Sensitivities of Some Imidazole-1-sulfonyl Azide Salts

Automated Synthesis for the Safe Production of Organic Azides from Primary Amines

Described herein is the development of an automated and reproducible process for the conversion of primary amines to organic azides utilizing prepacked capsules containing all the required reagents, including imidazole-1-sulfonyl azide tetrafluoroborate. Apart from manually loading the primary amine into the reaction vessel, the entire reaction and product isolation process can be achieved automatically, with no further user involvement, and delivers the desired organic azide in high purity. This practical and simple automated capsule-based method offers a convenient and safe way of generating organic azides without handling or exposure of potentially explosive reagents.

Practical Synthesis from Streptomycin and Regioselective Partial Deprotections of (-)-(1R,2S,3R,4R,5S,6S)-1,3-Di(deamino)-1,3-diazido-2,5,6-tri-O-benzylstreptamine

We describe the gram-scale synthesis of (-)-(1R,2S,3R,4R,5S,6S)-1,3-di(diamino)-1,3-diazido-2,5,6-tri-O-benzylstreptamine from streptomycin by (i) hydrolysis of the two streptomycin guanidine residues, (ii) reprotection of the amines as azides, (iii) protection of all alcohols as benzyl ethers, and (iv) glycosidic bond cleavage with HCl in methanol. Protocols for regioselective monodebenzylation and regioselective reduction of a single azide in the product are also described, providing four optically pure building blocks for exploitation in novel aminoglycoside synthesis.

Facile synthesis of C5-azido derivatives of thiosialosides and 2,3-dehydro-5-N-acetylneuraminic acid (DANA)

Neuraminic acid (Neu5Ac, also known as sialic acid) is an important monosaccharide found in glycoproteins and glycolipids which plays a vital role in regulation of physiological functions and pathological conditions. The study of sialoglycans has benefitted from the development of glycomimetic probes and inhibitors for proteins and enzymes that interact with and modify neuraminic acid in glycan chains. Methods to access sialoside intermediates with high yield are needed to facilitate the design of new targets. Here, we report the synthesis of C5-azido thiosialosides using a mild method to deprotect the C5-acetamido functional group followed by the use of a diazo-transfer reagent. We examined two diazo-transfer strategies and compared their yields and tolerance of acetate protecting groups. The same methods and comparisons were also performed for the 2,3-dehydro-5-N-acetylneuraminic acid (DANA) scaffold which is commonly used to generate inhibitors of neuraminidase (sialidase) enzymes. We found that C5-azido derivatives of both thiosialosides and DANA could be produced in five or six steps with yields up to 76 % and 83 %, respectively. Diazo-transfer reagents compared in this study were trifluoromethanesulfonyl azide (TfN3) and imidazole-1-sulfonyl azide (ImzSO2N3). We found that both reagents were compatible with this method and showed comparable yields. Finally, we show that C5-azido derivatives can help to avoid O, N-acyl protecting group migration which was observed in C5-NHAc analogs.

Diazo-Transfer Reaction of Nonactivated Ketones with 2-Azido-1,3-bis(2,6-diisopropylphenyl)imidazolium Hexafluorophosphate (IPrAP)

The diazo-transfer reaction of nonactivated ketone under mild reaction conditions was developed. Various nonactivated ketones such as aryl methyl ketones, sec-alkyl methyl ketones, and cyclic ketones were transformed into their corresponding α-diazoketones in one step by treating 2-azido-1,3-bis(2,6-diisopropylphenyl)imidazolium hexafluorophosphate (IPrAP) in the presence of iPr2NH in ethylene glycol. In the reaction of IPrAP with prim-alkyl methyl ketone and prim-alkyl aryl ketones, migratory amidation proceeded under the reaction conditions to afford the corresponding amides.

