Lactam Research Articles

Electrochemical oxidative selenocyclization of olefinic amides towards the synthesis of iminoisobenzofurans

We introduced an electrochemical oxidative radical cascade cyclization of olefinic amides and diselenides without a transition-metal catalyst and external oxidant. This selenocyclization reaction provided a facile method to construct C–Se and C–O bonds in one step.

A three-component difunctionalization of N-alkenyl amides via organophotoredox radical-polar crossover.

Herein, we report a three-component organophotoredox coupling of N-alkenyl amides with α-bromocarbonyls and various nucleophiles. This transition metal-free difunctionalization protocol installs sequential C-C and C-Y (Y = S/O/N) bonds in alkenes. This reaction works with terminal and internal alkenes containing both cyclic and acyclic amides via radical-polar crossover.

Modeling of selenocysteine-derived reactive intermediates utilizing a nano-sized molecular cavity as a protective cradle.

In the biological functions of selenoproteins, various highly reactive species formed by oxidative modification of selenocysteine residues have been postulated to play crucial roles. Representative examples of such species are selenocysteine selenenic acids (Sec-SeOHs) and selenocysteine selenenyl iodides (Sec-SeIs), which have been widely recognized as important intermediates in the catalytic cycle of glutathione peroxidase (GPx) and iodothyronine deiodinase, respectively. However, examples of even spectroscopic observation of Sec-SeOHs and Sec-SeIs in either protein or small-molecule model systems remain elusive so far, most likely due to their notorious instability. For the synthesis of small-molecule model compounds of these reactive species, it is essential to suppress their very facile bimolecular decomposition such as self-condensation and disproportionation. Here we outline a novel method for the synthesis of stable small-molecule model compounds of the selenocysteine-derived reactive species, in which a nano-sized molecular cavity is used as a protective cradle to accommodate the reactive selenocysteine unit. Stabilization by the molecular cradle led to the successful synthesis of Sec-SeOHs, which are stable in solution at low temperatures, and a Sec-SeI, which can be isolated as crystals. The catalytic cycle of GPx was investigated using the NMR-observable Sec-SeOH models, and all the chemical processes proposed for the catalytic cycle of GPx, including the bypass process from Sec-SeOH to the corresponding cyclic selenenyl amide, were experimentally confirmed. Detailed protocols for the syntheses of selenopeptide derivatives bearing the molecular cradle and for the spectroscopic monitoring of their reactions are provided.

Electrochemical cyclization ofN-cyanamide alkenes with CF3SO2Na to access C,N-(bis)trifluoromethylated cyclic amidines and related compounds

An electrochemical trifluoromethylative cyclization ofN-cyanamide alkenes and alkynes is presented, which afforded (bis)-C,N-trifluoromethylated cyclic amidines, azines and amides with selective multiple bond formations in a controllable manner.

The Application of 1,2-Oxazinanes as Chiral Cyclic Weinreb Amide-Type Auxiliaries Leading to a Three-Component, One-Pot Reaction

Abstract1,2-Oxazines were synthesised via a copper-catalysed aerobic acyl nitroso Diels–Alder reaction from 1,4-disubstituted 1,3-dienes and N-Boc-hydroxylamine. From this, 1,2-oxazinanes were obtained in a novel follow-up reaction path. The stability of several 1,2-oxazines and 1,2-oxazinanes towards organometallic compounds was tested to rate their operability as cyclic chiral Weinreb amide auxiliaries. 3,6-Di-tert-butyl-1,2-oxazinane gave the best results and was introduced as a chiral Weinreb amide-type auxiliary to yield chiral α-substituted ketones in a diastereomeric ratio of up to 98:2. The removal of the auxiliary can be performed with BuLi to form unsymmetrical α-chiral ketones. Thereafter, the chiral auxiliary can be re-isolated and purified by sublimation under vacuum.

Bioactive Diterpenes, Norditerpenes, and Sesquiterpenes from a Formosan Soft Coral Cespitularia sp.

Chemical investigation of the soft coral Cespitularia sp. led to the discovery of twelve new verticillane-type diterpenes and norditerpenes: cespitulins H–O (1–8), one cyclic diterpenoidal amide cespitulactam L (9), norditerpenes cespitulin P (10), cespitulins Q and R (11 and 12), four new sesquiterpenes: cespilins A–C (13–15) and cespitulolide (16), along with twelve known metabolites. The structures of these metabolites were established by extensive spectroscopic analyses, including 2D NMR experiments. Anti-inflammatory effects of the isolated compounds were studied by evaluating the suppression of pro-inflammatory protein tumor necrosis factor-α (TNF-α) and nitric oxide (NO) overproduction, and the inhibition of the gene expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), in lipopolysaccharide-induced dendritic cells. A number of these metabolites were found to exhibit promising anti-inflammatory activities.

