Dynamic Covalent Template-Guided Screen for Nucleic Acid-Targeting Agents.

Trinucleotide repeat diseases such as myotonic dystrophy type 1 (DM1) and Huntington's disease (HD) are caused by expanded DNA repeats that can be used as templates to synthesize their own inhibitors. Because it would be particularly advantageous to reversibly assemble multivalent nucleic acid-targeting agents in situ, we sought to develop a target-guided screen that uses dynamic covalent chemistry to identify multitarget inhibitors. We report the synthesis of a library of amine- or aldehyde-containing fragments. The assembly of these fragments led to a diverse set of hit combinations that was confirmed by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) in the presence of DM1 and HD repeat sequences. Of interest for both diseases, the resulting hit combinations inhibited transcription selectively and in a cooperative manner in vitro, with inhibitory concentration (IC50) values in the micromolar range. This dynamic covalent library and screening approach could be applied to identify compounds that reversibly assemble on other nucleic acid targets.

Synthesis and biological evaluation of thieno[3,2-c]pyrazol-3-amine derivatives as potent glycogen synthase kinase 3ß inhibitors for Alzheimer's disease.

Glycogen synthase kinase 3ß (GSK-3ß) catalyses the hyperphosphorylation of tau protein in the Alzheimer's disease (AD) pathology. A series of novel thieno[3,2-c]pyrazol-3-amine derivatives were designed and synthesised and evaluated as potential GSK-3ß inhibitors by structure-guided drug rational design approach. The thieno[3,2-c]pyrazol-3-amine derivative 16b was identified as a potent GSK-3ß inhibitor with an IC50 of 3.1 nM in vitro and showed accepted kinase selectivity. In cell levels, 16b showed no toxicity on the viability of SH-SY5Y cells at the concentration up to 50 µM and targeted GSK-3ß with the increased phosphorylated GSK-3ß at Ser9. Western blot analysis indicated that 16b decreased the phosphorylated tau at Ser396 in a dose-dependent way. Moreover, 16b effectively increased expressions of ß-catenin as well as the GAP43, N-myc, and MAP-2, and promoted the differentiated neuronal neurite outgrowth. Therefore, the thieno[3,2-c]pyrazol-3-amine derivative 16b could serve as a promising GSK-3ß inhibitor for the treatment of AD.

A new method for C(sp2)-H sulfonylmethylation with glyoxylic acid and sodium sulfinates.

We herein describe a C4 sulfonylmethylation of pyrazol-5-amines with glyoxylic acid and sodium sulfinates. The reaction only needed water as a solvent, and it featured mild reaction conditions, simple operation, and high regioselectivity. Various C4 sulfonylmethylated pyrazol-5-amines were obtained in good to excellent yields. Moreover, this sulfonylmethylation method was applicable for C(sp2)-H sulfonylmethylation of other substrates such as enamines, indoles, and antipyrines by adding a catalyst and changing the solvent. Biological evaluation revealed that some products had antiproliferative activity against cancer cell lines.

[Exhaustive Syntheses of Deuterium-labelled Compounds].

Deuterium (2H, D) is a stable isotope of hydrogen (1H). Deuterium-incorporated (labelled) compounds are widely utilized in various scientific fields such as mechanistic studies of organic reactions, elucidation of drug metabolism, application as tracers for microanalysis. Recently, development of heavy drugs and molecular imaging using techniques such as neutron scattering and Raman spectroscopy are spotlighted. We have developed various deuterium-incorporated compounds using D2O as an inexpensive deuterium source to construct novel functional materials. The use of platinum group metals on carbon as catalysts could result in the multi-deuteration of compounds in the mixed solvents of 2-propanol and D2O, and site-selectively deuterated compounds can be synthesized by organocatalytic methods. In this review, the latter deuteration methods using organocatalysts and their applications are summarized. Terminal alkynes smoothly underwent deuterium incorporation by using triethylamine as an organic base or a solid resin possessing the tertiary amine moiety in the same molecule to give mono-deuterated alkynes. These compounds were partially reduced over our prepared specific palladium catalyst under atmospheric D2 gas to produce tri-deuterated alkenes. Achiral or chiral di-deuterated ß-nitro alcohols were also prepared by the organic-base-catalyzed deuteration of nitromethane, followed by nitroaldol reactions in a one pot manner. The mono-deuteration of aromatic aldehyde could be effectively catalyzed by N-heterocyclic carbene. Furthermore, the α-deuteration of aliphatic aldehydes using a basic resin catalyst and the subsequent Knoevenagel condensation with malononitrile could provide γ-deuterium-incorporated α,ß-unsaturated nitrile derivatives. The deuterated compounds thus obtained can be important synthetic precursors to construct the deuterium-incorporated target functional materials.