Highly selective preparation of N-terminus Horseradish peroxidase-DNA conjugate with fully retained enzymatic activity: HRP-DNA structure - activity relation

Within the last decade, the field of bio-nanoengineering has achieved significant advances allowing us to generate, e.g., nanoscaled molecular machineries with arbitrary shapes. To unleash the full potential of novel methods such as DNA origami technology, it is important to functionalise complex molecules and nanostructures precisely. Thus, considerable attention has been given to site-selective modifications of proteins allowing further incorporation of various functionalities. Here, we describe a method for the covalent attachment of oligonucleotides to the glycosylated horseradish peroxidase protein (HRP) with high N-terminus selectivity and significant yield while conserving the enzymatic activity. This two-step process includes a pH-controlled metal-free diazotransfer reaction using imidazole-1-sulfonyl azide hydrogen sulfate, which at pH 8.5 results in an N-terminal azide-functionalized protein, followed by the Cu-free click SPAAC reaction to dibenzocyclooctyne- (DBCO) modified oligonucleotides. The reaction conditions were optimised to achieve maximum yield and the best performance. The resulting protein-oligonucleotide conjugates (HRP-DNA) were characterised by electrophoresis and mass spectrometry (MS). Native-PAGE experiments demonstrated different migration patterns for HRP-DNA and the azido-modified protein allowing zymogram experiments. Structure-activity relationships of novel HRP-DNA conjugates were assessed using molecular dynamics simulations, characterising the molecular interactions that define the structural and dynamical properties of the obtained protein-oligonucleotide conjugates (POC).

Modulating the Surface Properties of Lithium Niobate Nanoparticles by Multifunctional Coatings Using Water-in-Oil Microemulsions

Inorganic nanoparticles (NPs) have emerged as promising tools in biomedical applications, owing to their inherent physicochemical properties and their ease of functionalization. In all potential applications, the surface functionalization strategy is a key step to ensure that NPs are able to overcome the barriers encountered in physiological media, while introducing specific reactive moieties to enable post-functionalization. Silanization appears as a versatile NP-coating strategy, due to the biocompatibility and stability of silica, thus justifying the need for robust and well controlled silanization protocols. Herein, we describe a procedure for the silica coating of harmonic metal oxide NPs (LiNbO₃, LNO) using a water-in-oil microemulsion (W/O ME) approach. Through optimized ME conditions, the silanization of LNO NPs was achieved by the condensation of silica precursors (TEOS, APTES derivatives) on the oxide surface, resulting in the formation of coated NPs displaying carboxyl (LNO@COOH) or azide (LNO@N₃) reactive moieties. LNO@COOH NPs were further conjugated to an unnatural azido-containing small peptide to obtain silica-coated LNO NPs (LNO@Talys), displaying both azide and carboxyl moieties, which are well suited for biomedical applications due to the orthogonality of their surface functional groups, their colloidal stability in aqueous medium, and their anti-fouling properties.

Importance of Co-operative Hydrogen Bonding in the Apramycin-Ribosomal Decoding A-Site Interaction

An intramolecular hydrogen bond between the protonated equatorial 7'-methylamino group of apramycin and the vicinal axial 6'-hydroxy group acidifies the 6'-hydroxy group leading to a strong hydrogen bond to A1408 in the ribosomal drug binding pocket in the decoding A site of the small ribosomal subunit. In 6'-epiapramycin, the trans-nature of the 6'-hydroxy group and the 7'-methylamino group results in a much weaker intramolecular hydrogen bond, and a consequently weaker cooperative hydrogen bonding network with A1408, resulting overall in reduced inhibition of protein synthesis and antibacterial activity.

Chemoselective restoration of para-azido-phenylalanine at multiple sites in proteins

The site-specific incorporation of nonstandard amino acids (nsAAs) during translation has expanded the chemistry and function of proteins. The nsAA para-azido-phenylalanine (pAzF) encodes a biorthogonal chemical moiety that facilitates "click" reactions to attach diverse chemical groups for protein functionalization. However, the azide moiety is unstable in physiological conditions and is reduced to para-amino-phenylalanine (pAF). Azide reduction decreases the yield of pAzF residues in proteins to 50%-60% per azide and limits protein functionalization by click reactions. Here, we describe the use of a pH-tunable diazotransfer reaction that converts pAF to pAzF at >95% efficiency in proteins. The method selectively restores pAzF at multiple sites per protein without introducing off-target modifications. This work addresses a key limitation in the production of pAzF-containing proteins by restoring azides for multi-site functionalization with diverse chemical moieties, setting the stage for the production of genetically encoded biomaterials with broad applications in biotherapeutics, materials science, and biotechnology.

