Mechanistic insights into CrCEP1: A dual-function cysteine protease with endo- and transpeptidase activity

Proteases, essential regulators of plant stress responses, remain enigmatic in their precise functional roles. By employing activity-based probes for real-time monitoring, this study aimed to delve into protease activities in Chlamydomonas reinhardtii exposed to oxidative stress induced by hydrogen peroxide. However, our work revealed that the activity-based probes strongly labelled three non-proteolytic proteins-PsbO, PsbP, and PsbQ-integral components of photosystem II's oxygen-evolving complex. Subsequent biochemical assays and mass spectrometry experiments revealed the involvement of CrCEP1, a previously uncharacterized papain-like cysteine protease, as the catalyst of this labelling reaction. Further experiments with recombinant CrCEP1 and PsbO proteins replicated the reaction in vitro. Our data unveiled that endopeptidase CrCEP1 also has transpeptidase activity, ligating probes and peptides to the N-termini of Psb proteins, thereby expanding the repertoire of its enzymatic activities. The hitherto unknown transpeptidase activity of CrCEP1, working in conjunction with its proteolytic activity, unveils putative complex and versatile roles for proteases in cellular processes during stress responses.

Recent Advances in the Nickel-Catalyzed Alkylation of C-H Bonds

Functionalization of C-H bonds has emerged as a powerful strategy for converting inert, nonfunctional C-H bonds into their reactive counterparts. A wide range of C-H bond functionalization reactions has become possible by the catalysis of metals, typically from the second row of transition metals. First-row transition metals can also catalyze C-H functionalization, and they have the merits of greater earth-abundance, lower cost and better environmental friendliness in comparison to their second-row counterparts. C-H bond alkylation is a particularly important C-H functionalization reaction due to its chemical significance and its applications in natural product synthesis. This review covers Ni-catalyzed C-H bond alkylation reactions using alkyl halides and olefins as alkyl sources.

Synthesis of Six-Membered N-Heterocyclic Carbene Precursors Based on Camphor

The endo- and exo-N-heterocyclic carbene precursors based on camphor were prepared diastereoselectively in five synthetic steps starting from (1S)-(+)-ketopinic acid. The obtained N-heterocyclic carbene precursors were investigated in an asymmetric benzoin reaction. All new compounds were fully characterized, and the absolute configurations were determined via X-ray diffraction and NOESY measurements.

Synthesis and Cholinesterase Inhibitory Activity of Selected Indole-Based Compounds

Synthesis and anticholinesterase activity of 18 previously unpublished indole- and tryptophan-derived compounds are disclosed. These sp3-rich compounds containing an indole structural unit exhibit selective submicromolar inhibition of human butyrylcholinesterase (hBChE). The structures of the newly synthesized compounds were confirmed by 1H and 13C NMR, IR spectroscopy, and high-resolution mass spectrometry.

Catalytic Photoredox C-H Arylation of 4-Oxo-4H-pyrido[1,2-a]pyrimidine-3-diazonium Tetrafluoroborates and Related Heteroaryl Diazonium Salts

Irradiation of mixtures of title diazonium salts and heteroarenes with green light (510 nm) in the presence of eosin Y disodium salt (EY-Na2) as a photocatalyst furnished the corresponding arylation products in 8-63% yields. The proposed photocatalytic cycle is analogous to that proposed previously for closely related photoredox C-H arylations with aryl diazonium salts as aryl radical sources. This method has a broad substrate scope and represents a metal-free alternative for the synthesis of 3-heteroaryl-substituted 4H-quinolizin-4-ones and azino- and azolo-fused pyrimidones with a bridgehead nitrogen atom.

Regioselective Synthesis of 5- and 3-Hydroxy-N-Aryl-1H-Pyrazole-4-Carboxylates and Their Evaluation as Inhibitors of Plasmodium falciparum Dihydroorotate Dehydrogenase

