Nitrogen Substituents Research Articles

NLOphoric unsymmetrically substituted D-π-A benzodifuranone dyes: Density functional theory, time dependent-density functional theory, and non-linear optical studies

The linear and non-linear optical properties of thirty-five unsymmetrically substituted compounds are studied using density functional theory and time-dependent density functional theory methods (B3LYP/6311++G(d,p), CAM-B3LYP/6311++G(d,p) and M06-2X/6311++G(d,p)). A comparable set of functionals is also used to investigate vertical excitation. It is observed that the inclusion of the nitrogen-substituted electron-donating group along with the electron-withdrawing group led to more red-shifted absorption maxima and exhibited an excellent (non-linear optical) NLO response. The geometrical framework, dipole moment, and other descriptors, HOMO-LUMO energy gaps, linear polarizability, first-order and second-order hyperpolarizability are calculated to investigate the effect of different electron donating and accepting substituents on the NLO properties of benzodifuranone chromophores. In cases where nitrogen substituents are added, the electron density is more widely spread throughout the donor in HOMO and more displaced to the acceptor in LUMO. The computed first-order and second-order hyperpolarizability values and decreasing HOMO-LUMO energy gaps in disubstituted nitrogen-containing compounds show that 1a-1e, 4a-4e, 5a-5e are promising candidates in all functionals for better NLO properties.

Tailoring N skeleton substituted cobalt phthalocyanine/reduced graphene oxide nanostructures for boosting redox kinetics and regulating Li2S nucleation enabled high rate performance of lithium-sulfur batteries

The shuttle and sluggish conversion kinetics of polysulfides (LiPS) significantly hinder the sulfur utilization and cycle performance of Li–S batteries. Herein, reduced Graphene Oxide supported Cobalt phthalocyanines(CoPc/rGO) and its skeleton Nitrogen substituent Cobalt Tetrapyridinoporphyrazine (CoTAP/rGO), are fabricated using a preform-solid synthesis process. When employed as separator modification, the CoTAP/rGO can capture and electrocatalyze LiPS by the active central Co–N4 units. And the Co–N4 sites are proved that can augment the LiPS redox kinetics especially the oxidation as well as the Li + diffusion rate. The introduced substituent N atoms in the skeleton match the LiPS redox ability and further enhance the Li + diffusion ability. Distribution of relaxation time (DRT) analysis shows that CoTAP nanoparticles can reduce the resistance of LiPS as well as Li + diffusion in Li2S precipitation procedure, accomplishing the loose three dimension deposition on cathode. As a result, the CoTAP/rGO separator exhibits a high initial capacity of 1132.7 mAh g−1 at 0.2C, excellent rate capacity of 672.5 mAh g−1 at 5C and superior long-term stability with a low capacity decay of 0.57 ‰ at 2C after 500 cycles.

Synthesis and Properties of Fused Polycyclic Donor–Acceptor Compounds Containing Carbazole and Diazapyrene Skeletons

Fused polycyclic aromatic compounds containing carbazole and diazapyrene skeletons as electron donors and acceptors, respectively, were synthesized in a few steps from readily accessible starting materials. The incorporation of diazapyrene units into the polycyclic compounds resulted in significant bathochromic shifts in their absorption and emission bands compared to those of the corresponding carbazole derivatives. Electrochemical measurements and density functional theory calculations were performed to gain further insight into their electronic properties. Our findings demonstrate that the incorporation of nitrogen atoms and substituents, as well as the different topologies of the fused‐ring system, exert a profound effect on the electronic properties of the polycyclic compounds.

An Update on the Nitrogen Heterocycle Compositions and Properties of U.S. FDA-Approved Pharmaceuticals (2013-2023).

This Perspective is a continuation of our analysis of U.S. FDA-approved small-molecule drugs (1938-2012) containing nitrogen heterocycles. In this study we report drug structure and property analyses of 321 unique new small-molecule drugs approved from January 2013 to December 2023 as well as information about frequency of important heteroatoms such as sulfur and fluorine and key small nitrogen substituents (CN and NO2). The most notable change is an incredible increase in drugs containing at least one nitrogen heterocycle─82%, compared to 59% from preceding decades─as well as a significant increase in the number of nitrogen heterocycles per drug. Pyridine has claimed the #1 high-frequency nitrogen heterocycle occurrence spot from piperidine (#2), with pyrimidine (#5), pyrazole (#6), and morpholine (#9) being the big top 10 climbers. Also notable is high number of fused nitrogen heterocycles, apparently driven largely by newly approved cancer drugs.