Syntheses of Legionaminic Acid, Pseudaminic Acid, Acetaminic Acid, 8-epi-Acetaminic Acid, and 8-epi-Legionaminic Acid Glycosyl Donors from N-Acetylneuraminic Acid by Side Chain Exchange

Metaperiodate cleavage of the glycerol side chain from an N-acetyl neuraminic acid-derived thioglycoside and condensation with the two enantiomers of the Ellman sulfinamide afford two diastereomeric N-sulfinylimines from which bacterial sialic acid donors with the legionaminic and acetaminic acid configurations and their 8-epi-isomers are obtained by samarium iodide-mediated coupling with acetaldehyde and subsequent manipulations. A variation on the theme, with inversion of the configuration at C5, similarly provides two differentially protected pseudaminic acid donors.

One-pot synthesis of polysulfonate by cascading sulfur(VI) fluorine exchange (SuFEx) reaction and cyanosilylation of aldehyde

As a kind of excellent engineering polymer material, the synthesis of polysulfonate has attracted intense attention in recent years. In this work, four new polysulfonates with cyano substitution on the...

Generation of Tosyl Azide in Continuous Flow Using an Azide Resin, and Telescoping with Diazo Transfer and Rhodium Acetate-Catalyzed O-H Insertion

Generation of tosyl azide 12 in acetonitrile in flow under water-free conditions using an azide resin and its use in diazo transfer to a series of aryl acetates are described. Successful telescoping with a rhodium acetate-catalyzed O-H insertion has been achieved, thereby transforming the aryl acetate 8 to α-hydroxy ester 10, a key intermediate in the synthesis of clopidogrel 11, without requiring isolation or handling of either tosyl azide 12 or α-aryl-α-diazoacetate 9, or indeed having significant amounts of either present at any point. Significantly, the solution of α-diazo ester 9 was sufficiently clean to progress directly to the rhodium acetate-catalyzed step without any detrimental impact on the efficiency of the O-H insertion. In addition, the rhodium acetate-catalyzed O-H insertion process is cleaner in flow than under traditional batch conditions. Use of the azide resin offers clear safety advantages and, in addition, this approach complements earlier protocols for the generation of tosyl azide 12 in flow; this protocol is especially useful with less acidic substrates.

Protected N-Acetyl Muramic Acid Probes Improve Bacterial Peptidoglycan Incorporation via Metabolic Labeling

Metabolic glycan probes have emerged as an excellent tool to investigate vital questions in biology. Recently, methodology to incorporate metabolic bacterial glycan probes into the cell wall of a variety of bacterial species has been developed. In order to improve this method, a scalable synthesis of the peptidoglycan precursors is developed here, allowing for access to essential peptidoglycan immunological fragments and cell wall building blocks. The question was asked if masking polar groups of the glycan probe would increase overall incorporation, a common strategy exploited in mammalian glycobiology. Here, we show, through cellular assays, that E. coli do not utilize peracetylated peptidoglycan substrates but do employ methyl esters. The 10-fold improvement of probe utilization indicates that (i) masking the carboxylic acid is favorable for transport and (ii) bacterial esterases are capable of removing the methyl ester for use in peptidoglycan biosynthesis. This investigation advances bacterial cell wall biology, offering a prescription on how to best deliver and utilize bacterial metabolic glycan probes.

DNA-Encoded Chemistry: Drug Discovery from a Few Good Reactions

Click chemistry, proposed nearly 20 years ago, promised access to novel chemical space by empowering combinatorial library synthesis with a "few good reactions". These click reactions fulfilled key criteria (broad scope, quantitative yield, abundant starting material, mild reaction conditions, and high chemoselectivity), keeping the focus on molecules that would be easy to make, yet structurally diverse. This philosophy bears a striking resemblance to DNA-encoded library (DEL) technology, the now-dominant combinatorial chemistry paradigm. This review highlights the similarities between click and DEL reaction design and deployment in combinatorial library settings, providing a framework for the design of new DEL synthesis technologies to enable next-generation drug discovery.

