Selective Amination Research Articles

From Hazardous Waste to Green Applications: Selective Surface Functionalization of Waste Cigarette Filters for High-Performance Robust Triboelectric Nanogenerators and CO2 Adsorbents.

This article reports a novel and rational approach to convert waste cigarette filters (CFs), one of the largest sources of ocean pollution, into high-performance triboelectric nanogenerators (TENGs) and efficient CO2-capturing adsorbents. CFs are plasticized cellulose acetate, which take several years to degrade. To revalorize these fibers, selective amine surface functionalization is performed (10PAL-20T-CFs). For the proof of concept, when the modified fibers are employed in a TENG, it could generate an output voltage (96.63 V) and current (9.37 μA) that are, respectively, 43 and 8 times higher than those obtained employing the pristine CFs for the nanogenerator. The proposed TENG displays an instantaneous peak power of 3.75 mW, which is higher than that of many recently reported TENGs made from cellulose materials. Moreover, the TENG displayed outstanding durability to humidity and high-performance stability when it is subjected to cyclic loading (i.e., 12,000 cycles of loading-unloading). A 9 cm2 TENG could effectively light up 100 or more colored light-emitting diodes when it is manually pressed. Finally, the modified filter fibers show an excellent CO2 adsorption capacity of 1.93 mmol/g, which is 9.2 times higher than that obtained using the pristine fibers. These results demonstrate that hazardous wastes such as CFs can be upcycled into valuable resources.

The Synthesis and Application of 2-Cyano and -Ester Containing Anilines: Selective Copper-Catalyzed Reductive Amination, N-Benz­ylation, and Cyclization Reactions

AbstractA convenient and practical pathway to 2-cyano and 2-ester anilines is described via efficient and selective copper(II)-catalyzed reductive amination via hydrosilylation process. Both 2-cyano and 2-ester anilines were successfully synthesized with good functional group tolerance and high selectivity. The application of the 2-cyano and -iodine containing anilines was developed in the synthesis of indoloindole derivatives via CuSO4-catalyzed N-benzylation and cyclization reaction in ‘one pot’. More interestingly, the photophysical property investigations of these 2-cyano and 2-ester containing anilines exhibit excellent fluorescent properties, which have great potential application in the development of interesting near-ultraviolet optical devices in the near future.

A versatile AIE fluorogen with selective reactivity to primary amines for monitoring amination, protein labeling, and mitochondrial staining

AbstractSpecific bioconjugation for native primary amines is highly valuable for both chemistry and biomedical research. Despite all the efforts, scientists lack a proper strategy to achieve high selectivity for primary amines, not to mention the requirement of fast response in real applications. Herein, we report a chromone‐based aggregation‐induced emission (AIE) fluorogen called CMVMN as a self‐reporting bioconjugation reagent for selective primary amine identification, and its applications for monitoring bioprocesses of amination and protein labeling. CMVMN is AIE‐active and capable of solid‐state sensing. Thus, its electrospun films are manufactured for visualization of amine diffusion and leakage process. CMVMN also shows good biocompatibility and potential mitochondria‐staining ability, which provides new insight for organelle‐staining probe design. Combined with its facile synthesis and good reversibility, CMVMN would not only show wide potential applications in biology, but also offer new possibilities for molecular engineering.

A Biocatalytic Platform for the Synthesis of Enantiopure Propargylic Alcohols and Amines.

Propargylic alcohols and amines are versatile building blocks in organic synthesis. We demonstrate a straightforward enzymatic cascade to synthesize enantiomerically pure propargylic alcohols and amines from readily available racemic starting materials. In the first step, the peroxygenase from Agrocybe aegerita converted the racemic propargylic alcohols into the corresponding ketones, which then were converted into the enantiomerically pure alcohols using the (R)-selective alcohol dehydrogenase from Lactobacillus kefir or the (S)-selective alcohol dehydrogenase from Thermoanaerobacter brokii. Moreover, an enzymatic Mitsunobu-type conversion of the racemic alcohols into enantiomerically enriched propargylic amines using (R)-selective amine transaminase from Aspergillus terreus or (S)-selective amine transaminase from Chromobacterium violaceum was established. The one-pot two-step cascade reaction yielded a broad range of enantioenriched alcohol and amine products in 70–99% yield.