In silico evaluation of various regioisomeric 5- and 3-hydroxy-substituted alkyl 1-aryl-1H-pyrazole-4-carboxylates and their acyclic precursors yielded promising results with respect to their binding in the active site of dihydroorotate dehydrogenase of Plasmodium falciparum (PfDHODH). Consequently, four ethyl 1-aryl-5-hydroxy-1H-pyrazole-4-carboxylates and their 3-hydroxy regioisomers were prepared by two-step syntheses via enaminone-type reagents or key intermediates. The synthesis of 5-hydroxy-1H-pyrazoles was carried out using the literature protocol comprising acid-catalyzed transamination of diethyl [(dimethylamino)methylene]malonate with arylhydrazines followed by base-catalyzed cyclization of the intermediate hydrazones. For the synthesis of isomeric methyl 1-aryl-3-hydroxy-1H-pyrazole-4-carboxylates, a novel two-step synthesis was developed. It comprises acylation of hydrazines with methyl malonyl chloride followed by cyclization of the hydrazines with tert-butoxy-bis(dimethylamino)methane. Testing the pyrazole derivatives for the inhibition of PfDHODH showed that 1-(naphthalene-2-yl)-5-hydroxy-1H-pyrazole-4-carboxylate and 1-(naphthalene-2-yl)-, 1-(2,4,6-trichlorophenyl)-, and 1-[4-(trifluoromethyl)phenyl]-3-hydroxy-1H-pyrazole-4-carboxylates (~30% inhibition) were slightly more potent than a known inhibitor, diethyl α-{[(1H-indazol-5-yl)amino]methylidene}malonate (19% inhibition).

Synthesis and kinetic characterization of hyperbolic inhibitors of human cathepsins K and S based on a succinimide scaffold

Cathepsins K and S are closely related papain-like cysteine peptidases and potential therapeutic targets for metabolic and inflammatory diseases such as osteoporosis and arthritis. Here we describe the reduction of a previously characterized succinimide (2,5-dioxopyrrolidine)-containing hyperbolic inhibitor of cathepsin K (methyl (RS)-N-[1-(4-methoxyphenyl)-2,5-dioxopyrrolidin-3-yl]glycinate), to obtain a better and more selective compound (compound 4a - methyl (2,5-dioxopyrrolidin-3-yl)glycinate), which acted as a hyperbolic mixed inhibitor/activator similar to already known allosteric effectors of cathepsin K. We then investigated the potential of the succinimide scaffold as inhibitors of cathepsins K and/or S and synthesized a library of such compounds by 1,4-addition of α-amino acid esters and related compounds to N-substituted maleimides. From the generated library, we identified the first small molecule hyperbolic inhibitors of cathepsin S (methyl ((R)-2,5-dioxopyrrolidin-3-yl)-l-threoninate (compound R-4c) and 3-{[(1S,2R,3'S)-2-hydroxycyclohexyl]amino}pyrrolidine-2,5-dione (compound (1S,2R,3'S-10)). The former acted via a similar mechanism to compound 4a, while the latter was a hyperbolic specific inhibitor of cathepsin S. Given the versatility of the scaffold, the identified compounds will be used as the basis for the development of high-affinity hyperbolic inhibitors of the individual peptidases and to explore the potential of hyperbolic inhibitors for the inhibition of cysteine cathepsins in in vitro models.

Visible-Light Driven Selective C-N Bond Scission in anti-Bimane-Like Derivatives

In the present study, we report the photochemical transformation of pyrazolo[1,2-a]pyrazolone substrates that reach an excited state upon irradiation with visible light to initiate the homolytic C-N bond cleavage process that yields the corresponding N1-substituted pyrazoles. Moreover, chemoselective heterolytic C-N bond cleavage is possible in the pyrazolo[1,2-a]pyrazole core in the presence of bromomalonate.

Efficient Chitosan/Nitrogen-Doped Reduced Graphene Oxide Composite Membranes for Direct Alkaline Ethanol Fuel Cells

Herein, we prepared a series of nanocomposite membranes based on chitosan (CS) and three compositionally and structurally different N-doped graphene derivatives. Two-dimensional (2D) and quasi 1D N-doped reduced graphene oxides (N-rGO) and nanoribbons (N-rGONRs), as well as 3D porous N-doped graphitic polyenaminone particles (N-pEAO), were synthesized and characterized fully to confirm their graphitic structure, morphology, and nitrogen (pyridinic, pyrrolic, and quaternary or graphitic) group contents. The largest (0.07%) loading of N-doped graphene derivatives impacted the morphology of the CS membrane significantly, reducing the crystallinity, tensile properties, and the KOH uptake, and increasing (by almost 10-fold) the ethanol permeability. Within direct alkaline ethanol test cells, it was found that CS/N rGONRs (0.07 %) membrane (Pmax. = 3.7 mWcm-2) outperformed the pristine CS membrane significantly (Pmax. = 2.2 mWcm-2), suggesting the potential of the newly proposed membranes for application in direct ethanol fuel cells.

