Chiral squaramide-catalyzed asymmetric synthesis of pyranones and pyranonaphthoquinones via cascade reactions of 1,3-dicarbonyls with Morita-Baylis-Hillman acetates of nitroalkenes

Stereocontrolled Construction of Spirooxindole-Containing 5,6,7,8-Tetrahydropyrrolo[1,2-a]pyridine via Michael/Friedel-Crafts Domino Reaction Promoted by Secondary Amine-Squaramide

An asymmetric Michael/Friedel-Crafts cascade reaction with Morita-Baylis-Hillman (MBH) nitroallylic esters and 3-pyrrolyloxindoles has been developed for the stereoselective construction of spirooxindole-containing tetrahydroindolizines. A range of tetracyclic scaffolds possessing three consecutive chiral centers, including an all-carbon quaternary stereocenter, were generated in 53-85% isolated yields with high diastereoselectivities and enantiopurities (≥3:1 dr, 50-98% ee). A newly synthesized bifunctional secondary amine/squaramide organocatalyst was demonstrated to exhibit better stereochemical control than their tertiary analogues.

Bifunctional Squaramide-Catalyzed Asymmetric Cascade Reaction of Benzothiazoles with 2-Nitroallylic Acetates or Nitroenynes

We describe here an organocatalytic asymmetric cascade formal [3 + 3] cycloaddition of benzothiazoles with 2-nitroallylic acetates and nitroenynes. This dearomative methodology provided a facile and efficient strategy for the construction of a broad range of valuable benzothiazolopyridines bearing two adjacent stereogenic centers in moderate to good yields with good to excellent stereocontrol.

Dimedone nanoparticle as a promising approach against toxoplasmosis: In vitro and in vivo evaluation

Toxoplasma gondii, an intracellular parasite, has shown drug resistance and therapeutic failure in recent years. Dimedone (DIM) has been introduced as a new chemical compound with anti-bacterial and anti-cancer properties. The aim of this study was to investigate the potential protective role of DIM nanoparticles in an animal model of toxoplasmosis. Cytotoxicity of DIM on Vero cell line assessed using MTT, and the effect of DIM on Toxoplasma gondii was evaluated by counting the number of parasites compared to the control group in vitro. The rate of pathogenesis and virulence of the parasite was checked on the liver cells of the animal model using hematoxylin-eosin staining. Furthermore, various parameters indicating oxidative stress were compared in mouse liver tissue in different groups. The release of the nanoparticle form was significantly longer than the free drugs. The IC50 of Nano-DIM was 60 µM and the reduction of intracellular parasite proliferation in the group Nano-DIM and Nano-PYR (Nano-primethamine) was significantly lower than the free drugs in vitro. Histopathology examination in the groups treated with dimedone nanomedicine showed that the degree of disintegration of the epithelium of the central vein of the liver and infiltration and vacuolization of liver cells were lower compared to the toxoplasmosis group. Additionally, the level of some oxidative stress indicators was observed to be lower in the nano-treated groups compared to other groups. The results of this study showed DIM can be used as a promising compound for anti-T. gondii activity and can prevent the proliferation of it in cells.

Recent advances in the synthetic applications of Morita-Baylis-Hillman and Rauhut-Currier adducts of nitroalkenes

The Morita-Baylis-Hillman (MBH) and Rauhut-Currier (RC) adducts of nitroalkenes are important synthetic intermediates in organic synthesis. This review discusses the applications of different MBH and RC adducts of nitroalkenes such as MBH alcohols, acetates, bromides and hydrazinonitroalkenes as well as ketoalkylnitroalkenes in the synthesis of complex molecules including carbocycles and heterocycles. It also covers the mechanistic aspects, including the key intermediates and the reaction pathways. Early reports on MBH and RC reactions of nitroalkenes and applications of the products were covered in previous reviews. The present review covers the reports that appeared in the timeline of 2015-2023.