N‐Ligand‐Enabled Aromatic Nucleophilic Amination of 1,2‐Diaryl‐o‐Carboranes with (R2N)2Mg for Selective Synthesis of 4‐R2N‐o‐Carboranes and 2‐R2N‐m‐Carboranes

AbstractThe nucleophilic aromatic BH substitution reaction of carboranes is uncommon, compared to the electrophilic one. This work reported a pyridine‐enabled transition‐metal‐free regioselective nucleophilic aromatic cage B(4)‐H amination of 1,2‐diaryl‐o‐carboranes with magnesium bisamides, giving a series of B(4)‐aminated o‐carboranes. DFT calculations showcased a stepwise B−N formation/B−H cleavage process, in which Mg−H formation/cage closure is the rate‐determining step. Unprecedentedly, in the presence of 4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl (dtbpy), a tandem B(4)‐amination/cage isomerization reaction of o‐carboranes was discovered for the facile preparation of B(2)‐aminated m‐carboranes. Control experiments indicated that magnesium complex, bidentate ligand (dtbpy) and reaction temperature were crucial in the cage isomerization process. This direct nucleophilic aromatic cage B−H amination reaction offers an alternative strategy for selective amination of o‐ and m‐carboranes.

N-Ligand-Enabled Aromatic Nucleophilic Amination of 1,2-Diaryl-o-Carboranes with (R2 N)2 Mg for Selective Synthesis of 4-R2 N-o-Carboranes and 2-R2 N-m-Carboranes.

The nucleophilic aromatic BH substitution reaction of carboranes is uncommon, compared to the electrophilic one. This work reported a pyridine-enabled transition-metal-free regioselective nucleophilic aromatic cage B(4)-H amination of 1,2-diaryl-o-carboranes with magnesium bisamides, giving a series of B(4)-aminated o-carboranes. DFT calculations showcased a stepwise B-N formation/B-H cleavage process, in which Mg-H formation/cage closure is the rate-determining step. Unprecedentedly, in the presence of 4,4'-di-tert-butyl-2,2'-dipyridyl (dtbpy), a tandem B(4)-amination/cage isomerization reaction of o-carboranes was discovered for the facile preparation of B(2)-aminated m-carboranes. Control experiments indicated that magnesium complex, bidentate ligand (dtbpy) and reaction temperature were crucial in the cage isomerization process. This direct nucleophilic aromatic cage B-H amination reaction offers an alternative strategy for selective amination of o- and m-carboranes.

Nickel- and cobalt-based heterogeneous catalytic systems for selective primary amination of alcohol with ammonia

It is one of the critical fields of green chemistry to catalyze the selective conversion of biomass-derived alcohol and ammonia to primary amines with extensive application. Recently, catalytic systems consisting of non-noble metal nickel- and cobalt-based catalysts have been developed for catalytic alcohol amination. This paper reviewed these two types of catalytic systems, which are classified as skeleton Co and Ni catalytic systems, supported and modified Co and Ni catalytic systems, emphasized on catalysts and catalysis, and clearly explained where zero-valent cobalt or nickel is active species for catalytic reaction. In supported catalysts, the catalytic active sites constituted by the catalytic active species and its micro-environment can regulate the efficiency of catalytic the reaction. While in modified catalysts, modifiers such as metal Fe, Re and Bi may modulate the catalytic active sites and change the catalytic selectivity. There are differences in structure and size between catalysts prepared by different methods, resulting in distinct interface and electronic properties for alcohol amination, which determines the structure–activity relationships of the catalytic system.

Controlling One- or Two-Electron Oxidation for Selective Amine Functionalization by Alternating Current Frequency.

