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Cysteine (Cys) is a key amino acid in many therapeutic peptides. For research and industrial purposes, solid-phase peptide synthesis is the method of choice for the preparation of most peptides. The solid-phase synthesis of C-terminal Cys peptide acids is problematic because it is accompanied by a side reaction, namely, the abstraction of α-H from the Cys residue, which leads to the formation of three side products: the epimer and two N-piperidinyl-Ala epimer peptides. Here, we used a chlorotrityl chloride resin to conduct a rational and in-depth study of this side reaction. The following variables were examined: removal of the fluorenylmethoxycarbonyl (Fmoc) group by different bases, the presence or absence of an acid rectifier for buffering the base, and thiol side-chain protection. In conclusion, the use of Fmoc-Cys protected with tetrahydropyran (Thp) and 4-methoxytrityl (Mmt) along with 30% 4-methylpiperidine in 0.5 M OxymaPure-DMF for Fmoc removal assures minimization of the side reaction, as demonstrated in a model peptide and confirmed for the elongation of somatostatin., This work was partially funded by the National Research Foundation (NRF) (Blue Sky’s Research Programme # 120386).

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., This work was partially funded by the National Research Foundation (NRF) (Blue Sky’s Research Program no. 120386). We thank Geraldo. A. Acosta, University of Barcelona, for the HRMS and NMR characterization.

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., We thank Dr. Thomas Bruckdorfer (Iris Biotech GmbH, Marktredwitz, Germany) for encouraging this work and for the generous gift of Fmoc-Cys(SIT)-OH. This work was partially funded by National Research Foundation (NRF) (Blue Sky’s Research Programme No. 120386).

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., We thank Dr. Thomas Bruckdorfer (Iris Biotech GmbH, Marktredwitz, Germany) for encouraging this work and for the generous gift of Fmoc-Cys(SIT)-OH. This work was partially funded by National Research Foundation (NRF) (Blue Sky’s Research Programme # 120386).

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., We thank Dr. Thomas Bruckdorfer (Iris Biotech GmbH, Marktredwitz, Germany) for encouraging this work and for the generous gift of Fmoc-Cys(SIT)-OH; Jonathan Collins (CEM Corp., Matthews, NC, USA) for facilitating the use of the CEM Liberty Blue microwave peptide synthesizer; and Yoav Luxembourg (Luxembourg Biotechnologies, Ness Ziona, Israel) for a generous gift of coupling reagents. The work was funded in part by Marató TV3 Foundation 2018 (no. 20183530) and the Republic of South Africa’s National Research Foundation Blue Skies Research Programme (no. 120386).

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., This work was funded in part by the National Research Foundation (NRF), the University of Kwazulu-Natal (South Africa), and the Generalitat de Catalunya (2017 SGR 1439). The authors thank CEM Corp. (Charlotte, NC) for allowing the use of a Liberty Blue.

A unique property of 2,4,6-trichloro-1,3,5-triazine (TCT) is its ability to undergoes a nucleophilic aromatic substitution reaction (SNAr) under temperature-controlled conditions. Using a convenient and biologically friendly protocol, mono-substituted s-triazines were treated with excess nucleophiles to obtain tri-substituted triazines in 1 + 2 mode (one nucleophile as the first substitution followed by another nucleophile for the other two positions). The nucleophiles used for this study were phenol, thiol and amine, and the best order of incorporation was phenol or thiol for the first position followed by amine for the last two positions., The work was funded by: Researchers Supporting Project at King Saud University (RSP-2020/50) (Saudi Arabia); National Research Foundation (NRF) and the University of KwaZulu-Natal (South Africa); the Spanish Ministry of Economy, Industry, and Competitiveness (MINECO) (RTI2018-093831-B-100), CIBER-BBN, and the Generalitat de Catalunya (2017 SGR 1439) (Spain). Rotimi Sheyi thanks to MINTEK for a predoctoral fellowship.

