N-Acylbenzotriazoles: neutral acylating reagents for the preparation of primary, secondary, and tertiary amides

Dearomatization of (Hetero)arenes through Photodriven Interplay between Polysulfide Anions and Formate

The facile construction of C(sp3 )-rich carbo- and heterocyclic compounds is a pivotal synthetic strategy to foster contemporary drug discovery programs. The downstream dearomatization of readily accessible two-dimensional (2D) planar arenes represents a direct pathway towards accessing three-dimensional (3D) aliphatic scaffolds. Here, we demonstrate that polysulfide anions are capable of catalyzing a dearomatization process of substituted naphthalenes, indoles, and other related heteroaromatic compounds in the presence of potassium formate and methanol under visible light irradiation. The developed protocol exhibits broad functional group tolerance, operational simplicity, scalability, and cost-effectiveness, representing a practical and sustainable synthetic tool for the arene dearomatization.

B2(OH)4-Mediated Reductive Transamidation of N-Acyl Benzotriazoles with Nitro Compounds En Route to Aqueous Amide Synthesis

We herein developed a reductive transamidation reaction between N-acyl benzotriazoles (AcBt) and organic nitro compounds or NaNO₂ under mild conditions. This protocol employed the stable and readily available B₂(OH)₄ as the reducing agent and H₂O as the ideal solvent. N-Deuterated amides can be synthesized when conducting the reaction in D₂O. A reasonable reaction mechanism involving bond metathesis between the AcBt amide and amino boric acid intermediate was proposed to explain the unique nature of AcBt.

Vicinal Diaryl-Substituted Isoxazole and Pyrazole Derivatives with In Vitro Growth Inhibitory and In Vivo Antitumor Activity

The vicinal diaryl heterocyclic framework has been widely used for the development of compounds with significant bioactivities. In this study, a series of diaryl heterocycles were designed and synthesized based on an in-house diaryl isoxazole derivative (9), and most of the newly synthesized derivatives demonstrated moderate to good antiproliferative activities against a panel of hepatocellular carcinoma and breast cancer cells, exemplified with the diaryl isoxazole 11 and the diaryl pyrazole 85 with IC₅₀ values in the range of 0.7-9.5 μM. Treatments with both 11 and 85 induced apoptosis in these tumor cells, and they displayed antitumor activity in vivo in the Mahlavu hepatocellular carcinoma and the MDA-MB-231 breast cancer xenograft models, indicating that these compounds could be considered as leads for further development of antitumor agents. Important structural features of this compound class for the antitumor activity have also been proposed, which warrant further exploration to guide the design of new and more potent diaryl heterocycles.

Design, synthesis, in silico and biological evaluations of novel polysubstituted pyrroles as selective acetylcholinesterase inhibitors against Alzheimer's disease

The objective of this study was to design new polysubstituted pyrrole derivatives as selective acetylcholinesterase (AChE) inhibitors to target Alzheimer's disease. In this context, a highly efficient, one-pot, sequential, multi-component synthesis of a diverse range of polysubstituted pyrroles was developed through a sequential domino strategy by the condensation of amines with 1,1-bis(methylthio)-2-nitroethene (BMTNE), Knovenagle reaction of arylglyoxals with malono derivatives and subsequent Michael addition and intramolecular cyclization reaction in EtOH at reflux. Thirty-nine synthesized compounds were evaluated as AChE and butyrylcholinesterase (BChE) inhibitors. Among the synthesized compounds, compound 4ad (IC₅₀ = 2.95 ± 1.31 µM) was the most potent and selective AChE inhibitor with no significant inhibition against butyrylcholinesterase BChE. A kinetic study of 4ad revealed that this compound inhibited AChE in an uncompetitive mode. Based on a molecular modeling study, compound 4ad due to its small size properly fitted into the active site of AChE compared to BChE and stabilized by H-bond and hydrophobic interactions with the critical residues of the AChE binding pocket. Consequently, it was proposed that the 4ad derivative can be an ideal lead candidate against AD with a simple and practical operation of synthetic procedures.

