Fast, efficient and selective deprotection of the tert-butoxycarbonyl (Boc) group using HCl/dioxane (4 m)

Proline Analogues

Within the canonical repertoire of the amino acid involved in protein biogenesis, proline plays a unique role as an amino acid presenting a modified backbone rather than a side-chain. Chemical structures that mimic proline but introduce changes into its specific molecular features are defined as proline analogues. This review article summarizes the existing chemical, physicochemical, and biochemical knowledge about this peculiar family of structures. We group proline analogues from the following compounds: substituted prolines, unsaturated and fused structures, ring size homologues, heterocyclic, e.g., pseudoproline, and bridged proline-resembling structures. We overview (1) the occurrence of proline analogues in nature and their chemical synthesis, (2) physicochemical properties including ring conformation and cis/trans amide isomerization, (3) use in commercial drugs such as nirmatrelvir recently approved against COVID-19, (4) peptide and protein synthesis involving proline analogues, (5) specific opportunities created in peptide engineering, and (6) cases of protein engineering with the analogues. The review aims to provide a summary to anyone interested in using proline analogues in systems ranging from specific biochemical setups to complex biological systems.

Selective Thermal Deprotection of N-Boc Protected Amines in Continuous Flow

Thermal N-Boc deprotection of a range of amines is readily effected in continuous flow, in the absence of an acid catalyst. While the optimum results were obtained in methanol or trifluoroethanol, deprotection can be effected in a range of solvents of different polarities. Sequential selective deprotection of N-Boc groups has been demonstrated through temperature control, as exemplified by effective removal of an aryl N-Boc group in the presence of an alkyl N-Boc group. As a proof of principle, a telescoped sequence involving selective deprotection of an aryl N-Boc group from 9h followed by benzoylation and deprotection of the remaining alkyl N-Boc group to form amide 13 proved successful.

Synthesis and evaluation of druglike parameters via in silico techniques for a series of heterocyclic monosquarate-amide derivatives as potential carboxylic acid bioisosteres

Herein, we present a synthetic compound library comprising of 13 structurally diverse heterocyclic monosquarate-amide derivatives. The compounds featured in this library were designed as potential bioisosteric replacements carboxylic acid moiety's. A good selection of the compounds presented exhibit unique molecular architecture and have shown promising results following in silico evaluation of 'druglike properties' using Swiss ADME. The research presented in this work focuses on the preparation of derivatives of 3,4-dihydroxycyclobut-3-ene-1,2-dione, a known carboxylic acid bioisostere.

DrugMap: A quantitative pan-cancer analysis of cysteine ligandability

Cysteine-focused chemical proteomic platforms have accelerated the clinical development of covalent inhibitors of a wide-range of targets in cancer. However, how different oncogenic contexts influence cysteine targeting remains unknown. To address this question, we have developed DrugMap , an atlas of cysteine ligandability compiled across 416 cancer cell lines. We unexpectedly find that cysteine ligandability varies across cancer cell lines, and we attribute this to differences in cellular redox states, protein conformational changes, and genetic mutations. Leveraging these findings, we identify actionable cysteines in NFκB1 and SOX10 and develop corresponding covalent ligands that block the activity of these transcription factors. We demonstrate that the NFκB1 probe blocks DNA binding, whereas the SOX10 ligand increases SOX10-SOX10 interactions and disrupts melanoma transcriptional signaling. Our findings reveal heterogeneity in cysteine ligandability across cancers, pinpoint cell-intrinsic features driving cysteine targeting, and illustrate the use of covalent probes to disrupt oncogenic transcription factor activity.

MEPIRAPIM-derived synthetic cannabinoids inhibit T-type calcium channels with divergent effects on seizures in rodent models of epilepsy