Structure-activity relationship study of tryptophan-based butyrylcholinesterase inhibitors

A series of tryptophan-based selective nanomolar butyrylcholinesterase (BChE) inhibitors was designed and synthesized. Compounds were optimized in terms of potency, selectivity, and synthetic accessibility. The crystal structure of the inhibitor 18 in complex with BChE revealed the molecular basis for its low nanomolar inhibition (IC₅₀ = 2.8 nM). The favourable in vitro results enabled a first-in-animal in vivo efficacy and safety trial, which demonstrated a positive impact on fear-motivated and spatial long-term memory retrieval without any concomitant adverse motor effects. Altogether, this research culminated in a handful of new lead compounds with promising potential for symptomatic treatment of patients with Alzheimer's disease.

Stereodivergent Synthesis of Camphor-Derived Diamines and Their Application as Thiourea Organocatalysts

A series of 18 regio- and stereo-chemically diverse chiral non-racemic 1,2-, 1,3-, and 1,4-diamines have been synthesized from commercial (1S)-(+)-ketopinic acid and (1S)-(+)-10-camphorsulfonic acid. The structures of the diamines are all based on the d-(+)-camphor scaffold and feature isomeric diversity in terms of regioisomeric attachment of the primary and the tertiary amine function and the exo/endo-isomerism. Diamines were transformed into the corresponding noncovalent bifunctional thiourea organocatalysts, which have been evaluated for catalytic activity in the conjugative addition of 1,3-dicarbonyl nucleophiles (dimethyl malonate, acetylacetone, and dibenzoylmethane) to trans-β-nitrostyrene. The highest enantioselectivity was achieved in the reaction with acetylacetone as nucleophile using endo-1,3-diamine derived catalyst 52 (91.5:8.5 er). All new organocatalysts 48-63 have been fully characterized. The structures and the absolute configurations of eight intermediates and thiourea derivative 52 were also determined by X-ray diffraction.

Self-Assembly of Multinuclear Sandwich Silver(I) Complexes by Cooperation of Hexakis(azaheteroaryl)benzene Ligands, Argentophilic Interactions, and Fluoride Inclusion

Self-assembly of AgOTf and AgF with the hexatopic ligands hexakis(pyridin-2-yl)benzene (2) and 2,4,6-tris(pyridin-2-yl)-1,3,5-tris(quinolin-2-yl)benzene (3) affords the discrete sandwich-shaped complexes [Ag₄F(2)₂](OTf)₃, [Ag₄F(3)₂](OTf)₃, and [Ag₅F(2)₂](OTf)₄. The solid-state structures of the complexes were characterized by single-crystal X-ray diffraction analysis, which revealed that the fluoride anion is coordinated in the center of the Ag₄-square or Ag₅-pentagon units which are positioned between two molecules of the hexakis(azaheteroaryl)benzene. The generation of complexes is dictated by a unique cooperation of ligand coordination, argentophilicity, and fluoride anion inclusion. All three complexes adopt highly symmetrical structures in solution, as evidenced by appearance of one set of proton resonances for the two ligands arranged face to face.

Multinuclear sandwich-shaped silver(I) complexes are readily assembled by a unique cooperation of nitrogen-coordinating hexaheteroarylbenzene ligands, silver atoms, and fluoride anion.

Tetrahydro-1H,5H-pyrazolo[1,2-a]pyrazole-1-carboxylates as inhibitors of Plasmodium falciparum dihydroorotate dehydrogenase

The reactions between 5-substituted pyrazolidine-3-ones, aldehydes, and methyl methacrylate provided tetrahydropyrazolo[1,2-a]pyrazole-1-carboxylates as mixtures of syn- and anti-diastereomers. Testing for inhibition of dihydroorotate dehydrogenase of Plasmodium falciparum (PfDHODH) revealed high activity of some anti-isomers of the methyl esters, while the corresponding carboxylic acids and carboxamides were not active. The most active representative, methyl (1S*,3S*,5R*)-1,5-dimethyl-7-oxo-3-phenyltetrahydro-1H,5H-pyrazolo[1,2-a]pyrazole-1-carboxylate (IC₅₀ = 2.9 ± 0.3 μM), also exhibited very high selectivity of the parasite enzyme vs. the human enzyme, PfDHODH/HsDHODH > 350. According to the molecular docking score, this high activity is explainable by synergic interactions of the methyl, phenyl and the CO₂Me substituent with the hydrophobic pockets in the active site of the enzyme. The carboxylic acid and carboxamides derived from this compound did not inhibit PfDHODH.

