotes (LC₅₀’s = 3 and 16 μM, respectively) but, in contrast to the irreversible membrane damage caused on bacteria and reproduced by its N-terminal peptides, it only induced a mild and transient plasma membrane destabilization on Leishmania donovani promastigotes. To assess the contribution of RNase activity to the overall leishmanicidal activity of ECP, parasites were challenged in parallel with a single-mutant version, ECP-H15A, devoid of RNase activity, that fully preserves the conformation and liposome permeabilization ability. ECP-H15A showed a similar uptake to ECP on promastigotes, but with higher LC₅₀’s (>25 μM) for both parasite stages. ECP-treated promastigotes showed a degraded RNA pattern, absent in ECP-H15A-treated samples. Moreover ECP, but not ECP-H15A, reduced more than 2-fold the parasite burden of infected macrophages. Altogether, our results suggest that ECP enters the Leishmania cytoplasm by an endocytic pathway, ultimately leading to RNA degradation as a key contribution to the leishmanicidal mechanism. Thus, ECP combines both membrane destabilization and enzymatic activities to effect parasite killing. Taken together, our data highlight the microbicidal versatility of ECP as an innate immunity component and support the development of cell-penetrating RNases as putative leishmanicidal agents.

Understanding OxymaPure as a Peptide Coupling Additive: A Guide to New Oxyma Derivatives

An in silico study, using the GALAS algorithm available in ACD/PhysChem Suite, was performed to calculate the pK _a(s) of various oximes with potential application as peptide coupling additives. Among the known oximes and predicted structures, OxymaPure is superior based on the pK _a values calculated, confirming the results described in the literature and validating this algorithm for further use in that field. Among the nondescribed oximes, based on pK _a calculation, ethyl 2-(hydroxyimino)-2-nitroacetate seems to be a potential candidate to be used as an additive during peptide coupling.

2021 FDA TIDES (Peptides and Oligonucleotides) Harvest

From the medical, pharmaceutical, and social perspectives, 2021 has been a year dominated by the COVID-19 pandemic. However, despite this global health crisis, the pharmaceutical industry has continued its endeavors, and 2021 could be considered an excellent year in terms of the drugs accepted by the US Food and Drug Administration (FDA). Thus, during this year, the FDA has approved 50 novel drugs, of which 36 are new chemical entities and 14 biologics. It has also authorized 10 TIDES (8 peptides, 2 oligonucleotides), in addition to 2 antibody-drug conjugates (ADCs) whose structures contain peptides. Thus, TIDES have accounted for about 24% of the approvals in the various drug categories. Importantly, this percentage has surpassed the figure in 2020 (10%), thus reflecting the remarkable success of TIDES. In this review, the approved TIDE-based drugs are analyzed on the basis of their chemical structure, medical target, mode of action, administration route, and adverse effects.

Linkers: An Assurance for Controlled Delivery of Antibody-Drug Conjugate

As one of the major therapeutic options for cancer treatment, chemotherapy has limited selectivity against cancer cells. Consequently, this therapeutic strategy offers a small therapeutic window with potentially high toxicity and thus limited efficacy of doses that can be tolerated by patients. Antibody-drug conjugates (ADCs) are an emerging class of anti-cancer therapeutic drugs that can deliver highly cytotoxic molecules directly to cancer cells. To date, twelve ADCs have received market approval, with several others in clinical stages. ADCs have become a powerful class of therapeutic agents in oncology and hematology. ADCs consist of recombinant monoclonal antibodies that are covalently bound to cytotoxic chemicals via synthetic linkers. The linker has a key role in ADC outcomes because its characteristics substantially impact the therapeutic index efficacy and pharmacokinetics of these drugs. Stable linkers and ADCs can maintain antibody concentration in blood circulation, and they do not release the cytotoxic drug before it reaches its target, thus resulting in minimum off-target effects. The linkers used in ADC development can be classified as cleavable and non-cleavable. The former, in turn, can be grouped into three types: hydrazone, disulfide, or peptide linkers. In this review, we highlight the various linkers used in ADC development and their design strategy, release mechanisms, and future perspectives.