Background: T-type Ca²⁺ channels (Ca_v3) represent emerging therapeutic targets for a range of neurological disorders, including epilepsy and pain. To aid the development and optimisation of new therapeutics, there is a need to identify novel chemical entities which act at these ion channels. A number of synthetic cannabinoid receptor agonists (SCRAs) have been found to exhibit activity at T-type channels, suggesting that cannabinoids may provide convenient chemical scaffolds on which to design novel Ca_v3 inhibitors. However, activity at cannabinoid type 1 (CB₁) receptors can be problematic because of central and peripheral toxicities associated with potent SCRAs. The putative SCRA MEPIRAPIM and its analogues were recently identified as Ca_v3 inhibitors with only minimal activity at CB₁ receptors, opening the possibility that this scaffold may be exploited to develop novel, selective Ca_v3 inhibitors. Here we present the pharmacological characterisation of SB2193 and SB2193F, two novel Ca_v3 inhibitors derived from MEPIRAPIM. Methods: The potency of SB2193 and SB2193F was evaluated in vitro using a fluorometric Ca²⁺ flux assay and confirmed using whole-cell patch-clamp electrophysiology. In silico docking to the cryo-EM structure of Ca_v3.1 was also performed to elucidate structural insights into T-type channel inhibition. Next, in vivo pharmacokinetic parameters in mouse brain and plasma were determined using liquid chromatography-mass spectroscopy. Finally, anticonvulsant activity was assayed in established genetic and electrically-induced rodent seizure models. Results: Both MEPIRAPIM derivatives produced potent inhibition of Ca_v3 channels and were brain penetrant, with SB2193 exhibiting a brain/plasma ratio of 2.7. SB2193 was further examined in mouse seizure models where it acutely protected against 6 Hz-induced seizures. However, SB2193 did not reduce spontaneous seizures in the Scn1a ^+/- mouse model of Dravet syndrome, nor absence seizures in the Genetic Absence Epilepsy Rat from Strasbourg (GAERS). Surprisingly, SB2193 appeared to increase the incidence and duration of spike-and-wave discharges in GAERS animals over a 4 h recording period. Conclusion: These results show that MEPIRAPIM analogues provide novel chemical scaffolds to advance Ca_v3 inhibitors against certain seizure types.

A Brønsted Acidic Deep Eutectic Solvent for N-Boc Deprotection

The tert-butyloxycarbonyl (Boc) group is one of the most widely used amine-protecting groups in multistep reactions in synthetic organic chemistry as well as in peptide synthesis. Traditional methods to remove the Boc group have disadvantages in terms of high acidity, the use of expensive reagents, excessive amounts of catalysts and harmful solvents as well as high temperatures, making them environmentally unsustainable. Therefore, more efforts must be stepwise tightened to make Boc removal practical, clean, and minimize any potential impact. We describe an efficient and sustainable method for N-Boc deprotection by means of a choline chloride/p-toluenesulfonic acid deep eutectic solvent (DES), which is used as a reaction medium plus catalyst. The adopted conditions allow the deprotection of a wide variety of N-Boc derivatives in excellent yields. The strategy has found advantages in greening, simplicity, and short reaction times, resulting in a useful alternative to standard methods.

Hairy Conjugated Microporous Polymer Nanoparticles Facilitate Heterogeneous Photoredox Catalysis with Solvent-Specific Dispersibility

Substrate accessibility is a key limiting factor for the efficiency of heterogeneous photoredox catalysis. Recently, a high photoactive surface area of conjugated microporous polymer nanoparticles (CMP NPs) has made them promising candidates for overcoming the mass transfer limitation to achieve high photocatalytic efficiency. However, this potential has not been realized due to limited dispersibility of CMP NPs in many solvents, particularly in water. Here, we report a polymer grafting strategy that furnishes versatile hairy CMP NPs with enhanced solvent-specific dispersibility. The method associates hundreds of solvent-miscible repeating units with one chain end of the photocatalyst surface, allowing minimal modification to the CMP network that preserves its photocatalytic activity. Therefore, the enhanced dispersibility of hairy CMP NPs in organic solvents or aqueous solutions affords high efficiency in various photocatalytic organic transformations.

The impact of counterions in biological activity: case study of antibacterial alkylguanidino ureas

Abstract

Trifluoroacetic acid (TFA), due to its strong acidity and low boiling point, is extensively used in protecting groups-based synthetic strategies. Indeed, synthetic compounds bearing basic functions, such as amines or guanidines (commonly found in peptido or peptidomimetic derivatives), developed in the frame of drug discovery programmes, are often isolated as trifluoroacetate (TF-Acetate) salts and their biological activity is assessed as such in in vitro, ex vivo, or in vivo experiments. However, the presence of residual amounts of TFA was reported to potentially affect the accuracy and reproducibility of a broad range of cellular assays (e. g. antimicrobial susceptibility testing, and cytotoxicity assays) limiting the further development of these derivatives. Furthermore, the impact of the counterion on biological activity, including TF-Acetate, is still controversial. Herein, we present a focused case study aiming to evaluate the activity of an antibacterial AlkylGuanidino Urea (AGU) compound obtained as TF-Acetate (1a) and hydrochloride (1b) salt forms to highlight the role of counterions in affecting the biological activity. We also prepared and tested the corresponding free base (1c). The exchange of the counterions applied to polyguanidino compounds represents an unexplored and challenging field, which required significant efforts for the successful optimization of reliable methods of preparation, also reported in this work. In the end, the biological evaluation revealed a quite similar biological profile for the salt derivatives 1a and 1b and a lower potency was found for the free base 1c.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11030-022-10505-6.

