Mild and Efficient DBU-Catalyzed Amidation of Cyanoacetates

A First-in-Class Pyrazole-isoxazole Enhanced Antifungal Activity of Voriconazole: Synergy Studies in an Azole-Resistant Candida albicans Strain, Computational Investigation and in Vivo Validation in a Galleria mellonella Fungal Infection Model

The widespread and irrational use of azole antifungal agents has led to an increase of azole-resistant Candida albicans strains with an urgent need for combination drug therapy, enhancing the treatment efficacy. Here, we report the discovery of a first-in-class pyrazole-isoxazole, namely, 5b, that showed remarkable growth inhibition against the C. albicans ATCC 10231 strain in combination with voriconazole, acting as a downregulator of ERG 11 (Cyp51) gene expression with a significant reduction of the yeast-to-hypha morphological transition. Furthermore, C. albicans CYP51 enzyme assay and in-depth molecular docking studies unveiled the unique ability of the combination of 5b and voriconazole to completely fill the CYP51 binding sites. In vivo studies using a Galleria mellonella model confirmed the previously in vitro observed synergistic effect of 5b with voriconazole. Also considering its biocompatibility in a cellular model of human keratinocytes, these results indicate that 5b represents a promising compound for a further optimization campaign.

Hydroxy-directed peptide bond formation from α-amino acid-derived inert esters enabled by boronic acid catalysis

A boronic acid-catalyzed peptide bond formation from α-amino acid methyl esters is described. The catalysis showed high chemoselectivity for β-hydroxy-α-amino esters, affording the peptides in high to excellent yields with high functional group tolerance. This hydroxy-directed peptide bond formation could be applicable to oligopeptide syntheses. This is the first successful example of organoboron-catalyzed peptide bond formation from α-amino acid-derived inert esters.

A sustainable metal and base-free direct amidation of esters using water as a green solvent

Herein, we report a simple and efficient synthetic approach for direct amidation of esters via C(acyl)-O bond cleavage without any additional reagents or catalysts, using only water as a green solvent. Subsequently, the reaction byproduct is recovered and utilized for the next phase of ester synthesis. This method emphasized metal-free, additive-free, and base-free characteristics making it a new, sustainable, and eco-friendly way to realize direct amide bond formation. In addition, the synthesis of the drug molecule diethyltoluamide and the Gram-scale synthesis of a representative amide are demonstrated.

Electron-Deficient Benzo[de]isoquinolino[1,8-gh]quinoline Diamide π-Electron Systems

Synthetically versatile electron-deficient π-electron systems are urgently needed for organic electronics, yet their design and synthesis are challenging due to the low reactivity from large electron affinities. In this work, we report a benzo[de]isoquinolino[1,8-gh]quinoline diamide (BQQDA) π-electron system. The electron-rich condensed amide as opposed to the generally-employed imide provides a suitable electronic feature for chemical versatility to tailor the BQQDA π-electron system for various electronic applications. We demonstrate an effective synthetic method to furnish the target BQQDA parent structure, and highly selective functionalization can be performed on bay positions of the π-skeleton. In addition, thionation of BQQDA can be accomplished under mild conditions. Fine-tuning of fundamental properties and supramolecular packing motifs are achieved via chemical modifications, and the cyanated BQQDA organic semiconductor demonstrates a high air-stable electron-carrier mobility.

Mechanistic Understanding of KOtBu-Mediated Direct Amidation of Esters with Anilines: An Experimental Study and Computational Approach

A sustainable and cost-effective protocol has been reported for the synthesis of amide bonds from unactivated esters and non-nucleophilic amines promoted by potassium tert -butoxide under aerobic conditions. The reaction proceeds under relatively mild conditions, encompassing wide substrate scope. A combined experimental and quantum chemical study has been performed to shed light on the mechanism, which implied that a radical pathway is operating for the present protocol.

