Biocatalytic Synthesis of N-trans-feruloyltyramine Using an Amide Bond Synthetase with an ATP Recycling

N-trans-feruloyltyramine (FLA) is one kind of phenylpropanoid compound found in various plants. Numerous studies have confirmed that it exhibits a wide range of physiological functions, such as antioxidant, ɑ-glucosidase inhibition, and anti-inflammatory activity. However, the low content of FLA in plants greatly limits its potential use in food and pharmaceutical industries. It is, therefore, very important to establish an effective synthesis of FLA. In this study, a green and efficient method to synthesize FLA was sought using an amide bond synthetase (ABS) biocatalyst. Ten kinds of ABS enzymes, including AlCfaL from Azospirillum lipoferum, were screened as the potential biocatalysts for the production of FLA. To obtain optimum reaction conditions, the effects of various parameters on conversion of FLA were firstly evaluated. Under the optimum conditions using 1 mM N-trans-ferulic acid, 50 mM tyramine (substrate ratio of 1:50), 10 mM MgCl₂, 8 mM ATP, and 35 µM AlCfaL enzyme at 30 °C with a shaking speed of 500 r/min for 48 h, maximum conversion rate of 74% was reached. Given that the amidation reaction is mediated by relative expensive ATP, we further optimized reaction systems to incorporate an ATP recycling system consisting of a polyphosphate kinase enzyme (CHU) and an inexpensive polyphosphate (PolyP) as the phosphate donor. Response surface methodology (RSM) based on five-level, five-variable central composite design (CCD) was used to evaluate the optimal parameters for the production of FLA. The effects of AMP, PolyP, AlCfaL, CHU concentrations, and reaction time on the conversion rate of FLA were analyzed. The optimum conditions derived via RSM were 7.12 mM AMP, 5.96 mg/mL PolyP, 39.72 μM AlCfaL, 27.68 μM CHU, and a reaction time of 36 h. Validation experiments conducted under these optimized conditions yielded an actual conversion rate of 63.5%, which compared well to the maximum predicted value of 64.2%.

Cathode-Anode Synergy Electrosynthesis of Propanamide via a Bipolar C-N Coupling Reaction

Propanamide is a crucial synthetic intermediate in pharmaceuticals for the preparation of antibacterial and anticancer drugs. Conventional synthesis of propanamide involves the reaction of carboxylic acid derivatives with amines, which requires harsh reaction conditions, leading to an unfavorable environmental footprint. Here, we present a cathode-anode synergistic electrochemical strategy to transform nitrate and n-propanol into propanamide under ambient conditions, where both the cathode catalyst Co3O4/SiC and the anode catalyst Ti contribute distinctively to the electrochemical process. The CH3CH2CHO produced at the Ti anode can diffuse and react with the adsorbed intermediate *NH2OH on the surface of the cathode catalyst to form propanamide. The synergistic reactions at both electrodes collectively enhance the efficiency of the propanamide synthesis. This design enables efficient propanamide production in a flow cell at the gram scale with a remarkable yield of 986.13 μmol/(cm2·h) at current densities of up to 650 mA/cm2. Our reports present a new option for environmentally friendly C-N bond synthesis, and the insights can be useful for the electrosynthesis of a wider scope of amides.

Green procedures for synthesizing potential hNMDA receptor allosteric modulators through reduction and one-pot reductive acetylation of nitro(hetero)arenes using a superparamagnetic Fe3O4@APTMS@Cp2ZrCl x (x = 0, 1, 2) nanocatalyst

The conversion of nitro(hetero)arenes to corresponding (hetero)aryl amines and other practical organic compounds plays a crucial role in various sciences, especially environmental remediation and public health. In the current research work, diverse green and efficient strategies for the convenient reduction (hydrogenation) and one-pot two-step reductive acetylation of nitro(hetero)arenes using a core-shell-type mesoporous zirconocene-containing magnetically recoverable nanocomposite (viz. Fe3O4@APTMS@Cp2ZrCl x (x = 0, 1, 2)) as a powerful nanocatalytic system have been developed. In the presented organic transformations, the superparamagnetic Fe3O4@APTMS@Cp2ZrCl x (x = 0, 1, 2) nanocomposite exhibited satisfactory turnover numbers (TONs) and turnover frequencies (TOFs), along with acceptable reusability. On the other hand, we investigated the potential biological effect of the synthesized (hetero)aryl amines and N-(hetero)aryl acetamides against the transmembrane domain (TMD) of the human N-methyl-d-aspartate (hNMDA) receptor based on molecular docking studies. Furthermore, the drug-likeness properties of our hit compound (viz. N-(3-(1-hydroxyethyl)phenyl)acetamide) have been scrutinized by in silico ADMET analyses.

Sequence-defined peptoids via iterative exponential growth

Synthetic control over polymer sequence, composition, and stereochemistry is critical to understanding their influence on the intramolecular and intermolecular interactions of polymers. We report an iterative exponential growth (IEG) strategy for peptoids, a class of sequence-defined peptidomimetics, relying on orthogonally protected monomers. The IEG technique enables the synthesis of monodisperse peptoids with varied sequences, side chains, and stereoconfigurations on a scale that is useful for material science applications. The method allows for direct monitoring of the reaction progress without the need for cleavage from a solid-support. This IEG strategy offers higher molecular weights than other solution-phase sequence-defined synthetic strategies for peptoids and seeks to mimic the precise structural organization of sequence-defined biopolymers for a synthetic polymer system, which we anticipate will enable the rational design of functional polymer materials.