Chemoselective Disulfide Formation by Thiol-Disulfide Interchange in SIT-Protected Cysteinyl Peptides

Chemoselective disulfide formation is accomplished through a thiol-disulfide interchange approach using sec-isoamyl mercaptan (SIT) as an alkyl sulfenyl-protecting group of one of the Cys residues involved in the pairing. SIT has a dual and unique characteristic, acting as a masking group during the synthesis and directing disulfide formation in the presence of a free thiol. This novel approach is illustrated by the synthesis of several peptides of biological interest.

A native mass spectrometry platform identifies HOP inhibitors that modulate the HSP90-HOP protein-protein interaction

Herein we describe a native mass spectromery protein-peptide model as a competent surrogate for the HOP-HSP90 protein-protein interaction (PPI), application of which led to the qualititive identification of two new peptides capable of in vitro PPI disruption. This proof of concept study offers a viable alternative for PPI inhibitor screening.

Amide Formation: Choosing the Safer Carbodiimide in Combination with OxymaPure to Avoid HCN Release

It has been reported that DIC can react with OxymaPure to render an oxadiazole compound with the concomitant formation of HCN. Here we demonstrate that this reaction is not a feature of all carbodiimides but rather depends on the alkyl structure that flanks the two N atoms of the carbodiimide. Furthermore, we have identified two carbodiimides, TBEC and EDC·HCl, whose reaction with OxymaPure is exempt from HCN formation.

Novel Biomimetic Human TLR2-Derived Peptides for Potential Targeting of Lipoteichoic Acid: An In Silico Assessment

Antimicrobial resistance is one of the most significant threats to health and economy around the globe and has been compounded by the emergence of COVID-19, raising important consequences for antimicrobial resistance development. Contrary to conventional targeting approaches, the use of biomimetic application via nanoparticles for enhanced cellular targeting, cell penetration and localized antibiotic delivery has been highlighted as a superior approach to identify novel targeting ligands for combatting antimicrobial resistance. Gram-positive bacterial cell walls contain lipoteichoic acid (LTA), which binds specifically to Toll-like receptor 2 (TLR2) on human macrophages. This phenomenon has the potential to be exploited for the design of biomimetic peptides for antibacterial application. In this study, we have derived peptides from sequences present in human TLR2 that bind to LTA with high affinity. In silico approaches including molecular modelling, molecular docking, molecular dynamics, and thermodynamics have enabled the identification of these crucial binding amino acids, the design of four novel biomimetic TLR2-derived peptides and their LTA binding potential. The outcomes of this study have revealed that one of these novel peptides binds to LTA more strongly and stably than the other three peptides and has the potential to enhance LTA targeting and bacterial cell penetration.

Super-Cationic Peptide Dendrimers-Synthesis and Evaluation as Antimicrobial Agents

Microbial infections are a major public health concern. Antimicrobial peptides (AMPs) have been demonstrated to be a plausible alternative to the current arsenal of drugs that has become inefficient due to multidrug resistance. Herein we describe a new AMP family, namely the super-cationic peptide dendrimers (SCPDs). Although all members of the series exert some antibacterial activity, we propose that special attention should be given to (KLK)2KLLKLL-NH2 (G1KLK-L2KL2), which shows selectivity for Gram-negative bacteria and virtually no cytotoxicity in HepG2 and HEK293. These results reinforce the validity of the SCPD family as a valuable class of AMP and support G1KLK-L2KL2 as a strong lead candidate for the future development of an antibacterial agent against Gram-negative bacteria.

s-Triazine: A Privileged Structure for Drug Discovery and Bioconjugation

This review provides an overview of the broad applicability of s-triazine. Our many years working with this intriguing moiety allow us to discuss its wide activity spectrum (inhibition against MAO-A and -B, anticancer/antiproliferative and antimicrobial activity, antibacterial activity against MDR clinical isolates, antileishmanial agent, and use as drug nano delivery system). Most of the compounds addressed in our studies and those performed by other groups contain only N-substitution. Exploiting the concept of orthogonal chemoselectivity, first described by our group, we have successfully incorporated different nucleophiles in different orders into s-triazine core for application in peptides/proteins at a temperature compatible with biological systems.