Visible-Light-Promoted Fe(III)-Catalyzed N-H Alkylation of Amides and N-Heterocycles

The combination of the radical chemistry of ligand-to-metal charge transfer with metal catalysis by a single iron salt helps to realize the visible-light-promoted N-H alkylation of amides and N-heterocycles. A wide variety of amides and nitrogen-containing heterocycles were tolerated in our protocol to give N-alkylated products. The applicability of this protocol was further demonstrated by late-stage alkylation of N-H-containing pharmaceuticals. Moreover, N-H-alkylated α-amino tetrahydrofurans could be transformed into versatile ring-opened amino alcohols under reducing conditions. A mechanistic study revealed that hydrogen atom transfer by a tert-butoxyl radical and a chlorine radical was responsible for the activation of C(sp³)-H precursors.

Improved Cathepsin Probes for Sensitive Molecular Imaging

Cysteine cathepsin proteases are found under normal conditions in the lysosomal compartments of cells, where they play pivotal roles in a variety of cellular processes such as protein and lipid metabolism, autophagy, antigen presentation, and cell growth and proliferation. As a consequence, aberrant localization and activity contribute to several pathologic conditions such as a variety of malignancies, cardiovascular diseases, osteoporosis, and other diseases. Hence, there is a resurgence of interest to expand the toolkit to monitor intracellular cathepsin activity and better ascertain their functions under these circumstances. Previous fluorescent activity-based probes (ABPs) that target cathepsins B, L, and S enabled detection of their activity in intact cells as well as non-invasive detection in animal disease models. However, their binding potency is suboptimal compared to the cathepsin inhibitor on which they were based, as the P1 positive charge was capped by a reporter tag. Here, we show the development of an improved cathepsin ABP that has a P1 positive charge by linking the tag on an additional amino acid at the end of the probe. While enhancing potency towards recombinant cathepsins, the new probe had reduced cell permeability due to additional peptide bonds. At a second phase, the probe was trimmed; the fluorophore was linked to an extended carbobenzoxy moiety, leading to enhanced cell permeability and superb detection of cathepsin activity in intact cells. In conclusion, this work introduces a prototype design for the next generation of highly sensitive ABPs that have excellent detection of cellular cathepsin activity.

Rapid and column-free syntheses of acyl fluorides and peptides using ex situ generated thionyl fluoride

Thionyl fluoride (SOF₂) was first isolated in 1896, but there have been less than 10 subsequent reports of its use as a reagent for organic synthesis. This is partly due to a lack of facile, lab-scale methods for its generation. Herein we report a novel protocol for the ex situ generation of SOF₂ and subsequent demonstration of its ability to access both aliphatic and aromatic acyl fluorides in 55-98% isolated yields under mild conditions and short reaction times. We further demonstrate its aptitude in amino acid couplings, with a one-pot, column-free strategy that affords the corresponding dipeptides in 65-97% isolated yields with minimal to no epimerization. The broad scope allows for a wide range of protecting groups and both natural and unnatural amino acids. Finally, we demonstrated that this new method can be used in sequential liquid phase peptide synthesis (LPPS) to afford tri-, tetra-, penta-, and decapeptides in 14-88% yields without the need for column chromatography. We also demonstrated that this new method is amenable to solid phase peptide synthesis (SPPS), affording di- and pentapeptides in 80-98% yields.

Synthesis of Isotopically Labeled, Spin-Isolated Tyrosine and Phenylalanine for Protein NMR Applications

Isotopically labeled amino acids are widely used to study the structure and dynamics of proteins by NMR. Herein we describe a facile, gram-scale synthesis of compounds 1b and 2b under standard laboratory conditions from the common intermediate 7. 2b is obtained via simple deprotection, while 1b is accessed through a reductive deoxygenation/deuteration sequence and deprotection. 1b and 2b provide improved signal intensity using lower amounts of labeled precursor and are alternatives to existing labeling approaches.

