Investigations on 5,6,7,8-tetrahydro-[1,2,4]triazolo[1,2-a]pyridazin-1-amines and related compounds: synthesis, chemical behaviour, structure elucidation and iNOS inhibitory activity.

The present work reports on the preparation of the hitherto unknown title compounds 5, with various synthetic routes described. The initially pursued concept of S-N exchange with varioius 1-substituted 3-methylsulfanyl-5,6,7,8-tetrahydro-1 H -[1,2,4]triazolo[1,2- a ]pyridazines 4 by using nitrogen nucleophiles was only marginally successful. The reactions proceeded slowly and the yields were low, mainly because of the pronounced formation of 5,6,7,8-tetrahydro-[1,2,4]triazolo[1,2- a ]pyridazin-1-imines 7 by oxidation of the heterocyclic amines 5 initially formed. The integration of the synthesis of 3-acylsulfanyl analogues with the more reactive leaving groups also failed. On the other hand, the cyclization of the hydrohalides of hexahydropyridazine-1-carboximidamide with aromatic aldehydes and some low molecular weight ketones gives significantly better results in the synthesis of the title compounds 5. The use of the hydrochloride 6b proved to be advantageous in comparison to the hydroiodide 6a because the yields were significantly better and the imines 7 formed at the same time only to a small extent. In addition, the starting compound 6b can be prepared in a single-step synthesis in very good yield from hexahydropyridazine hydrochloride 1 and cyanamide. The cyclization of N' -phenylhexahydropyridazine-1-carboximidamide hydrochloride 6c with substituted benzaldehydes gives the 3-aryl-substituted 2-phenyl-2,3,5,6,7,8-hexahydro -1H -[1,2,4]triazolo[1,2- a ] pyridazin-1-imines 8. In the context with the study of the reaction of hexahydropyridazine-1-carboximidamide hydroiodide 6a with cyclohexanone, the hexahydropyridazine-1-carboxamide 9 was specifically synthesized. This can be reacted with aromatic aldehydes to give the 5,6,7,8-tetrahydro-1 H -[1,2,4]triazolo[1,2- a ]pyridazin-1-ones 10 in very good yields. The results of the biological testing of representatives of the synthesized 5,6,7,8-tetrahydro-[1,2,4] triazolo[1,2-a]pyridazine-1-amines 5 show, in comparison to the already examined thions 3 and 3-methylsulfanyl derivatives 4, significantly less inducible nitric oxide synthase (iNOS) inhibitory activity.

[Development of Organocatalytic Reactions for the Synthesis of Natural Products and Pharmaceuticals].

This review describes novel organocatalytic methods for the enantioselective construction of spiroindans and spirochromans and the application of the methods to the total synthesis of natural products. We developed an intramolecular Friedel-Craftstype 1,4-addition in which the substrates were a resorcinol derivative and 2-cyclohexenone linked by an alkyl chain. The reaction proceeded smoothly in the presence of a cinchonidine-based primary amine (30 mol%) with water and p-bromophenol as additives. A variety of spiroindanes were obtained with high enantioselectivity under these conditions. The reaction was applied in the first total synthesis of the unusual proaporphine alkaloid (-)-misramine, which included the key steps of enantioselective spirocyclization and double reductive amination of the keto-aldehyde to form a piperidine ring toward the end of the synthesis. The total synthesis of misrametine was achieved by selective demethylation of the methoxy group from the precursor to misramine. Next, a method for highly enantioselective organocatalytic construction of spirochromans containing a tetrasubstituted stereocenter was developed. An intramolecular oxy-Michael addition was catalyzed by a bifunctional cinchona alkaloid thiourea catalyst. A variety of spirochroman compounds containing a tetrasubstituted stereocenter were obtained with excellent enantioselectivity of up to 99% enantiomeric excess. The reaction was applied to the asymmetric formal synthesis of (-)-(R)-cordiachromene.

Synthesis of C3'-Foused Aryl/Penta-1,4-Dien-3-One/Amine Hybrids as HSP90C-Terminal Inhibitors.

24 C3'-focused hybrids of aryl/penta-1,4-dien-3-one/amine (APDA) were designed and synthesized. Of these hybrids, 2 n demonstrated improved antiproliferative effects on HER2-positive breast cancer cells (SKBr3 and BT474) and triple-negative breast cancer (TNBC) cells (MDA-MB-231 and MDA-MB-468) with IC50 values ranging from 7.45 to 10.75 µM, but less toxicity to normal breast cells MCF-10A than the first generation of hybrid 1. Additionally, 2 n retained its ability to inhibit HSP90C-terminus, leading to the degradation of HSP90 client proteins HER2, EGFR, pAKT, AKT, and CDK4, without inducing a heat-shock response. Notably, 2 n also demonstrated improved thermostability compared to 1 and maintained in vitro metabolic stability in simulated intestinal fluid. These findings will provide a scientific basis for developing HSP90C-terminal inhibitors in the future.

Supported-amine-catalyzed cascade synthesis of spiro-thiazolone-tetrahydrothiophenes: assessing HSA binding activity.