Enantioselective Synthesis of α-Trifluoromethyl Amines via Biocatalytic N-H Bond Insertion with Acceptor-Acceptor Carbene Donors.

The biocatalytic toolbox has recently been expanded to include enzyme-catalyzed carbene transfer reactions not occurring in Nature. Herein, we report the development of a biocatalytic strategy for the synthesis of enantioenriched α-trifluoromethyl amines through an asymmetric N-H carbene insertion reaction catalyzed by engineered variants of cytochrome c552 from Hydrogenobacter thermophilus. Using a combination of protein and substrate engineering, this metalloprotein scaffold was redesigned to enable the synthesis of chiral α-trifluoromethyl amino esters with up to >99% yield and 95:5 er using benzyl 2-diazotrifluoropropanoate as the carbene donor. When the diazo reagent was varied, the enantioselectivity of the enzyme could be inverted to produce the opposite enantiomers of these products with up to 99.5:0.5 er. This methodology is applicable to a broad range of aryl amine substrates, and it can be leveraged to obtain chemoenzymatic access to enantioenriched ß-trifluoromethyl-ß-amino alcohols and halides. Computational analyses provide insights into the interplay of protein- and reagent-mediated control on the enantioselectivity of this reaction. This work introduces the first example of a biocatalytic N-H carbenoid insertion with an acceptor-acceptor carbene donor, and it offers a biocatalytic solution for the enantioselective synthesis of α-trifluoromethylated amines as valuable synthons for medicinal chemistry and the synthesis of bioactive molecules.

Development of naringenin-O-alkylamine derivatives as multifunctional agents for the treatment of Alzheimer's disease.

In this study, a series of naringenin-O-alkylamine derivatives were designed and obtained by introducing an alkylamine fragment into the naringenin skeleton. The in vitro biological activity results revealed that compounds 5f and 7k showed good antioxidant activity with ORAC values of 2.3eq and 1.2eq, respectively. Compounds 5f and 7k were reversible and excellent huAChE inhibitors with IC50 values of 0.91 µM and 0.57 µM, respectively. Moreover, compounds 5f and 7k could inhibit self-induced Aß1-42 aggregation with 62.1% and 43.8% inhibition rate, respectively, and significantly inhibited huAChE-Aß1-40 aggregation with 51.7% and 43.4% inhibition rate, respectively. In addition, compounds 5f and 7k were selective metal chelators and remarkably inhibited Cu2+-induced Aß1-42 aggregation with 73.5% and 68.7% inhibition rates, respectively. Furthermore, compounds 5f and 7k could cross the blood-brain barrier in vitro and displayed good neuroprotective effects and anti-inflammatory properties. Further investigation showed that compound 5f did not show obvious hepatotoxicity and displayed a good hepatoprotective effect by its antioxidant activity. The in vivo study displayed that compound 5f significantly improved scopolamine-induced mice memory impairment. Therefore, compound 5f was a potential multifunctional candidate for the treatment of AD.

Synthesis of N-Aminated Salts of Aliphatic tert-Amines, (Trialkyl)amidines, and (Pentaalkyl)guanidines by Electrophilic Amination in an Ethereal Solvent.

The electrophilic amination of nitrogen-based nucleophiles, including strong organic bases, was conducted in an Et2O solvent using O-(mesitylenesulfonyl)hydroxylamine. Aliphatic tert-amines and N,N,N'-(trialkyl)amidines rapidly formed precipitates of the corresponding aminated salts in high yields. The amination of the highly basic and sterically hindered N,N,N',N',N″-(pentaalkyl)guanidines was achieved under modified conditions, although the yields were moderate because of a competing side reaction caused by the acid-base equilibrium.