Disulfide-Based Protecting Groups for the Cysteine Side Chain

Two new disulfide-based protecting groups (SIT and MOT) are proposed for Cys thiol in the substitution of StBu, which is often difficult to remove. Both groups are based on a secondary thiol with a branched point in the β-position for an efficient modulation of its lability and/or stability. This unique structure allows them to be fully compatible with Fmoc/tBu SPPS. At the end of the synthesis, these groups are removed in a straightforward manner with dithiothreitol with some H₂O.

Synthesis and characterisation of thiobarbituric acid enamine derivatives, and evaluation of their α-glucosidase inhibitory and anti-glycation activity

A new series of thiobarbituric (thiopyrimidine trione) enamine derivatives and its analogues barbituric acid derivatives was synthesised, characterised, and screen for in vitro evaluation of α-glucosidase enzyme inhibition and anti-glycation activity. This series of compounds were found to inhibit α-glucosidase activity in a reversible mixed-type manner with IC50 between 264.07 ± 1.87 and 448.63 ± 2.46 µM. Molecular docking studies indicated that compounds of 3g, 3i, 3j, and 5 are located close to the active site of α-glucosidase, which may cover the active pocket, thereby inhibiting the binding of the substrate to the enzyme. Thiopyrimidine trione derivatives also inhibited the generation of advanced glycation end-products (AGEs), which cause long-term complications in diabetes. While, compounds 3a-k, 5, and 6 showed significant to moderate anti-glycation activity (IC50 = 31.5 ± 0.81 to 554.76 ± 9.1 µM).

OxymaPure Coupling Reagents: Beyond Solid-Phase Peptide Synthesis

OxymaPure [ethyl 2-cyano-2-(hydroxyimino)acetate] is an exceptional reagent with which to suppress racemization and enhance coupling efficiency during amide bond formation. The tremendous popularity of OxymaPure has led to the development of several Oxyma-based reagents. OxymaPure and its derived reagents are widely used in solid- and solution-phase peptide chemistry. This review summarizes the recent developments and applications of OxymaPure and Oxyma-based reagents in peptide chemistry, in particular in solution-phase chemistry. Moreover, the side reaction associated with OxymaPure is also discussed.

1 Introduction

2 Oxyma-Based Coupling Reagents

2.1 Aminium/Uronium Salts of OxymaPure

2.2 Phosphonium Salts of OxymaPure

2.3 Oxyma-Based Phosphates

2.4 Sulfonate Esters of OxymaPure

2.5 Benzoate Esters of OxymaPure

2.6 Carbonates of OxymaPure Derivatives

3 OxymaPure Derivatives

4 Other Oxime-Based Additives and Coupling Reagents

5 Side Reactions Using OxymaPure Derivatives

6 Conclusion

7 List of Abbreviations

Protocol for efficient solid-phase synthesis of peptides containing 1-hydroxypyridine-2-one (1,2-HOPO)

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Metal chelation has found many applications that directly affect human's life.

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Natural siderophores are one of the most potent chelators for Fe (III)

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1-Hydroxypyridine-2-one (1,2-HOPO) (Fig. 1a), which is shown in 4-carboxy-1-hydroxypyridin-2-one (1,2-HOPO-4-COOH) (Fig. 1b), is a moiety that electronically resembles the hydroxamate group found in natural siderophores (Fig. 1c). Of note, 1,2-HOPO moiety is present in the natural siderophore cepabactin [1]

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Synthesis of 1,2-HOPO containing chelators has been carried in solid phase using carboxylic acid derivatives of 1,2-HOPO and required the protection of the reactive hydroxyl group usually with benzyl group (Bzl). After the peptide elongation, the Bzl group has been removed on the same solid phase using a bit harsh conditions: 0.1 M BBr₃ in DCM for 60 min [2], 10% HBr in AcOH for 14 h [3]; in solution: 1 M BCl₃ in DCM for 2 d [4], 50% HCl in AcOH for 4 d [5], H2-Pd/C, AcOH-MeOH [6].

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First of all, a method for the incorporation of the 1,2-HOPO-4-COOH through its carboxyl group into the peptide backbone without protecting the N-OH is proposed (the presence of the carboxyl group facilitates the attachment).