Improved Diazo-Transfer Reaction for DNA-Encoded Chemistry and Its Potential Application for Macrocyclic DEL-Libraries

DNA-encoded libraries (DEL) are increasingly being used to identify new starting points for medicinal chemistry in drug discovery. Herein, we discuss the development of methods that allow the conversion of both primary amines and anilines, attached to DNA, to their corresponding azides in excellent yields. The scope of these diazo-transfer reactions was investigated, and a proof-of-concept has been devised to allow for the synthesis of macrocycles on DNA.

Rapid Self-Healing and Thixotropic Organogelation of Amphiphilic Oleanolic Acid-Spermine Conjugates

Natural and abundant plant triterpenoids are attractive starting materials for the synthesis of conformationally rigid and chiral building blocks for functional soft materials. Here, we report the rational design of three oleanolic acid-triazole-spermine conjugates, containing either one or two spermine units in the target molecules, using the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. The resulting amphiphile-like molecules 2 and 3, bearing just one spermine unit in the respective molecules, self-assemble into highly entangled fibrous networks leading to gelation at a concentration as low as 0.5% in alcoholic solvents. Using step-strain rheological measurements, we show rapid self-recovery (up to 96% of the initial storage modulus) and sol ⇔ gel transition under several cycles. Interestingly, rheological flow curves reveal the thixotropic behavior of the gels. To the best of our knowledge, this kind of behavior was not shown in the literature before, neither for a triterpenoid nor for its derivatives. Conjugate 4, having a bolaamphiphile-like structure, was found to be a nongelator. Our results indicate that the position and number of spermine units alter the gelation properties, gel strength, and their self-assembly behavior. Preliminary cytotoxicity studies of the target compounds 2-4 in four human cancer cell lines suggest that the position and number of spermine units affect the biological activity. Our results also encourage exploring other triterpenoids and their derivatives as sustainable, renewable, and biologically active building blocks for multifunctional soft organic nanomaterials.

Discovery of a novel family of FKBP12 "reshapers" and their use as calcium modulators in skeletal muscle under nitro-oxidative stress

The hypothesis of rescuing FKBP12/RyR1 interaction and intracellular calcium homeostasis through molecular "reshaping" of FKBP12 was investigated. To this end, novel 4-arylthioalkyl-1-carboxyalkyl-1,2,3-triazoles were designed and synthesized, and their efficacy was tested in human myotubes. A library of 17 compounds (10a-n) designed to dock the FKBP12/RyR1 hot-spot interface contact residues, was readily prepared from free α-amino acids and arylthioalkynes using CuAAC "click" protocols amenable to one-pot transformations in high overall yields and total configurational integrity. To model nitro-oxidative stress, human myotubes were treated with the peroxynitrite donor SIN1, and evidence was found that some triazoles 10 were able to normalize calcium levels, as well as FKBP12/RyR1 interaction. For example, compound 10 b at 150 nM rescued 46% of FKBP12/RyR1 interaction and up to 70% of resting cytosolic calcium levels in human myotubes under nitro-oxidative stress. All compounds 10 analyzed showed target engagement to FKBP12 and low levels of cytotoxicity in vitro. Compounds 10b, 10c, 10h, and 10iR were identified as potential therapeutic candidates to protect myotubes in muscle disorders with underlying nitro-oxidative stress, FKBP12/RyR1 dysfunction and calcium dysregulation.

Synthesis and optimisation of P3 substituted vinyl sulfone-based inhibitors as anti-trypanosomal agents

A series of lysine-based vinyl sulfone peptidomimetics were synthesised and evaluated for anti-trypanosomal activity against bloodstream forms of T. brucei. This focused set of compounds, varying in the P₃ position, were accessed in a divergent manner from a common intermediate (ammonium salt 8). Several P₃ analogues exhibited sub-micromolar EC₅₀ values, with thiourea 14, urea 15 and amide 21 representing the most potent anti-trypanosomal derivatives of the series. In order to establish an in vitro selectivity index the most active anti-trypanosomal compounds were also assessed for their impact on cell viability and cytotoxity effects in mammalian cells. Encouragingly, all compounds only reduced cellular metabolic activity in mammalian cells to a modest level and little, or no cytotoxicity, was observed with the series.