Here, we report a unique electrosynthetic method that enables the selective one-electron oxidation of tertiary amines to generate α-amino radical intermediates over two-electron oxidation to iminium cations, providing easy access to arylation products by simply applying an optimal alternating current (AC) frequency. More importantly, we have discovered an electrochemical descriptor from cyclic voltammetry studies to predict the optimal AC frequency for various amine substrates, circumventing the time-consuming trial-and-error methods for optimizing reaction conditions. This new development in AC electrolysis provides an alternative strategy to solving challenging chemoselectivity problems in synthetic organic chemistry.

Advances in the Catalytic Reductive Amination of Furfural to Furfural Amine: The Momentous Role of Active Metal Sites.

One-pot synthesis of sustainable primary amines by catalytic reductive amination of bio-based carbonyl compounds with NH3 and H2 is emerging as a promising and robust approach. The primary amines, especially furfuryl amine (FUA) derived from furfural (FUR), with a wide range of applications from pharmaceuticals to agrochemicals, have attracted much attention due to their versatility. This Review is majorly comprised of two segments on the reductive amination of FUR to FUA, one with precious (Ru, Pd, Rh) and the other with non-precious (Co, Ni) metals on different supports and in various solvent systems in the presence of NH3 and H2 . The active metal sites generated on multiple supports are accentuated with experimental evidence based on CO-diffuse reflectance infrared Fourier-transform spectroscopy, H2 temperature-programmed reduction, X-ray photoelectron spectroscopy, and calorimetry. Moreover, this Review comprehensively describes the role of acidic and basic support for the metal on the yield of FUA. Overall, this Review provides an insight into how to design and develop an efficiently robust catalyst for the selective reductive amination of a broad spectrum of carbonyl compounds to corresponding amines.

Photocatalytic selective amines oxidation coupled with H2O2 production over hyper-cross-linked polymers

Herein, a series of hyper-cross-linked polymers (HCPs) photocatalysts were synthesized through Friedel-Crafts alkylation reaction, in which benzene served as monomer and dichloromethane (DCM), dichloroethane (DCE) as well as 1,4-dimethoxybenzene (DMB) served as crosslinker. It was found that different crosslinker can change the energy level of conduction and valence band of HCPs, which is crucial for the generation of reactive oxygen species (ROS), and the separation efficiency as well as mobility of photo-generated carriers. Among of these prepared HCPs photocatalysts, DCM-HCPs exhibited highest conversion and selectivity toward benzylamine oxidation under the irradiation of blue LED lamp (455 nm) and sunlight in air atmosphere. The highest apparent quantum yield (AQY) of DCM-HCPs is 0.44%. More importantly, a high yield of H2O2 (TOF = 5712.67 μmol gcat−1 h−1) was synchronously obtained during the process of benzylamine oxidation. Synchronous-illumination X-ray photoelectron spectroscopy (SI-XPS) was used to investigate the charge transfer mechanism of HCPs. The results revealed that the photoelectrons transferred from crosslinker (–CH2-) to benzene ring for inducing benzylamine oxidation to N-benzylidenebenzylamine and H2O2 production. In addition, a series of amines and sulfides can also be smoothly oxidized at the similar conditions.

Effect of Graphite Oxide on the Catalytic Behavior of (S)-Selective Amine Transaminases

Graphite oxide (GO) has been used for the immobilization of several classes of enzymes, exhibiting very interesting properties as an immobilization matrix. However, the effect the nanomaterial has on the enzyme cannot be predicted. Herein, the effect GO has on the catalytic behavior of several (S)-selective amine transaminases [(S)-ATAs] has been investigated. These enzymes were the focus of this work as they are homodimers with pyridoxal 5′-phosphate in their active site, significantly more complex systems than other enzymes previously studied. Addition of GO (up to 0.1 mg/ml) in the reaction medium leads to activation (up to 50% improved activity) for most enzymes studied, while they maintain their temperature profile (they perform better between 40 and 45°C) and their stability. However, the effect is not universal and there are enzymes that are negatively influenced by the presence of the nanomaterial. More profound is the effect on the (S)-ATA from Chromobacterium violaceum which loses almost 50% of its activity in the presence of 0.1 mg/ml GO, while the stability was significantly decreased, losing its activity after 2 h incubation at 40°C, in the presence of 25 μg/ml GO. This negative effect seems to rise from minor secondary structure alterations; namely, a loss of α-helices and subsequent increase in random coil (∼3% in the presence of 25 μg/ml GO). We hypothesize that the effect the GO has on (S)-ATAs is correlated to the surface chemistry of the enzymes; the less negatively-charged enzymes are deactivated from the interaction with GO. This insight will aid the rationalization of ATA immobilization onto carbon-based nanomaterials.