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Furthermore, in the cases that Bzl protection is required for the N-OH, a friendlier method for removing the Bzl is described. The removal of the Bzl is done concomitantly to the global deprotection and cleavage of the peptide from the resin using TFA- TFMSA-H₂O (8:3:1).

Novel 4,6-Disubstituted s-Triazin-2-yl Amino Acid Derivatives as Promising Antifungal Agents

A novel series of 4,6-disubstituted s-triazin-2-yl amino acid derivatives was prepared and characterized. Most of them showed antifungal activity against Candida albicans compared to clotrimazole (standard drug). Compounds bearing aniline derivatives, piperidine and glycine on the triazine core showed the highest inhibition zones at concentrations of 50, 100, 200, and 300 μg per disc. In addition, docking studies revealed that all the compounds accommodated well in the active site residues of N-myristoltransferase (NMT) and exhibited complementarity, which explains the observed antifungal activity. Interestingly, none of these compounds showed antibacterial activity.

Novel formulation of antimicrobial peptides enhances antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA)

Antimicrobial peptides (AMPs) have the ability to penetrate as well as transport cargo across bacterial cell membranes, and they have been labeled as exceptional candidates to function in drug delivery. The aim of this study was to investigate the effectiveness of novel formulation of AMPs for enhanced MRSA activity. The strategy was carried out through the formulation of liposomes by thin-layer film hydration methodology, containing phosphatidylcholine, cholesterol, oleic acid, the novel AMP, as well as vancomycin (VCM). Characterization of the AMPs and liposomes included HPLC and LCMS for peptide purity and mass determination; DLS (size, polydispersity, zeta potential), TEM (surface morphology), dialysis (drug release), broth dilution, and flow cytometry (antibacterial activity); MTT assay, haemolysis and intracellular antibacterial studies. The size, PDI, and zeta potential of the drug-loaded AMP₂-Lipo-1 were 102.6 ± 1.81 nm, 0.157 ± 0.01, and - 9.81 ± 1.69 mV, respectively, while for AMP₃-Lipo-2 drug-loaded formulation, it was 146.4 ± 1.90 nm, 0.412 ± 0.05, and - 4.27 ± 1.25 mV respectively at pH 7.4. However, in acidic pH for both formulations, we observed an increase in size, PDI, and a switch to positive zeta potential, which indicated the pH responsiveness of our liposomal systems. The in vitro drug release studies demonstrated that liposomal formulations released VCM-HCl at a faster rate at pH 6.0 compared to pH 7.4. In vitro antibacterial activity against S. aureus and MRSA revealed that liposomes had enhanced activity at pH 6 compared to pH 7.4. The study revealed that the formulation can potentially be used to enhance activity and penetration of AMPs, thereby improving the treatment of bacterial infections.

N-Butylpyrrolidinone for Solid-Phase Peptide Synthesis is Environmentally Friendlier and Synthetically Better than DMF

Solid-phase peptide synthesis (SPPS) is the method of choice for the preparation of peptides in both laboratory scale and large production. Although the methodology has been improved during the last decades allowing the achievement of long peptides and challenging sequences in good yields and purities, the process was not revised from an environmental point of view. One of the main problems in this regard is the large amount of solvents used, and therefore the tons of generated waste. Moreover, the solvent of choice for the SPPS is N,N-dimethylformamide (DMF), which is considered as reprotoxic; thus, there is an urgent necessity to replace it with safer solvents. The DMF substitution by a green solvent is not a trivial task, because it should solubilize all the reagents and byproducts involved in the process, and, in addition to facilitating the coupling of the different amino acids, it should not favor the formation of side-reactions compared with DMF. Herein, it was demonstrated that the use of the green solvent N-butylpyrrolidinone (NBP) as a replacement of DMF was beneficial in two well-documented side reactions in peptide synthesis, racemization and aspartimide formation. The use of NBP rendered a lower or equal level of racemization in the amino acids more prone to this side reaction than DMF, whilst the aspartimide formation was clearly lower when NBP was used as solvent. Our findings demonstrate that the use of a green solvent does not hamper the synthetic process and could even improve it, making it environmentally friendlier and synthetically better.