Carbon dioxide transformation as a green alternative to phosgene and chloroformates: N-carboxyalkylation of lactams and analogues

A clean, safe, and efficient method for the N-carboxyalkylation of lactams was designed and studied in the current report. This three-component coupling of the substrate, carbon dioxide and an alkyl halide, has been developed as a green alternative to phosgene and chloroformates, and takes place at ambient temperature and low pressure of CO2. This provided an improved protocol for the protection of cyclic amides and other functional groups and allowed the obtention of non-classical N-carboxyalkyl derivatives for which the corresponding chloroformates are not accessible or commercially available. The model reaction was successfully performed with car diesel engine emissions and opens the way for new perspectives of carbon capture and use solutions.

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

Review of Kinetic Hydrate Inhibitors Based on Cyclic Amides and Effect of Various Synergists

This Review presents a comprehensive literature review of an important class of kinetic hydrate inhibitors (KHIs) that is based on cyclic amides (lactams). The major aspects of the KHIs, such as their synthesis, inhibition mechanism, toxicity, biodegradability, performance, and cloud point, are thoroughly discussed. Data for 70 KHIs made of homo/co/terpolymers from 330 experiments are collected and evaluated for performance. The effects of the inhibitor concentration, molecular weight, monomer ratio of the co/terpolymers, and 35 different synergist chemicals on various KHIs are also studied. In conclusion, the top 10 KHIs with the highest performances that had a cloud point above 70 °C are presented. The copolymer (1:1) N-vinylpyrrolidone/N-vinyl-caprolactam (VP/VCap) is found to have the highest induction time (IT) of 13 to 14 h at 0.25 wt % and at a cooling rate of 1 °C/h. Some KHIs like Inhibex BIO-800 and poly(N-vinyl azacyclooctanone) (PVACO) also have a very high ITs (17 and 13.5 h, respectively) at 0.25 wt % and at a cooling rate of 1 °C/h, but they have low cloud points (<25 °C). Guanidinium salts (n-Bu6GuanCl/n-Bu6GuanBr) and a phosphonium salt, (n-Pe)4PBr, are found to be the best synergists for the cyclic-amide-based KHIs. When used at 0.15 to 0.30 wt % along with the KHIs, they further increase the IT by 3–5 h.

Catalytic hydrothermal conversion of algal residue to bio-bitumen

After extraction of high-added value components of Spirulina sp., the remaining residues can be valorized by hydrothermal liquefaction to produce an oily water insoluble viscous phase (biocrude) which is very similar to petroleum bitumen. This hydrophobic fraction is composed of various N-,O-containing cyclic compounds, fatty acids, amides, nitriles, alkenes and alkanes. In order to optimize the rheological properties of the biocrude, we studied the addition of different catalysts with various loadings: ZrO2 or CeO2, or Ce(NO3)3.6H2O as well as the effect of residence time during HTL. The biocrude has been systematically characterized by GCxGC, GPC, elemental analyses and dynamic shear rheology and compared to a petroleum bitumen. The different catalysts tested had little influence on the composition of the HTL hydrophobic fraction in the chosen operating conditions. In contrast, increasing the reaction time (from 1 to 7 h) was found to promote condensation reactions, thereby increasing the average molecular weight of the biocrude, leading to a viscoelastic material very similar to a petroleum bitumen.

Raja 42, a novel gamma lactam compound, is effective against Clostridioides difficile.

Clostridioides difficile infection (CDI) is the primary cause of hospital-acquired diarrhea, and responsible for over 500,000 enteric infections a year in the United States alone. Although most patients with CDI are successfully treated with metronidazole or vancomycin, the high rate of recurrence is still a serious problem, in which case these antibiotics are usually not very effective. The primary objective of this research is to develop a potentially effective therapeutic agent against C. difficile that are resistant to metronidazole or vancomycin. The susceptibility to metronidazole and vancomycin was examined with 194 C. difficile clinical isolates. Sixty of these isolates chosen based on a variety of criteria were examined for their susceptibility against the 4-chloro-1-piperidin-1ylmethyl-1H-indole-2,3-dione compound (Raja 42), a novel isatin–benzothiazole analogue containing a gamma-lactam structure, as we previously found that this novel compound is effective against a variety of different bacteria. Most of the 60 isolates were resistant to ceftriaxone and ciprofloxacin, raising the possibility that they might have been exposed previously to these or structurally similar antibiotics (e.g., β-lactam and quinolone compounds). Among the isolates, 48 (80%) and 54 (90%) were susceptible to metronidazole and vancomycin, respectively. Raja 42 was found to be effective against most of the isolates, especially so against metronidazole-resistant C. difficile. Most importantly, five isolates that show resistance to metronidazole and vancomycin were sensitive to Raja 42. Thus, Raja 42, a gamma lactam antibiotic, has the potential to effectively control C. difficile strains that are resistant to metronidazole and vancomycin.

