Alicyclic-Amine-Derived Imine-BF3 Complexes: Easy-to-Make Building Blocks for the Synthesis of Valuable α-Functionalized Azacycles

A new strategy to access α-functionalized alicyclic amines via their corresponding imine-BF3 complexes is reported. Isolable imine-BF3 complexes, readily prepared via dehydrohalogenation of N-bromoamines in a base-promoted/18-crown-6 catalyzed process followed by addition of boron trifluoride etherate, undergo reactions with a wide range of organometallic nucleophiles to afford α-functionalized azacycles. Organozinc and organomagnesium nucleophiles add at ambient temperatures, obviating the need for cryogenic conditions. In situ preparation of imine-BF3 complexes provides access to α-functionalized morpholines and piperazines directly from their parent amines in a single operation. α-Functionalized morpholines can be elaborated further, for instance by installing a second substituent in the α'-position.

Computational modeling of imines based anti-oxidant and anti-esterases compounds: Synthesis, single crystal and In-vitro assessment

Molecular modeling strategy was adopted to check the biological potential of the imine based molecules against free radical, acetylcholine esterase and butyrylcholine esterase. Three Schiff based compounds as (E)-2-(((4-bromophenyl)imino)methyl)-4-methylphenol (1), (E)-2-(((3-fluorophenyl)imino)methyl)-4-methylphenol (2) and (2E,2E)-2-(2-(2-hydroxy-5-methylbenzylidene)hydrazono)-1,2-diphenylethanone (3) were synthesized with high yield. The synthesized compounds were characterized with the help of modern techniques such as UV, FTIR and NMR while exact structure was depicted with Single Crystal X-Ray diffraction technique which disclosed that compound 1 is orthorhombic, while 2 and 3 are monoclinic. A hybrid functional (B3LYP) method with general basis set of 6-31 G(d,p) were applied to optimize synthesized Schiff bases. The contribution of in-between molecular contacts within a crystalline assembly of compounds were studied using Hirshfeld surface analysis (HS). In order to check the ability of the synthesized compounds toward free radical and enzyme inhibition, in vitro models were used to assess the radical scavenging and enzyme inhibition potential which depicted that compound 3 showed highest potential (57.43 ± 1.0%; DPPH, 75.09 ± 1.0%; AChE and 64.47 ± 1.0%; BChE). The ADMET assessments suggested the drug like properties of the synthesized compounds. It was concluded from results (in vitro and in silico) that synthesized compound have ability to cure the disorder related to free radical and enzyme inhibition. Compound 3 was shown to be the most active compared to other compounds.

Selective oxidation of amines powered with green light and oxygen over an anthraquinone covalent organic framework

The exploration of emerging photocatalysts like covalent organic frameworks (COFs) is an essential but challenging endeavor to find sustainable solutions for selective organic transformations. Anthraquinones are envisaged to construct COFs for visible light photocatalysis because their derivatives are employed industrially as oxidation catalysts or organic dyes. Herein, an anthraquinone COF, TpAQ-COF, is successfully constructed with 1,3,5-triformylphloroglucinol (Tp) and 2,6-diaminoanthraquinone (AQ). Then, the selective oxidation of amines over TpAQ-COF is implemented. Amines can be effectively converted into corresponding imines over TpAQ-COF powered with green light and oxygen, during which superoxide radical anion is discerned as the pivotal reactive oxygen species. This work suggests that COFs could inherit the advantages of molecular building blocks for selective reactions powered with broad visible light.

Chemoselective Oxidation of Alcohols in the Presence of Amines Using an Oxoammonium Salt

The oxidation of alcohols in the presence of reactive amines employing the commercially available oxoammonium cation, "Bobbitt's salt" is described. The oxidation is accomplished under acidic conditions and subsequent treatment with a suitable base affords a convenient one-pot method to access imines in good to excellent isolated yields (74-99%).

Alkyl Formates as Transfer Hydroalkylation Reagents and Their Use in the Catalytic Conversion of Imines to Alkylamines

Easily accessible via a simple esterification of alcohols with formic acid, alkyl formates are used as a novel class of transfer hydroalkylation reagents, CO₂ acting as a traceless linker. As a proof-of-concept, their reactivity in the transfer hydroalkylation of imines is investigated, using a ruthenium-based catalyst and LiI as promoter to cleave the C-O σ-bond of the formate scaffold. Providing tertiary amines, the reaction displays a divergent regioselectivity compared to previously reported transfer hydroalkylation strategies.