Cysteine is present in a large number of natural and synthetic (bio)molecules. Although the thiol side chain of Cys can be in a free form, in most cases it forms a disulfide bond either with a second Cys (bridge) or with another thiol, as in the case of protecting groups. Efficient reduction of these disulfide bridges is a requirement for many applications of Cys‐containing molecules in the fields of chemistry and biochemistry. Here we review reducing methods for disulfide bonds, taking into consideration the solubility of the substrates when selecting the appropriate reducing reagent., This work was funded in part by the following: the National Research Foundation (NRF) and the University of KwaZulu‐Natal, MINECO, (RTI2018‐093831‐B‐100), and the Generalitat de Catalunya (2017 SGR 1439) (Spain).

The skin glands of amphibian species hold a major component of their innate immunity, namely a unique set of antimicrobial peptides (AMPs). Although most of them have common characteristics, differences in AMP sequences allow a huge repertoire of biological activity with varying degrees of efficacy. We present the first study of the AMPs from Pleurodema somuncurence (Anura: Leptodactylidae: Leiuperinae). Among the 11 identified mature peptides, three presented antimicrobial activity. Somuncurin-1 (FIIWPLRYRK), somuncurin-2 (FILKRSYPQYY), and thaulin-3 (NLVGSLLGGILKK) inhibited Escherichia coli growth. Somuncurin-1 also showed antimicrobial activity against Staphylococcus aureus. Biophysical membrane model studies revealed that this peptide had a greater permeation effect in prokaryotic-like membranes and capacity to restructure liposomes, suggesting fusogenic activity, which could lead to cell aggregation and disruption of cell morphology. This study contributes to the characterization of peptides with new sequences to enrich the databases for the design of therapeutic agents. Furthermore, it highlights the importance of investing in nature conservation and the power of genetic description as a strategy to identify new compounds. Fil: Cancelarich, Natalia Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina Fil: Wilke, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentina Fil: Fanani, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentina Fil: Moreira, Daniel C.. Universidade do Brasília; Brasil Fil: Perez, Luis Orlando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Ciencias Sociales y Humanas; Argentina Fil: Alves Barbosa, Eder. Universidade do Brasília; Brasil Fil: Plácido, Alexandra. Universidad de Porto; Portugal Fil: Socodato, Renato. Universidad de Porto; Portugal Fil: Portugal, Camila C.. Universidad de Porto; Portugal Fil: Relvas, João B.. Universidad de Porto; Portugal Fil: De la Torre, Beatriz G.. University of Kwazulu-Natal; Sudáfrica Fil: Albericio, Fernando. University of Kwazulu-Natal; Sudáfrica Fil: Basso, Nestor Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Diversidad y Evolución Austral; Argentina Fil: Leite, José. Universidade do Brasília; Brasil Fil: Marani, Mariela Mirta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina

In recent years, the work of various research groups has allowed the substitution of the hazardous solvents most widely used in solid-phase peptide synthesis, namely DMF, NMP, DCM, DEE, among others, by several much less hazardous solvents. Indeed, greener alternatives have been found for almost all steps of the process, with the exception of the cleavage of protected peptides from 2-chlorotrityl chloride resin. Here, after careful screening of several of the so-called green solvents, we propose 2% TFA in either anisole or 1,3-dimethoxybenzene as optimal for the cleavage step. The higher boiling point of these solvents compared with the DCM allows the preparation of protected peptides with less risk of premature removal of the most labile protecting groups, such as the Trt of His. Our findings once again evidence the value/versatility of green solvents in strict chemical terms., The work was funded in part by the following: the National Research Foundation (NRF) (# 105892 and Blue Sky’s Research Programme # 120386) and the University of KwaZulu-Natal (South Africa); and the Spanish Ministry of Science, Innovation, and Universities (RTI2018-093831- B-100) and the Generalitat de Catalunya (2017 SGR 1439) (Spain).

