Reductive Amination Method Research Articles

Synthesis and unambiguous NMR characterization of linear and branched N-alkyl chitosan derivatives

Chitosan, sourced from abundant chitin-rich waste streams, emerges as a promising candidate in the realm of future functional materials and chemicals. While showing numerous advantageous properties, chitosan sometimes falls short of competing with today's non-renewable alternatives. Chemical derivatization, particularly through N-alkylation, proves promising in enhancing hydrophobic functionalities. This study synthesizes fifteen chitosan derivatives (degree of substitution = 2–10 %) using an improved reductive amination method. Next, selective depolymerization through acid hydrolysis reduced the chain rigidity imposed by the polymer backbone. This facilitated unambiguous structural characterization of the synthesized compounds using a combination of common NMR techniques. Two potential side reactions are identified for the first time, emphasizing the need for detailed structural information to unlock the true potential of these derivatives in future applications. HypothesisThe increase in chain mobility induced by the selective depolymerization of aliphatic N-alkyl chitosan derivatives allows for an unambiguous NMR characterization.

Iridium-catalysed reductive allylic amination of α,β-unsaturated aldehydes.

Allylic amination is a powerful tool for constructing N-allylic amines widely found in bioactive molecules. Generally, allylic alcohols and unsaturated hydrocarbons have been considered for allylic amination reactions to minimize waste production. Herein, we present an iridium-catalysed method for reductive allylic amination of α,β-unsaturated aldehydes with amines to afford N-allylic amines under air conditions. This protocol is demonstrated to provide products from many substrates (41 examples) in moderate-to-excellent yields. This synthetic methodology is also highlighted by the synthesis of drug molecules, optically pure products, as well as scale-up experiments.

Making and Breaking of C-N Bonds: Applications in the Synthesis of Unsymmetric Tertiary Amines and α-Amino Carbonyl Derivatives.

An operationally simple process has been developed for the synthesis of unsymmetrical amines and α-amino carbonyl derivatives in the absence of a catalyst, ligand, oxidant, or any additives. Contrary to known reductive amination methods, this protocol is amenable to substrates containing other reducible groups. This process effectively results in consecutive cleavage and formation of C-N bonds. DFT studies and Hammett analysis provide useful insight into the mechanism. The role of noncovalent interactions as a stabilizing factor have been examined in the protocol. A wide range of alkyl-bromides have been coupled efficiently with a variety of dimethyl anilines to get unsymmetric tertiary amines with yields up to 90%. This methodology was further extended to the synthesis of α-amino carbonyl derivatives with yields up to 93%.

Impurity profiling of methamphetamine synthesized from methyl α-acetylphenylacetate.

The group of P2P precursors including α-phenylacetoacetonitrile (APAAN), α-phenylacetoamide (APAA) and methyl α-acetylphenylacetate (MAPA) has become increasingly popular in Europe and other parts of the world in the last decade. Previous investigations have reported the use of APAAN in the synthesis of amphetamine and methamphetamine and identified a range of characteristic impurities. This research has expanded upon the current literature by investigating the use of MAPA in the synthesis of methamphetamine. In this study methamphetamine was synthesized via three common clandestine methods: the Leuckart synthesis and two reductive amination methods. We report the identification of seven impurities, four of which are methyl ester equivalents of impurities previously reported for the detection of APAAN. These are methyl 2-phenylbut-2-enoate, methyl 2-phenyl-3-hydroxybutanoate, methyl 3-(methylamino)-2-phenylbut-2-enoate and methyl 3-(methylamino)-2-phenylbutanoate. The other impurities identified are ethyl ester compounds formed via transesterification of the methyl ester due to the reaction solvent. This susceptibility for transesterification suggests that identification of the pre-precursor used may not always be straightforward and may be dependent on the reaction conditions employed. Of the impurities reported, methyl 3-(methylamino)-2-phenylbutanoate was deemed to be a potentially reliable impurity for detection of the use of MAPA; however, it is expected that lower levels of characteristic impurities may be detected in methamphetamine synthesized from MAPA than that from APAAN.

Impurity profiling of methamphetamine synthesised from α-phenylacetoacetonitrile (APAAN).