Asymmetric Synthesis of Spiropyrazolone-Fused Dihydrofuran-naphthoquinones Bearing Contiguous Stereocenters via a Michael Addition/Chlorination/Nucleophilic Substitution Sequence

An enantioselective synthesis of spiropyrazolone-fused dihydrofuran-naphthoquinones is first demonstrated via a Michael addition/Chlorination/Nucleophilic substitution sequence. The reactions of 2-hydroxy-1,4-naphthoquinone and α,β-unsaturated pyrazolones in the presence of the cinchona alkaloid derived hydrogen-bonding catalyst and NCS provide spiropyrazolone-fused 2,3-dihydronaphtho[2,3-b]furan-4,9-diones bearing contiguous stereocenters, of which one is the spiro quaternary stereocenter in high yields with exclusive diastereoselectivity and good to excellent enantioselectivities.

Design, synthesis, and biological evaluation of tetrahydro-αcarbolines as Akt1 inhibitors that inhibit colorectal cancer cells proliferation

A series of densely functionalized THαCs were designed and synthesized as Akt1 inhibitors. Organocatalytic [3+3] annulation between indolin-2-imines 1 and nitroallylic acetates 2 provided rapid access to this pharmacologically interesting framework. In vitro kinase inhibitory abilities and cytotoxicity assays revealed that compound 3af was the most potent Akt1 inhibitor, and mechanistic study indicated that compound 3af suppressed the proliferation of colorectal cancer cells via inducing apoptosis and autophagy. Molecular docking suggested that the indole fragment of 3af was inserted into the hydrophobic pocket of Akt1 protein, and the H-bond between 3af and residue Lys179 also contributed to the stable binding. This article provides an efficient strategy to design and synthesize biologically important compounds as novel Akt1 inhibitors.

Regio- and stereoselective synthesis of functionalized and fused heterocycles from Morita-Baylis-Hillman adducts of dicyclopentadienone

An efficient protocol for the Morita-Baylis-Hillman (MBH) reaction of dicyclopentadienone using CTAB has been developed. The MBH adduct was subsequently transformed to its acetate and bromide derivatives. The 1,3-bielectrophilic character of the MBH acetate and bromide was further explored with various 1,3-binucleophiles to construct various oxa-, thia- and aza-heterocycles. These reactions proceed through a cascade double Michael addition of 1,3-binucleophiles to the MBH acetate/bromide under basic conditions. Amenability of these reactions to scale-up and applications of the products in the synthesis of cyclopentenone-fused chromenones and thiopyranoindoles have been demonstrated.

Asymmetric organocatalytic Michael addition of cyclopentane-1,2-dione to alkylidene oxindole

An asymmetric Michael reaction between cyclopentane-1,2-dione and alkylidene oxindole was studied in the presence of a multifunctional squaramide catalyst. Michael adducts were obtained in high enantioselectivities and in moderate diastereoselectivities.

Synthesis of β-triazolylenones via metal-free desulfonylative alkylation of N-tosyl-1,2,3-triazoles

Desulfonylative alkylation of N-tosyl-1,2,3-triazoles under metal-free conditions leading to β-triazolylenones is reported here. The present study encompasses the synthesis of triazoles with a new substitution pattern in a single step from cyclic 1,3-dicarbonyl compounds and N-tosyl triazole in moderate to high yields. Our synthesis takes place with complete regioselectivity as confirmed by crystallographic analysis which is rationalized by a suitable mechanistic proposal. This method provides an efficient, versatile and straightforward strategy towards the synthesis of new functionalized 1,2,3-triazoles.

2-Nitroallyl carbonate-based green bifunctional reagents for catalytic asymmetric annulation reactions

2-Nitroallylic carbonates, a new class of "green" 1,3-bielectrophilic reagents for organic synthesis and catalysis, have been prepared. The bifunctional tertiary amine-catalyzed asymmetric [3 + 3] annulations of cyclic enols with these reagents occur much faster than corresponding reactions with 2-nitroallylic esters and produce no acidic by-products poisoning the catalyst. Furthermore, 2-nitroallylic carbonates enable highly enantioselective one-pot synthesis of a variety of fused dihydropyrane derivatives from available precursors bearing pharmacophoric fragments.