Tryptophan-derived butyrylcholinesterase inhibitors as promising leads against Alzheimer's disease

We have identified tryptophan-based selective nanomolar butyrylcholinesterase (BChE) inhibitors. They are defined according to their chemical modularity, novel binding mode revealed by five solved crystal structures with human BChE, low cytotoxicity, and predicted permeability of the blood-brain barrier. Altogether, these factors indicate their potential as unique lead compounds for symptomatic therapy against Alzheimer's disease.

Copper-Catalyzed Azomethine Imine–Alkyne Cycloadditions (CuAIAC)

Although the first example of copper-catalyzed azomethine imine–alkyne cycloaddition (CuAIAC) was published only a year after the seminal papers of Meldal and Sharpless on Cu-catalyzed azide–alkyne cycloaddition (CuAAC), the CuAIAC reaction has remained overlooked by the synthetic community for almost a decade. Since 2010, however, CuAIAC reaction started to emerge as a promising supplement to the well-known CuAAC reaction. The present review surveys primarily the literature on CuAIAC reaction since 2003. Beside this, azomethine imine–alkyne cycloadditions catalyzed by other metals, selected examples of metal-free reactions, and related [3+3] and [3+4] cycloadditions of azomethine imines are presented. All these experimental data indicate the viability of CuAIAC in organic synthesis and the applicability in ‘click’ chemistry.

1 Introduction

2 Reactions with Acyclic Azomethine Imines

3 Reactions with C,N-Cyclic Azomethine Imines

4 Reactions with N,N-Cyclic Azomethine Imines

5 Reactions with C,N,N-Cyclic Azomethine Imines

6 The Mechanism of the CuAIAC Reaction

7 Conclusions and Outlook

Ruthenium(II)-Catalyzed Microwave-Promoted Multiple C-H Activation in Synthesis of Hexa(heteroaryl)benzenes in Water

A series of hexa(heteroaryl)benzenes were synthesized by the Ru(II)-carboxylate-catalyzed multiple C-H activation of benzenes carrying pyridyl, pyrimidyl, or pyrazolyl directing groups using N-heteroaryl bromides as coupling partners. The reactions proceeded with high selectivity under microwave irradiation in water. Iterative penta-arylation could be implemented via activation of C-H bonds of generated intermediates by cascade chelation assistance of in situ installed pyridyl groups. This strategy provides multidentate ligands for selective complexation of transition metals and potential building of photoredox systems.

Synthesis of functionalized pyrazole derivatives by regioselective [3+2] cycloadditions of N-Boc-α-amino acid-derived ynones

[3+2] cycloadditions of ynones derived from glycine and (S)-alanine and some other dipolarophiles with azomethine imines, nitrile oxides, diazoacetate, and azidoacetate were studied. The dipolarophiles were obtained from α-amino acids, either by the reduction of the carboxy function with ethynylmagnesium bromide or by propiolation of the amino function. Cu-catalyzed cycloadditions of ynones to azomethine imines were regioselective and gave the expected cycloadducts as inseparable mixtures of diastereomers. In some instances, further oxidative hydrolytic ring-opening took place to afford 3,3-dimethyl-3-(1H-pyrazol-1-yl)propanoic acids. Acid-catalyzed cycloadditions of 3-butenone were also regioselective and provided mixtures of diastereomeric cycloadducts, which were separated by chromatography. In the reactions of title ynones with alkyl diazoacetates, in situ-formed benzonitrile oxides, and tert-butyl azidoacetate, all cycloadducts were obtained as single regioisomers. The structures of all novel compounds were established by nuclear magnetic resonance and X-ray diffraction.

Asymmetric Bio- and Chemoreduction of 2-Benzylidenecyclopentanone Derivatives

Highly efficient asymmetric reduction of 2-benzylidenecyclopentanone derivatives to give the respective exocyclic allylic alcohols in ee's up to 96% was performed with chiral oxazaborolidine-based catalysts. Complete enantioselectivity furnishing (S)-configured alcohol product could be achieved by bioreduction of 2-(4-chlorobenzylidene)cyclopentanone with Daucus carota root. The synthesized compounds may be used as enantiomerically enriched standards for the monitoring of the enzyme-catalyzed redox processes.