Similar to last year, 2021 will be remembered for the COVID-19 pandemic. Although five vaccines have been approved by the two most important drug regulatory agencies, namely the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA), the pandemic has still not been brought under control. However, despite the context of a global pandemic, 2021 has been an excellent year with respect to drug approvals by the FDA. In 2021, 50 drugs have been authorized, making it the fourth-best year after 2018 (59 drugs) and 1996 and 2020 (53 each). Regarding biologics, 2021 has been the third-best year to date, with 14 approvals, and it has also witnessed the authorization of 36 small molecules. Of note, nine peptides, eight monoclonal antibodies, two antibody-drug conjugates, and two oligonucleotides have been approved this year. From them, five of the molecules are pegylated and three of them highly pegylated. The presence of nitrogen aromatic heterocycles and/or fluorine atoms are once again predominant among the so-called small molecules. This report analyzes the 50 new drugs approved in 2021 from a chemical perspective, as it did for those authorized in the previous five years. On the basis of chemical structure alone, the drugs that received approval in 2021 are classified as the following: biologics (antibodies, antibody-drug conjugates, enzymes, and pegylated proteins); TIDES (peptide and oligonucleotides); combined drugs; natural products; nitrogen aromatic heterocycles; fluorine-containing molecules; and other small molecules., The work performed by the authors laboratory is funded by the National Research Foundation (NRF) and the University of KwaZulu-Natal.

The undesired reaction between carbodiimides (peptide coupling reagent) and OxymaPure (peptide coupling additive), which takes place in very low extension during peptide bond formation, is dependent on the steric hindrance around the carbodiimide backbone. Carbodiimides containing tertiary substituents on N such as di-tert-butylcarbodiimide do not activate the carboxylic group properly; the presence of secondary substituents such as in the case of diisopropylcarbodiimide (DIC) leads to the formation of oxadiazole and HCN; finally, primary substituents render an adduct of oxadiazine and no formation of HCN. tert-Butylethylcarbodiimide (TBEC), which is a hybrid of primary and tertiary substituents, leads to the formation of oxadiazine with no concomitant formation of HCN. Furthermore, TBEC outperforms DIC in terms of yield and minimization of racemization as it is demonstrated herein., Thanks go to Yoav Luxembourg and Gyorgy Orosz (Luxembourg Bio Technologies) for encouraging this work and for the generous gift of TBEC, DIC, and OxymaPure. This work was partially funded by the National Research Foundation (NRF) (Blue Sky’s Research Programme # 120386).

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.

DMB (Dimethylbarbituric) and DETB (Diethylthiobarbituric) are both barbituric and thiobarbituric acid derivatives respectively, that forms enamines with the Nα amine of amino acids. These compounds were found to be stable crystalline solids and show stability in the standard acidic and basic conditions used for solid-phase peptide synthesis (SPPS) strategies. These protecting groups are cleaved by a mild solution of 2 % hydrazine hydrate in DMF and 2 % hydroxylamine in DMF, both at short reaction times. Their use in SPPS showed that DMB-protected amino acids allow the preparation of peptides and therefore could be an alternative to the Fmoc strategy currently used. A further advantage of these protecting groups is that their preparation does not involve the concourse of phosgene derivatives and therefore they could be considered greener protecting groups than the carbamate-based one., This work was funded in part by the National Research Foundation (NRF) (#105892 and Blue Sky's Research Programme#120386). The authors thank the Deanship of Scientific Research at King Saud University for funding this work through research group no. (RG-1441-365, Saudi Arabia). Special thanks go to Merck-Millipore-Sigma Aldrich for financial support and Dr. Peter White for continuous advice.

Disulfide-reducing agents play a crucial role in bioconjugate chemistry. Herein, we describe the synthesis of a new disulfide-reducing agent [2-(dibenzylamino)butane-1,4-dithiol (DABDT)] that is conveniently prepared from inexpensive aspartic acid. Being nonmalodorous and highly soluble in a broad range of solvents, DABDT is user-friendly. We have demonstrated its performance both in solution and in the solid phase.