Intermolecular Enantioselective Amination Reactions Mediated by Visible Light and a Chiral Iron Porphyrin Complex.

In the presence of 1 mol % of a chiral iron porphyrin catalyst, various 3-arylmethyl-substituted 2-quinolones and 2-pyridones underwent an enantioselective amination reaction (20 examples; 93-99 % ee). The substrates were used as the limiting reagents, and fluorinated aryl azides (1.5 equivalents) served as nitrene precursors. The reaction is triggered by visible light which allows a facile dediazotation at ambient temperature. The selectivity of the reaction is governed by a two-point hydrogen bond interaction between the ligand of the iron catalyst and the substrate. Hydrogen bonding directs the amination to a specific hydrogen atom within the substrate that is displaced by the nitrogen substituent either in a concerted fashion or by a rebound mechanism.

Intermolecular Enantioselective Amination Reactions Mediated by Visible Light and a Chiral Iron Porphyrin Complex

AbstractIn the presence of 1 mol % of a chiral iron porphyrin catalyst, various 3‐arylmethyl‐substituted 2‐quinolones and 2‐pyridones underwent an enantioselective amination reaction (20 examples; 93–99 % ee). The substrates were used as the limiting reagents, and fluorinated aryl azides (1.5 equivalents) served as nitrene precursors. The reaction is triggered by visible light which allows a facile dediazotation at ambient temperature. The selectivity of the reaction is governed by a two‐point hydrogen bond interaction between the ligand of the iron catalyst and the substrate. Hydrogen bonding directs the amination to a specific hydrogen atom within the substrate that is displaced by the nitrogen substituent either in a concerted fashion or by a rebound mechanism.

A True Reverse Anomeric Effect Does Exist After All: A Hydrogen Bonding Stereocontrolling Effect in 2-Iminoaldoses.

The reverse anomeric effect is usually associated with the equatorial preference of nitrogen substituents at the anomeric center. Once postulated as another anomeric effect with explanations ranging from electrostatic interactions to delocalization effects, it is now firmly considered to be essentially steric in nature. Through an extensive research on aryl imines from 2-amino-2-deoxyaldoses, spanning nearly two decades, we realized that such substances often show an anomalous anomeric behavior that cannot easily be rationalized on the basis of purely steric grounds. The apparent preference, or stabilization, of the β-anomer takes place to an extent that not only neutralizes but also overcomes the normal anomeric effect. Calculations indicate that there is no stereoelectronic effect opposing the anomeric effect, resulting from the repulsion between electron lone pairs on the imine nitrogen and the endocyclic oxygen. Such data and compelling structural evidence unravel why the exoanomeric effect is largely inhibited. We are now confident, as witnessed by 2-iminoaldoses, that elimination of the exo-anomeric effect in the α-anomer is due to the formation of an intramolecular hydrogen bond between the anomeric hydroxyl and the iminic nitrogen, thereby accounting for a true electronic effect. In addition, discrete solvation may help justify the observed preference for the β-anomer.

Novel acrylonitrile derived imidazo[4,5-b]pyridines as antioxidants and potent antiproliferative agents for pancreatic adenocarcinoma

We present the design, synthesis, computational analysis, and biological assessment of several acrylonitrile derived imidazo[4,5-b]pyridines, which were evaluated for their anticancer and antioxidant properties. Our aim was to explore how the number of hydroxy groups and the nature of nitrogen substituents influence their biological activity. The prepared derivatives exhibited robust and selective antiproliferative effects against several pancreatic adenocarcinoma cells, most markedly targeting Capan-1 cells (IC50 1.2–5.3 μM), while their selectivity was probed relative to normal PBMC cells. Notably, compound 55, featuring dihydroxy and bromo substituents, emerged as a promising lead molecule. It displayed the most prominent antiproliferative activity without any adverse impact on the viability of normal cells. Furthermore, the majority of studied derivatives also exhibited significant antioxidative activity within the FRAP assay, even surpassing the reference molecule BHT. Computational analysis rationalized the results by highlighting the dominance of the electron ionization for the antioxidant features with the trend in the computed ionization energies well matching the observed activities. Still, in trihydroxy derivatives, their ability to release hydrogen atoms and form a stable O–H⋯O•⋯H–O fragment upon the H• abstraction prevails, promoting them as excellent antioxidants in DPPH• assays as well.