Synthesis of Novel 3D-Rich α-Amino Acid-Derived 3-Pyrazolidinones

Synthetic approaches towards novel 3-pyrazolidinone derivatives functionalized at positions N(1) and/or C(5) were studied. 5-Aminoalkyl-3-pyrazolidinones were prepared in four steps from N-protected glycines via Masamune-Claisen homologation, reduction, O-mesylation, and cyclisation with a hydrazine derivative. The free amines were prepared by acidolytic deprotection. Title compound was also prepared by 'ring switching' transformation of N-Boc-pyrrolin-2(5H)-one with hydrazine hydrate. Hydrogenolytic deprotection of 5-(N-alkyl-N-Cbz-aminomethyl)pyrazolidine-3-ones followed by cyclisation with 1,1'-carbonyldiimidazole (CDI) gave two novel representatives of perhydroimidazo[1,5-b] pyrazole, which is an almost unexplored heterocyclic system. Amidation of 3-oxopyrazolidine-5-carboxylic acid gave the corresponding carboxamides in moderate yields. Diastereomeric non-racemic carboxamides obtained from (S)-AlaOMe and (S)-ProOMe were separated by MPLC.

Synthesis and Reduction of 10-Phthalimidocamphor Oxime

10-Phthalimidocamphor oxime was prepared from easily available 10-iodocamphor in two steps. Reduction of the oxime functionality resulted in the formation of two novel polycyclic isoindolinone heterocycles, the attempted preparation of the primary amine failed. The structures of novel heterocycles were unambiguously confirmed by single crystal X-ray diffraction as well as NMR techniques.

Synthesis of Novel 5-(N-Boc-N-Benzyl-2-aminoethyl)-7-oxo-4,7-dihydropyrazolo[1,5-a]pyrimidin-3-carboxamides and Their Inhibition of Cathepsins B and K

Eight novel 5-(N-Boc-N-benzyl-2-aminoethyl)-7-oxo-4,7-dihydropyrazolo[1,5-a]pyrimidin-3-carboxamides were prepared in three steps from methyl 3-amino-1H-pyrazole-4-carboxylate and methyl 5-(benzyl(tert-butoxycarbonyl)amino)-3-oxopentanoate. The synthetic procedure comprises cyclocondensation of the above starting compounds, hydrolysis of the ester, and bis(pentafluorophenyl) carbonate (BPC)-mediated amidation. Title carboxamides were tested for inhibition of cathepsins K and B. The N-butylcarboxamide 5a exhibited appreciable inhibition of cathepsin K (IC50 ~ 25 μM), while the strongest inhibition of cathepsin B was achieved with N-(2-picolyl)carboxamide 5c (IC50 ~ 45 μM).

In vitro assessment of potential bladder papillary neoplasm treatment with functionalized polyethyleneimine coated magnetic nanoparticles

Normal porcine urothelial cells have been shown to have a much lower rate of endocytosis than urothelial papillary neoplasm cells. This could be used as a mechanism for selective delivery of toxic compounds, such as polyethyleneimine coated nanoparticles (NPs). However, these NPs induce nonselective toxicity through direct membrane disruption. This toxicity can be reduced by functionalization of NPs with L-glutathione reduced or bovine serum albumin by reducing their surface charge. Functionalization was confirmed with Fourier Transform Infrared Spectroscopy, Dynamic Light Scattering and zeta potential measurements. Viability assays showed that bovine serum albumin coating reduced NPs cytotoxicity immediately after 3 h exposure and that such NPs were more toxic to urothelial papillary neoplasm cells compared to normal porcine urothelial cells at 50 μg/ml NPs concentration. However, 24 h after exposure, bovine serum albumin functionalized NPs had similar effect on viability of both cell lines. NPs showed some selective toxicity towards urothelial papillary neoplasm cells compared to normal cells after 3 h, however this was not confirmed after 24 h.

Combinatorial Synthesis of Acacen-Type Ligands and Their Coordination Compounds

A highly modular synthetic method for the preparation of acacen-type ligands and their coordination compounds was developed. A series of 46 acacen-type ligands were synthesized by a combinatorial acid-catalyzed transamination between six primary diamines and eight enaminones. The bis-enaminone products were used as tetradentate ligands for coordination of copper(II), nickel(II), cobalt(II), and palladium(II). Dependence of the preferred E- or Z-configuration of the enaminone ligand on the α-substituent of the enaminone moiety in solution was determined by NMR and confirmed by X-ray diffraction. The copper(II) complexes were tested for their suitability as catalysts in 3 + 2 cycloaddition of azomethine imine to methyl propiolate.