Transaminases as suitable catalysts for the synthesis of enantiopure ß,ß-difluoroamines.

Transaminases have shown the ability to catalyze the amination of a series of aliphatic and (hetero)aromatic α,α-difluorinated ketones with high stereoselectivity, thus providing the corresponding ß,ß-difluoroamines in high isolated yields (55-82%) and excellent enantiomeric excess (>99%). It was also observed that these activated substrates could be quantitatively transformed by employing a small molar excess of the amine donor since this amination process was thermodynamically favored. Selected transformations could be scaled up to 500 mg, showing the robustness of this methodology.

A Chemoenzymatic Cascade Combining a Hydration Catalyst with an Amine Dehydrogenase: Synthesis of Chiral Amines.

The combination of biocatalysis and transition-metal catalysis can complement synthetic gaps only in a chemical or biological process. However, the intrinsic mutual deactivation between enzymatic and chemical species is a significant challenge in a single operation. To address the above issue, we developed an encapsulated Au/carbene combined with a free amine dehydrogenase as a co-catalyst system that enables an efficient hydration/amination enantioselective cascade process to be accomplished. The mechanistic investigation discloses dual catalysis comprised of alkyne hydration, followed by a reductive amination process.

Direct Enzymatic Synthesis of Fatty Amines from Renewable Triglycerides and Oils.

Fatty amines represent an important class of commodity chemicals which have broad applicability in different industries. The synthesis of fatty amines starts from renewable sources such as vegetable oils or animal fats, but the process has multiple drawbacks that compromise the overall effectiveness and efficiency of the synthesis. Herein, we report a proof-of-concept biocatalytic alternative towards the synthesis of primary fatty amines from renewable triglycerides and oils. By coupling a lipase with a carboxylic acid reductase (CAR) and a transaminase (TA), we have accomplished the direct synthesis of multiple medium and long chain primary fatty amines in one pot with analytical yields as high as 97 %. We have also performed a 75 mL preparative scale reaction for the synthesis of laurylamine from trilaurin, obtaining 73 % isolated yield.

XGBoost-based intelligence yield prediction and reaction factors analysis of amination reaction.

Buchwald-Hartwig amination reaction catalyzed by palladium plays an important role in drug synthesis. In the last few years, machine learning-assisted strategies emerged and quickly gained attention. In this article, an importance and relevance-based integrated feature screening method is proposed to effectively filter high-dimensional feature descriptor data. Then, a regularized machine learning boosting tree model, eXtreme Gradient Boosting, is introduced to intelligently predict reaction performance in multidimensional chemistry space. Furthermore, convergence, interpretability, generalization, and the internal association between reaction conditions and yields are excavated, which provides intelligent assistance for the optimal design of coupling reaction system and evaluating the reaction conditions. Compared with recently published results, the proposed method requires fewer feature descriptors, takes less time, and achieves more accurate prediction accuracy.

Electrochemical Synthesis of Allylic Amines from Terminal Alkenes and Secondary Amines.

Allylic amines are valuable synthetic targets en route to diverse biologically active amine products. Current allylic C-H amination strategies remain limited with respect to the viable N-substituents. Herein, we disclose a new electrochemical process to prepare aliphatic allylic amines by coupling two abundant starting materials: secondary amines and unactivated alkenes. This oxidative transformation proceeds via electrochemical generation of an electrophilic adduct between thianthrene and the alkene substrates. Treatment of these adducts with aliphatic amine nucleophiles and base provides allylic amine products in high yield. This synthetic strategy is also amenable to functionalization of feedstock gaseous alkenes at 1 atm. In the case of 1-butene, high Z-selective crotylation is observed. This strategy, however, is not limited to the synthesis of simple building blocks; complex biologically active molecules are suitable as both alkene and amine coupling partners. Preliminary mechanistic studies implicate vinylthianthrenium salts as key reactive intermediates.

Dual Nickel/Photoredox-Catalyzed Deaminative Cross-Coupling of Sterically Hindered Primary Amines.