Facile Synthetic Protocols for the preparation of New Impurities in Pemetrexed Disodium Heptahydrate as an Anti-Cancer Drug

A facile synthetic protocols were employed to prepare process-related impurities associated with the synthesis of pemetrexed disodium heptahydrate, Alimta. The research work is described for the development of the novel synthetic methods and their structure elucidation of Pemetrexed glutamide, N-methyl pemetrexed, and N-methyl pemetrexed glutamide impurities. The listed impurities were deduced through spectral analysis such as 1H-NMR, 13CNMR, and HRMS. The target compounds can be used as the reference substances for the quality control.

Discovery of 3-phenyl- and 3-N-piperidinyl-isothiazolo[4,3-b]pyridines as highly potent inhibitors of cyclin G-associated kinase

Structural modifications at position 3 of the isothiazolo[4,3-b]pyridine scaffold afforded a new series of cyclin G-associated kinase (GAK) inhibitors. It was shown that the insertion of a carboxamide residue at position 3 of a phenyl or piperidinyl moiety generated potent GAK inhibitors with IC₅₀ values in a low nanomolar range. This potent GAK binding affinity was rationalized by molecular modelling demonstrating that the carboxamide moiety engages in an extra hydrogen bond with GAK. Moreover, this new series of compounds was also endowed with antiviral activity against dengue virus, highlighting the potential utility of GAK as a target for the development of antiviral drugs.

Efficient, continuous N-Boc deprotection of amines using solid acid catalysts

Rapid, catalytic N-Boc deprotection of aromatic and aliphatic amines is achieved using readily-available porous inorganic solid acids in flow.

Mild deprotection of the N-tert-butyloxycarbonyl (N-Boc) group using oxalyl chloride

We report a mild method for the selective deprotection of the N-Boc group from a structurally diverse set of compounds, encompassing aliphatic, aromatic, and heterocyclic substrates by using oxalyl chloride in methanol. The reactions take place under room temperature conditions for 1–4 h with yields up to 90%. This mild procedure was applied to a hybrid, medicinally active compound FC1, which is a novel dual inhibitor of IDO1 and DNA Pol gamma. A broader mechanism involving the electrophilic character of oxalyl chloride is postulated for this deprotection strategy.

We report a mild method for the selective deprotection of the N-Boc group from a structurally diverse set of compounds, encompassing aliphatic, aromatic, and heterocyclic substrates by using oxalyl chloride in methanol.

Synthesis, Antitubercular Activity, Molecular Modeling and Docking Studies of Novel Thiazolidin-4-One Linked Dinitrobenzamide Derivatives

Background:

Tuberculosis is a catastrophe sprawled across the world. The World Health Organization Global Tuberculosis Report 2017 inferred that there were an estimated 10.4 million people suffered from tuberculosis including 490000 Multidrug-Resistant TB (MDR-TB) cases. Several new lead molecules like dinitrobenzamide derivatives were found to be highly active against multidrugresistant strains of M. tuberculosis. To further explore the pharmacophoric space around the dinitobenzamide moiety, a series of compounds have been synthesized by linking it with the thiazolidin- 4-one. The presented work is an effort to study the biological effect of thiazolidin-4-one scaffold on dinitrobenzamide derivatives as antitubercular agents. A molecular modeling study was also performed on the synthesized molecules to reveal the requirements for further lead optimization.

Methods:

The thiazolidin-4-one linked 3,5-dinitrobenzamide derivatives have been synthesized by onepot three-component condensation reaction of an amine, substituted aldehydes and thioglycolic acid in presence of N, N'-Dicyclohexylcarbodiimide (DCC). These compounds were evaluated against Mycobacterium tuberculosis H37Ra. A pharmacophore modeling approach has been used in order to explore the collection of possible pharmacophore queries of thiazolidin-4-one linked 3, 5-dinitrobenzamide derivatives against M. tuberculosis. The synthesized compounds were docked on to the M. tuberculosis DprE1 enzyme to identify the structural features requirement of these analogs against this potential target of M. tuberculosis.

Results:

The synthesized compounds showed the antitubercular activity in the range of 6.25-50 μg/ml. The pharmacophore modeling suggests that the presence of aromatic moiety, thiazolidin-4-one ring and one of the nitro groups are significant for inhibiting the enzymatic activity. While docking studies showed that hydrophobic and hydrogen bond interactions of the aromatic moiety and nitro group crucial to inactivate the DprE1 enzyme.