Organocatalyzed umpolung addition for synthesis of heterocyclic-fused arylidene-imidazolones as anticancer agents

A strategy of "Nature-to-new" with iterative scaffold-hopping was considered for investigation of privileged ring/functional motif-elaborated analogs of natural aurones. An organocatalyzed umpolung chemistry based method was established for molecular-diversity feasible synthesis of title class of chemotypes i.e. (Z)-2-Arylideneimidazo[1,2-a]pyridinones and (Z)-2-Arylidenebenzo[d]imidazo[2,1-b]thiazol-3-ones. Various biophysical experiments indicated their important biological properties. The analogs showed characteristic anticancer activities with efficiency more than an anticancer drug. The compounds induced apoptosis with arrest in the S phase of the cell cycle regulation. The compounds' significant effect in up/down-regulation of various apoptotic proteins, an apoptosis cascade, and the inhibition of topoisomerases-mediated DNA relaxation process was identified. The analysis of the structure-activity relationship, interference with biological events and the drug-likeness physicochemical properties of the compounds in the acceptable window indicated distinctive medicinal molecule-to-properties of the investigated chemotypes.

Synthesis and characterization of dendritic compounds containing nitrogen: monomer precursors in the construction of biomimetic membranes

In this article, we synthesized a novel dendritic 2-oxazoline, 2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-4,5-dihydro-1,3-oxazole), and its amide precursor N-(2-hydroxyethyl)-3,4,5-tris(4-dodecyloxybenzyloxy)benzamide. Of the distinct synthetic routes explored, it was established that the direct amidation of esters with sodium methoxide followed by the dehydrative cyclisation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as oxidizing agent and triphenylphosphine was the most efficient route to synthesize the dendritic 2-oxazoline. Besides, N-(2-hydroxyethyl)-3,4,5-tris(4-dodecyloxybenzyloxy)benzamide exhibited a monotropic columnar mesophase, whilst the dendritic 2-oxazoline does not exhibited a liquid crystalline mesophase. At the end, the first attempts to polymerize the 2-oxazoline monomer via cationic ring opening polymerization showed promising results. Therefore, the dendritic 2-oxazoline could be used as a mesogenic monomer in the synthesis of side-chain liquid-crystalline polyoxazolines that might self-assembly into columnar structures.

6-Halo-2-pyridone as an efficient organocatalyst for ester aminolysis

It was found that 6-halo-2-pyridones catalysed ester aminolysis in which not only reactive aryl esters but also relatively less reactive methyl and benzyl esters could be used as a substrate. The reaction could be performed without strictly dry and anaerobic conditions and the 6-chloro-2-pyridone catalyst could be recovered quantitatively after reaction. The method could be applied to dipeptide synthesis from methyl or benzyl esters of amino acids, where a high enantiomeric purity of the products was maintained. The mechanism involving dual activation of ester and amine substrates through hydrogen bonding between catalyst and substrates is proposed where 6-halo-2-pyridones act as a bifunctional Brønsted acid/base catalyst.

6-Halo-2-pyridones effectively catalyse ester aminolysis as bifunctional catalysts. This reaction did not require any special conditions and was operationally convenient.

Design, synthesis and SAR of antitubercular benzylpiperazine ureas

N-furfuryl piperazine ureas disclosed by scientists at GSK Tres Cantos were chosen as antimycobacterial hits from a phenotypic whole-cell screen. Bioisosteric replacement of the furan ring in the GSK Tres Cantos molecules with a phenyl ring led to molecule (I) with an MIC of 1 μM against Mtb H37Rv, low cellular toxicity (HepG2 IC₅₀ ~ 80 μM), good DMPK properties and specificity for Mtb. With the aim of delineating the SAR associated with (I), fifty-five analogs were synthesized and screened against Mtb. The SAR suggests that the piperazine ring, benzyl urea and piperonyl moieties are essential signatures of this series. Active compounds in this series are metabolically stable, have low cellular toxicity and are valuable leads for optimization. Molecular docking suggests these molecules occupy the Q0 site of QcrB like Q203. Bioisosteric replacement of N-furfuryl piperazine-1-carboxamides yielded molecule (I) a novel lead with satisfactory PD, metabolism, and toxicity profiles.