We report a method to activate α-3° amines for deaminative arylation via condensation with an electron-rich aldehyde and merge this reactivity with nickel metallaphotoredox to generate benzylic quaternary centers, a common motif in pharmaceuticals and natural products. The reaction is accelerated by added ammonium salts. Evidence is provided in support of two roles for the additive: inhibition of nickel black formation and acceleration of the overall reaction rate. We demonstrate a robust scope of amine and haloarene coupling partners and show an expedited synthesis of ALK2 inhibitors.

Tunable and Practical Homogeneous Organic Reductants for Cross-Electrophile Coupling.

The syntheses of four new tunable homogeneous organic reductants based on a tetraaminoethylene scaffold are reported. The new reductants have enhanced air stability compared to current homogeneous reductants for metal-mediated reductive transformations, such as cross-electrophile coupling (XEC), and are solids at room temperature. In particular, the weakest reductant is indefinitely stable in air and has a reduction potential of -0.85 V versus ferrocene, which is significantly milder than conventional reductants used in XEC. All of the new reductants can facilitate C(sp2)-C(sp3) Ni-catalyzed XEC reactions and are compatible with complex substrates that are relevant to medicinal chemistry. The reductants span a range of nearly 0.5 V in reduction potential, which allows for control over the rate of electron transfer events in XEC. Specifically, we report a new strategy for controlled alkyl radical generation in Ni-catalyzed C(sp2)-C(sp3) XEC. The key to our approach is to tune the rate of alkyl radical generation from Katritzky salts, which liberate alkyl radicals upon single electron reduction, by varying the redox potentials of the reductant and Katritzky salt utilized in catalysis. Using our method, we perform XEC reactions between benzylic Katritzky salts and aryl halides. The method tolerates a variety of functional groups, some of which are particularly challenging for most XEC transformations. Overall, we expect that our new reductants will both replace conventional homogeneous reductants in current reductive transformations due to their stability and relatively facile synthesis and lead to the development of novel synthetic methods due to their tunability.

Photoenzymatic Synthesis of α-Tertiary Amines by Engineered Flavin-Dependent "Ene"-Reductases.

α-Tertiary amines are a common motif in pharmaceutically important molecules but are challenging to prepare using asymmetric catalysis. Here, we demonstrate engineered flavin-dependent 'ene'-reductases (EREDs) can catalyze radical additions into oximes to prepare this motif. Two different EREDs were evolved into competent catalysts for this transformation with high levels of stereoselectivity. Mechanistic studies indicate that the oxime contributes to the enzyme templated charge-transfer complex formed between the substrate and cofactor. These products can be further derivatized to prepare a variety of motifs, highlighting the versatility of ERED photoenzymatic catalysis for organic synthesis.

Site-Selective α-C-H Functionalization of Trialkylamines via Reversible Hydrogen Atom Transfer Catalysis.

Trialkylamines are widely found in naturally occurring alkaloids, synthetic agrochemicals, biological probes, and especially pharmaceuticals agents and preclinical candidates. Despite the recent breakthrough of catalytic alkylation of dialkylamines, the selective α-C(sp3)-H bond functionalization of widely available trialkylamine scaffolds holds promise to streamline complex trialkylamine synthesis, accelerate drug discovery, and execute late-stage pharmaceutical modification with complementary reactivity. However, the canonical methods always result in functionalization at the less-crowded site. Herein, we describe a solution to switch the reaction site through fundamentally overcoming the steric control that dominates such processes. By rapidly establishing an equilibrium between α-amino C(sp3)-H bonds and a highly electrophilic thiol radical via reversible hydrogen atom transfer, we leverage a slower radical-trapping step with electron-deficient olefins to selectively forge a C(sp3)-C(sp3) bond with the more-crowded α-amino radical, with the overall selectivity guided by the Curtin-Hammett principle. This subtle reaction profile has unlocked a new strategic concept in direct C-H functionalization arena for forging C-C bonds from a diverse set of trialkylamines with high levels of site selectivity and preparative utility. Simple correlation of site selectivity and 13C NMR shift serves as a qualitative predictive guide. The broad consequences of this dynamic system, together with the ability to forge N-substituted quaternary carbon centers and implement late-stage functionalization techniques, hold potential to streamline complex trialkylamine synthesis and accelerate small-molecule drug discovery.