Graphene Oxide-Modified Resin for Selective dsRNA Removal from In Vitro-Transcribed mRNA

Messenger RNA (mRNA) has proven to be an effective vaccine agent against unexpected pandemics, offering the advantage of rapidly producing customized therapeutics targeting specific pathogens. However, undesired byproducts, such as double-stranded RNA (dsRNA), generated during in vitro transcription (IVT) reactions may impede translation efficiency and trigger inflammatory cytokines in cells after mRNA uptake. In this study, we developed a facile method using PEGylated polystyrene resins that were further surface-modified with graphene oxide (GO@PEG-PS) for the removal of dsRNA from IVT mRNA. The GO@PEG-PS resin adsorbed mRNA due to the property of graphene oxide (GO), which preferentially adsorbs single-stranded nucleic acids over double-stranded nucleic acids in the presence of Mg2+. The resin-bound single-stranded (ss) RNA was readily desorbed with a mixture of EDTA and urea, possibly by chelating Mg2+ and disrupting hydrogen bonding, respectively. Spin-column chromatography with GO@PEG-PS for IVT mRNA eliminated at least 80% of dsRNA, recovering approximately 85% of mRNA. Furthermore, this procedure precluded the salt precipitation step after the IVT reaction, which fractionates mRNAs from the IVT components, including nucleotides and enzymes. The purified mRNA exhibited enhanced protein translation with reduced secretion of interferon (IFN)-β upon mRNA transfection. We anticipate that the mRNA purification chromatography system employing GO@PEG-PS resin will facilitate the removal of dsRNA contamination during mRNA production.

Preparation, separation and storage of N-monofluoromethyl amides and carbamates

N-monofluoromethyl (N-CH2F) amides, combining amide and monofluoromethyl motifs, represent a practical modification of the amide bond that can mimic N-CH3 amides. Despite the potential value in transforming peptides and peptidomimetics with N-CH2F, the very existence of this structure has been controversial. Here we report the preparation of N-CH2F amides and carbamates via simple and robust chemical methods. The syntheses of N-CH2F amides were achieved via successive acylation and fluorination of imines and directly used in the modification of drugs, peptides and heteroaryl amides without racemization or epimerization. The use of triethylamine is the key to the separation of N-CH2F amides. The stability of nine structurally diverse N-CH2F amides was tested in eight different media, showing that most compounds remained 60-100% intact for 24 h.

Synthesis of Mono-Boc-2,5-Diketopiperazine: A Key Building Block for Amide and Peptide Synthesis

Diketopiperazine (DKP), a versatile scaffold, is extensively used in the synthesis of complex natural products, bioactive molecules, and smart materials in organic chemistry. Recently, activated DKPs, such as Boc-DKPs, have emerged as key building blocks for peptide elongation in peptide synthesis. In this study, we developed a facile protocol for synthesizing mono-Boc-protected DKPs from readily accessible N-4-methoxybenzyl (N-PMB)-amino acids and amino acid methyl esters. This protocol involved a sequence of reactions encompassing the formation of dipeptides from N-PMB-amino acids and amino acid methyl esters, cyclization of N-PMB-dipeptides to form PMB-DKPs, Boc-protection of PMB-DKPs, and subsequent PMB-deprotection of PMB-DKP-Boc to afford mono-Boc-DKPs. The protocol demonstrated a broad substrate scope, accommodating diverse amino acids with various side chains, affording mono-Boc-DKPs in good yields with excellent stereoselectivities (>20:1 dr). The synthetic utility of mono-Boc-DKPs was showcased in peptide synthesis by synthesizing pentapeptide Boc-l-Tyr(t-Bu)-Gly-l-Phe-Gly-l-Val-OtBu by 2-fold peptide elongation with two mono-Boc-DKPs. Furthermore, we synthesized Leu-enkephalin pentapeptide by reacting cyclo(Boc-l-Tyr(t-Bu)-Gly-) with H-Gly-l-Phe-l-Leu-Ot-Bu, resulting in a good yield and excellent optical purity.

HFIP-Promoted Aromatic Electrophilic Amidation of Indoles and Pyrroles with Isocyanates

A mild and practical method for synthesizing amidoindoles and amidopyrroles was described via the direct amidation of indoles or pyrroles with isocyanates promoted by 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). In this reaction, HFIP acted as a strong hydrogen bond-donating solvent to activate isocyanates, enabling the amidation of electron-rich nitrogen-containing heterocycles.

Nickel-Catalyzed Hydrocarbamoylation of Alkenes with Isocyanates

The hydrocarbamoylation of alkenes with isocyanates is a promising method for synthesizing amides. However, applying this strategy to more inert, simple alkenes, such as styrenes, α-olefins, and internal alkenes, poses significant challenges. Here, we report the first nickel-catalyzed hydrocarbamoylation of alkenes with isocyanates, facilitated by triethoxysilane to reduce nickelacycle intermediates. By switching ligands─including 6,6'-dimethyl-2,2'-bipyridine and N-heterocyclic carbene─this method efficiently produces amides from a diverse array of alkenes, including styrenes, α-olefins, internal alkenes, and gaseous olefins.

Enzymatic Cascades for Stereoselective and Regioselective Amide Bond Assembly

Amide bond formation is fundamental in nature and is widely used in the synthesis of pharmaceuticals and other valuable products. Current methods for amide synthesis are often step and atom inefficient, requiring the use of protecting groups, deleterious reagents and organic solvents that create significant waste. The development of cleaner and more efficient catalytic methods for amide synthesis remains an urgent unmet need. Herein, we present novel biocatalytic cascade reactions for synthesising various amides under mild aqueous conditions from readily available organic nitriles combining nitrile hydrolysing enzymes and amide bond synthetase enzymes. These cooperative biocatalytic cascades enable kinetic resolution of racemic nitriles and provide a highly enantioselective biocatalytic extension of the Strecker reaction. The regioselective non-directed C-H bond amidation of simple arenes was demonstrated through the incorporation of photoredox catalysis to the front end of the cascade. C-H bond amidation of simple aromatic precursors was also achieved via a CO2 fixation cascade combining enzymatic carboxylation and amide bond synthesis in one-pot.

Photocatalytic Pyridyl-carbamoylation of Alkenes for Accessing β-Pyridyl Amides

The β-pyridyl amide is a critical scaffold in medical discovery yet lacks efficient synthetic methods. Here, we describe, for the first time, a visible-light-induced, redox-neutral radical cross-coupling reaction involving alkenes, oxamic acids, and cyanopyridines that offers a versatile assembly of β-pyridylamides. This approach features mild reaction conditions, high step efficiency, and substrate breadth, providing a green and efficient strategy for alkene pyridyl-carbamoylation. Achieving this transformation relies on the efficient catalytic system, which adeptly avoids the competing cross-coupling of the nucleophilic carbamoyl radical with the electrophilic pyridyl radical, enabling the three-component radical tandem reaction process with high chemoselectivity.