Design of Radiolabeled Analogs of Minigastrin by Multiple Amide-to-Triazole Substitutions

The insertion of single 1,4-disubstituted 1,2,3-triazoles as metabolically stable bioisosteres of trans-amide bonds (triazole scan) was recently applied to the ¹⁷⁷Lu-labeled tumor-targeting analog of minigastrin, [Nle¹⁵]MG11. The reported novel mono-triazolo-peptidomimetics of [Nle¹⁵]MG11 showed either improved resistance against enzymatic degradation or a significantly increased affinity toward the target receptor but never both. To enhance further the tumor-targeting properties of the minigastrin analogs, we studied conjugates with multiple amide-to-triazole substitutions for additive or synergistic effects. Promising candidates were identified by modification of two or three amide bonds, which yielded both improved stability and increased receptor affinity of the peptidomimetics in vitro. Biodistribution studies of radiolabeled multi-triazolo-peptidomimetics in mice bearing receptor-positive tumor xenografts revealed up to 4-fold increased tumor uptake in comparison to the all-amide reference compound [Nle¹⁵]MG11. In addition, we report here for the first time a linear peptidomimetic with three triazole insertions in its backbone and maintained biological activity.

Triazolo-Peptidomimetics: Novel Radiolabeled Minigastrin Analogs for Improved Tumor Targeting

MG11 is a truncated analog of minigastrin, a peptide with high affinity and specificity toward the cholecystokinin-2 receptor (CCK2R), which is overexpressed by different tumors. Thus, radiolabeled MG11 derivatives have great potential for use in cancer diagnosis and therapy. A drawback of MG11 is its fast degradation by proteases, leading to moderate tumor uptake in vivo. We introduced 1,4-disubstituted 1,2,3-triazoles as metabolically stable bioisosteres to replace labile amide bonds of the peptide. The "triazole scan" yielded peptidomimetics with improved resistance to enzymatic degradation and/or enhanced affinity toward the CCK2R. Remarkably, our lead compound achieved a 10-fold increase in receptor affinity, resulting in a 2.6-fold improved tumor uptake in vivo. Modeling of the ligand-CCK2R complex suggests that an additional cation-π interaction of the aromatic triazole moiety with the Arg³⁵⁶ residue of the receptor is accountable for these observations. We show for the first time that the amide-to-triazole substitution strategy offers new opportunities in drug development that go beyond the metabolic stabilization of bioactive peptides.

Stereospecific synthesis of methyl 2-amino-2,4-dideoxy-6S-deuterio-α-D-xylo-hexopyranoside and methyl 2-amino-2,4-dideoxy-6S-deuterio-4-propyl-α-d-glucopyranoside: Side chain conformation of the novel aminoglycoside antibiotic propylamycin

The stereospecific syntheses of methyl 2-amino-2,4-dideoxy-4-C-propyl-α-d-glucopyranoside and of methyl 2-amino-2,4-dideoxy-α-D-xylo-hexopyranoside and of their 6S-deuterioisotopomers are described as models for ring I of the aminoglycoside antibiotics propylamycin and 4'-deoxyparomomycin, respectively. Analysis of the ¹H NMR spectra of these compounds and of methyl 2-amino-2-deoxy-α-d-glucopyranoside, a model for paromomycin itself, reveals that neither deoxygenation at the 4-position, nor substitution of the C-O bond at the 4-postion by a C-C bond significantly changes the distribution of the side chain population between the three possible staggered conformations. From this it is concluded that the beneficial effect on antiribosomal and antibacterial activity of the propyl group in propylamycin does not derive from a change in side chain conformation. Rather, enhanced basicity of the ring oxygen and increased hydrophobicity and/or solvation effects are implicated.