Nitrene transfers mediated by natural and artificial iron enzymes.

Amines are ubiquitous in biology and pharmacy. As a consequence, introducing N functionalities in organic molecules is attracting strong continuous interest. The past decade has witnessed the emergence of very efficient and selective catalytic systems achieving this goal thanks to engineered hemoproteins. In this review, we examine how these enzymes have been engineered focusing rather on the rationale behind it than the methodology employed. These studies are put in perspective with respect to in vitro and in vivo nitrene transfer processes performed by cytochromes P450. An emphasis is put on mechanistic aspects which are confronted to current molecular knowledge of these reactions. Forthcoming developments are delineated.

Anti-Markovnikov hydro(amino)alkylation of vinylarenes via photoredox catalysis.

Photoredox catalysis is a powerful means to generate odd-electron species under mild reaction conditions from a wide array of radical precursors. Herein, we present the application of this powerful catalytic manifold to address the hydroalkylation and hydroaminoalkylation of electronically diverse vinylarenes. This reaction allows for generalized alkene hydroalkylation leveraging common alkyl radical precursors, such as organotrifluoroborate salts and carboxylic acids. Furthermore, utilizing easily accessible α-silyl amine reagents or tertiary amines directly, secondary and tertiary amine moieties can be installed onto monoaryl and diaryl alkenes to access valuable products, including γ,γ-diarylamines pharmacophores. Thus, under a unified system, both hydroalkylation and hydroaminoalkylation of alkenes are achieved. The substrate scope is evaluated through 57 examples, the synthetic utility of the method is demonstrated, and preliminary mechanistic insights are presented.

Discovery of a 2,4-diphenyl-5,6-dihydrobenzo(h)quinolin-8-amine derivative as a novel DNA intercalating topoisomerase IIα poison.

Several anticancer agents have been developed and innovative approaches have been made toward cancer type-specific medicines for cancer treatment. As a continuous effort to develop potential chemotherapeutic agents, a novel series of 2,4-diphenyl-5,6-dihydrobenzo(h)quinolin-8-amines containing amino groups, hydroxyphenyl and fluorine functionalities were designed and synthesized. The compounds were evaluated for topo IIα inhibitory and cytotoxicity against HCT15, and HeLa human cancer cell lines. Among synthesized thirty compounds, the majority exhibited strong topo IIα inhibition and anti-proliferation against HCT15 colorectal adenocarcinoma cell line. The structure-activity relationship study revealed that compounds with -CF3 and -OCF3 substituents at 4- position and 3' or 4'-hydroxyphenyl at 2-position attached to the central pyridine ring displayed potent topo IIα and anti-proliferative activity in colorectal and cervix cancer cell line. In vitro studies provided the evidence that compounds 16, 19, 22, and 28 possess excellent topo IIα inhibition and antiproliferative activity. For a better understanding, topo IIα cleavage complex, EtBr displacement, KI quenching assays and molecular docking of compound 19 was performed and the results revealed the mode of action as a DNA intercalative topo IIα poison inhibitor. The results obtained from this study provide insight into the DNA binding mechanism of 2,4-diphenyl-5,6-dihydrobenzo(h)quinolin-8-amines and alteration in topo IIα inhibitory and antiproliferative activity with modifications in the rigid structure.

Dual-function enzyme catalysis for enantioselective carbon-nitrogen bond formation.

Chiral amines can be made by insertion of a carbene into an N-H bond using two-catalyst systems that combine a transition metal-based carbene-transfer catalyst and a chiral proton-transfer catalyst to enforce stereocontrol. Haem proteins can effect carbene N-H insertion, but asymmetric protonation in an active site replete with proton sources is challenging. Here we describe engineered cytochrome P450 enzymes that catalyse carbene N-H insertion to prepare biologically relevant α-amino lactones with high activity and enantioselectivity (up to 32,100 total turnovers, >99% yield and 98% e.e.). These enzymes serve as dual-function catalysts, inducing carbene transfer and promoting the subsequent proton transfer with excellent stereoselectivity in a single active site. Computational studies uncover the detailed mechanism of this new-to-nature enzymatic reaction and explain how active-site residues accelerate this transformation and provide stereocontrol.