Magnetic N-doped CNT stabilized Cu2O as a catalyst for N-arylation of nitriles and aryl halides in a biocompatible deep eutectic solvent

This study documented the hydrolysis of nitriles by copper(i) oxide immobilized on nitrogen-doped carbon nanotubes (N-CNT/Fe3O4-Cu2O) to yield corresponding amides in the presence of a deep eutectic solvent (ChOH/Gly). Furthermore, the aforementioned catalyst can facilitate the coupling reaction between aryl halides and amides derived by nitrile hydrolysis. Consequently, the integration of two copper-catalyzed processes can efficiently provide N-aryl amides. Choline hydroxide in a deep eutectic solvent serves as a cost-effective organic catalyst in nitrie hydrolysis by forming hydrogen bonds with nitrile, thereby activating it. The catalyst generated higher to satisfactory product yields. One of the special benefits of the catalyst is that it can be restored through the addition of an external magnetic field.

Borate-catalysed direct amidation reactions of coordinating substrates

The catalytic activity of different classes of boron catalysts was studied in amidation reactions with 4-phenylbutylamine/benzoic acid, and with 2-aminopyridine/phenylacetic acid. Whilst a simple boronic acid catalyst showed high catalytic activity with the former substrates, it was completely inactive in the latter reaction. In contrast, a borate ester catalyst was able to mediate the amidation of both substrate pairs with moderate activity. By screening a range of borate esters we were able to identify a novel borate catalyst that shows high reactivity with a range of challenging carboxylic acids/amine pairs, enabling catalystic amidation reactions to be achieved effectively with these industrially relevant compounds. The reactions can be performed on multigram scale with high levels of efficiency, and in situ catalyst generation from commercially available reagents renders the process readily accessible for everyday laboratory use. Further experiments showed that the deactivating effect of 2-aminopyridine on boronic acid catalysts was due to its ability to stabilise catalytically inactive boroxines.

Visible-Light-Induced Secondary Benzylic C(sp3)-H Functionalization for Nucleophilic Substitution: An Intermolecular C-X (C-N, C-C, and C-Br) Bond Forming Reaction

Exploring new synthetic methods that harness visible light represents a breakthrough in organic synthesis. Amides, amines, nitriles, and halides are essential functional groups and serve as key building blocks in the synthesis of complex molecules in organic and medicinal chemistry. This study introduces a novel intermolecular benzylic C-X (C-N, C-C, and C-Br) bond formation via photoredox benzylic C(sp3)-H bonds. This methodology enables the synthesis of secondary amides, nitriles, and halides through reacting secondary benzylic substrates with readily accessible reagents including BocNH2, benzamide, acetamide, TMSCN, and TBAB. This approach displays the potential of being sustainable and efficient to afford amidation, cyanation, and halogenation products in good yields.

Synthesis and Evaluation of Boron-Containing Heterocyclic Compounds with Antimicrobial and Anticancer Activities

Organoboron compounds, especially those containing boronic acid and benzoxaborole in their structure, have been gaining prominence in medicinal chemistry, following the FDA approval of tavaborole for the treatment of onychomycosis and bortezomib for multiple myeloma. The antimicrobial and anticancer effects of organoboron compounds motivate the investigation of the effects of the novel derivatives described here. A total of fourteen new boronic derivatives were synthesized and characterized using analytical methods. The antimicrobial activities were evaluated against M. tuberculosis (Mtb) H37Rv strains and fungal dermatophytes (C. albicans, ATCC 90028; T. rubrum, ATCC 28189; and T. mentagrophytes, ATCC 11481), while the anticancer effect was evaluated against oral squamous cell carcinoma (SCC) cell lines. Several promising boron-containing prototypes were identified, providing a foundation for further molecular optimization in the development of new antimicrobial and anticancer compounds.

Condensation of carboxylic acids with amines using the Boc2O/DMAP system under solvent-free conditions

The present study describes the use of the di-tert-butyl dicarbonate (Boc2O)/4-(N,N-dimethylamino)pyridine (DMAP) system for the amidation of carboxylic acids under neat conditions without heating. A set of carboxylic acids was explored, such as non-steroidal anti-inflammatory drugs (NSAIDs), fatty acids and protected prolines in the presence of aromatic, benzylic and aliphatic amines as nucleophilic partners. The scope of this easy approach was extended to the preparation of thirty-two diverse carboxylic amides, which were recovered with isolated yields varying from moderate to excellent. To increase the value of this protocol, a scalable chemoselective amidation of oleic acid with ethanolamine was successfully established. The corresponding fatty carboxylic amide, N-oleoylethanolamide (OEA), was recovered with 73% yield. This study highlights the potency of the use of mixed anhydrides formed in situ and the pursuit of the reaction profile reveals sequential steps rather than a one-pot process.

Light-Dependent Amide or Thioamide Formation of Acylsilanes with Amines using Elemental Sulfur

Due to the diverse chemical and physical properties of functional groups, mild and controllable ligation methods are often required to construct complex drugs and functional materials. To make diverse sets of products with tunable physicochemical properties, it is also useful to employ complimentary ligation methods that adopt the same starting materials. Here, we disclose the efficient and modular synthesis of amides or thioamides through the chemical ligation of acylsilanes with amines, simply by turning a light on or off. This method is fast, mild, high-yielding and displays excellent functional-group tolerance. The versatility of these reactions is highlighted by their ability to perform post-synthetic modifications on a variety of marketed medications, peptides, natural substances, and compounds with biological activity. In-depth computational and experimental studies clarified the photo-dependent umpolung of reactivity of acylsilanes, namely: photoexcitation leads to nucleophilic O-silyl carbenes that react with S8 to form O-silyl thionoesters and eventually amides. In contrast, acylsilanes react as electrophiles with amines thermally in the dark, with C→O silyl transfer, prior to reacting with S8 to form thioamides. These mechanistic details are expected to guide the development of similar coupling reactions.