Conclusion:

The study showed that the linking of thiazolidin-4-one with dinitrobenzamide leads to compounds active against M. tuberculosis. These findings also suggested that further lead optimization would be carried out by focusing on the aromatic system along with electron-rich substituents placed on the thiazolidin-4-one for making better hydrophobic and hydrogen bond interactions with the DprE1 target.

Binaphthyl-Based Macrocycles as Optical Sensors for Aromatic Diphenols

The synthesis of several rigid, homochiral organic macrocycles possessing, respectively, average molecular D₂ and D₃ symmetries, is described. They have been obtained from aromatic dicarboxylic acids, in combination with an axially-chiral, suitable dibenzylic alcohol, derived from 1,1'-binaphthyl-2,2'-diol (BINOL) using one-pot esterification reactions in good isolated yields. NMR and circular dichroism (CD) spectroscopies detect the structural and shape variability in the scaffolds, reflected both in terms of the changes in chemical shifts and the shape of selected proton resonances, and in terms of the variation of the CD signature related to the dihedral angle defined by the binaphthyl units embedded in the rigid cyclic skeleton. The D₂ cyclic adducts are able to form stable complexes with aromatic diphenols, with binding strengths that are dependent on small variations in the spacing units, and therefore on the shapes of the internal cavities of the cyclic structures.

Acyl azide generation and amide bond formation in continuous-flow for the synthesis of peptides

Acyl azides were safely generated by using nitrous acid in water and reactedin situwithin a flow system. The acyl azide was efficiently extracted into the organic phase containing an amine nucleophile for a highly enantioselective peptide coupling.

Synthesis of Piperidine Conjugated Dihydroquinazolin-4(1H)-ones and their Antiproliferative Activity, Molecular Docking Studies and DFT Calculations

Background:

Xanthatin, fluoropyrimidine and thienopyrimidine, pyrazolopyrimidine, pyrimidine carboxamides, and SKLB1002 are reported as VEGFR2 tyrosine kinase inhibitors. Recently, many studies related to different heterocycles conjugated with dihydroquinazolinones are known to have very good biological activities. In this study, we are intended to explore the cytotoxic studies of piperidine conjugated dihydroquinazolinones against colorectal/colon cancer cell lines and along with molecular docking studies and DFT calculations.

Methods:

The colorectal/colon cell lines HCT116 and A549 cell lines were treated with these compounds and cytotoxic activities were evaluated by MTT dye uptake method. We performed molecular modelling for compound 3d using the Auto Dock software. The binding of compound 3d with target proteins was studied with the collection of experimentally determined PDB database. Optimized geometry by DFT calculations was performed with B3LYP/6-31G (d) basis set.

Results:

Piperidine-conjugated dihydroquinazolinone analogues displayed anticancer activity. Particularly, the compound 3d with electron-withdrawing substituents on a phenyl ring showed significant cytotoxicity against HCT116 and A549 cell lines. Molecular docking studies proved that the compound 3d has good fitting by forming hydrogen bonds with amino acid residues at the active sites of VEGFR2. The HOMO, LUMO, their energies and UV visible spectrum were predicted using DFT calculations.

Conclusion:

Four piperidine-conjugated dihydroquinazolinones were synthesized and evaluated against colorectal and colon cancer cell lines. Compound 3d significantly inhibited the growth of HCT116 and A549. Molecular docking studies displayed good fitting of compound 3d by forming different H-bonds with the amino acid at the active sites of the VEGFR2 target. Using a theoretical approach, we optimized HOMO and LUMO plots for the compound 3d.

Study of the cartilage matrix production-promoting effect of chicken leg extract and identification of the active ingredient

BACKGROUND/OBJECTIVES

Osteoarthritis (OA) is a major public health issue in Japan and other countries, and foods that prevent or treat OA are in strong demand. Proteins and peptides in chicken meat and bones are known for being rich in functional and nutritional ingredients for the improvement of osteoporosis. We speculated that chicken legs, a food consumed in many regions of the world, may also contain such ingredients. In this study, we aim to (i) evaluate the effect of chicken leg extract (CLE) on the promotion of cartilage matrix production and (ii) identify the active ingredient in CLE that contributes to this function.