Phosphine-Catalyzed Vinylation at Low Acetylene Pressure.

The vinylation of various nucleophiles with acetylene at a maximum pressure of 1.5 bar is achieved by organocatalysis with easily accessible phosphines like tri-n-butylphosphine. A detailed mechanistic investigation by quantum-chemical and experimental methods supports a nucleophilic activation of acetylene by the phosphine catalyst. At 140 °C and typically 5 mol % catalyst loading, cyclic amides, oxazolidinones, ureas, unsaturated cyclic amines, and alcohols were successfully vinylated. Furthermore, the in situ generation of a vinyl phosphonium species can also be utilized in Wittig-type functionalization of aldehydes.

Evaluation of Cyclic Amides as Activating Groups in N-C Bond Cross-Coupling: Discovery of N-Acyl-δ-valerolactams as Effective Twisted Amide Precursors for Cross-Coupling Reactions.

The development of efficient methods for facilitating N-C(O) bond activation in amides is an important objective in organic synthesis that permits the manipulation of the traditionally unreactive amide bonds. Herein, we report a comparative evaluation of a series of cyclic amides as activating groups in amide N-C(O) bond cross-coupling. Evaluation of N-acyl-imides, N-acyl-lactams, and N-acyl-oxazolidinones bearing five- and six-membered rings using Pd(II)-NHC and Pd-phosphine systems reveals the relative reactivity order of N-activating groups in Suzuki-Miyaura cross-coupling. The reactivity of activated phenolic esters and thioesters is evaluated for comparison in O-C(O) and S-C(O) cross-coupling under the same reaction conditions. Most notably, the study reveals N-acyl-δ-valerolactams as a highly effective class of mono-N-acyl-activated amide precursors in cross-coupling. The X-ray structure of the model N-acyl-δ-valerolactam is characterized by an additive Winkler-Dunitz distortion parameter Σ(τ+χN) of 54.0°, placing this amide in a medium distortion range of twisted amides. Computational studies provide insight into the structural and energetic parameters of the amide bond, including amidic resonance, N/O-protonation aptitude, and the rotational barrier around the N-C(O) axis. This class of N-acyl-lactams will be a valuable addition to the growing portfolio of amide electrophiles for cross-coupling reactions by acyl-metal intermediates.

Bisavenathramide Analogues as Nrf2 Inductors and Neuroprotectors in In Vitro Models of Oxidative Stress and Hyperphosphorylation.

Oxidative stress is crucial to the outbreak and advancement of neurodegenerative diseases and is a common factor to many of them. We describe the synthesis of a library of derivatives of the 4-arylmethylen-2-pyrrolin-5-one framework by sequential application of a three-component reaction of primary amines, β-dicarbonyl compounds, and α-haloketones and a Knoevenagel condensation. These compounds can be viewed as cyclic amides of caffeic and ferulic acids, and are also structurally related to the bisavenanthramide family of natural antioxidants. Most members of the library showed low cytotoxicity and good activity as inductors of Nrf2, a transcription factor that acts as the master regulator of the antioxidant response associated with activation of the antioxidant response element (ARE). Nrf2-dependent protein expression was also proved by the significant increase in the levels of the HMOX1 and NQO1 proteins. Some compounds exerted neuroprotective properties in oxidative stress situations, such as rotenone/oligomycin-induced toxicity, and also against protein hyperphosphorylation induced by the phosphatase inhibitor okadaic acid. Compound 3i, which can be considered a good candidate for further hit-to-lead development against neurodegenerative diseases due to its well-balanced multitarget profile, was further characterized by proving its ability to reduce phosphorylated Tau levels.

Exploring Azatidinone Moiety: An Insight into its Anti-tubercular Potency.

TB is becoming a worldwide problem and it was declared since 1993 by the World Health Organization (WHO), a global health emergency. The current problem of tuberculosis therapy is the emergence of multi-drug resistant (MDR) strains, caused by the improper use of antibiotics in chemotherapy of TB patients. Azatidinones, a β-lactam cyclic amide with four atoms in a ring, has been considered as a magic moiety (wonder nucleus) which possesses almost all types of biological activities. This diversity in the biological response profile has attracted the attention of many researchers to explore this skeleton to its multiple potential against several activities. Present article is sincere attempt to review chemistry, method of synthesis of azatidinones and to study azatidinones synthesized in last few years which have shown potent antitubercular activity.