Synthesis of the conjugation-ready β-mannosamine-containing O-antigen repeat from Vibrio cholerae O14

Chemical synthesis of the trisaccharide repeating unit of the O-antigen from Vibrio cholerae has been accomplished through a linear strategy. The reducing end 1,2-cis mannosamine unit has been achieved through the azide inversion of the 2-OH position of a suitably protected glucose moiety. The crucial (S)-3-hydroxybutyric acid is inserted successfully at the last stage through EDC-HOBt coupling. The target trisaccharide, in the form of its 2-aminoethyl glycoside, is ready for further conjugation.

Total synthesis of linear lipodepsipeptide kavaratamide A and its C25-epimer

We report the stereoselective total synthesis of kavaratamide A, a linear lipodepsipeptide from the cyanobacterium Moorena bouillonii (collected in Kavaratti, India), and its unnatural C25-epimer. The convergent approach employs Keck asymmetric allylation to construct the chiral β-hydroxy carboxylic acid fragment [(3S)-HDA; 3-hydroxydecanoic acid], while the peptide unit was assembled from L-Val, N-Me-L-Ala, (S)-Hiva, and (S)-iPr-O-Me-pyr using well-orchestrated coupling methods to prevent racemization. Modifications to the Keck allylation conditions enabled the synthesis of the C25-epimer with good yield. Cytotoxicity of kavaratamide A and C25-epi-kavaratamide A, assessed using the MTT assay, demonstrated moderate activity against HepG2 and PANC-1 cell lines.

Iron-Assisted and Cu-Mediated Direct Aminocarbonylation of Nitroarene with Boronic Acid

Herein, we have established the formation of diaryl amide by aminocarbonylation of nitrobenzene with boronic acids. The method works in the catalytic presence of economical and commercially available CuI salt, which was significantly promoted by the Fe3Se2(CO)9 cluster. Mo(CO)6 serves as a source of CO, and it also acts as a reductant with a combination of iron cluster. Moreover, all the reaction worked under the ligand-free system and produced the desired diaryl amide in a significant time of 10 h. Water, a green solvent, was used as a source of hydrogen for the reduction of nitrobenzene to aniline. The method depicts a suitable functional group tolerance and produces a wide range of substrates in good to excellent amounts. To the best of our knowledge, this is the first report for the direct aminocarbonylation mediated by highly economical CuI. Moreover, water as a source of hydrogen for the reduction of nitroarene is always appreciated.

Divergent alkynylative difunctionalization of amide bonds through C-O deoxygenation versus C-N deamination

The transformation and utilization of amides are significant in organic synthesis and drug discovery. Here we demonstrate a divergent alkynylative difunctionalization of amides in a single transformation. In this reaction, amides react with an organometallic nucleophile to form a tetrahedral intermediate. By altering the N-substitution or the acyl group, the tetrahedral intermediate species selectively undergoes C-O or C-N cleavage with a concomitant capture by an alkynyl nucleophile generated in situ. This process enables the selective introduction of two different functional groups into the amide molecular architecture, producing valuable propargyl amine and propargyl alcohol products. The selectivity between deoxygenation and deamination process has been further elucidated by DFT calculations. Overall, this reaction successfully transforms the traditional mode of nucleophilic acyl addition to amides to a divergent C-O/C-N cleavage. The particularly wide substrate scope, including late-stage modification of bioactive molecules, demonstrates its potential broad applications in organic synthesis.

Photochemical Deracemization of N-Carboxyanhydrides En Route to Chiral α-Amino Acid Derivatives

Readily accessible, racemic N-carboxyanhydrides (NCAs) of α-amino acids underwent a deracemization reaction upon irradiation at λ=366 nm in the presence of a chiral benzophenone catalyst. The enantioenriched NCAs (up to 98 % ee) serve as activated α-amino acid surrogates and, due to their instability, they were directly converted into consecutive products. N-Protected α-amino acid esters were obtained after reaction with MeOH and N-benzoylation (14 examples, 70 %-quant., 82-96 % ee). Other consecutive reactions included amide (ten examples, 65 %-quant., 90-98 % ee) and peptide (three examples, 75-89 %, d. r.=97/3 to 94/6) bond formation. Limitations of the method relate for some NCAs to issues with solubility, photooxidation, and high configurational lability.

Synthesis of novel α-spinasterol derivatives and their inhibitory effects on CCL17 and CCL22 chemokine expression

Natural α-spinasterol is well known for its various biological activities. In this study, we investigated the anti-inflammatory effects of newly synthesized α-spinasterol derivatives by tracking the expression of CCL17 and CCL22 chemokines, which serve as biomarkers for immune cell trafficking in skin inflammation. Initially, the 3-epimer of α-spinasterol, which results from inversion of stereochemistry at the C-3 position of α-spinasterol, was synthesized using the Mitsunobu reaction. Subsequently, new compounds were synthesized by introducing azido, amino, and amide groups at the C-3 position of α-spinasterol or 3-epi-α-spinasterol. The anti-inflammatory activity of these compounds was evaluated by examining their inhibitory effects on the mRNA expression of CCL17 and CCL22. Among these derivatives, 3α-8, 3α-12b, and 3α-12c exhibited potential anti-inflammatory activity in vitro, compared to α-spinasterol. Furthermore, compound 3α-8 showed even greater activity than 3α-12b and 3α-12c, underscoring its potential as a highly effective agent. These results suggest that the newly synthesized α-spinasterol derivatives hold promise as candidates for skin inflammation therapeutics.

Rapid Synthesis of Primary Amides Using Ammonia Borane

We report the rapid synthesis of primary amides by directly using commercially available ammonia borane (NH3·BH3), sodium hexamethyldisilazide (NaHMDS), and esters. The success of this protocol relies on NH3·BH3 as the nitrogen source being considerably more convenient and NaHMDS being an excellent proton abstractor but not participating in the nucleophilic addition reaction. The reaction had a wide substrate scope containing bioactive molecules, and most of the substrates were efficiently amidated over 90% yields.