The rise in popularity of 'designer' precursor compounds for the synthesis of amphetamine-type stimulants poses a significant challenge to law enforcement agencies. One such precursor is α-phenylacetoacetonitrile (APAAN). APAAN emerged in Europe in 2010 and quickly became one of the most popular precursors for amphetamine synthesis in that region. Previous literature has identified four APAAN-specific impurities formed in the synthesis of amphetamine; however, there is currently no research on the use of APAAN in the synthesis of methamphetamine, which is more likely to be employed in a non-European market. In this study methamphetamine was synthesised via three common clandestine methods: the Leuckart method and two reductive amination methods. We report the identification of five new impurities and two previously identified impurities characteristic for the use of APAAN in the synthesis of methamphetamine. The newly identified impurities were characterised by MS and NMR and determined to be (E)-3-(methylamino)-2-phenylbut-2-enenitrile, 3-(methylamino)-2-phenylbutanenitrile, 3-methyl-2,4-diphenylpentanedinitrile, 2-phenylbutyronitrile and 3-hydroxy-2-phenylbutanenitrile.

Earth-abundant Metal-catalyzed Reductive Amination: Recent Advances and Prospect for Future Catalysis.

Nitrogen-containing compounds, as an important class of chemicals, have been used widely in pharmaceuticals, materials synthesis. Transition metal-catalyzed reductive amination of an aldehyde or a ketone with ammonia or an amine has been proved to be an efficient and practical method for the preparation of nitrogen-containing compounds in academia and industry for a century. Given the above, several effective methods using transition metals have been developed in recent years. Noble transition metals like Pd, Pt, and Au-based catalysts have been predominately used in reductive amination. Because of their high prices, strict official regulations of residues in pharmaceuticals, and deleterious effects on the biological system, their industrial applications are severely hampered. With the increasing sustainable and environmental problems, the Earth-abundant transition metals including Ti, Fe, Co, Ni, and Zr have also been investigated for the reductive amination reaction and showed great potential to the advancement of sustainable and cost-effective reductive amination processes. This critical review will mainly summarize the work using Earth-abundant metals. The effects of different transition metals used in catalytic reduction amination were discussed and compared, and some suggestions were given. The last section highlights the catalytic activities of bi- and tri-metallic catalysts. Indeed, this latter family is very promising and simultaneously benefits from increased stability, and selectivity, compared to monometallic NPs, due to synergistic substrate activation. Few comprehensive reviews focusing on Earth-abundant transition metals catalyst has been published since 1948, although several authors reported some summaries dealing with one or the other part of this aspect. It is hoped that this critical review will inspire researchers to develop new efficient and selective earth-abundant metal catalysts for highly, environmentally sustainable reductive amination methods, as well as improve the pharmaceutical industry and related chemical synthesis company traditional method with the utilization of the green method widely.

Fluorescent labeling affected the structural/conformational properties of arabinoxylans

Three fluorescent-labeling methods, including DMSO/DBTD, reductive amination and fluoresceinamine (FA), were applied to label arabinoxylan (AX). The conjugates were named AF, ATF and ACF, respectively. Compared to AX, the water solubility of AF significantly decreased while that of ATF significantly increased (p < 0.05); both showed decreased solubility with increasing degree of substitution (DS). However, AX was not successfully labeled by the FA method due to poor solubility. The structural and conformational properties of the AF and ATF conjugates under different DS were compared. Results showed that fluorochrome (FITC) was successfully grafted onto AX molecule by using the DMSO/DBTD and reductive amination methods. A slight increased Mw was noticed for both AF and ATF. AF existed in a more compact conformation, while the chain conformation of ATF was more elongated at a lower DS (1.15 %) and more compact at a higher DS (1.34 %).