Copper Nanoparticles Supported on Zinc Oxide as Efficient Catalyst for the N‐Arylation of (Hetero)cyclic and Acyclic Amides

AbstractCopper nanoparticles (CuNPs) supported on ZnO are highly active and selective heterogeneous catalyst for the N‐arylation of cyclic and acyclic amides (Golberg coupling). The reaction conditions are mild, featuring K3PO4 as a base and N,N’‐dimethylethylendiamine (DMEDA) as ligand in refluxing acetonitrile. The CuNPs/ZnO catalyst can be recovered and reused in six cycles with only little loss of activity. The methodology can be successfully scaled up to gram scale without decreasing the catalytic activity.

Radical Cyclization of Olefinic Amides through α-C(sp3)–H Functionalization of Ketones under Catalyst-, Ligand-, and Base-Free Conditions

AbstractA new, efficient, and practical radical cyclization of olefinic amides with ketones through α-C(sp3)–H functionalization in the presence of tert-butyl peroxybenzoate (TBPB) is described for the first time. This protocol assembles a wide range of pivotal and useful benzoxazines in good to excellent yields under mild, catalyst-free, ligand-free, and base-free conditions with wide functional group tolerance. Moreover, the mechanistic study indicates that the α-carbonyl radical is involved in this transformation.

Dearomatization of Unactivated Arenes via Catalytic Hydroalkylation

The dearomative cyclization of linear amides to complex spirocyclic butyrolactams has been enabled by photoredox catalysis through a reductive radical-polar crossover mechanism. This mechanism operates with precision on unactivated aromatic substrates to give a wide range of 1,4-hydroalkylation products. This method utilizes a simple organic catalyst/reductant pair to deliver products in a highly flexible manner with respect to substitution, and the products can be further functionalized under simple conditions to afford a collection of motifs. The mechanistic analysis performed here outlines the salient features of this strategy, which were applied to prepare a collection of complex scaffolds including the anticonvulsive agent gabapentin.

Rational design of flavonoid based potential inhibitors targeting SARS-CoV 3CL protease for the treatment of COVID-19

The current outbreak of Coronavirus Disease 2019 (COVID-19) pandemic has reported thousands of deaths worldwide due to the rapid transmission rate and the lack of antiviral drugs and vaccinations. There is an urgent need to develop potential antiviral drug candidates for the prevention of COVID-19 infection. In the present study, a series of potential inhibitors targeting SARS-CoV 3CL protease were rationally designed by incorporating gamma lactam ring, and various fluoro substituted heterocyclic ring systems to the flavonoid scaffold. The prediction of drug-likeness, oral bioavailability, toxicity, synthetic accessibility, and ADMET properties was made by computational means. Quercetin was used as standard. The binding affinity of the ligands towards the 3CL protease target was examined using docking simulations. The designed ligands possess favourable pharmacokinetic and pharmacodynamic properties. Ligand L4, L8, and L14 appeared to be the lead compounds in the series and can be considered for further in-vivo and in-vitro validation.

Indene Derived Phosphorus‐Thioether Ligands for the Ir‐Catalyzed Asymmetric Hydrogenation of Olefins with Diverse Substitution Patterns and Different Functional Groups

AbstractA family of phosphite/phosphinite‐thioether ligands have been tested in the Ir‐catalyzed asymmetric hydrogenation of a range of olefins (50 substrates in total). The presented ligands are synthesized in three steps from cheap indene and they are air‐stable solids. Their modular architecture has been crucial to maximize the catalytic performance for each type of substrate. Improving most Ir‐catalysts reported so far, this ligand family presents a broader substrate scope, covering different substitution patterns with different functional groups, ranging from unfunctionalized olefins, through olefins with poorly coordinative groups, to olefins with coordinative functional groups. α,β‐Unsaturated acyclic and cyclic esters, ketones and amides were hydrogenated in enantioselectivities ranging from 83 to 99% ee. Enantioselectivities ranging from 91 to 98% ee were also achieved for challenging substrates such as unfunctionalized 1,1′‐disubstituted olefins, functionalized tri‐ and 1,1′‐disubstituted vinyl phosphonates, and β‐cyclic enamides. The catalytic performance of the Ir‐ligand assemblies was maintained when the environmentally benign 1,2‐propylene carbonate was used as solvent.magnified image