An example of triorthogonal chemoselectivity is reported here for the first time. In this regard, a series of 43 reactions were performed using tridentate s-triazine as a model. In all of the possible cases, the three substitutions were carried out using different nucleophiles at a temperature compatible with biological systems.

s-Triazine is considered a privileged structure, as it is found in several FDA-approved drugs. In the framework of our ongoing medicinal chemistry project based on the use of s-triazine as a scaffold, we synthesized a series of mono- and di-pyrazolyl-s-triazine derivatives and tested them against four human cancer cell lines, namely Human breast carcinoma (MCF 7 and MDA-MB-231), hepatocellular carcinoma (HepG2), colorectal carcinoma (LoVo), and leukemia (K562). The cell viability assay revealed that most of the s-triazine compounds induced cytotoxicity in all four types of human cancer cell lines, however, compounds 4a, and 6g, both of them have a piperidine moiety in their structure were most effective. These two compounds affected the cell viability of cancer cells, with IC50 values within the range between 5 to 9 µM. The cell cycle analysis showed that 4a and 6g induced S and G2/M phase cell cycle arrest in K562 cells. This could be the mechanism by which these molecules induced cytotoxicity in tested cancer cells. The prepared compounds were tested in zebrafish embryos to evaluate in vivo and developmental toxicity of the pyrazolyl-s-triazine derivatives in animals. None of the derivatives were lethal in the concentration range tested.

The synthesis of peptides for both research and API production is conveniently carried out using the solid-phase strategy. However, the main drawback of this approach is the large amounts of hazard...

A new phosphonium based coupling reagent DEPO-B has been synthesized from 5- (hydroxyimino)-1,3-dimethylpyrimidine-2,4,6 (1H,3H,5H)-trione (Oxyma B) and diethyl chlorophosphate in presence of base. It is a solid material and the hydrolytic stability and solubility was evaluated for confirming its capability for usage in automated peptide synthesizer.

Several derivatives containing morpholine/piperidine, anilines, and dipeptides as pending moieties were prepared using s-triazine as a scaffold. These compounds were evaluated for their anticancer activity against two human breast cancer cell lines (MCF-7 and MDA-MB-231), a colon cancer cell line (HCT-116), and a non-tumorigenic cell line (HEK 293). Tamoxifen was used as a reference. Animal toxicity tests were carried out in zebrafish embryos. Most of these compounds showed a higher activity against breast cancer than colon cancer. Compound 3a—which contains morpholine, aniline, and glycylglycinate methyl ester—showed a high level of cytotoxicity against MCF-7 cells with IC50 values of less than 1 µM. This compound showed a much lower level of toxicity against the non-tumorigenic HEK-293 cell line, and in the in vivo studies using zebrafish embryos. Furthermore, it induced cell cycle arrest at the G2/M phase, and apoptosis in MCF-7 cells. On the basis of our results, 3a emerges as a potential candidate for further development as a therapeutic drug to treat hormone receptor-positive breast cancer., The work was funded in part by the National Research Foundation (NRF) (# 105892 and Blue Sky’s Research Programme # 120386). This study was funded by the Deanship of Scientific Research, King Saud University, through the Vice Deanship of Scientific Research Chairs.

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., We thank Yoav Luxembourg (Luxembourg Bio Technologies) for encouraging this work. This project received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Marie Skłodowska-Curie Grant Agreement 861190 (PAVE). O.L.’s work was funded by PAVE. The authors acknowledge an American Chemical Society (ACS) Green Chemistry Institute (GCI) Pharmaceutical Roundtable Ignition Grant awarded to S.R.M. The work carried out in South Africa was partially funded by the National Research Foundation (NRF) (Blue Sky’s Research Programme 120386). Peptide preparation was performed at the NANBIOSIS–CIBER BBN Peptide Synthesis Unit (U3).

Although the pharmaceutical industry will remember 2020 as the year of COVID-19, it is important to highlight that this year has been the second-best—together with 1996—in terms of the number of drugs accepted by the US Food and Drug Administration (FDA). Each of these two years witnessed the authorization of 53 drugs—a number surpassed only in 2018 with 59 pharmaceutical agents. The 53 approvals in 2020 are divided between 40 new chemical entities and 13 biologic drugs (biologics). Of note, ten monoclonal antibodies, two antibody–drug conjugates, three peptides, and two oligonucleotides have been approved in 2020. Close inspection of the so-called small molecules reveals the significant presence of fluorine atoms and/or nitrogen aromatic heterocycles. This report analyzes the 53 new drugs of the 2020 harvest from a strictly chemical perspective, as it did for those authorized in the previous four years. On the basis of chemical structure alone, the drugs that received approval in 2020 are classified as the following: biologics (antibodies, antibody-drug conjugates, and proteins); TIDES (peptide and oligonucleotides); natural products; fluorine-containing molecules; nitrogen aromatic heterocycles; and other small molecules, The work performed by the authors is funded by the National Research Foundation (NRF) and the University of KwaZulu-Natal.