Glyco-functionalized graphene oxides as green antibacterial absorbent materials

Abstract Green glyco-conjugated graphene oxides, incorporating mannose and glucose, developed in the design of new antibacterial absorbents. In this context, graphene oxide (GO) was functionalized by ethylenediamine (EDA). Then, the aminated GO (rG-NH2) modified by Glucose (Glu) and Mannose (Man) separately via reductive amination method to fabricate glyco-conjugated GOs known as rG-NH-Glu and rG-NH-Man respectively. The biofunctionalized GOs were characterized by FTIR spectroscopy, X-ray diffraction, Raman spectroscopy, SEM and TGA technique. The glyco-conjugated GOs showed antibacterial activities. The mannose conjugated GOs exhibited higher bactericidal efficiency than GO and rGO-NH-Glu. Moreover, the obtained glyco-conjugated GOs used as absorbent. The results showed that they could effectively remove MB. The maximum adsorption capacity of rGO-NH-Glu and rGO-NH-Man were 100 and 96 mg/g, respectively. Glucose conjugated GOs could remove MB very faster than mannose conjugated ones. Finally, the adsorption kinetics was studied. The results showed that Kinetics data were fitted with the pseudo second order model. Glyco-conjugated GOs could develop new promising materials with enhanced antibacterial activities as well as adsorbent with higher adsorption capacities. The glyco-conjugated GOs could be applied for treatment of polluted waters by pathogenic bacteria and dyes and especially those conjugated with mannose could be considered as potent bacterial targeting agents.

N-Benzyl-N-methyl-dodecan-1-amine, a novel compound from garlic, exerts anti-cancer effects on human A549 lung cancer cells overexpressing cancer upregulated gene (CUG)2

Dietary garlic has been suggested to possess anticancer properties, and several attempts have been made to isolate the anticancer compounds. In this study, we efficiently synthesized N-benzyl-N-methyl-dodecan-1-amine (BMDA) by the reductive amination method. We evaluated the potential anticancer activities of BMDA against A549 lung cancer cells with cancer stem cell-like phenotypes due to the overexpression of cancer upregulated gene (CUG)2. N-Benzyl-N-methyl-dodecan-1-amine treatment sensitized A549 cells overexpressing CUG2 (A549-CUG2) to apoptosis and autophagy compared with those of the control cells. The treatment with BMDA also reduced tumor development in xenografted nude mice. Furthermore, BMDA inhibited cell migration, invasion, and sphere formation in A549-CUG2 cells, in which TGF-β signaling is involved. Further analysis showed that BMDA hindered TGF-β promoter activity, protein synthesis, and phosphorylation of Smad2, thus decreasing the expression of TGF-β-targeted proteins, including Snail and Twist. N-Benzyl-N-methyl-dodecan-1-amine also decreased Twist expression in vivo. In addition, BMDA inhibited Akt-ERK activities, β-catenin expression, and its transcriptional activity. These results suggest that BMDA can be a promising anticancer agent against cancer cells overexpressing CUG2.

Reductive Amination Combining Dimethylation for Quantitative Analysis of Early-Stage Glycated Proteins.

Due to the critical role glycation plays in many serious pathological conditions, such as diabetes, it is of great significance to discover protein glycation at an early stage for precaution and prediction of the disease. Here, a method of reductive amination combining dimethylation (RAD) was developed for the quantification of early-stage glycated proteins. The quantitative analysis was first carried out by reducing the samples using NaBH3CN or NaBD3CN, resulting in a 1 Da mass shift and the stabilization of early-stage protein glycation. The two samples were then digested and isotopically dimethylated to achieve the mass shift of 4 m + 3 n ( m represents the number of N-termini and Lys residues, and n represents the number of glycated sites) between light- and heavy-labeled glycated peptides for quantification. Consequently, the false positive result can be removed according to the different mass shifts of glycated peptides and non-glycated peptides. In quantification of glycated myoglobin, RAD showed good linearity ( R2 > 0.99) and reproducibility (CVs ≤ 1.6%) in 2 orders of magnitude (1:10-10:1). RAD was then applied to quantify the endogenous glycated proteins in the serum of diabetic patients, revealing significant differences in the glycation level between the patients with complicated retinal detachment and those without. In conclusion, RAD is an effective method for quantifying endogenous glycated proteins.

Reductive Amination by Photoredox Catalysis and Polarity-Matched Hydrogen Atom Transfer.