Homoleptic ruthenium(II) complexes bearing imidazol(in)ium-2-dithiocarboxylate ligands: synthesis, characterization, and redox properties.

Five cationic ruthenium(II) chelates with the generic formula [Ru(S2C·NHC)3](PF6)2 were readily obtained upon cleavage of the [RuCl2(p-cymene)]2 dimer with representative imidazol(in)ium-2-dithiocarboxylate zwitterions (NHC·CS2) in the presence of KPF6. The homoleptic complexes were fully characterized by various analytical techniques and the molecular structure of one of them was determined by single-crystal X-ray diffraction analysis. As expected, it featured an octahedral RuS6 core surrounded by three imidazol(in)ium rings and their nitrogen substituents. The robustness of the Ru-S bonds combined with the chelate effect of the κ2-S,S'-dithiocarboxylate units and the steric protection imparted by bulky 1,3-diarylimidazol(in)ium groups most likely accounted for the outstanding stability of these species in solution. Cyclic voltammetry showed that the five homoleptic complexes featured characteristic waves for a monoelectronic redox process corresponding to the RuIII/RuII couple with E1/2 values ranging between 0.97 and 1.27 V vs. Ag/AgCl. This half-wave potential was clearly dependent on the nature of their ancillary ligands as the evolution of the Ep,ox values roughly paralleled the basicity sequence of the NHCs used to prepare them, in line with the trends observed when monitoring the chemical shifts of the CS2- unit on 13C NMR spectroscopy and the CS2- asymmetric stretching vibration wavenumbers on IR spectroscopy.

Diastereoselective Pd-catalyzed Decarboxylative (4 + 2) Cycloaddition Reactions of 4-Vinylbenzoxazinanones and 2-Nitro-1,3-enynes.

A formal palladium-catalyzed decarboxylative (4 + 2) cycloaddition reaction between 4-vinylbenzoxazinanones and 2-nitro-1,3-enynes has been developed to produce highly valuable, densely functionalized tetrahydroquinolines in moderate to excellent yields with high diastereoselectivity under mild reaction conditions. The optimised protocol tolerates a range of substituted 2-nitro-1,3-enynes, which represent an under-utilized class of dipolarophile for transition-metal catalyzed cycloadditions. The employed reaction methodology facilitates efficient cycloaddition with both N-H- and N-Ts-4-vinylbenzoxazinanone dipole precursors. The stereochemistry of the major and minor diastereomeric (4 + 2) cycloadducts was determined by single crystal X-ray analyses. A mechanistic rationale for the high intrinsic diastereoselectivity and preliminary enantioselective experiments are also presented. The tetrahydroquinoline cycloadduct products feature numerous pendant functionalities, including a vinyl handle, an internal alkyne motif and a nitro functionality (which functions as a latent C-3 nitrogen substituent) for further synthetic manipulations.

Gold-Catalyzed Cyclization of Yndiamides with Isoxazoles via α-Imino Gold Fischer Carbenes.

Gold catalysis is an important method for alkyne functionalization. Here we report the gold-catalyzed formal [3+2] aminative cyclization of yndiamides and isoxazoles in a direct synthesis of polysubstituted diaminopyrroles, which are important motifs in drug discovery. Key to this process is the formation, and subsequent cyclization, of an α-imino gold Fischer carbene, which represents a new type of gold carbene intermediate. The reaction proceeds rapidly under mild conditions, with high regioselectivity being achieved by introducing a subtle steric bias between the nitrogen substituents on the yndiamide. DFT calculations revealed that the key to this regioselectivity was the interconversion of isomeric gold keteniminiun ions via a low-barrier π-complex transition state, which establishes a Curtin-Hammett scenario for isoxazole addition. By using benzisoxazoles as substrates, the reaction outcome could be switched to a formal [5+2] cyclization, leading to 1,4-oxazepines.

Iridium(III)-Catalyzed Intermolecular C(sp3 )-H Amidation for the Synthesis of Chiral 1,2-Diamines.