MATERIALS/METHODS

Artificial CLE digest was prepared, and the acid mucopolysaccharide production-promoting activity of the CLE digest was evaluated by alcian blue staining of ATDC5 cells. CLE was orally administered to rabbits with burr holes in the knee joint of the femur, and the degree of regeneration of cartilage matrix was evaluated. Furthermore, we investigated orally administered CLE-derived peptides in human plasma using LC-MS. From measuring the acid mucopolysaccharide production-promotion activity of these peptides, a molecule considered to be an active ingredient in the CLE digest was identified.

RESULTS

CLE digest promoted acid mucopolysaccharide production and facilitated regeneration of cartilage matrix in in vitro and in vivo experiments. Four peptides including phenylalanyl-hydroxyproline (Phe-Hyp) were detected as CLE-derived peptides in human plasma. The effect of CLE was inferred to be due to Phe-Hyp, which was confirmed to be present in the CLE digest.

CONCLUSIONS

It was shown that CLE stimulated the production of articular cartilage matrix both in vitro and in vivo, and that CLE could be an effective food for preventing or treating OA. Furthermore, only Phe-Hyp was confirmed as the active compound in the CLE digest, suggesting that the activity of CLE was due to Phe-Hyp.

Counteracting in Vitro Toxicity of the Ionophoric Mycotoxin Beauvericin-Synthetic Receptors to the Rescue

Beauvericin (BEA) and enniatins are toxic ionophoric cyclodepsipeptides that mainly occur in grains. As such, their presence in food commodities poses a concern for public health. To date, despite recent European Food Safety Authority emphasis on the need for more data to evaluate long-term toxicity effects, no suitable affinity reagents are available to detect the presence of BEA and derivatives in food samples. We here report on the synthesis of a small library of artificial receptors with varying cavity sizes and different hydrophobic building blocks. Immobilization of one of the receptors on solid support resulted in a strong retention of beauvericin, thus revealing promising properties as solid-phase extraction material for sample pretreatment. Furthermore, treatment of HepG2 cells with the most promising receptor markedly reduced beauvericin-induced cytotoxicity, hinting toward the possibility of using synthetic receptors as antidotes against ionophoric toxins.

Cationic Amphiphiles with Specificity against Gram-Positive and Gram-Negative Bacteria: Chemical Composition and Architecture Combat Bacterial Membranes

Small-molecule cationic amphiphiles (CAms) were designed to combat the rapid rise in drug-resistant bacteria. CAms were designed to target and compromise the structural integrity of bacteria membranes, leading to cell rupture and death. Discrete structural features of CAms were varied, and structure-activity relationship studies were performed to guide the rational design of potent antimicrobials with desirable selectivity and cytocompatibility profiles. In particular, the effects of cationic conformational flexibility, hydrophobic domain flexibility, and hydrophobic domain architecture were evaluated. Their influence on antimicrobial efficacy in Gram-positive and Gram-negative bacteria was determined, and their safety profiles were established by assessing their impact on mammalian cells. All CAms have a potent activity against bacteria, and hydrophobic domain rigidity and branched architecture contribute to specificity. The insights gained from this project will aid in the optimization of CAm structures.

Mild and Efficient Preparation of Phytosteryl Amino Acid Ester Hydrochlorides and Their Emulsifying Properties

The aim of this work was to produce a series of phytosteryl amino acid ester hydrochlorides by a two-step method, which involved esterification of phytosterols with N- tert-butoxycarbonyl (BOC) amino acid and deprotection of the BOC group. The highest yield of over 95.0% was obtained when the catalysts were the mixtures of 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochlide, 4-dimethylaminopyridine, and triethylamine. It was found that batch charging of the reactants and catalysts was conducive to improving the yield. In addition, over 99.0% of the BOC group deprotection degree was achieved using the HCl/ethyl acetate deprotection method. All of the compounds were characterized by fourier transform infrared spectroscopy, mass spectroscopy, and nuclear magnetic resonance spectroscopy. The emulsifying properties of phytosterols and phytosteryl amino acid ester hydrochlorides were also investigated. The results showed higher emulsifying properties of phytosteryl amino acid ester hydrochlorides, which could favor its wide application in food systems.

Solution-phase total synthesis of teixobactin

The first solution-phase total synthesis of the cyclic depsipeptide teixobactin is described. Stereoselective construction of l-allo-enduracididine was established, and the protective groups for the peptide coupling reactions and conditions for the assembly of the fragments were also optimised. The longest linear sequence for the total synthesis was 20 steps from the known l-cis-4-hydroxyproline derivative and gave a 5.6% overall yield. This solution-phase total synthesis could serve as a complement to the current solid-phase synthesis of teixobactin.