Aminocarbonylation using CO surrogates

Aminocarbonylation reactions play a critical role in the synthesis of amides. Traditional aminocarbonylation processes often rely on carbon monoxide (CO) gas, a highly toxic and challenging reagent to handle. Recent advancements in CO surrogates address these challenges. This review looks at the various CO substitutes used in aminocarbonylation reactions. These include metal carbonyls, acids, formates, chloroform, and others that release CO. Use of CO surrogates not only improves safety but also broadens the substrate scope and operational simplicity of the aminocarbonylation reactions. This review provides a summary of recent progress made in aminocarbonylation reactions using different CO surrogates. We discuss key methodologies, catalytic systems, and mechanistic insights, highlighting the efficiency and versatility of CO surrogates in amide bond formation.

Silver-Catalyzed Decarboxylative Coupling of Oxamic Acids with Styrenes to Synthesize E-Cinnamamides: A Distinguish Reaction Pathway

A silver-catalyzed decarboxylative coupling of oxamic acids with styrenes has been developed to produce E-cinnamamides. Oxamic acids act as efficient precursors for carbamoy radicals. Based on the mechanistic experiments and intermediate analysis, the proposed mechanism involves radical addition to styrenes, followed by oxidation and solvent participation, ultimately leading to the formation of cinnamamides which is different from the reported cases.

Dioxazolones as electrophilic amide sources in copper-catalyzed and -mediated transformations

Over the past decade, dioxazolones have been widely used as N-acylamide sources in amidation processes of challenging substrates, typically employing precious transition metals. However, these catalytic systems often present several challenges associated with cost, toxicity, stability, and recyclability. Among the 3d transition metals, copper catalysts have been gaining increasing attention owing to their abundance, cost-effectiveness, and sustainability. Recently, these catalytic systems have been applied to the chemical transformation of dioxazolones, conferring a convenient protocol towards amidated products. This review highlights recent advancements in the synthetic transformations of dioxazolones, with particular examples of copper salts.

DMTMM-mediated amidation of sodium alginate in aqueous solutions: pH-dependent efficiency of conjugation

DMTMM-mediated amidation of sodium alginate is one of the methods used for the chemical modification of alginate with amines. However, there is a limited understanding of how the reaction conditions, particularly the pH value, influence the conjugation efficiency (CE) and the resulting degree of substitution (DS). In this study, we investigated the effect of the pH during the reaction, focusing on both neutral and weakly basic conditions, using water and buffer as solvents. Two model amines with high pKaH values were selected, furfurylamine (FFA, pKaH = 9.12) and 4-(2-aminoethyl)morpholine (AEM, pKaH = 9.93). Sodium alginate with a high mannuronate content (60 mol%) and molar mass of 168 kg·mol-1 was used for amidation. Our results show that both FFA and AEM effectively conjugate to sodium alginate under the selected reaction conditions. We found that pH significantly affects both CE and DS, which varied between 2 % to 40 % and 3 % to 53 %, respectively, depending on the specific reaction conditions. Optimal conditions were observed at neutral pH in water, whereas weak basic pH led to lower CE. Our findings thus offer a recommendation for optimizing the DMTMM-mediated amidation of sodium alginate, emphasizing the importance of pH values during the reaction.

General chemoselective hindered amide coupling enabled by TCFH-catalytic Oxyma and transient imine protection

We report a general chemoselective strategy for amide bond formation with poorly nucleophilic amines in the presence of reactive primary alcohols or amines as the competing nucleophiles. The selectivity for less reactive amines over competing alcohols was achieved using TCFH and catalytic Oxyma as a highly reactive, inexpensive, and safe reagent combination. By temporarily masking more reactive amines as imines through the use of electron-deficient aldehydes, the hindered amines could be similarly coupled with high efficiency and selectivity.

Surface Functionalization of Elastomers with Biopolymers

Biopolymer coatings on elastomeric surfaces have significant impact for advancements in biomedicine as they combine flexible devices with complex biological functionality. Biopolymers offer increased ability for antimicrobial coatings, sensing of relevant biological markers, and controlled drug delivery. The methodologies available to conjugate these important biopolymers to flexible elastomeric substrates are vast and rapidly evolving. This chapter aims to compile methodologies across the application space of biopolymer conjugation to elastomers. We present a guide to the field and methods ranging from surface activation and functionalization, grafting-to and grafting-from of biopolymers, and characterization of the resulting substrates.

Biomimetic Dehydrogenative Intermolecular Formal Allylic Amidation of Branched α-Olefins

Allylic amide moieties are commonly encountered in natural products and are privileged structures in pharmaceuticals and agrochemicals. Moreover, because allylic amide can be to converted into an array of high-value motifs, they have been widely employed in organic synthesis. However, the development of catalytic systems for intermolecular allylic amidation of olefins, particularly branched α-olefins, has proven to be challenging. Here, a biomimetic, synergistic catalytic method is reported that combines photoredox, cobalt, and Brønsted base catalysis for the synthesis of substituted allylic amides from branched α-olefins and simple imides without using oxidants. This low-cost, operationally simple method features a broad substrate scope and excellent functional group compatibility. Moreover, it is successfully used for the functionalization of several structurally complex molecules demonstrating the method's potential utility for medicinal chemistry applications. Mechanistic studies revealed that C(sp3)─N bond formation is mediated by a nitrogen-centered radical intermediate, which is generated via a sequence involving deprotonation and single-electron oxidation.

Aerobic Reconstruction of Amines to Amides: A C-N/C-C Bond Cleavage Approach

Herein, an aerobic reconstruction of amines to amides via C(sp3)-N bond and C(sp2)-C(sp3) bond cleavage is described. This method features a metal-free reaction, insensitivity to oxygen or moisture, and ambient air as the terminal oxidant. Preliminary mechanistic studies suggest that the reaction pathway of amine oxidation, followed by imine exchange and Beckmann rearrangement, is involved.

Development of a Triazinyluronium-Based Dehydrative Condensing Reagent with No Heteroatomic Bonds

A triazinyluronium-based dehydrative condensing reagent, 2-(4,6-dimethoxy-1,3,5-triazin-2-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (DMT-TU), has been developed. Unlike commonly used guanidinium- and uronium-based reagents, DMT-TU does not contain high-energy N-N and N-O bonds, reducing its explosivity, as suggested by differential scanning calorimetry. Using DMT-TU in the presence of iPr2EtN at room temperature, carboxylic acids and amines were effectively converted to their corresponding amides. Additionally, peptide bond formation with DMT-TU exhibited suppressed racemization ratios.