We have devised a supported-amine-catalyzed efficient synthesis of spiro-thiazolone-tetrahydrothiophenes via a sulfa-Michael/aldol cascade approach. The catalyst demonstrated sustained efficacy over 21 cycles. These derivatives were found to exhibit excellent binding abilities with purified human serum albumin as indicated by both in silico and in vitro-based experiments.

Asymmetric hydrogenation of ketimines with minimally different alkyl groups.

Asymmetric catalysis enables the synthesis of optically active compounds, often requiring the differentiation between two substituents on prochiral substrates1. Despite decades of development of mainly noble metal catalysts, achieving differentiation between substituents with similar steric and electronic properties remains a notable challenge2,3. Here we introduce a class of Earth-abundant manganese catalysts for the asymmetric hydrogenation of dialkyl ketimines to give a range of chiral amine products. These catalysts distinguish between pairs of minimally differentiated alkyl groups bound to the ketimine, such as methyl and ethyl, and even subtler distinctions, such as ethyl and n-propyl. The degree of enantioselectivity can be adjusted by modifying the components of the chiral manganese catalyst. This reaction demonstrates a wide substrate scope and achieves a turnover number of up to 107,800. Our mechanistic studies indicate that exceptional stereoselectivity arises from the modular assembly of confined chiral catalysts and cooperative non-covalent interactions between the catalyst and the substrate.

Development of Efficient Synthetic Reactions Using Enamines and Enamides Carrying Oxygen Atom Substituent on Nitrogen Atom.

We have developed efficient synthetic reactions using enamines and enamides carrying oxygen atom substituent on nitrogen, such as N-alkoxyenamines, N,α-dialkoxyenamines, N-alkoxyanamides, and N-(benzoyloxy)enamides. The umpolung reaction by polarity inversion at the ß-position of N-alkoxyenamines afforded α-alkyl-, α-aryl-, α-alkenyl-, and α-heteroarylketones by using aluminum reagent as nucleophiles. Furthermore, one-pot umpolung α-phenylation of ketones has been also developed. We applied this method to umpolung reaction of N,α-dialkoxyenamine, generated from N-alkoxyamide to afford α-arylamides. The vicinal functionalization of N-alkoxyenamines has been achieved with the formation of two new carbon-carbon bonds by using an organo-aluminum reagent and subsequent allyl magnesium bromide or tributyltin cyanide. A sequential retro-ene arylation has been developed for the conversion of N-alkoxyenamides to the corresponding tert-alkylamines. The [3,3]-sigmatropic rearrangement of N-(benzoyloxy)enamides followed by arylation afforded cyclic ß-aryl-ß-amino alcohols bearing a tetrasubstituted carbon center. The resulting products were converted into the corresponding sterically congested cyclic ß-amino alcohols, as well as the dissociative anesthetic agent Tiletamine.

N-Functionalization of ß-aminophosphonates: cytotoxic effects of the new derivatives.

ß-Aminophosphonates obtained by the Michael addition of primary amines to the double bond of diethyl vinylphosphonate proved to be suitable starting materials (amine components) in the Kabachnik-Fields reaction with formaldehyde and dialkyl phosphites or secondary phosphine oxides to afford N-phosphonylmethyl- and N-phosphinoylmethyl-ß-aminophosphonates. On the other hand, the starting aminophosphonates were modified by N-acylation using acid chlorides. The N-acyl products were found to exist in a dynamic equilibrium of two conformers as suggested by the broad NMR signals. At 26 °C, there may be rotation around the N-C axis of the acylamide function. At the same time, low-temperature NMR measurements at -5 °C revealed the presence of two distinct rotamers that could be characterized by 31P, 13C and 1H NMR data. The modified ß-aminophosphonic derivatives were subjected to a comparative structure-activity analysis on MDA-MB-231, PC-3, A431 and Ebc-1 tumor cell lines, and in a few cases, significant activity was detected.

Synthesis of Pharmaceutically Relevant Arylamines Enabled by a Nitroreductase from Bacillus tequilensis.

Arylamines are essential building blocks for the manufacture of valuable pharmaceuticals, pigments and dyes. However, their current industrial production involves the use of chemocatalytic procedures with a significant environmental impact. As a result, flavin-dependent nitroreductases (NRs) have received increasing attention as sustainable catalysts for more ecofriendly synthesis of arylamines. In this study, we assessed a novel NR from Bacillus tequilensis, named BtNR, for the synthesis of pharmaceutically relevant arylamines, including valuable synthons used in the manufacture of blockbuster drugs such as vismodegib, sonidegib, linezolid and sildenafil. After optimizing the enzymatic reaction conditions, high conversion of nitroaromatics to arylamines (up to 97 %) and good product yields (up to 56 %) were achieved. Our results indicate that BtNR has a broad substrate scope, including bulky nitro benzenes, nitro pyrazoles and nitro pyridines. Hence, BtNR is an interesting biocatalyst for the synthesis of pharmaceutically relevant amine-functionalized aromatics, providing an attractive alternative to traditional chemical synthesis methodologies.

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.

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.

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.

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.

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.

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.

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.