Inside Perspective of the Synthetic and Computational Toolbox of JAK Inhibitors: Recent Updates

The mechanisms of inflammation and cancer are intertwined by complex networks of signaling pathways. Dysregulations in the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway underlie several pathogenic conditions related to chronic inflammatory states, autoimmune diseases and cancer. Historically, the potential application of JAK inhibition has been thoroughly explored, thus triggering an escalation of favorable results in this field. So far, five JAK inhibitors have been approved by the Food and Drug Administration (FDA) for the treatment of different diseases. Considering the complexity of JAK-depending processes and their involvement in multiple disorders, JAK inhibitors are the perfect candidates for drug repurposing and for the assessment of multitarget strategies. Herein we reviewed the recent progress concerning JAK inhibition, including the innovations provided by the release of JAKs crystal structures and the improvement of synthetic strategies aimed to simplify of the industrial scale-up.

Exploring the scope of DBU-promoted amidations of 7-methoxycarbonylpterin

The synthetic utility of pterins is often hampered by the notorious insolubility of this heterocycle, slowing the development of medicinally relevant pteridine derivatives. Reactions which expedite the development of new pterins are thus of great importance. Through a dual role of diazabicycloundecene (DBU), 7-carboxymethylpterin is converted to the soluble DBU salt, with additional DBU promoting an ester-to-amide transformation. We have explored this reaction to assess its scope and identify structural features in the amines which significantly affect success, monitored the reaction kinetics using a pseudo-first order kinetics model, and further adapted the reaction conditions to allow for product formation in as little as 5 min, with yields often >80%.

Glycoconjugation as a Promising Treatment Strategy for Psoriasis

Despite the progress in the development of novel treatment modalities, a significant portion of patients with psoriasis remains undertreated relative to the severity of their disease. Recent evidence points to targeting the glucose transporter 1 and sugar metabolism as a novel therapeutic strategy for the treatment of psoriasis and other hyperproliferative skin diseases. In this review, we discuss glycoconjugation, an approach that facilitates the pharmacokinetics of cytotoxic molecules and ensures their preferential influx through glucose transporters. We propose pathways of glycoconjugate synthesis to increase effectiveness, cellular selectivity, and tolerability of widely used antipsoriatic drugs. The presented approach exploiting the heightened glucose requirement of proliferating keratinocytes bears the potential to revolutionize the management of psoriasis. SIGNIFICANCE STATEMENT: Recent findings concerning the fundamental role of enhanced glucose metabolism and glucose transporter 1 overexpression in the pathogenesis of psoriasis brought to light approaches that proved successful in cancer treatment. Substantial advances in the emerging field of glycoconjugation highlight the rationale for the development of glucose-conjugated antipsoriatic drugs to increase their effectiveness, cellular selectivity, and tolerability. The presented approach offers a novel therapeutic strategy for the treatment of psoriasis and other hyperproliferative skin diseases.

Solvent-Free Iron(III) Chloride-Catalyzed Direct Amidation of Esters

Amide functional groups are prominent in a broad range of organic compounds with diverse beneficial applications. In this work, we report the synthesis of these functional groups via an iron(iii) chloride-catalyzed direct amidation of esters. The reactions are conducted under solvent-free conditions and found to be compatible with a range of amine and ester substrates generating the desired amides in short reaction times and good to excellent yields at a catalyst loading of 15 mol%.

Graphene oxide: a convenient metal-free carbocatalyst for facilitating amidation of esters with amines

Herein, we have reported a graphene oxide (GO) catalyzed condensation of non-activated esters and amines, that can enable diverse amides to be synthesized from abundant ethyl esters forming only volatile alcohol as a by-product.

Stereoelectronic Effects in Ligand Design: Enantioselective Rhodium-Catalyzed Hydrogenation of Aliphatic Cyclic Tetrasubstituted Enamides and Concise Synthesis of (R)-Tofacitinib

We herein report the development of a conformationally defined, electron-rich, C₂ -symmetric, P-chiral bisphosphorus ligand, ArcPhos, by taking advantage of stereoelectronic effects in ligand design. With the Rh-ArcPhos catalyst, excellent enantioselectivities and unprecedentedly high turnovers (TON up to 10 000) were achieved in the asymmetric hydrogenation of aliphatic carbocyclic and heterocyclic tetrasubstituted enamides, to generate a series of chiral cis-2-alkyl-substituted carbocyclic and heterocyclic amine derivatives in excellent enantiomeric ratios. This method also enabled an efficient and practical synthesis of the Janus kinase inhibitor (R)-tofacitinib.