Defect-Engineered Metal-Organic Frameworks as Bioinspired Heterogeneous Catalysts for Amide Bond Formation

The synthesis of amides from amines and carboxylic acids is the most widely carried out reaction in medicinal chemistry. Yet, most amide couplings are still conducted using stoichiometric reagents, leading to significant waste; few synthetic catalysts for this transformation have been adopted industrially due to their limited scope and/or poor recyclability. The majority of catalytic approaches focus on a single activation mode, such as enhancing the electrophilicity of the carboxylic acid partner using a Lewis acid. In contrast, nature effortlessly forges and breaks amide bonds using precise arrays of Lewis/Brønsted acidic and basic functional groups. Drawing inspiration from these systems, herein we report a simple defect engineering strategy to colocalize Lewis acidic Zr sites with other catalytically active species within porous metal-organic frameworks (MOFs). Specifically, the combination of pyridine N-oxide and Zr open metal sites within the defective framework MOF-808-py-Nox produces a heterogeneous catalyst that facilitates amide bond formation with broad functional group compatibility from amines and carboxylic acids, esters, or primary amides. Extensive density functional theory (DFT) calculations using cluster models support that the formation of a hydrogen-bonding network at the defect sites facilitates amide bond formation in this material. MOF-808-py-Nox can be recycled at least five times without losing significant crystallinity, porosity, or catalytic activity and can be employed in continuous flow. This defect engineering strategy can be potentially generalized to produce libraries of catalytically active MOFs with different combinations of colocalized functional groups.

A practical method for the synthesis of small peptides using DCC and HOBt as activators in H2O-THF while avoiding the use of protecting groups

The synthesis of peptides in solution proceeds through successive steps involving the removal of a protecting group and the formation of the peptide bond. While most methodological efforts have focused on the development of new protecting groups and coupling agents, methodologies based on minimal protecting groups have been less explored. In this research, a peptide synthesis methodology was developed using DCC and HOBt in THF-H2O, avoiding the use of protecting groups, reducing reaction times, and reusing HOBt during successive couplings. The reaction conditions allow the production of peptides that can directly serve as the starting material for the next coupling, leading to the creation of small peptide sequences, which in turn are precursors to biologically important molecules. Here we explore the example of Sansalvamide as a template for other active peptides. Unlike SPPS, our methodology constructs the sequence from the N-terminus to C-terminus. This unique approach could streamline peptide synthesis and facilitate the development of complex peptides efficiently.

Theoretical study of Ni(0)-catalyzed intermolecular hydroamination of branched 1,3-dienes: reaction mechanism, regioselectivity, enantioselectivity, and prediction of the ligand

CONTEXT

Nickel-catalyzed hydroamination of dienes with phenylmethanamines was studied theoretically to investigate reaction mechanism. These calculated results revealed that Ni-catalyzed hydroamination began with the O - H bond activation of trifluoroethanol, including three important elementary steps: the ligand-to-ligand hydrogen migration, the nucleophilic attack of phenylmethanamine, and hydrogen migration. The nucleophilic attack of phenylmethanamine was the rate-determining step, and the branched product of 3,4-addition with (S)-chirality was the most dominant. The N - H bond activation of phenylmethanamine occurred more difficultly than the O - H bond of trifluoroethanol, because of high ΔG and ΔG≠. In addition, the origin of regioselectivity and enantioselectivity, and prediction of the ligand were also discussed in this text.

METHODS

All computations were performed with Gaussian09 program. All geometries were optimized at the ωB97XD/6-31G(d,p) level (SDD for Ni), and to obtain more accurate potential energy, single-point calculation was carried out at the ωB97XD/cc-pVDZ level (SDD for Ni). The Cramer-Truhlar continuum solvation model (SMD) was used to evaluate solvation effect of mesitylene, and a correction of the translational entropy was made with the procedure of Whitesides group.

Ligand-controlled palladium-catalyzed regiodivergent aminocarbonylation of tert-alcohols

Alcohols are widely available, abundant, and diverse in both commercial and natural resources. They possess low toxicity, making their use as reactants for carbonylation extremely promising. Herein, we present a robust ligand-controlled regioselective aminocarbonylation of tert-alcohols. Utilizing a commercially available palladium salt and ligand as the catalytic system, various amides containing an α-quaternary carbon or β-substituted amides can be selectively accessible. Notably, water is the only by-product of this reaction, which is consistent with the concept of green chemistry. This protocol offers a broad substrate scope, high regioselectivity, and excellent performance in scale-up reactions.

Enrichable Protein Footprinting for Structural Proteomics

Protein footprinting is a useful method for studying protein higher order structure and conformational changes induced by interactions with various ligands via addition of covalent modifications onto the protein. Compared to other methods that provide single amino acid-level structural resolution, such as cryo-EM, X-ray diffraction, and NMR, mass spectrometry (MS)-based methods can be advantageous as they require lower protein amounts and purity. As with other MS-based proteomic methods, such as post-translational modification analysis, enrichment techniques have proven necessary for both optimal sensitivity and sequence coverage when analyzing highly complex proteomes. Currently used reagents for footprinting via covalent labeling, such as hydroxyl radicals and carbodiimide-based methods, do not yet have a suitable enrichment method, limiting their applicability to whole proteome analysis. Here, we report a method for enrichable covalent labeling built upon the GEE/EDC system commonly used to covalently label aspartic acid and glutamic acid residues. Novel labeling reagents containing alkynyl functionality can be "clicked" to any azido-containing molecule with copper-catalyzed azide-alkyne cycloaddition (CuAAC), allowing for enrichment or further labeling. Multiple azide- and alkyne-containing GEE-like molecules were tested, and the most efficient method was determined to be the EDC-facilitated coupling of glycine propargyl amide (GPA) to proteins. The pipeline we report includes clicking via CuAAC to a commercially available biotin-azide containing a photocleavable linker, followed by enrichment using a streptavidin resin and subsequent cleavage under ultraviolet light. The enrichment process was optimized through the screening of clickable amines, coupling reagents, and enrichment scaffolds and methods with pure model proteins and has also been applied to complex mixtures of proteins isolated from the model plant, Arabidopsis thaliana, suggesting that our method may ultimately be used to measure protein conformation on a proteomic scale.