Dispersion of Nanoparticles in Different Media Importantly Determines the Composition of Their Protein Corona

Protein corona of nanoparticles (NPs), which forms when these particles come in to contact with protein-containing fluids, is considered as an overlooked factor in nanomedicine. Through numerous studies it has been becoming increasingly evident that it importantly dictates the interaction of NPs with their surroundings. Several factors that determine the compositions of NPs protein corona have been identified in recent years, but one has remained largely ignored-the composition of media used for dispersion of NPs. Here, we determined the effect of dispersion media on the composition of protein corona of polyacrylic acid-coated cobalt ferrite NPs (PAA NPs) and silica NPs. Our results confirmed some of the basic premises such as NPs type-dependent specificity of the protein corona. But more importantly, we demonstrated the effect of the dispersion media on the protein corona composition. The differences between constituents of the media used for dispersion of NPs, such as divalent ions and macromolecules were responsible for the differences in protein corona composition formed in the presence of fetal bovine serum (FBS). Our results suggest that the protein corona composition is a complex function of the constituents present in the media used for dispersion of NPs. Regardless of the dispersion media and FBS concentration, majority of proteins from either PAA NPs or silica NPs coronas were involved in the process of transport and hemostasis. Interestingly, corona of silica NPs contained three complement system related proteins: complement factor H, complement C3 and complement C4 while PAA NPs bound only one immune system related protein, α-2-glycoprotein. Importantly, relative abundance of complement C3 protein in corona of silica NPs was increased when NPs were dispersed in NaCl, which further implies the relevance of dispersion media used to prepare NPs.

Absolute Configuration Determination of 2,3-Dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles Using Chiroptical Methods at Different Wavelengths

A correlation between the absolute configuration and chiroptical properties of nonracemic 1,6,7-trisubstituted 2,3-dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles was studied. A series of 16 novel representatives were prepared by Cu-catalyzed [3 + 2] cycloadditions of racemic (Z)-2-benzylidene-5-oxopyrazolidin-2-ium-1-ides to tert-butyl (S)-(3-oxopent-4-yn-2-yl)carbamate, and their structures were determined by NMR, VCD, ECD, and X-ray diffraction. A clear correlation between the sign of specific rotation and configuration at position C(1) allows for easy determination of the absolute configuration of 1,6,7-trisubstituted 2,3-dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles by ECD and NMR. While VCD, requiring milligram quantities, allowed the determination of the correct relative and absolute configuration without additional information from other methods, the stereochemical analysis by ECD required knowledge of the relative configuration derived from NMR at a comparable computational level.

Synthesis of 3D-Rich Heterocycles: Hexahydropyrazolo[1,5-a]pyridin-2(1H)-ones and Octahydro-2H-2a,2a1-diazacyclopenta[cd]inden-2-ones

Two cyclic azomethine imines, 7-methyl- and 7-phenyl-2-oxo-Δ⁷-hexahydropyrazolo[1,5-a]pyridin-8-ium-1-ide, were prepared in seven steps from the respective commercially available δ-keto acids. The addition of Grignard reagents followed by N-alkylation at position 1 afforded the 1,7,7-trisubstituted hexahydropyrazolo[1,5-a]pyridin-2(1H)-ones, whereas 1,3-dipolar cycloadditions of these dipoles to typical acetylenic and olefinic dipolarophiles gave 4a-substituted 2a,2a¹-diazacyclopenta[cd]indene derivatives as the first representatives of a novel heterocyclic system. Regio- and stereoselectivity as well as the mechanism of these [3 + 2]-cycloadditions were evaluated using computational and experimental methods. The data obtained were in agreement with the polar concerted cycloaddition mechanism via the energetically favorable syn/endo-transition states.