Thermal Stability and Explosive Hazard Assessment of Diazo Compounds and Diazo Transfer Reagents

Despite their wide use in academia as metal-carbene precursors, diazo compounds are often avoided in industry owing to concerns over their instability, exothermic decomposition, and potential explosive behavior. The stability of sulfonyl azides and other diazo transfer reagents is relatively well understood, but there is little reliable data available for diazo compounds. This work first collates available sensitivity and thermal analysis data for diazo transfer reagents and diazo compounds to act as an accessible reference resource. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and accelerating rate calorimetry (ARC) data for the model donor/acceptor diazo compound ethyl (phenyl)diazoacetate are presented. We also present a rigorous DSC dataset with 43 other diazo compounds, enabling direct comparison to other energetic materials to provide a clear reference work to the academic and industrial chemistry communities. Interestingly, there is a wide range of onset temperatures (T _onset) for this series of compounds, which varied between 75 and 160 °C. The thermal stability variation depends on the electronic effect of substituents and the amount of charge delocalization. A statistical model is demonstrated to predict the thermal stability of differently substituted phenyl diazoacetates. A maximum recommended process temperature (T _D24) to avoid decomposition is estimated for selected diazo compounds. The average enthalpy of decomposition (ΔH _D) for diazo compounds without other energetic functional groups is -102 kJ mol^-1. Several diazo transfer reagents are analyzed using the same DSC protocol and found to have higher thermal stability, which is in general agreement with the reported values. For sulfonyl azide reagents, an average ΔH _D of -201 kJ mol^-1 is observed. High-quality thermal data from ARC experiments shows the initiation of decomposition for ethyl (phenyl)diazoacetate to be 60 °C, compared to that of 100 °C for the common diazo transfer reagent p-acetamidobenzenesulfonyl azide (p-ABSA). The Yoshida correlation is applied to DSC data for each diazo compound to provide an indication of both their impact sensitivity (IS) and explosivity. As a neat substance, none of the diazo compounds tested are predicted to be explosive, but many (particularly donor/acceptor diazo compounds) are predicted to be impact-sensitive. It is therefore recommended that manipulation, agitation, and other processing of neat diazo compounds are conducted with due care to avoid impacts, particularly in large quantities. The full dataset is presented to inform chemists of the nature and magnitude of hazards when using diazo compounds and diazo transfer reagents. Given the demonstrated potential for rapid heat generation and gas evolution, adequate temperature control and cautious addition of reagents that begin a reaction are strongly recommended when conducting reactions with diazo compounds.

Enhancing Potency and Selectivity of a DC-SIGN Glycomimetic Ligand by Fragment-Based Design: Structural Basis

Chemical modification of pseudo-dimannoside ligands guided by fragment-based design allowed for the exploitation of an ammonium-binding region in the vicinity of the mannose-binding site of DC-SIGN, leading to the synthesis of a glycomimetic antagonist (compound 16) of unprecedented affinity and selectivity against the related lectin langerin. Here, the computational design of pseudo-dimannoside derivatives as DC-SIGN ligands, their synthesis, their evaluation as DC-SIGN selective antagonists, the biophysical characterization of the DC-SIGN/16 complex, and the structural basis for the ligand activity are presented. On the way to the characterization of this ligand, an unusual bridging interaction within the crystals shed light on the plasticity and potential secondary binding sites within the DC-SIGN carbohydrate recognition domain.

Modification at the 2'-Position of the 4,5-Series of 2-Deoxystreptamine Aminoglycoside Antibiotics To Resist Aminoglycoside Modifying Enzymes and Increase Ribosomal Target Selectivity

A series of derivatives of the 4,5-disubstituted class of 2-deoxystreptamine aminoglycoside antibiotics neomycin, paromomycin, and ribostamycin was prepared and assayed for (i) their ability to inhibit protein synthesis by bacterial ribosomes and by engineered bacterial ribosomes carrying eukaryotic decoding A sites, (ii) antibacterial activity against wild type Gram negative and positive pathogens, and (iii) overcoming resistance due to the presence of aminoacyl transferases acting at the 2′-position. The presence of five suitably positioned residual basic amino groups was found to be necessary for activity to be retained upon removal or alkylation of the 2′-position amine. As alkylation of the 2′-amino group overcomes the action of resistance determinants acting at that position and in addition results in increased selectivity for the prokaryotic over eukaryotic ribosomes, it constitutes an attractive modification for introduction into next generation aminoglycosides. In the neomycin series, the installation of small (formamide) or basic (glycinamide) amido groups on the 2′-amino group is tolerated.