Nickel-Catalyzed Reductive Cross-Coupling of N-Acyl and N-Sulfonyl Benzotriazoles with Diverse Nitro Compounds: Rapid Access to Amides and Sulfonamides

Herein we report a Ni-catalyzed reductive transamidation of conveniently available N-acyl benzotriazoles with alkyl, alkenyl, and aryl nitro compounds, which afforded various amides with good yields and a broad substrate scope. The same catalytic reaction conditions were also applicable for N-sulfonyl benzotriazoles, which could undergo smooth reductive coupling with nitroarenes and nitroalkanes to afford the corresponding sulfonamides.

Alternative and Uncommon Acylating Agents - An Alive and Kicking Methodology

Functionalizing and derivatising organic molecules is a centerpiece in organic synthesis. Succinctly manipulating and installing acyl moieties in organic molecules spurred the interest of chemists owing to its occurrence in natural products, bioactive molecules, pharmaceuticals, and advanced materials. Traditionally, access to acylation reaction was achieved by Friedel-Crafts reaction, Schotten-Baumann, and Vilsmeier-Haack acylation, however, these protocols own pitfalls. Further to make the acylation process attractive and environmentally friendly, toluene, aldehydes, alcohols, α-keto acids, amines, amides, esters, ethers, nitriles, alkynes, alkenes, ketenes, N-acylbenzotriazoles, ketones, thioacids, oximes, thiazolium carbinols, PIDA, diacyl disulfides and acyl salts were used as an acyl surrogates/reagents. Amusingly, these acylating reagents are considered uncommon and alternative to carboxylic acids, acid chlorides and acetic anhydrides. This short review aims to encompass the usage of acylating agents in transition-metal, metal-free, light-driven and other demanding conditions, and thus reveals their practicality.

Synthesis of Azido and Triazolyl Purine Ribonucleosides

Here, we describe detailed synthetic protocols for preparation of 6-amino/thio-2-triazolylpurine ribonucleosides. First, 9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)-2,6-diazido-9H-purine, to be used as a key starting material, is synthesized in an S_N Ar reaction with NaN₃ starting from commercially available 9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)-2,6-dichloro-9H-purine. Next, 2,6-bis-triazolylpurine ribonucleoside is obtained in a CuAAC reaction between diazidopurine derivative and phenyl acetylene, and used in S_N Ar reactions with N- and S-nucleophiles. In these reactions, the triazolyl ring at the purine C6 position acts as a good leaving group. Cleavage of acetyl protecting groups from the ribosyl moiety is achieved in presence of piperidine. In the S_N Ar reaction with amino acid derivatives, the acetyl groups remain intact. Moreover, 9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)-2,6-diazido-9H-purine is selectively reduced at the C6 position using a CuSO₄ ·5H₂ O/sodium ascorbate system. This provides a straightforward approach for synthesis of 9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)-6-amino-2-azido-9H-purine. © 2021 Wiley Periodicals LLC Basic Protocol 1: Synthesis of 6-amino-2-triazolylpurine ribonucleosides Basic Protocol 2: Synthesis of 6-thio-2-triazolylpurine ribonucleosides Basic Protocol 3: Synthesis of 6-amino-2-azidopurine ribonucleoside.

Recent approaches towards one-carbon homologation-functionalization of aldehydes

One-carbon homologation-functionalization in organic synthesis is a quite challenging and difficult task in terms of atom economy, ease of reaction, selectivity and number of steps involved. Due to the reactivity associated with most classes of carbonyls, these groups have always attracted a great deal of attention from synthetic chemists to transform them into various functionalities. In this context various researchers developed new methods for one-carbon extension-functionalization of carbonyls that serve as effective synthetic methodologies and are widely used in target-oriented and natural product synthesis. On account of the vast applicability associated with these transformations, herein we seek to summarize and highlight the important synthetic achievements in this advancing arena for various one-carbon homologation cum functionalization reactions of aldehydes and deep dive into some modern approaches adopted by organic chemists.