Radio frequency gradient enhanced diffusion-edited semi-solid state NMR spectroscopy for detailed structural characterization of chemically modified hyaluronic acid hydrogels

Applications of functionalized hyaluronic acid (HA) hydrogels for numerous biomedical applications requires their detailed structural characterization. Since these materials are prepared by multistep chemical modifications in the solid phase and not amenable to characterization by standard analytical tools, we employed high-resolution solid-state NMR spectroscopy to gain detailed insights into the structures of the functionalized HA hydrogels. Divinyl sulfone crosslinked HA hydrogels were converted into maleimide-functionalized hydrogels, which were subjected to chemoselective thiol-maleimide reaction using L-cysteine as the protein mimetic thiol reagent. To overcome challenges associated with obtaining high-resolution NMR spectra of crosslinked hydrogels (such as line broadening and overlapping of signals of the hydrogel with those of residual reagents and solvents used during multi-step reaction processes on insoluble polymer matrices), we devised a radio frequency mediated diffusion-edited semi solid-state NMR technique. This technique enabled us to record NMR spectra of hydrogels exclusively by effectively suppressing signals associated with low molecular weight impurities. Thus, it became possible to perform in-depth characterization of these chemically modified HA hydrogels including quantification of reaction outcome for each reaction step.

Low-valent germanium and tin hydrides as catalysts for hydroboration, hydrodeoxygenation (HDO), and hydrodesulfurization (HDS) of heterocumulenes

The low-valent germanium and tin hydrides, [LMH; L = {(ArHN)(ArN)-CN-C(NAr)(NHAr); Ar = 2,6-Et2-C6H3}; M = Ge; (Ge-1), Sn (Sn-2)] bearing bis-guanidinato anions are employed as catalysts for chemoselective reduction of heterocumulenes via hydroboration reactions. This protocol demonstrates that a wide range of carbodiimides (CDI), isocyanates, isothiocyanates, and isoselenocyanates undergo partial reduction, yielding the corresponding N-boryl formamidine, N-boryl formamide, N-boryl thioformamide, and N-boryl selenoformamide products, respectively. Isocyanates and isothiocyanates are further converted into N-boryl methyl amines through hydrodeoxygenation (HDO) and hydrodesulfurization (HDS) reactions in the presence of catalyst Ge-1. Additionally, catalyst Sn-2 exhibits excellent inter and intra-molecular chemoselectivity over other functional groups. Based on stoichiometric experiments, a plausible catalytic cycle for chemoselective hydroboration of heterocumulenes is proposed.

Leveraging the Redox Promiscuity of Nickel To Catalyze C-N Coupling Reactions

This perspective details advances made in the field of Ni-catalyzed C-N bond formation. The use of this Earth abundant metal to decorate amines, amides, lactams, and heterocycles enables direct access to a variety of biologically active and industrially relevant compounds in a sustainable manner. Herein, different strategies that leverage the propensity of Ni to facilitate both one- and two-electron processes will be surveyed. The first part of this Perspective focuses on strategies that facilitate C-N couplings at room temperature by accessing oxidized Ni(III) intermediates. In this context, advances in photochemical, electrochemical, and chemically mediated processes will be analyzed. A special emphasis has been put on providing a comprehensive explanation of the different mechanistic avenues that have been proposed to facilitate these chemistries; either Ni(I/III) self-sustained cycles or Ni(0/II/III) photochemically mediated pathways. The second part of this Perspective details the ligand designs that also enable access to this reactivity via a two-electron Ni(0/II) mechanism. Finally, we discuss our thoughts on possible future directions of the field.

Enantioselective Deoxygenative Amino-Cyanation of Carboxylic Acids via Ti-Multicatalysis

Carboxylic acids are valued synthetic building blocks that offer shelf life stability, structural diversity, and wide commercial availability. Despite the remarkable synthetic utility of carboxylic acids, a direct enantioselective deoxygenative functionalization of carboxylic acids remains rare. We present enantioselective deoxygenative amino-cyanation of carboxylic acids using a novel TiIV-multicatalytic system that catalytically modified each C-O bond of carboxylic acid to C-C, C-N, and C-H bonds, generating enantio-enriched chiral α-amino nitriles (up to 98:2 er).

Synthesis, crystal structure and Hirshfeld surface analysis of N-(4-meth-oxy-phen-yl)picolinamide

The synthesis, crystal structure, and Hirshfeld surface analysis of N-(4-meth-oxy-phen-yl)picolinamide (MPPA), C13H12N2O2, are presented. MPPA crystallizes in the monoclinic space group P21/n, with a single mol-ecule in the asymmetric unit. Structural analysis reveals that all non-hydrogen atoms are nearly coplanar, and the mol-ecule exhibits two intra-molecular hydrogen bonds that stabilize its conformation. Supra-molecular features include significant inter-molecular inter-actions, primarily C-H⋯π and various hydrogen bonds, contributing to the overall crystal cohesion, as confirmed by energy framework calculations yielding a total inter-action energy of -138.3 kJ mol-1. Hirshfeld surface analysis indicates that H⋯H inter-actions dominate, followed by C⋯H and O⋯H inter-actions, highlighting the role of van der Waals forces and hydrogen bonding in crystal packing.

Computer-Aided Identification and Design of Ligands for Multi-Targeting Inhibition of a Molecular Acute Myeloid Leukemia Network

BACKGROUND/OBJECTIVES

Acute myeloid leukemia (AML) is characterized by therapeutic failure and long-term risk for disease relapses. As several therapeutic targets participate in networks, they can rewire to eventually evade single-target drugs. Hence, multi-targeting approaches are considered on the expectation that interference with many different components could synergistically hinder activation of alternative pathways and demolish the network one-off, leading to complete disease remission.

METHODS

Herein, we established a network-based, computer-aided approach for the rational design of drug combinations and de novo agents that interact with many AML network components simultaneously.