Pd(II)‐Catalyzed Selective Amination of Inert γ‐C(sp3)−O Bonds of Aliphatic Amides with Hydrazines

AbstractThe first palladium‐catalyzed selective amination of inert methyl and methylene γ‐C(sp3)−O bonds of aliphatic amides with hydrazines by using the strategy of 8‐aminoquinoline‐directed C(sp3)−H activation/β‐O elimination/hydrofunctionalization is reported. This method features a broad scope of hydrazines, affording an efficient and simple method for the synthesis of corresponding γ‐hydrazine substituted carboxylic acid derivatives that are commonly seen in drug molecules and other bioactive compounds.

Hydroamination, Aminoboration, and Carboamination with Electrophilic Amination Reagents: Umpolung-Enabled Regio- and Stereoselective Synthesis of N-Containing Molecules from Alkenes and Alkynes.

Nitrogen (N) is ubiquitously found in bioactive molecules, pharmaceutical agents, and organic functional materials. Accordingly, development of new C-N bond-forming catalysis has been one of the long-standing research subjects in synthetic organic chemistry. In this Perspective, recent advances in highly selective amination reactions with electrophilic amination reagents are described: by taking advantage of the concept of nitrogen umpolung, otherwise challenging aminofunctionalizations, such as hydroamination, aminoboration, and carboamination, of readily available feedstock-like alkenes and alkynes are possible, giving densely functionalized complex and often chiral alkylamines with high selectivity. The scope, limitations, and reaction mechanism are briefly summarized.

Cu(ii)-Catalyzed C2-site functionalization of p-aminophenols: an approach for selective cross-dehydrogenative aminations

Site selective cross dehydrogenative aminations from precursors without preactivated C–H and N–H bonds have been challenging.

Cobalt single-atom catalysts for domino reductive amination and amidation of levulinic acid and related molecules to N-heterocycles

The development of single-atom-based catalysts (SACs), which bridge the traditional areas of homogeneous and heterogeneous catalysis, continues to be important for achieving organic synthesis in a more efficient and practical manner. Here, we report reusable cobalt-based SACs for the selective and general reductive amination of levulinic acid and related keto acids, which is of interest in the context of valorization of biomass. The optimal Co-SAC-based catalyst is prepared by pyrolysis (800°C) of cobalt-phenanthroline complexe on carbon and subsequent acid treatment. The resulting Co-SACs showed amazing activity compared with the corresponding Co-nanoparticles and displayed an excellent substrate scope for various reductive domino transformations including reactions of levulinic acid with nitro compounds and nitriles to produce various N-substituted pyrrolidones in good to excellent yields. Further, the synthesis of diverse isoindolinones from aromatic ketoacids and amines/nitro compounds was performed with the optimal catalyst system. • Preparation of stable and reusable Co-SACs catalysts • Reductive amination and amidation of levulinic acid and related molecules • Synthesis of >90 functionalized and structurally diverse N-heterocycles • Applicable for the preparation of bioactive molecules The effective catalytic conversion of biomass-based feedstocks to produce bulk and fine chemicals is a major goal of current chemical research. In this respect, specifically reductive aminations and amidations are interesting, too. To improve the sustainability of such processes, inexpensive, earth-abundant base metals should be employed as catalysts to replace precious metals that currently dominate in this field. Here, we show that cobalt catalysts with isolated metal sites (SACs) enable efficient domino reductive amination and amidation of levulinic acid and related molecules to give a wide array of N-heterocycles. We anticipate that these Co-catalytic systems will create more opportunities for the conversion of biomass-based feedstocks to many value-added compounds. The effective conversion of renewable resources, especially biomass-based feedstocks, to produce chemicals, fuels, and energy is of central importance. To valorize these feedstocks, the development of suitable catalysts, especially single-atom catalysts (SACs), which bridge traditional homogeneous and heterogeneous catalysis, is highly desired. In this respect, we developed Co-based SACs, which allow for the domino reductive amination and amidation of levulinic acid and related molecules to produce functionalized and structurally diverse N-heterocycles including bioactive molecules.