Convergent Strategy to Dizocilpine MK-801 and Derivatives

A convergent total synthesis of MK-801 has been achieved. Key synthetic transformations include a multicomponent Barbier-type reaction to construct the α-branched amine, a selective Heck α-coupling tactic to generate the exocyclic alkene skeleton, and a late-stage intramolecular hydroamination reaction between the exocyclic alkene and the secondary protected amine. The efficacy of this method was demonstrated by the synthesis of two news analogues substituted on the aromatic rings.

Synthesis, Characterization, and Activity of a Triazine Bridged Antioxidant Small Molecule

Metal-ion misregulation and oxidative stress continue to be components of the continually evolving hypothesis describing the molecular origins of Alzheimer's disease. Therefore, these features are viable targets for synthetic chemists to explore through hybridizations of metal-binding ligands and antioxidant units. To date, the metal-binding unit in potential therapeutic small molecules has largely been inspired by clioquinol with the exception of a handful of heterocyclic small molecules and open-chain systems. Heterocyclic small molecules such as cyclen (1,4,7,10-tetraazacyclododecane) have the advantage of straightforward N-based modifications, allowing the addition of functional groups. In this work, we report the synthesis of a triazine bridged system containing two cyclen metal-binding units and an antioxidant coumarin appendage inspired by nature. This new potential therapeutic molecule shows the ability to bind copper in a unique manner compared to other chelates proposed to treat Alzheimer's disease. DPPH and TEAC assays exploring the activity of N-(2-((4,6-di(1,4,7,10-tetraazacyclododecan-1-yl)-1,3,5-triazin-2-yl)amino)ethyl)-2-oxo-2H-chromene-3-carboxamide (molecule 1) show that the molecule is antioxidant. Cellular studies of molecule 1 indicate a low toxicity (EC₅₀ = 80 μM) and the ability to protect HT-22 neuronal cells from cell death induced by Aβ + copper(II), thus demonstrating the potential for molecule 1 to serve as a multimodal therapeutic for Alzheimer's disease.

Development of Fluorescent Probes that Target Serotonin 5-HT2B Receptors

Some 5-HT2B fluorescent probes were obtained by tagging 1-(2,5-dimethoxy-4-iodophenyl)-propan-2-amine (DOI) with a subset of fluorescent amines. Some of the resulting fluorescent ligands showed excellent affinity and selectivity profiles at the 5-HT2B receptors (e.g. 12b), while retain the agonistic functional behaviour of the model ligand (DOI). The study highlighted the most salient features of the structure-activity relationship in this series and these were substantiated by a molecular modelling study based on a receptor-driven docking model constructed on the basis of the crystal structure of the human 5-HT2B receptor. One of the fluorescent ligands developed in this work, compound 12i, specifically labelled CHO-K1 cells expressing 5-HT2B receptors and not parental CHO-K1 cells in a concentration-dependent manner. 12i enables imaging and quantification of specific 5-HT2B receptor labelling in live cells by automated fluorescence microscopy as well as quantification by measurements of fluorescence intensity using a fluorescence plate reader.

"Grafting-from" synthesis and characterization of poly (2-ethyl-2-oxazoline)-b-poly (benzyl L-glutamate) micellar nanoparticles for potential biomedical applications

Introduction: Recent advances in the field of poly (2-oxazolines) as bio-inspired synthetic pseudopeptides have proven their potential biomedical applications such as drug delivery and tissue engineering. Methods: In order to fabricate a biodegradable micellar nanoparticle of poly (2-ethyl 2-oxazoline)-b-poly (benzyl L-glutamate) or pEOx-b-pBLG, "grafting-from" synthesis approach was used involving consecutive steps of cationic ring-opening polymerization of 2-ethyl-2-oxazoline, amine functionalization of pEOx using 1-Boc-piperazine and N-carboxyanhydride polymerization of γ-benzyl- L-glutamate. Following hydrolysis of the copolymer, the protecting γ-benzyl groups were removed yielding a double-hydrophilic block ionomer of pEOx-b-poly (L-glutamic acid). The polymers were characterized by FTIR, 1H-NMR, size exclusion chromatography and differential scanning calorimetry (DSC). Aqueous assembly of the polymers was investigated by pyrene assay, dynamic light scattering, and transmission electron microscopy. MTT cytotoxicity assay was also performed to determine the cytocompatibility in various tumor cell lines. Results: The polymeric micelles presented a uni-modal size distribution with mean hydrodynamic diameter of 149.8 ± 10.6 nm and critical aggregation concentration of 60 µg/mL. The average molecular weight of pEOx increased from ~ 14 to 20 kDa for pEOx-b-poly (L-glutamic acid) as determined by light scattering (Debye plot), indicating a successful copolymerization. MTT assay showed little to no practical cytotoxicity at concentrations below 1 mg/mL. Conclusion: Multi-step synthesis of pEOx-b-pBLG and subsequent alkaline hydrolysis were performed to obtain the block ionomer pEOx-b-poly (L-glutamic acid). Both pEOx-based copolymers can be considered for various potential applications such as loading and delivery of drugs, genes, and contrast agents either by chemical conjugation or physical loading.