Chiral 1,2-diamines are privileged scaffolds among bioactive natural products, active pharmaceutical ingredients, ligands for transition-metal-based asymmetric catalysis and organocatalysts. Despite this interest, the construction of chiral 1,2-diamine motifs still remains a challenge. To address this, an iridium(III)-catalyzed intermolecular C(sp3 )-H amidation reaction was developed. This method relies on the design of a new, cheap and cleavable exo-protecting/directing group derived from camphorsulfonic acid, which is directly installed from easily accessible precursors, and furnishes scalemic free 1,2-diamines upon cleavage of both nitrogen substituents. It was found applicable to both α-secondary and α-tertiary-1,2-diamines, for which a two-step protocol involving intermolecular olefin hydroamination and C(sp3 )-H amidation was developed. Kinetic and computational studies provided insights into the observed reactivity difference between pairs of diastereoisomeric substrates.

Iridium(III)‐Catalyzed Intermolecular C(sp3)‐H Amidation for the Synthesis of Chiral 1,2‐Diamines

AbstractChiral 1,2‐diamines are privileged scaffolds among bioactive natural products, active pharmaceutical ingredients, ligands for transition‐metal‐based asymmetric catalysis and organocatalysts. Despite this interest, the construction of chiral 1,2‐diamine motifs still remains a challenge. To address this, an iridium(III)‐catalyzed intermolecular C(sp3)‐H amidation reaction was developed. This method relies on the design of a new, cheap and cleavable exo‐protecting/directing group derived from camphorsulfonic acid, which is directly installed from easily accessible precursors, and furnishes scalemic free 1,2‐diamines upon cleavage of both nitrogen substituents. It was found applicable to both α‐secondary and α‐tertiary‐1,2‐diamines, for which a two‐step protocol involving intermolecular olefin hydroamination and C(sp3)‐H amidation was developed. Kinetic and computational studies provided insights into the observed reactivity difference between pairs of diastereoisomeric substrates.

Tetrel bond involving -CH3 group in HnXCH3 (X = F, Cl, and Br, n = 0; X = O, S, and Se, n = 1; X = N, P, and As, n = 2). Cooperativity with triel bond and beryllium bond

The tetrel bond formed between the σ-hole on the C atom of HnXCH3 (X = F, Cl, and Br, n = 0; X = O, S, and Se, n = 1; X = N, P, and As, n = 2) and the N atom of NCM (M = Li and Na) was studied by ab initio calculations at the MP2/aug-cc-pVTZ level. The molecules involving nitrogen or oxygen group substituents engage in a weaker tetrel bond with interaction energies in the range of 5–12 kJ/mol. In contrast, a stronger tetrel bond is formed when the X atom of HnXCH3 is a halogen, with interaction energies in the range of 16–18 kJ/mol. The tetrel bond is further enhanced by the addition of the electron-deficient molecule BeH2 or BH3 to the X atom of HnXCH3 and the interaction energy can be increased to 38 kJ/mol. Moreover, the enhancing effect of beryllium bond on the tetrel bond is greater than that from the triel bond.

Catalytic Enantioselective Sulfur Alkylation of Sulfenamides for the Asymmetric Synthesis of Sulfoximines.

Sulfoximines are increasingly incorporated in agrochemicals and pharmaceuticals, with the two enantiomers of chiral sulfoximines often having profoundly different binding interactions with biomolecules. Therefore, their application to drug discovery and development requires the challenging preparation of single enantiomers rather than racemic mixtures. Here, we report a general and fundamentally new asymmetric synthesis of sulfoximines. The first S-alkylation of sulfenamides, which are readily accessible sulfur compounds with one carbon and one nitrogen substituent, represents the key step. A broad scope for S-alkylation was achieved by rhodium-catalyzed coupling with diazo compounds under mild conditions. When a chiral rhodium catalyst was utilized with loadings as low as 0.1 mol %, the S-alkylation products were obtained in high yields and with enantiomeric ratios up to 98:2 at the newly generated chiral sulfur center. The S-alkylation products were efficiently converted to a variety of sulfoximines with complete retention of stereochemistry. The utility of this approach was further demonstrated by the asymmetric synthesis of a complex sulfoximine agrochemical.