N,N’-diisopropylcarbodiimide (DIC) and OxymaPure are the reagents of choice for the formation of peptide bonds in Solid-Phase Peptide Synthesis (SPPS). The combined use of DIC and OxymaPure in model cases can be accompanied by a serious side reaction with the ultimate formation of oxadiazole and HCN. Here we demonstrate, in a practical case, that the first step of the reaction (formation of an adduct) takes place with approximately 1% respect to the amount of OxymaPure. Furthermore, we found that the second part of the side-reaction (formation of oxadiazole and HCN) can be minimized and even suppressed with an appropriate protocol for the sequence of reagent addition. Thus, the best conditions are preactivation of the Fmoc-amino acid with only DIC for 2–5 min followed by addition of the resulting mixture to the peptide-resin. OxymaPure can be added to the resin before adding the preactivation mixture or after first adding the preactivation mixture, the latter approach giving the best results. Ultimately, in standard research conditions, the combined use of DIC and OxymaPure as coupling method in SPPS is safe., We thank Yoav Luxembourg (Luxembourg Bio Technologies) for encouraging this work and for the generous gift of the DIC and OxymaPure. The authors acknowledge the American Chemical Society (ACS) Green Chemistry Institute (GCI) Pharmaceutical Roundtable Ignition grant awarded to SRM. The work was partially funded by National Research Foundation (NRF) (Blue Sky’s Research Programme # 120386).

In the field of bioconjugation, linker development has witnessed massive growth in recent years. 2,4,6-Trichloro-1,3,5-triazine (TCT) is a tridentate linker that can accommodate three distinct nucleophiles. Herein, the reaction of azido triazine derivatives with nucleophiles (amine, thiol and phenol) is studied. The replacement of first chlorine was performed at 0 °C while that of the last chlorine was achieved successfully at rt. As a proof of concept of this strategy with potential application in biological studies, pentapeptides (Ac-XGGFL-NH2 where X = Lys or Tyr or Cys) were reacted with 2-azido-4,6-dichlorotriazine to replace the first and second chlorine at 0 °C and at rt, respectively. The reactivity of 2-azido-4,6-dichlorotriazine was found to be similar for the α and ε amine group present in same peptide. These findings demonstrate the applicability of 2-azido-4,6-dichlorotriazine as a linker with potential further application in bioconjugation., The work was funded in part by the National Research Foundation (NRF) (# 105892 and Blue Sky’s Research Programme # 120386) The authors extend their appreciation to the Researchers Supporting Project at King Saud University, Riyadh, Saudi Arabia for funding this work through Project No. RSP-2020/50.

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.

During 2019, the US Food and Drug Administration (FDA) approved 48 new drugs (38 New Chemical Entities and 10 Biologics). Although this figure is slightly lower than that registered in 2018 (59 divided between 42 New Chemical Entities and 17 Biologics), a year that broke a record with respect to new drugs approved by this agency, it builds on the trend initiated in 2017, when 46 drugs were approved. Of note, three antibody drug conjugates, three peptides, and two oligonucleotides were approved in 2019. This report analyzes the 48 new drugs of the class of 2019 from a strictly chemical perspective. The classification, which was carried out on the basis of chemical structure, includes the following: Biologics (antibody drug conjugates, antibodies, and proteins); TIDES (peptide and oligonucleotides); drug combinations; natural products; and small molecules.