"Click" Chemistry: Application of Copper Metal in Cu-Catalyzed Azomethine Imine-Alkyne Cycloadditions

A series of 16 copper-catalyzed azomethine imine-alkyne cycloaddition (CuAIAC) reactions between four pyrazolidinone-1-azomethine imines and four terminal ynones gave the corresponding fluorescent cycloadducts as bimane analogues in very high yields. The applicability of CuAIAC was demonstrated by the fluorescent labeling of functionalized polystyrene and by using Cu-C and Cu-Fe as catalysts. Experimental evidence, kinetic measurements, and correlation between a clean catalyst surface and the reaction rate are in agreement with a homotopic catalytic system with catalytic Cu(I)-acetylide formed from Cu(0) by "in situ" oxidation. The availability of azomethine imines, mild reaction conditions, simple workup, and scalability make CuAIAC a viable supplement to the Cu-catalyzed azide-alkyne cycloaddition reaction in "click" chemistry.

A simple synthesis of dimethyl 2-[(Z)-3-amino-1-oxo-1-(substituted)but-2-en-2-yl]fumarates: potential intermediates in the synthesis of polysubstituted five- and six-membered heterocycles

In this communication, a simple synthesis of dimethyl 2-[(Z)-3-amino-1-oxo-1-(substituted)but-2-en-2-yl]fumarates is described. Methyl ketones were transformed by treatment with N,N-dimethylacetamide dimethyl acetal (DMADMA) into 3-dimethylamino-1-(substituted)but-2-en-1-ones, followed by treatment with ammonium acetate into (Z)-3-amino-1-(substituted)but-2-en-1-ones and addition to dimethyl acetylenedicarboxylate. These novel polysubstituted butadienes are potential intermediates for the metal-free preparation of polysubstituted five- and six-membered heterocycles.

Synthesis and preliminary biological evaluations of (+)-isocampholenic acid-derived amides

The synthesis of two novel (+)-isocampholenic acid-derived amines has been realized starting from commercially available (1S)-(+)-10-camphorsulfonic acid. The novel amines as well as (+)-isocampholenic acid have been used as building blocks in the construction of a library of amides using various aliphatic, aromatic, and amino acid-derived coupling partners using BPC and CDI as activating agents. Amide derivatives have been assayed against several enzymes that hold potential for the development of new drugs to battle bacterial infections and Alzheimer's disease. Compounds 20c and 20e showed promising selective sub-micromolar inhibition of human butyrylcholinesterase [Formula: see text] ([Formula: see text] values [Formula: see text] and [Formula: see text], respectively).

A Four-step Synthesis of Novel (S)-1-(heteroaryl)-1-aminoethanes from (S)-Boc-alanine

A series of (S)-1-(pyrimidin-4-yl)-, and regioisomeric (S)-1-(pyrazolo[1,5-a]pyrimidin-7-yl)-, and (S)-1-(pyrazolo[1,5-a]pyrimidin-5-yl)ethan-1-amines were prepared by cyclisation of (S)-N-Boc-alanine-derived ynone with N,N-1,3-dinucleophiles, such as amidines and α-aminoazoles, followed by acidolytic removal of the Boc group. Stereoselective catalytic hydrogenation of (S)-1-(pyrazolo[1,5-a]pyrimidin-7-yl)ethanamines lead to saturation of the pyrimidine ring to afford ~4:1 mixture of diastereomeric 4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidines. The structures of novel compounds were elucidated with NMR.

Reactions of Methyl Ketones and (Hetero)arylcarboxamides with N,N-Dimethylacetamide Dimethyl Acetal. A Simple Metal-Free Synthesis of 2,4,6-Trisubstituted Pyridines

Two metal-free syntheses of 2,4,6-trisubstituted pyridines 10a–m and 16a–j are described. N,N,6-Trimethyl-4-(substituted)pyridin-2-amines 10 were prepared from aryl or heteroaryl methyl ketones which were transformed with N,N-dimethylacetamide dimethyl acetal (DMADMA) into enaminones 4a–m, followed by treatment with ammonium acetate to give (Z)-3-amino-1-(substituted)but-2-en-1-ones 5a–m. These were treated with DMADMA under microwave irradiation in a closed vessel at 130°C, to give via intermediates 7–9 the final products 10a–m. N2,N2,N4,N4-Tetramethyl-6-(substituted) pyridine-2,4-diamines 16a–j were prepared in a one-pot synthesis from the corresponding carboxamides 11a–j by treatment with an excess of DMADMA in a closed vessel under microwave irradiation to give via intermediates 12a–j to 15a–j the final products 16a–j. X-Ray single crystal diffractometry studies of the enaminones 5c, 5g, 5i, 5j, and 5m and 2,4,6-trisubstituted pyridines 16a, 16b, 16g, 16i, and 16j were consistent with the expected structures.