Anthranilic acid-containing cyclic tetrapeptides: at the crossroads of conformational rigidity and synthetic accessibility

Each amino acid in a peptide contributes three atom units to main-chains, hence natural cyclic peptides can be 9, 12, 15, …. i.e. 3n membered-rings, where n is the number of amino acids. Cyclic peptides that are 9 or 12-membered ring compounds tend to be hard to prepare because of strain, while their one amino acid homologs (15-membered cyclic pentapeptides) are not conformationally homogeneous unless constrained by strategically placed proline or d-amino acid residues. We hypothesized that replacing one genetically encoded amino acid in a cyclic tetrapeptide with a rigid β-amino acid would render peptidomimetic designs that rest at a useful crossroads between synthetic accessibility and conformational rigidity. Thus this research explored non-proline containing 13-membered ring peptides 1 featuring one anthranilic acid (Anth) residue. Twelve cyclic peptides of this type were prepared, and in doing so the viability of both solution- and solid-phase methods was demonstrated. The library produced contained a complete set of four diastereoisomers of the sequence 1aaf (i.e. cyclo-AlaAlaPheAnth). Without exception, these four diastereoisomers each adopted one predominant conformation in solution; basically these conformations feature amide N-H vectors puckering above and below the equatorial plane, and approximately oriented their N-H[combining low line] atoms towards the polar axis. Moreover, the shapes of these conformers varied in a logical and predictable way (NOE, temperature coefficient, D/H exchange, circular dichroism). Comparisons were made of the side-chain orientations presented by compounds 1aaa in solution with ideal secondary structures and protein-protein interaction interfaces. Various 1aaa stereoisomers in solution present side-chains in similar orientations to regular and inverse γ-turns, and to the most common β-turns (types I and II). Consistent with this, compounds 1aaa have a tendency to mimic various turns and bends at protein-protein interfaces. Finally, proteolytic- and hydrolytic stabilities of the compounds at different pHs indicate they are robust relative to related linear peptides, and rates of permeability through an artificial membrane indicate their structures are conducive to cell permeability.

Functionalized Multi-Wall Carbon Nanotubes Enhance Transfection and Expression Efficiency of Plasmid DNA in Fish Cells

DNA vaccines are considered to be the most promising method against infectious diseases in the aquaculture industry. In the present study, we investigated the potency of ammonium group-functionalized multi-walled carbon nanotubes (MWCNTs) in enhancing the transfection and expression efficiency of plasmid DNA (pEGFP-vp5) in Ctenopharyngodon idellus kidney (CIK) cells. Agarose gel shift assay results show that ammonium group-functionalized carbon nanotubes are able to condense DNA in varying degrees. Scanning electron microscope (SEM) images shows that CIK cells show a great affinity for MWCNTs-NH₃⁺ and the CNTs covering the cell surface tend to orient their tips perpendicularly to the cell surface, and appear to be “needle-pricking the cells”. Transmission electron microscope (TEM) images confirmed that MWCNTs-NH₃⁺ penetrate the cell membranes and are widely dispersed in the CIK cell. Real-time PCR was used to detect the transfection efficiency through the expression of the outer capsid protein (VP5). The results showed that the MWCNTs-NH₃⁺:DNA complexes are able to transfect CIK cells effectively at different charge ratio than naked DNA. Subsequent studies confirmed that both functional groups and charge ratio are important factors that determine the transfection efficiency of plasmid DNA. All these results indicated that MWCNTs-NH₃⁺:DNA complexes could be suitable for developing DNA vaccine for the control of virus infection in the aquaculture industry.