Polarization Reorientation of Carbon Nitride Induced by Local Bridge Donor for Boosting Photocatalytic H2 Evolution Integrated with Selective Amines Oxidation

Polarization Reorientation of Carbon Nitride Induced by Local Bridge Donor for Boosting Photocatalytic H2 Evolution Integrated with Selective Amines Oxidation

Edge- and bridge-engineering-mediated exciton dissociation and charge separation in carbon nitride to boost photocatalytic H2 evolution integrated with selective amine oxidation

Edge and bridge units embedded in carbon nitride frameworks have been well-designed via a facile polymerization method to boost exciton dissociation and charge separation.

Primary amines from lignocellulose by direct amination of alcohol intermediates, catalyzed by RANEY® Ni.

Primary amines are crucially important building blocks for the synthesis of a wide range of industrially relevant products. Our comprehensive catalytic strategy presented here allows diverse primary amines from lignocellulosic biomass to be sourced in a straightforward manner and with minimal purification effort. The core of the methodology is the efficient RANEY® Ni-catalyzed hydrogen-borrowing amination (with ammonia) of the alcohol intermediates, namely alkyl-phenol derivatives as well as aliphatic alcohols, obtained through the two-stage LignoFlex process. Hereby the first stage entails the copper-doped porous metal oxide (Cu20PMO) catalyzed reductive catalytic fractionation (RCF) of pine lignocellulose into a crude bio-oil, rich in dihydroconiferyl alcohol (1G), which could be converted into dihydroconiferyl amine (1G amine) in high selectivity using ammonia gas, by applying our selective amination protocol. Notably also, the crude RCF-oil directly afforded 1G amine in a high 4.6 wt% isolated yield (based on lignin content). Finally it was also shown that the here developed Ni-catalysed heterogeneous catalytic procedure was equally capable of transforming a range of aliphatic linear/cyclic primary/secondary alcohols - available from the second stage of the LignoFlex procedure - into their respective primary amines.

Correction: A multifunctional photochromic metal–organic framework with Lewis acid sites for selective amine and anion sensing

Correction for ‘A multifunctional photochromic metal–organic framework with Lewis acid sites for selective amine and anion sensing’ by Jian-Jun Liu et al., CrystEngComm, 2020, 22, 4124–4129, DOI: 10.1039/D0CE00560F.

Transaminase Engineering and Process Development for a Whole-Cell Neat Organic Process to Produce (R)-α-Phenylethylamine

The production of (R)-α-phenylethylamine ((R)-α-PEA) from acetophenone is a classic reaction for the characterization of transaminases. However, developing a commercially viable transaminase process to manufacture (R)-α-PEA usually suffers from two drawbacks. One is related to the biocatalyst itself, since transaminases are easily inhibited by (R)-α-PEA at low concentrations. The other drawback is a common low space-time yield of typical transaminase processes, because the reaction equilibrium greatly favors the formation of acetophenone over (R)-α-PEA. In this study, an (R)-selective amine transaminase (TA) from Aspergillus fumigatus Af293 was engineered by a directed evolution for an efficient process to produce (R)-α-PEA. The evolved variant showed an over 3000-fold increase in activity and a tolerance with 2.0 M isopropylamine as well as the complete absence of inhibition by (R)-α-PEA. At the same time, using this evolved TA variant, a continuous neat organic process using whole-cells was developed where the biocatalyst and remaining acetophenone can be efficiently separated from (R)-α-PEA and reused repetitively. This not only decreases the overall cost and waste generation but also achieves a very high space-time yield of up to 168 g L–1 d–1 of (R)-α-PEA in an industrial pilot scale setup.