Environmental applications of a biodegradable cysteine-based surfactant

An improved method has been developed for the efficient synthesis of octanoyl-cysteine in single-chain form (N-octanoyl-cys) which operates as a surfactant over a wide pH range, is easily decomposed into natural products and has a high product yield. The compound offers an environmentally acceptable agent for the adsorption of a range of heavy metals from contaminated waters/soils, and it could also be used in general household detergents or personnel-cleaner formulations, and even in toothpastes. The surfactant was used as a co-surfactant for flotation of perfluorooctanoic acid (PFOA), a per/poly-fluoroalkyl substance (PFAS). The new surfactant produced significant foaming and removed 70% of the PFOA after 30min of foam fractionation. The compound is also potentially useful in facilitating the release of PFAS compounds; these are negatively charged and often bound to charged particles in sand, clay, and humic-acid-coated materials and microorganisms via bridging multivalent ions, such as Ca²⁺, Mg²⁺, Al³⁺ and Fe³⁺, as well as a range of other heavy-metal ions present in soil to varying degrees. In soils (and also in contaminated water), the common chelating agent EDTA is often used to encapsulate these ions (e.g. Ca²⁺, the dominant ion in soil) at moderately high pH to aid in the release of the bound PFAS compounds. However, it would be more environmentally acceptable to use this new biodegradable surfactant, which could combine chelation with foam-fractionation separation of surface-active (e.g. PFAS) components in soils.

An Efficient Greener Approach for N-Acylation of Amines in Water Using Benzotriazole Chemistry

A straightforward, mild and cost-efficient synthesis of various arylamides in water was accomplished using versatile benzotriazole chemistry. Acylation of various amines was achieved in water at room temperature as well as under microwave irradiation. The developed protocol unfolds the synthesis of amino acid aryl amides, drug conjugates and benzimidazoles. The environmentally friendly synthesis, short reaction time, simple workup, high yields, mild conditions and free of racemization are the key advantages of this protocol.

1-(2H-Azirine-2-carbonyl)benzotriazoles: building blocks for the synthesis of pyrrole-containing heterocycles

A one-pot method was developed for the preparation of 2H-azirine-2-carbonylbenzotriazoles, formed by the reaction of benzotriazole with 2H-azirine-2-carbonyl chlorides, which were generated by the Fe(ii)-catalyzed isomerization of 5-chloroisoxazoles. The Co(ii)-catalyzed reaction of 2H-azirine-2-carbonylbenzotriazoles with 1,3-diketones provides 2-((benzotriazol-1-yl)carbonyl)pyrroles in moderate to good yields. Base-promoted annulations of 2-((benzotriazol-1-yl)carbonyl)pyrroles with aldehydes, ketones, isocyanates and isothiocyanates afford various substituted pyrrolo[1,2-c]oxazole and 1H-pyrrolo[1,2-c]imidazole derivatives in moderate to high yields. The 6-acyl group of these adducts can be removed by triflic acid, giving further new pyrrolo-fused O- and N-heterocycles, such as 6-unsubstituted pyrrolo[1,2-c]oxazol-1(3H)-one and 1H-pyrrolo[1,2-c]imidazole-1,3(2H)-dione, while the 6-acetyl substituent of 1H-pyrrolo[1,2-c]imidazole-1,3(2H)-dione, when treated with POCl3/pyridine, is transformed into the 6-ethynyl substituent.

Synthesis of Fluorinated Amide Derivatives via a Radical N-Perfluoroalkylation-Defluorination Pathway

A one-pot approach to fluorinated hydroxamic acid, amide, and thioamide derivatives is reported. The reaction proceeds via an N-perfluoroalkylation of nitrosoarenes with perfluoroalkanesulfinates, resulting in labile N-perfluoroalkylated hydroxylamines. By the addition of suitable additives, a controllable oxy/thiodefluorination of the fluorinated hydroxylamine intermediates was achieved. The method highlights N-perfluoroalkylated amines as versatile intermediates for further synthesis.