Photoresponsive Dissipative Macrocycles Using Visible-Light-Switchable Azobenzenes

Visible light can be used to shift dynamic covalent imine assemblies out of equilibrium. We studied a fluorinated azobenzene building block that reliably undergoes geometric isomerism upon irradiation. The building block was used in combination with two different amines, ethylenediamine and R,R-1,2-diaminocyclohexane, to create a library of imine macrocycles. Whereas the simple amine can be used to access a polymeric state and a defined bowl-shaped macrocycle, the chiral amine gives access to a rich network of macrocycles that undergo both isomerisation as well as interconversion between different macrocyclic species, thereby allowing for control over the number of monomers involved in the cyclo-oligomerization; ¹ H- and ¹⁹ F-DOSY NMR, MALDI-MS measurements, and UV/Vis spectroscopy were used to study the processes.

Nickel-Catalyzed Reductive Alkylation of Heteroaryl Imines

The preparation of heterobenzylic amines by a Ni-catalyzed reductive cross-coupling between heteroaryl imines and C(sp3 ) electrophiles is reported. This umpolung-type alkylation proceeds under mild conditions, avoids the pre-generation of organometallic reagents, and exhibits good functional group tolerance. Mechanistic studies are consistent with the imine substrate acting as a redox-active ligand upon coordination to a low-valent Ni center. The resulting bis(2-imino)heterocycle⋅Ni complexes can engage in alkylation reactions with a variety of C(sp3 ) electrophiles, giving heterobenzylic amine products in good yields.

Hydrazone-linked 2D porphyrinic covalent organic framework photocatalysis for visible light-driven aerobic oxidation of amines to imines

Covalent organic frameworks (COFs) have recently gained rising consideration for visible light photocatalysis. Their property could be accurately established with specific reactions in which the most investigated one turns out to be the aerobic oxidation of amines. In this contribution, a hydrazone-linked 2D (two-dimensional) porphyrinic COF, Por-DETH-COF, was assembled from 5,10,15,20-tetrakis(4-benzaldehyde)porphyrin (p-Por-CHO) and 2,5-diethoxyterephthalohydrazide (DETH) and its photocatalytic activity was duly appraised with the aerobic oxidation of amines. Thereby, the red light-driven selective oxidation of benzyl amines to imines was obtained in very high conversions and selectivities with ambient air as the oxidant. Importantly, the photocatalytic system exhibited remarkable compatibility of functional groups and extensive scope of benzyl amines. Notably, the Por-DETH-COF photocatalyst displayed outstanding recyclability after five successive cycles. This work suggests that 2D COFs could contribute a unique juncture for selective organic transformations by photocatalysis.

In vitro and in vivo antiplasmodial activity of novel quinoline derivative compounds by molecular hybridization

Chloroquine (CQ) has been the main treatment for malaria in regions where there are no resistant strains. Molecular hybridization techniques have been used as a tool in the search for new drugs and was implemented in the present study in an attempt to produce compound candidates to treat malarial infections by CQ-resistant strains. Two groups of molecules were produced from the 4-aminoquinoline ring in conjugation to hydrazones (HQ) and imines (IQ). Physicochemical and pharmacokinetic properties were found to be favorable when analyzed in silico and cytotoxicity and antiplasmodial activity were assayed in vitro and in vivo showing low cytotoxicity and selectiveness to the parasites. Candidates IQ5 and IQ6 showed important values of parasite growth inhibition in vivo on the 5th day after infection (IQ5 15 mg/kg = 72.64% and IQ6 15 mg/kg = 71.15% and 25 mg/kg = 93.7%). IQ6 also showed interaction with ferriprotoporphyrin IX similarly to CQ. The process of applying condensation reactions to yield imines is promising and capable of producing molecules with antiplasmodial activity.

An efficient protocol for the synthesis of highly sensitive indole imines utilizing green chemistry: optimization of reaction conditions

Novel and highly sensitive indole-based imines have been synthesized. Their synthesis has been compared employing a variety of protocols. Ultimately, a convenient, economical and high yielding set of conditions employing green chemistry have been designed for their synthesis.

Facile synthesis of N- (4-bromophenyl)-1- (3-bromothiophen-2-yl)methanimine derivatives via Suzuki cross-coupling reaction: their characterization and DFT studies

A variety of imine derivatives have been synthesized via Suzuki cross coupling of N-(4-bromophenyl)-1-(3-bromothiophen-2-yl)methanimine with various arylboronic acids in moderate to good yields (58–72%). A wide range of electron donating and withdrawing functional groups were well tolerated in reaction conditions. To explore the structural properties, Density functional theory (DFT) investigations on all synthesized molecules (3a–3i) were performed. Conceptual DFT reactivity descriptors and molecular electrostatic potential analyses were performed by using B3LYP/6-31G(d,p) method to explore the reactivity and reacting sites of all derivatives (3a–3i).