Herein a friendly method for the preparation of 1-hydroxypyridine-2-one (1,2-HOPO)-containing peptides is described. The elongation of the peptide is carried out on a solid support, using a protecting group for the ε-amino of the Lys that is removable in very mild conditions and that does not provoke cleavage of the peptide from the resin. Once the ε-amino of the Lys is released, HOPO can be incorporated using a commercially available derivative (1,2-HOPO-4-COOH), which has a carboxylic acid at position 4 of the aromatic ring. 1,2-HOPO-4-COOH can be introduced with the free N-hydroxyl or protected with the benzyl group. The former is recommended in many cases. If the protected derivative is to be used, the benzyl group can be removed during global deprotection and cleavage from the resin by adding trifluoromethanesulfonic acid to the cleavage cocktail., The work was funded in part by the following: the National Research Foundation, South Africa (NRF) (# 105892 and Blue Sky’s Research Programme # 120386) and the University of KwaZulu-Natal (South Africa); and the Spanish Ministry of Science, Innovation, and Universities (RTI2018-093831-B-100), the Generalitat de Catalunya (2017 SGR 1439) (Spain), and Marató TV3 foundation 2018 (#20183530). We thank Professor Miquel Viñas (University of Barcelona) for fruitful discussions.

Peptides are gaining considerable attention as potential drugs. The so-called Fmoc/tBu solid-phase synthesis is the method of choice for the synthesis of these molecules in both research and industrial settings. This synthetic strategy involves a solid polymeric protecting group and allows the use of an excess of reagents to achieve quantitative yields. Intermediates are not isolated. However, extensive washing with solvents is carried out between the synthetic steps. Hazardous solvents, mainly DMF, NMP, and CH2Cl2, are currently being used for the chemical reactions and also for the washings. In recent years, several studies have proposed the use of greener solvents in solid-phase peptide synthesis (SPPS). Here we compile all the greening efforts done in this regard and analyze each synthetic step separately. In summary, we can conclude that in many cases green solvents do not impair the synthetic process and that their adoption in current synthetic schemes will be translated into a smaller impact on the environment and on human health., The work was funded in part by the following: the National Research Foundation (NRF) (# 105892 and Blue Sky’s Research Programme # 120386) and the University of KwaZulu-Natal (South Africa); and the Spanish Ministry of Science, Innovation, and Universities (RTI2018-093831-B-100) and the Generalitat de Catalunya (2017 SGR 1439) (Spain).

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., We are grateful to the American Chemical Society (ACS) Green Chemistry Institute (GCI) (Pharmaceutical Roundtable Ignition Grant) for funding S.R.M. In addition, the work in laboratory of the authors was funded in part by the following: the South African Agency for Science and Technology Advancement, The National Research Foundation (NRF) (Blue Sky’s Research Programme, Grant No. 120386) and the University of KwaZulu-Natal (South Africa); the Ministerio de Ciencia e Innovación (Spanish Ministry of Science, Innovation) (RTI2018-093831-B-100), the Departament d’Innovació, Universitats i Empresa, Generalitat de Catalunya (2017 SGR 1439) and the Ministerio de Economía y Competitividad; and the International Scientific Partnership Program ISPP at King Saud University, Saudi Arabia, Riyadh (ISPP# 0061).

Hydroxamic acids are an important class of molecules, in particular because of their metal-chelating ability. Microorganisms, including pathogenic bacteria, use hydroxamate-based entities (siderophores), among others, to acquire Fe (III). The “Trojan horse” strategy exploits the need of bacteria for this metal by using Fe (III) active transporters to carry antibacterial or bactericidal moieties into the bacterial cell. Many natural Trojan horses (sideromycins) are derived from hydroxamic acids, thereby reflecting their potency. Various artificial sideromycins and their antibacterial activities have been reported. This review discusses the structural aspects of the hydroxamate-siderophores isolated in the last two decades, the chemical synthesis of their building blocks, their binding affinity towards Fe (III), and their application as Trojan horses (weaknesses and strengths)., The work carried out in the laboratory was funded in part by the following: the National Research Foundation (NRF) (# 105892 and Blue Sky’s Research Programme # 120386) and the University of KwaZulu-Natal (South Africa); and Marató TV3 foundation 2018 (#20183530). We thank Professor Miquel Viñas (University of Barcelona) for fruitful discussions.