The excitation of a RuII photosensitizer in the presence of ascorbic acid leads to the reduction of iminium ions to electron-rich α-aminoalkyl radical intermediates, which are rapidly converted into reductive amination products by thiol-mediated hydrogen atom transfer (HAT). As a result, the reductive amination of carbonyl compounds with amines by photoredox catalysis proceeds in good to excellent yields and with broad substrate scope and good functional group tolerance. The three key features of this work are 1) the rapid interception of electron-rich α-aminoalkyl radical intermediates by polarity-matched HAT in a photoredox reaction, 2) the method of reductive amination by photoredox catalysis itself, and 3) the application of this new method for temporally and spatially controlled reactions on a solid support, as demonstrated by the attachment of a fluorescent dye on an activated cellulose support by photoredox-catalyzed reductive amination.

N-[4-(N,N,N-trimethylammonium)benzyl]chitosan chloride: Synthesis, interaction with DNA and evaluation of transfection efficiency

А novel cationic chitosan derivative, N-[4-(N,N,N-trimethylammonium)benzyl]chitosan chloride (TMAB-CS), with different degrees of substitution (DS) was synthesized by a chemoselective interaction of 4-formyl-N,N,N-trimethylanilinium iodide with chitosan amino groups using a reductive amination method. Several factors (pH, reactant ratio, reaction time, and chitosan structure) were studied for their effects on the DS of the resulting TMAB-CS. The obtained derivatives were characterized by 1H NMR and FTIR spectroscopy. Turbidimetric titration showed enhanced solubility over a wide pH range even for low-substituted TMAB-CS. TMAB-CS provided strong DS-dependent binding of plasmid DNA. Dynamic light scattering measurements revealed the formation of stable polyplexes with hydrodynamic diameters of 200–300nm and ζ-potential of 20–30mV. TMAB-CS with relatively low DS (25%) demonstrated more pronounced transfection efficiency (up to 2000 cell/cm2) of plasmid DNA into the HEK293 cell line promoted by free TMAB-CS. The positive effects of lower DS can be related to a better polyplex dissociation within the cell. The cytotoxicity of TMAB-CS was comparable to that of the initial chitosan at concentrations up to 300ng/μL, even at high DS.

Facile and Scalable One-Step Method for Amination of Graphene Using Leuckart Reaction

A very simple method of reductive amination, based on the Leuckart reaction, is reported. This method enables not only the reduction of graphite oxide but also results in reduced graphene oxide functionalized with amine groups, where the amination degree is 3.2 at. % as determined by XPS. The dominant nitrogen functional group was primary amine, but pyridines and lactam groups were also observed. It was found that the amino-functionalized reduced graphene oxide is a semi-metallic material because of the lack of band gap, unlike the graphite oxide that presented a band gap of 2.16 eV.

A method for the analysis of sugars in biological systems using reductive amination in combination with hydrophilic interaction chromatography and high resolution mass spectrometry

Separation of sugar isomers extracted from biological samples is challenging because of their natural occurrence as alpha and beta anomers and, in the case of hexoses, in their pyranose and furanose forms. A reductive amination method was developed for the tagging of sugars with the aim of it becoming part of a metabolomics work flow. The best separation of the common hexoses (glucose, fructose, mannose and galactose) was achieved when 2H5-aniline was used as the tagging reagent in combination with separation on a ZICHILIC column. The method was used to tag a range of sugars including pentoses and uronic acids. The method was simple to perform and was able to improve both the separation of sugars and their response to electrospray ionisation. The method was applied to the profiling of sugars in urine where a number of hexose and pentose isomers could be observed. It was also applied to the quantification of sugars in post-mortem brain samples from three control samples and three samples from individuals who had suffered from bipolar disorder.

Environmentally friendly synthesis of secondary amines via one-pot reductive amination over a heterogeneous Co–Nx catalyst

The application of earth-abundant transition metal catalysts in the mild and selective synthesis of secondary amines via the reductive amination method is very challenging.

Transfer hydrogenative reductive amination of aldehydes in aqueous sodium formate solution

A practical direct reductive amination reaction of aldehydes in aqueous sodium formate solution which produces amines in good yields under mild conditions is described. The amount and strength of the acid additives were critical factors to affect the reaction selectivities. This reductive amination method has great application potential for the synthesis of amine products given the mild conditions, short reaction time, the use of water as a solvent, and the use of benign hydrogen sources.