Stereoselective deconjugation of macrocyclic α,β-unsaturated esters by sequential amidation and olefin transposition: application to enantioselective phase-transfer catalysis

The stereoselective synthesis of chiral macrocycles bearing two aliphatic amide functional groups is reported. After the amidation mediated by TBD, a guanidine derivative, the olefin transposition step is performed with a slight excess of t-BuOK. The products are afforded in moderate to good combined yields (up to 59%) and with an excellent syn diastereoselectivity (dr > 49 : 1). Introducing enantiopure α-branched substituents was possible and it resulted in mixtures of diastereomers, which could be tested as phase-transfer catalysts using the formation of a phenylalanine analog as a test reaction (up to 43% ee). A clear matched-mismatched situation was observed in the two diastereomeric series.

Solvent- and transition metal-free amide synthesis from phenyl esters and aryl amines

A general, economical, and environmentally friendly method of amide synthesis from phenyl esters and aryl amines was developed. This new method has significant advantages compared to previously reported palladium-catalyzed approaches. The reaction is performed transition metal- and solvent-free, using a cheap and environmentally benign base, NaH. This approach enabled us to obtain target amides in high yields with high atom economy.

Mechanistic investigation-inspired activation mode of DBU and the function of the α-diazo group in the reaction of the α-amino ketone compound and EDA: [DBU-H]+-DMF-H2O and α-diazo as strong N-terminal nucleophiles

DFT calculations disclosed a dramatic electronic turnover of the α-diazo group based on an unexpected DBU activation mode.

Exploiting Ring-Opening Aminolysis-Condensation as a Polymerization Pathway to Structurally Diverse Biobased Polyamides

A pathway to biobased polyamides (PAs) via ring-opening aminolysis-condensation (ROAC) under benign conditions with diverse structure was designed. Ethylene brassylate (EB), a plant oil-derived cyclic dilactone, was used in combination with an array of diamines of diverse chemical structure, and ring-opening of the cyclic dilactone EB was revealed as a driving force for the reaction. The ROAC reactions were adjusted, and reaction conditions of 100 °C under atmospheric pressure using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a catalyst for 24 h were optimal. The structures of the polyamides were confirmed by mass spectroscopy, FTIR, and NMR, and the PAs had viscosity average molecular weights ( M_η) of ∼5-8 kDa. Glassy or semicrystalline PAs with glass transition temperatures between 48 and 55 °C, melting temperatures of 120-200 °C for the semicrystalline PAs, and thermal stabilities above 400 °C were obtained and were comparable to the existing PAs with similar structures. As a proof-of-concept of their usage, one of the PAs was shown to form fibers by electrospinning and films by melt pressing. Compared to conventional methods for PA synthesis, the ROAC route portrayed a reaction temperature at least 60-80 °C lower, could be readily carried out without a low-pressure environment, and eliminated the use of solvents and toxic chemicals. Together with the plant oil-derived monomer (EB), the ROAC route provided a sustainable alternative to design biobased PAs.

Synthesis of All Stereoisomers of 1-(4-Methoxyphenyl)-2,3,4,9-tetrahydro-N-methyl-1H-pyrido[3,4-b]indole-3-carboxamide

In this study, all four stereoisomers of tryptoline or tetrahydro-β-carboline were synthesized in high yields by the catalyst-free amidation of methyl ester using methylamine under mild conditions. All isomers of the obtained amide and the precursor methyl ester were subjected to cell viability measurements on HeLa cells. The results indicated that the stereochemistry of the derivatives is clearly related to cell viability.