N,N-Dimethylaminoxy Carbonyl, a Polar Protecting Group for Efficient Peptide Synthesis

Peptide coupling with minimal protection is one of the desired methods for the synthesis of peptides and proteins. To achieve regioselective amide bond formation, side chain protection is often essential; however, protecting groups potentially diminish peptide solubility and render the polar polyamide chain amphipathic due to their apolar nature. In this manuscript, we describe a new protecting group, N,N-dimethylaminoxy carbonyl (Dmaoc), and its use in peptide coupling reactions. The Dmaoc group has a relatively polar character compared to the Boc group, which is a conventional protecting group for the N^ε-amine of Lys residues. This polar protecting group is removable by reduction in the buffer containing (±)-dithiothreitol (DTT). Furthermore, the Dmaoc group proved compatible with peptide ligation strategies featuring the activation of N-acyl diaminobenzamides (Dbz) with sodium nitrate to generate the respective benzotriazole leaving group. The Dmaoc/Dbz strategy described in this manuscript provides a new method for the chemical synthesis of peptides.

A Facile Synthesis of Acylhydrazines from Acylbenzotriazoles

Acylbenzotriazoles were found to react with substituted hydrazines and aqueous hydrazine under very mild conditions, thus affording a facile synthesis of three types of acylhydrazines in moderate to excellent yields.

An Efficient Synthesis of α,β-Unsaturated Thiol Esters

α,β-Unsaturated thiol esters were synthesised conveniently from samarium thiolates and α,β-unsaturated N-acylbenzotriazoles under mild conditions with good to excellent yields.

Copper Complexes of Multidentate Carboxamide Ligands

The copper coordination chemistry of two multidentate carboxamido ligands derived from HL¹ (offering two quinolyl and one carboxamide donor) and H₄L² (with two pyridine(dicarboxamido) units linked by naphthalene spacers) was explored. The former was chosen because upon deprotonation it would provide a monoanionic mer-coordinating N-donor set that would model the putative deprotonated form of the His-brace in copper monooxygenases, while the latter was designed to bind two copper ions and enable comparisons to other systems with different ligand spacers. Upon reaction with Cu(I)-mesityl, HL¹ yielded a symmetric dimer (L¹Cu)₂ in which each bis(quinolyl)amide ligand binds via two N-donors to one Cu(I) ion and via the third to the other Cu(I) center. Monomeric Cu(II) complexes [L ¹ Cu(H ₂ O) ₂ ](OTf) and L ¹ ₂ Cu were also characterized. Treatment of H₄L² with Cu(OTf)₂ and excess Me₄NOH (in CH₃CN, pyridine/H₂O, or MeOH) yielded complexes with anions of general formula [L ² Cu ₂ (X)]^n-, where X = CH₃CONH^- (n = 1), CO₃ ^2- (n = 2), or MeO^- (n = 1). X-ray structures of these complexes revealed the (L²)^4- ligand binding to two Cu(II) ions in an open paddle-wheel geometry, with an additional bridging ligand (X) completing the square planar coordination sphere of each metal ion. The open paddlewheel motif differs from the more 'open' puckered geometry seen with related ligands with different spacer units.

Strategies towards the synthesis of anti-tuberculosis drugs

In this report, we reviewed the strategies towards the synthesis of anti-tuberculosis drugs. They include semisynthetic approaches, resolution based strategies, microbial transformations, solid phase synthesis, and asymmetric synthesis.

ROCK inhibitors 2. Improving potency, selectivity and solubility through the application of rationally designed solubilizing groups

Solubilizing groups have been frequently appended to kinase inhibitor drug molecules when solubility is insufficient for pharmaceutical development. Such groups are usually located at substitution sites that have minimal impact on target activity. In this report we describe the incorporation of solubilizing groups in a class of Rho kinase (ROCK) inhibitors that not only confer improved solubility, but also enhance target potency and selectivity against a closely related kinase, PKA.