Modular click chemistry libraries for functional screens using a diazotizing reagent

Click chemistry is a concept in which modular synthesis is used to rapidly find new molecules with desirable properties¹. Copper(I)-catalysed azide-alkyne cycloaddition (CuAAC) triazole annulation and sulfur(VI) fluoride exchange (SuFEx) catalysis are widely regarded as click reactions^2-4, providing rapid access to their products in yields approaching 100% while being largely orthogonal to other reactions. However, in the case of CuAAC reactions, the availability of azide reagents is limited owing to their potential toxicity and the risk of explosion involved in their preparation. Here we report another reaction to add to the click reaction family: the formation of azides from primary amines, one of the most abundant functional groups⁵. The reaction uses just one equivalent of a simple diazotizing species, fluorosulfuryl azide^6-11 (FSO₂N₃), and enables the preparation of over 1,200 azides on 96-well plates in a safe and practical manner. This reliable transformation is a powerful tool for the CuAAC triazole annulation, the most widely used click reaction at present. This method greatly expands the number of accessible azides and 1,2,3-triazoles and, given the ubiquity of the CuAAC reaction, it should find application in organic synthesis, medicinal chemistry, chemical biology and materials science.

Galactosyl and sialyl clusters: synthesis and evaluation against T. cruzi parasite

The multivalent effect of carbohydrates (glycoclusters) has been explored to study important biological targets and processes involving Trypanosoma cruzi (T. cruzi) infection. Likewise, CuAAC cycloaddition reactions (click chemistry) have been applied as useful strategy in the discovery of bioactive molecules. Hence, we describe the synthesis of 1,2,3-triazole-based tetravalent homoglycoclusters (1–3) and heteroglycoclusters (4 and 5) of d-galactopyranose (C-1 and C-6 positions) and sialic acid (C-2 position) to assess their potential to inhibit T. cruzi cell invasion and also its cell surface trans-sialidase (TcTS). The target compounds were synthesised in good yields (52–75 %) via click chemistry by coupling azidosugars galactopyranose and sialic acid with alkynylated pentaerythritol or tris(hydroxymethyl)-aminomethane (TRIS) scaffolds. T. cruzi cell invasion inhibition assays showed expressive low parasite infection index values (5.3–6.8) for most compounds. However, most glycoclusters proved to be weak TcTS inhibitors at 1 mM (<17 %), except the tetravalent sialic acid 3 (99 % at 1 mM, IC50 450 μM). Therefore, we assume that T. cruzi cell invasion blockage is not due to TcTS inhibition by itself, but rather by other mechanisms involved in this process. In addition, all glycoclusters were not cytotoxic and had significant trypanocidal activity upon parasite survival of amastigote forms.

Diazo-Transfer Reagent 2-Azido-4,6-dimethoxy-1,3,5-triazine Displays Highly Exothermic Decomposition Comparable to Tosyl Azide

2-Azido-4,6-dimethoxy-1,3,5-triazine (ADT) was reported recently as a new "intrinsically safe" diazo-transfer reagent. This assessment was based on differential scanning calorimetry data indicating that ADT exhibits endothermic decomposition. We present DSC data on ADT that show exothermic decomposition with an initiation temperature ( T_init) of 159 °C and an enthalpy of decomposition (Δ H_D) of -1135 J g^-1 (-207 kJ mol^-1). We conclude that ADT is potentially explosive and must be treated with caution, being of comparable exothermic magnitude to tosyl azide (TsN₃). A maximum recommended process temperature for ADT is 55 °C.

The growing applications of SuFEx click chemistry

SuFEx (Sulfur Fluoride Exchange) is a modular, next generation family of click reactions, geared towards the rapid and reliable assembly of functional molecules.