A Multicomponent Route to Functionalized Amides and Oxazolidinones

An organobase-mediated multicomponent reaction of unactivated esters, epoxides, and amines is reported, furnishing functionalized amide derivatives. A wide range of substrates are tolerated under the reaction conditions, including chiral epoxides, which react with no erosion of enantiopurity. Facile modification of the method through replacing the ester derivative with dimethyl carbonate enables access to the corresponding oxazolidinone derivatives.

Amidation of unactivated ester derivatives mediated by trifluoroethanol

A catalytic amidation protocol mediated by 2,2,2-trifluoroethanol has been developed, facilitating the condensation of unactivated esters and amines, furnishing both secondary and tertiary amides.

Propargyl-Assisted Selective Amidation Applied in C-terminal Glycine Peptide Conjugation

Alkyl esters, such as propargyl esters, typically lack the electron-withdrawing inductive effects needed to participate in nucleophilic acyl substitution reactions. Herein, we report an unusual observation in which glycine propargyl ester derivatives displayed selective, base-independent reactivity towards linear alkylamines under mild, metal-free conditions. Through global reaction route mapping (GRRM) modeling calculations, it is predicted that these observations may be governed by factors related to hydrogen-bonding and intermolecular interactions, rather than electron-withdrawing inductive effects. Based on this concept of propargyl-assisted selective amidation, a direct application was made to develop a novel site-specific C-terminal glycine peptide bioconjugation technique as a proof-of-concept, which relies upon the selective reactivity of glycine propargyl esters over that of aspartate and glutamate side-chain-linked propargyl esters.

p-Nitrophenyl carbonate promoted ring-opening reactions of DBU and DBN affording lactam carbamates

The amidine bases DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and DBN (1,5-diazabicyclo[4.3.0]non-5-ene) display nucleophilic behaviour towards highly electrophilic p-nitrophenyl carbonate derivatives with ring opening of the bicyclic ring to form corresponding substituted ε-caprolactam and γ-lactam derived carbamates. This simple method presents a unified strategy to synthesize structurally diverse ε-caprolactam and γ-lactam compounds with a large substrate scope.

Nonclassical Routes for Amide Bond Formation

The present review offers an overview of nonclassical (e.g., with no pre- or in situ activation of a carboxylic acid partner) approaches for the construction of amide bonds. The review aims to comprehensively discuss relevant work, which was mainly done in the field in the last 20 years. Organization of the data follows a subdivision according to substrate classes: catalytic direct formation of amides from carboxylic and amines ( section 2 ); the use of carboxylic acid surrogates ( section 3 ); and the use of amine surrogates ( section 4 ). The ligation strategies (NCL, Staudinger, KAHA, KATs, etc.) that could involve both carboxylic acid and amine surrogates are treated separately in section 5 .

Catalytic amidation of unactivated ester derivatives mediated by trifluoroethanol

A practical, catalytic protocol for amidation of unactivated esters has been developed using cheap and readily available reagents.

Novel hinge-binding motifs for Janus kinase 3 inhibitors: a comprehensive structure-activity relationship study on tofacitinib bioisosteres

The Janus kinases (JAKs) are a family of cytosolic tyrosine kinases crucially involved in cytokine signaling. JAKs have been demonstrated to be valid targets in the treatment of inflammatory and myeloproliferative disorders, and two inhibitors, tofacitinib and ruxolitinib, recently received their marketing authorization. Despite this success, selectivity within the JAK family remains a major issue. Both approved compounds share a common 7H-pyrrolo[2,3-d]pyrimidine hinge binding motif, and little is known about modifications tolerated at this heterocyclic core. In the current study, a library of tofacitinib bioisosteres was prepared and tested against JAK3. The compounds possessed the tofacitinib piperidinyl side chain, whereas the hinge binding motif was replaced by a variety of heterocycles mimicking its pharmacophore. In view of the promising expectations obtained from molecular modeling, most of the compounds proved to be poorly active. However, strategies for restoring activity within this series of novel chemotypes were discovered and crucial structure-activity relationships were deduced. The compounds presented may serve as starting point for developing novel JAK inhibitors and as a valuable training set for in silico models.