ROCK inhibitors 3: Design, synthesis and structure-activity relationships of 7-azaindole-based Rho kinase (ROCK) inhibitors

Rho kinase (ROCK) inhibitors are potential therapeutic agents for the treatment of a variety of disorders including hypertension, glaucoma and erectile dysfunction. Here we disclose a series of potent and selective ROCK inhibitors based on a substituted 7-azaindole scaffold. Substitution of the 3-position of 7-azaindole led to compounds such as 37, which possess excellent ROCK inhibitory potency and high selectivity against the closely related kinase PKA.

Walking and rolling of crystals induced thermally by phase transition

The mechanical motion of materials has been increasingly explored in terms of bending and expansion/contraction. However, the locomotion of materials has been limited. Here, we report walking and rolling locomotion of chiral azobenzene crystals, induced thermally by a reversible single-crystal-to-single-crystal phase transition. Long plate-like crystals with thickness gradient in the longitudinal direction walk slowly, like an inchworm, by repeated bending and straightening under heating and cooling cycles near the transition temperature. Furthermore, thinner, longer plate-like crystals with width gradient roll much faster by tilted bending and then flipping under only one process of heating or cooling. The length of the crystal is shortened above the transition temperature, which induces bending due to the temperature gradient to the thickness direction. The bending motion is necessarily converted to the walking and rolling locomotion due to the unsymmetrical shape of the crystal. This finding of the crystal locomotion can lead to a field of crystal robotics.

DBN hexafluorophosphate salts as convenient sulfonylating and phosphonylating agents

Air-stable N-sulfonyl and N-phosphonyl DBN hexafluorophosphate salts have been synthesised under mild conditions as sulfonylating and phosphonylating agents. These salts are highly efficient in the sulfonylation and phosphonylation of a range of N- and O-nucleophiles to generate sulfonamides, sulfonate esters, phosphoramidates and phosphonate esters in good yields.

Highly selective acylation of polyamines and aminoglycosides by 5-acyl-5-phenyl-1,5-dihydro-4H-pyrazol-4-ones

5-Acyl-5-phenyl-1,5-dihydro-4H-pyrazol-4-ones, accessible from arylpropargyl phenyldiazoacetates, are highly selective acyl transfer reagents for di- and polyamines, as well as aminoalcohols and aminothiols. As reagents with a carbon-based leaving group, they have been applied for benzoyl transfer with a broad selection of substrates containing aliphatic amino in combination with other competing nucleophilic functional groups. The substrate scope and levels of selectivity for direct benzoyl transfer exceed those of known benzoylating reagents. With exceptional selectivity for acylation between primary amines bound to primary and secondary carbons, these new reagents have been used in direct site-selective monobenzoylation of aminoglycoside antibiotics.

Diastereoselective synthesis of tetrahydropyrans via Prins–Ritter and Prins–arylthiolation cyclization reactions

Highly diastereoselective Prins–Ritter and Prins-arylthiolation cyclization reactions have been developed for the synthesis of two novel classes of tetrahydropyran derivatives.

Synthesis of highly functionalized 2,2'-bipyridines by cyclocondensation of β-ketoenamides - scope and limitations

The scope of a flexible route to unsymmetrically functionalized bipyridines is described. Starting from 1,3-diketones 1a–e, the corresponding β-ketoenamines 2a–e were converted into different β-ketoenamides 3a–g by N-acylation with 2-pyridinecarboxylic acid derivatives. These β-ketoenamides were treated with a mixture of TMSOTf and Hünig’s base to promote the cyclocondensation to 4-hydroxypyridine derivatives. Their immediate O-nonaflation employing nonafluorobutanesulfonyl fluoride provided the expected 4-nonafloxy-substituted bipyridine derivatives 5a–g in moderate to good overall yields. The bipyridyl nonaflates are excellent precursors for palladium-catalyzed reactions as demonstrated by representative Suzuki and Sonogashira couplings. Thus, a library of specifically substituted bipyridine derivatives was generated, showing the versatility of the simple 1,3-diketone-based approach to this important class of ligands.