RESULTS

A reconstructed AML network guided the selection of suitable protein hubs and corresponding multi-targeting strategies. For proteins responsive to existing drugs, a greedy algorithm identified the minimum amount of compounds targeting the maximum number of hubs. We predicted permissible combinations of amiodarone, artenimol, fostamatinib, ponatinib, procaine, and vismodegib that interfere with 3-8 hubs, and we elucidated the pharmacological mode of action of procaine on DNMT3A. For proteins that do not respond to any approved drugs, namely cyclins A1, D2, and E1, we used structure-based de novo drug design to generate a novel triple-targeting compound of the chemical formula C15H15NO5, with favorable pharmacological and drug-like properties.

CONCLUSIONS

Overall, by integrating network and structural pharmacology with molecular modeling, we determined two complementary strategies with the potential to annihilate the AML network, one in the form of repurposable drug combinations and the other as a de novo synthesized triple-targeting agent. These target-drug interactions could be prioritized for preclinical and clinical testing toward precision medicine for AML.

Perspectives of aminoacylases in biocatalytic synthesis of N-acyl-amino acids surfactants

Many industrial processes are performed using harmful chemicals. The current technical synthesis of N-acyl-amino acids relies on acyl chlorides, which are typically obtained from phosgene chemistry. A greener alternative is the application of whole cells or enzymes to carry out synthesis in an environmentally friendly manner. Aminoacylases belong to the hydrolase family and the resolution of racemic mixtures of N-acetyl-amino acids is a well-known industrial process. Several new enzymes accepting long-chain fatty acids as substrates were discovered in recent years. This article reviews the synthetic potential of aminoacylases to produce biobased N-acyl-amino acid surfactants. The focus lays on a survey of the different types of aminoacylases available for synthesis and their reaction products. The enzymes are categorized according to their protein family classification and their biochemical characteristics including substrate spectra, reaction optima and process stability, both in hydrolysis and under process conditions suitable for synthesis. Finally, the benefits and future challenges of enzymatic N-acyl-amino acid synthesis with aminoacylases will be discussed. KEY POINTS: • Enzymatic synthesis of N-acyl-amino acids, biobased surfactants by aminoacylases.

Metal and Photocatalyst-Free Amide Synthesis via Decarbonylative Condensation of Alkynes and Photoexcited Nitroarenes

Depending on the intrinsic photoactivity of nitroarenes, we herein developed a practical Brønsted acid-catalyzed decarbonylative amide synthesis from alkynes and photoexcited nitroarenes without any metal or photocatalyst. This method exhibited compatibility with water and air, broad substrate applicability, marvelous functional group tolerance, and wide applications in scale-up synthesis, late-stage functionalization, and total synthesis. Mechanism studies and DFT calculations supported that a 1,3,2-dioxazole intermediate was involved, and gaseous carbon monoxide was the only byproduct during amide construction.

Polyphosphoric Acid-Promoted Efficient Synthesis of Cinnamides via Aldol Condensation of Amide

Cinnamides are common core structures that exist in a great number of pharmaceuticals and natural products. The development of efficient methods for preparing cinnamides is in great need. We report herein an efficient polyphosphoric acid (PPA)-promoted direct aldol condensation of an amide for the convenient and straightforward preparation of cinnamides. A variety of cinnamides were obtained in moderate-to-excellent yields (65-89%). This strategy features the use of equivalent amides and a short reaction time.

Chemical Derivatization and Paper Spray Ionization Mass Spectrometry for Fast Screening of Retinoic Acid in Cosmetics

As a prescription drug, retinoic acid is listed as a banned cosmetic additive in the EU and China regulations. Currently, spectrophotometric methods, including thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and HPLC-MS/MS, are commonly used for the determination of retinoic acid. As these conventional methods require complex pretreatment and are time-consuming, chemical derivatization combined with paper spray ionization mass spectrometry was developed for the fast detection of retinoic acid in cosmetics. N,N-dimethylpiperazine iodide (DMPI) was utilized as a derivatization reagent. Carboxylic acid in retinoic acid was derivatized to carry a positive charge and was subjected to mass spectrometry analysis. Results showed that compared with non-derivatized compounds, the detection limit was increased by about 50 times. The linearity in the range of 0.005-1 μg·mL-1 was good. The limit of detection (LOD) was 0.0013 μg·mL-1, and the limit of quantification (LOQ) was 0.0043 μg·mL-1. The recoveries of spiked samples were in the range of 95-105%, and the RSDs were below 5%. Derivatization and paper spray ionization MS render a quick, sensitive, and accurate method for the detection of retinoic acid in a complex matrix.

To homeostasis and beyond! Recent advances in the medicinal chemistry of heterobifunctional derivatives

The field of induced proximity therapeutics has expanded dramatically over the past 3 years, and heterobifunctional derivatives continue to form a significant component of the activities in this field. Here, we review recent advances in the field from the perspective of the medicinal chemist, with a particular focus upon informative case studies, alongside a review of emerging topics such as Direct-To-Biology (D2B) methodology and utilities for heterobifunctional compounds beyond E3 ligase mediated degradation. We also include a critical evaluation of the latest thinking around the optimisation of physicochemical and pharmacokinetic attributes of these beyond Role of Five molecules, to deliver appropriate therapeutic exposure in vivo.

Efficient synthesis of amides from secondary alcohols and CH3CN promoted by Fe(NO3)3·9H2O

The Ritter reaction is the most attractive method for synthesizing amides, and various acids have been used to promote this reaction. Compared to these acids, Fe(NO3)3·9H2O is less toxic and costly, and it shows relatively high Lewis acidity and great catalytic activity. In this study, a simple and efficient protocol involving Fe(NO3)3·9H2O as an additive for the synthesis of amides was developed. Various secondary alcohols could be reacted with CH3CN to obtain their corresponding products, with CH3CN being used as a reactant and solvent. This protocol was found to be applicable to a wide range of alcohols and nitrile substrates. In general, it was found that substrates containing electron-donating-groups offered the corresponding amides in good to excellent yields, while those with electron-withdrawing groups offered low to moderate yields. Meanwhile, this approach was scalable to the gram level, offering an attractive opportunity for further application in organic synthesis.