A novel reductive amination method with isotopic formaldehydes for the preparation of internal standard and standards for determining organosulfur compounds in garlic

Garlic (Allium sativum) is a long-cultivated plant that is widely utilized in cooking and has been employed as a medicine for over 4000years. In this study, we fabricated standards and internal standards (ISs) for absolute quantification via reductive amination with isotopic formaldehydes. Garlic has four abundant organosulfur compounds (OSCs): S-allylcysteine, S-allylcysteinine sulfoxide, S-methylcysteine, and S-ethylcysteine are abundant in garlic. OSCs with primary amine groups were reacted with isotopic formaldehydes to synthesize ISs and standards. Cooked and uncooked garlic samples were compared, and we utilized tandem mass spectrometry equipped with a selective reaction monitoring technique to absolutely quantify the four organosulfur compounds.

Preparation and Characteristic of Dextran-BSA Antibody and Establishment of its ELISA Immunoassay

The enzyme-linked immunosorbent assay (ELISA) is a potential tool for the determination of dextran. In this study, dextran neoglycoprotein antigens were prepared by Reductive Amination method, and were confirmed by SDS-PAGE and free amino detection. The impact factors such as different oxidation degree of dextran, the conjugate reaction time to BSA were investigated. The best preparation conditions were obtained (ndextran/noxidant of NaIO4 = 1/120, the reaction time of 24 h), and the antigen with best combination with standard was obtained. The antigens interacted with standard antibody and were evaluated through ELISA. The immunogen was immunized with white rabbits to obtained antibody, respectively. A general and broad class-specific ELISA immunoassay was developed for dextran detection according to ELISA theory. The optimized conditions of assay used coating antigen at 10 μg/mL, reaction time of antibody and rabbit-anti-bovine IgG in 45 min, blocking reagents with 5% calf serum. The developed ELISA detection method with good linear and accuracy was put to use for quantitative analysis of dextran T40 in commercial sugarpractical for detection of dextran.

ChemInform Abstract: Reductive Amination Without an External Hydrogen Source.

A method of reductive amination without an external hydrogen source is reported. Carbon monoxide is used as the reductant. The reaction proceeds efficiently for a variety of carbonyl compounds and amines at low catalyst loadings and is mechanistically interesting as it does not seem to involve molecular hydrogen.

Immunization and chemical conjugation of Bm95 obtained from Pichia pastoris enhances the immune response against vaccinal protein and Neisseria meningitidis capsular polysaccharide

The ectoparasite Rhipicephalus (Boophilus) microplus causes severe economic losses to the cattle industry in tropical and subtropical regions, and transmits endoparasites, such as Babesia bovis. The glycoprotein Bm95 is homologous to Bm86, a surface membrane protein of gut epithelial cells in R. microplus, and has been shown to efficiently control this ectoparasite in regions of the Americas. The immunostimulant properties of Bm86 have already been demonstrated after its coinjection with hepatitis B surface antigen (HBsAg) and the infectious bovine rhinotracheitis virus. This study evaluated the carrier and immunostimulant properties of Bm95 using low immunogenic Neisseria meningitidis capsular C polysaccharide (Men CpS) and HBsAg. We produced two polysaccharide-Bm95 conjugates by carbodiimide (MenCpSBm-c) and reductive amination (MenCpSBm-ra) methods. These conjugates were characterized and evaluated in mice. Antibody titers against Men CpS were significantly higher in mice immunized with MenCpSBm-ra (2,350±250, P<0.01) than in those immunized with MenCpSBm-c (250±75) or Men CpS (570±104). The study data indicate effective immunological memory after booster inoculation in mice immunized with MenCpSBm-ra. Additionally, significant humoral immunity against HBsAg was documented in mice coimmunized via the intranasal route with recombinant Bm95 (11,400±345) and HBsAg (128,000±250) compared with mice immunized only with HBsAg (400±40) or Bm95 (5,461±150, P<0.01). In conclusion, the immunostimulatory properties of recombinant Bm95 make it a useful element for developing safer conjugated vaccines against bacterial pathogens and for evaluation against ticks and tick-borne diseases in the context of a polyvalent veterinary vaccine.