Design, Synthesis and Biological Evaluation of Some Triazole Schiff's Base Derivatives as Potential Antitubercular Agents

Background:

Tuberculosis (TB) is the second important cause of death worldwide caused by a bacterium called Mycobacterium tuberculosis. There is a need to find and develop new Anti-TB medications that are effective, inexpensive and suitable with human immunodeficiency virus and other anti-TB drugs used in many countries and mainly the developing countries where the disease is widespread. These drugs must be designed to shorten treatment time and to be active against resistant forms of the mycobacteria that will help to increase the patients compliance. A key compound which could be used as a lead to meet these requirements, is the thiolactomycin (TLM). This antibiotic which is naturally available has an ability to treat M. tuberculosis by inhibiting condensing enzymes called FAS II (mtFabH, KasA and KasB) which are related to biosynthesis of mycolic acid.

Methods:

Our main aims are to design and synthesize analogues of TLM as new lead molecules which could be a possible anti–TB candidate. To overcome the synthetic challenges associated with preparing the chiral TLM analogues; we synthesized and investigated a series of triazole analogues as inhibitors of KasA enzyme and the whole cell Mycobacteria. A series of twelve compounds were synthesized, purified and fully characterized using several spectroscopic techniques. Molecular modelling studies for our synthesised compounds were achieved by using a modelling program called AutoDock 4.2 utilising rigid docking.

Results:

Our results indicate that analogues of TLM show a good activity as compared to TLM.

Conclusion:

The activity obtained for the synthesized compounds against Mycobacteria tuberculosis indicate that the synthesised compounds 1, 2, 6 and 9 are pharmacologically active as they restrained the growth of the Mycobacteria bacteria.

Accelerated generation of (protonated) imines and quinoxalines by formation of C=N bonds in the microdroplets of a nebuliser

Ions corresponding to protonated imines appear in the positive ion electrospray mass spectra of mixtures of the parent aromatic aldehyde and arylamine. The formation of these imine products occurs readily in the electrospray source nebuliser, even without the application of a spray potential. This accelerated formation of C=N bonds in the nebuliser has been extended to encompass the preparation of quinoxalines from a range of substituted phenylenediamines and benzils. The condensation may be induced either under conventional positive ion electrospray conditions (to give the protonated quinoxalines) or when the nebuliser is disconnected from the mass spectrometer (to give the neutral quinoxaline). Ions corresponding to intermediate adducts formed by condensation of the phenylenediamine component with the protonated benzil are observed in many cases when the condensation occurs in the mass spectrometer. This finding supports an interpretation based on nucleophilic addition in droplets generated by the nebuliser.

Optical properties of unsymmetrical azomethines with one imine bonds

We have explored the photoluminescence (PL) and electronic properties, that is, orbital energies and resulting energy gap calculated theoretically by density functional theory (DFT) of four unsymmetrical (UAz1-UAz4) azomethines. All of the investigated compounds exhibited mesomorphic behavior. The photoluminescence studies have shown that molecular structure of the imines influenced both the PL properties and HOMO-LUMO levels of azomethines. Azomethines emitted violet, blue or green light. The effect of excitation wavelength and concentration on the PL properties has been detected as well. Unsymmetrical imine UAz3 posses carbazole unit exhibited lower both HOMO and LUMO energies compare to others investigated azomethines. Additionally, azomethines were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Two unsymmetrical imines (UAz2 and UAz3) exhibited irreversible oxidation behavior. The HOMO level of the compound with ethylcarbazole (UAz2) moiety was observed at -5.22 eV, while for the UAz3 with phenoxybiphenyl unit was found at -5.64 eV. The data obtained by theoretical calculation using DFT method was very similar to the results obtained by electrochemical measurements.

Regio- and Stereoselective Direct Cross-Coupling of Aromatic Imines with Allenic Alcohols

We describe a titanium-mediated reaction for the convergent coupling of allenic alcohols with aromatic imines. Overall, the bond formation occurs at the central carbon of the allene, proceeds with net allylic transposition, and provides substituted 1,3-dienes bearing allylic amine functionality in a regio- and stereoselective fashion.

The Critical Importance of Water in the Asymmetric Allylboration of N-Trimethylsilylbenzaldimines with B-Allyldiisopinocampheylborane

The free aldimine is probably the intermediate in the asymmetric allylboration of N-trimethylsilylaldimines in the presence of water (see scheme), which is critical for the reaction. The aldimine is rapidly captured by the allylborating agent. Ipc₂ BAll=B-allyldiisopinocampheylborane.

Amine Additives Greatly Expand the Scope of Asymmetric Hydrosilylation of Imines

Slow addition of a primary amine to the reaction mixture greatly increases the scope of the titanium-catalyzed asymmetric reduction of imines 1. An important added feature of this method is that chiral secondary amines 2 can be obtained in much higher optical purity (up to 99 % ee) than would be predicted from the E:Z ratios of the starting imines 1.