Intrinsically Safe and Shelf-Stable Diazo-Transfer Reagent for Fast Synthesis of Diazo Compounds

We report a crystalline compound 2-azido-4,6-dimethoxy-1,3,5-triazine (ADT) as an intrinsically safe, highly efficient, and shelf-stable diazo-transfer reagent. Because the decomposition of ADT is an endothermal process (Δ H = 30.3 kJ mol^-1), ADT is intrinsically nonexplosive, as proved by thermal, friction, and impact tests. The diazo-transfer reaction based on ADT gives diazo compounds in excellent yields within several minutes at room temperature. ADT is very stable upon >1 year storage under air at room temperature.

Azidoimidazolinium Salts: Safe and Efficient Diazo-transfer Reagents and Unique Azido-donors

2-Azido-1,3-dimethylimidazolinium chloride (ADMC) and its corresponding hexafluorophosphate (ADMP) were found to be efficient diazo-transfer reagents to various organic compounds. ADMC was prepared by the reaction of 2-chloro-1,3-dimethylimidazolinium chloride (DMC) and sodium azide. ADMP was isolated as a crystal having good thermal stability and low explosibility. ADMC and ADMP reacted with 1,3-dicarbonyl compounds under mild basic conditions to give 2-diazo-1,3-dicarbonyl compounds in high yields, which were easily isolated in virtue of the high water solubility of the by-products. ADMP showed high diazo-transfer ability to primary amines even in the absence of metal salt such as Cu(II). Using this diazotization approach, various alkyl/aryl azides were directly obtained from their corresponding primary amines in high yields. Furthermore, naphthols reacted with ADMC to give the corresponding diazonaphthoquinones in good to high yields. In addition, 2-azido-1,3-dimethylimidazolinium salts were employed as azide-transfer and migratory amidation reagents.

Synthesis of 11C-labeled Sulfonyl Carbamates through a Multicomponent Reaction Employing Sulfonyl Azides, Alcohols, and [11C]CO

We describe the development of a new methodology focusing on 11C-labeling of sulfonyl carbamates in a multicomponent reaction comprised of a sulfonyl azide, an alkyl alcohol, and [11C]CO. A number of 11C-labeled sulfonyl carbamates were synthesized and isolated, and the developed methodology was then applied in the preparation of a biologically active molecule. The target compound was obtained in 24±10 % isolated radiochemical yield and was evaluated for binding properties in a tumor cell assay; in vivo biodistribution and imaging studies were also performed. This represents the first successful radiolabeling of a non-peptide angiotensin II receptor subtype 2 agonist, C21, currently in clinical trials for the treatment of idiopathic pulmonary fibrosis.

CuAAC: An Efficient Click Chemistry Reaction on Solid Phase

Click chemistry is an approach that uses efficient and reliable reactions, such as Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC), to bind two molecular building blocks. CuAAC has broad applications in medicinal chemistry and other fields of chemistry. This review describes the general features and applications of CuAAC in solid-phase synthesis (CuAAC-SP), highlighting the suitability of this kind of reaction for peptides, nucleotides, small molecules, supramolecular structures, and polymers, among others. This versatile reaction is expected to become pivotal for meeting future challenges in solid-phase chemistry.

Taming tosyl azide: the development of a scalable continuous diazo transfer process

In situ generation and use of tosyl azide in flow enables enhanced safety and ready scale-up in diazo transfer processes.

Synthesis and Antiribosomal Activities of 4'-O-, 6'-O-, 4″-O-, 4',6'-O- and 4″,6″-O-Derivatives in the Kanamycin Series Indicate Differing Target Selectivity Patterns between the 4,5- and 4,6-Series of Disubstituted 2-Deoxystreptamine Aminoglycoside Antibiotics

Chemistry for the efficient modification of the kanamycin class of 4,6-aminoglycosides at the 4'-position is presented. In all kanamycins but kanamycin B, 4'-O-alkylation is strongly detrimental to antiribosomal and antibacterial activity. Ethylation of kanamycin B at the 4″-position entails little loss of antiribosomal and antibacterial activity, but no increase of ribosomal selectivity. These results are contrasted with those for the 4,5-aminoglycosides, where 4'-O-alkylation of paromomycin causes only a minimal loss of activity but results in a significant increase in selectivity with a concomitant loss of ototoxicity.