Persistent radicals in irradiated imidazolium ionic liquids probed by EPR spectroscopy

Long-lived radicals were observed in irradiated room temperature ionic liquids (RTILs) composed of the bis(trifluoromethylsulfonyl)imide anion (Tf2N−) with 1-hexyl-3-methylimidazolium (hmim+) and1-butyl-3-methylimidazolium (bmim+) cations. The EPR signal intensity increases within hours and the spectral pattern changes during the time after irradiation. The kinetics data obtained indicate the existence of at least two distinct radical cations that have different formation and decay rates. We demonstrate that oxygen does not react rapidly with the radical species formed. The bmim + Tf2N− was selectively deuterated at various positions which allowed us to suggest possible structures of the stable radicals formed. The first structure is a radical cation containing 2 nitrogens and 6 protons all with ca. 8.2 Gauss hyperfine splittings, and 2 protons with 2.8 Gauss splitting. The structure of the second radical cation is similar, but characterized by an odd number of hydrogens with ca. 8.2 Gauss splitting. Extensive quantum chemistry calculations were performed to attempt to identify the structure of these persistent radicals. The most likely candidates are imidazole radical cations having methyl groups at the nitrogen atoms and substituents in the second position of the imidazole ring.

Stereoselective Synthesis and Application of Gibberellic Acid-Derived Aminodiols.

A series of gibberellic acid-based aminodiols was designed and synthesized from commercially available gibberellic acid. Exposure of gibberellic acid to hydrochloric acid under reflux conditions resulted in aromatization followed by rearrangement to form allo-gibberic acid. The key intermediate, ethyl allo-gibberate, was prepared according to literature methods. Epoxidation of key intermediate and subsequent ring-opening of the corresponding epoxide with different nucleophiles resulted in N-substituted aminodiols. The regioselective ring closure of N-benzyl-substituted aminodiol with formaldehyde was also investigated. All aminodiol derivatives were well characterized using modern spectroscopic techniques and evaluated for their antiproliferative activity against a panel of human cancer cell lines. In addition, structure–activity relationships were examined by assessing substituent effects on the aminodiol systems. The results indicated that aminodiols containing aromatic rings on their nitrogen substituents displayed significant cytotoxic effects. Among these agents, N-naphthylmethyl-substituted aminodiols were found to be the most potent candidates in this series. One of these molecules exhibited a modest cancer selectivity determined by non-cancerous fibroblast cells. A docking study was also made to exploit the observed results.

β-Amino Acid Organocatalysts in the Asymmetric Michael Addition of Isobutyraldehyde to N-Substituted Maleimides

Asymmetric Michael additions of carbonyl compounds to N-substituted maleimides are among the most convenient reactions to prepare optically pure succinimide building blocks. Although a few β-amino acids were found to be highly efficient organocatalysts in the addition of α-branched aldehydes, the effect of their structure on the results of these reactions has not yet been investigated. In the present study, we disclose several unexpected and interesting structural effects of aliphatic and cycloaliphatic β-amino acids obtained in the enantioselective conjugate addition of isobutyraldehyde to N-benzylmaleimide. The dependence of the sense of the enantioselectivity on the bulkiness of the substituent on the β-carbon atom, the beneficial spatial arrangements of the functional groups in cis isomers with cyclohexane scaffold and the inversion of the enantioselectivity depending on the absence of a base additive observed with some trans isomers are unprecedented findings. The minor influence of the nitrogen substituent of the maleimide ring on both the reaction rate and the enantioselectivity was also evidenced using alicyclic β-amino acid prepared from an easily available terpene derivative.

Aryl Ketone Mediated Light-Driven Naphthylation of C(sp3)–H Bonds Attached to either Oxygen or Nitrogen Substituents

AbstractA light-driven naphthylation was achieved at C(sp3)–H bonds attached to either oxygen or nitrogen substituents using sulfonylnaphthalenes as a naphthalene precursor in the presence of 4-benzoylpyridine at ambient temperature. The present transformation is proposed to proceed through the generation of a carbon radical species via chemoselective cleavage of the heteroatom-substituted C(sp3)–H bond by photoexcited 4-benzoylpyridine, the addition of the derived carbon radical to the electron-deficient sulfonylnaphthalene, and then rearomatization by releasing sulfinyl radical.

Studies on Synthesis of Porphyrins – β ‐Substituted with Multiple Nitrogen‐containing Groups

The preparation of highly β-substituted amino-/nitro-porphyrins is described. They were formed in two-step transformation: electrophilic nitration/nucleophilic amination via attractive substitution of hydrogen reaction (VNS). This type of porphyrins, bearing up to four nitrogen groups, are practically not available by alternative methods. They are valuable starting materials in the synthesis of more complex moieties, e. g. anticancer PDT agents.