Synthesis of tetrahydrothiopyrano[2,3-b]indoles via [3+3] annulation of nitroallylic acetates with indoline-2-thiones

[3+3] annulation of 1,3-binucleophilic indolin-2-thione with 1,3-bielectrophilic nitroallylic acetate via an S_N2-reaction-6-endo-trig cyclization takes place with high regio- and stereoselectivity to afford tetrahydrothiopyranoindoles.

Synthesis of quinones with highlighted biological applications: A critical update on the strategies towards bioactive compounds with emphasis on lapachones

Naphthoquinones are of key importance in organic synthesis and medicinal chemistry. In the last few years, various synthetic routes have been developed to prepare bioactive compounds derived or based on lapachones. In this sense, this review is mainly focused on the synthetic aspects and strategies used for the design of these compounds on the basis of their biological activities for the development of drugs against the neglected diseases leishmaniases and Chagas disease and also cancer. Three strategies used to develop bioactive quinones are discussed and categorized: (i) C-ring modification, (ii) redox centre modification and (iii) A-ring modification. Framed within these strategies for the development of naphthoquinoidal compounds against T. cruzi. Leishmania and cancer, reactions including copper-catalyzed azide-alkyne cycloaddition (click chemistry), palladium-catalysed cross couplings, C-H activation reactions, Ullmann couplings and heterocyclisations reported up to July 2019 will be discussed. The aim of derivatisation is the generation of novel molecules that can potentially inhibit cellular organelles/processes, generate reactive oxygen species and increase lipophilicity to enhance penetration through the plasma membrane. Modified lapachones have emerged as promising prototypes for the development of drugs against leishmaniases, Chagas disease and cancer.

Nickel-Mediated Asymmetric Allylic Alkylation between Nitroallylic Acetates and Acyl Imidazoles

A nickel-mediated asymmetric allylic alkylation reaction between imidazole-modified ketones and nitroallylic acetates is presented. This reaction is catalyzed by a simple chiral diamine-nickel catalyst under mild conditions and leads to a series of novel enantioenriched α-allylic adducts in moderate to good yields with excellent enantioselectivities. Furthermore, transformation of the allylic adducts could smoothly lead to chiral γ-nitro-esters containing three continuous stereocenters in good yields.

Kinetic Analysis and Mechanism of the Hydrolytic Degradation of Squaramides and Squaramic Acids

The hydrolytic degradation of squaramides and squaramic acids, the product of partial hydrolysis of squaramides, has been evaluated by UV spectroscopy at 37 °C in the pH range 3-10. Under these conditions, the compounds are kinetically stable over long time periods (>100 days). At pH >10, the hydrolysis of the squaramate anions shows first-order dependence on both squaramate and OH^-. At the same temperature and [OH^-], the hydrolysis of squaramides usually displays biphasic spectral changes (A → B → C kinetic model) with formation of squaramates as detectable reaction intermediates. The measured rates for the first step (k₁ ≈ 10^-4 M^-1 s^-1) are 2-3 orders of magnitude faster than those for the second step (k₂ ≈ 10^-6 M^-1 s^-1). Experiments at different temperatures provide activation parameters with values of ΔH^⧧ ≈ 9-18 kcal mol^-1 and ΔS^⧧ ≈ -5 to -30 cal K^-1 mol^-1. DFT calculations show that the mechanism for the alkaline hydrolysis of squaramic acids is quite similar to that of amides.

Synthesis and antitumor activity of selenium-containing quinone-based triazoles possessing two redox centres, and their mechanistic insights

Selenium-containing quinone-based 1,2,3-triazoles were synthesized using click chemistry, the copper catalyzed azide-alkyne 1,3-dipolar cycloaddition, and evaluated against six types of cancer cell lines: HL-60 (human promyelocytic leukemia cells), HCT-116 (human colon carcinoma cells), PC3 (human prostate cells), SF295 (human glioblastoma cells), MDA-MB-435 (melanoma cells) and OVCAR-8 (human ovarian carcinoma cells). Some compounds showed IC50 values < 0.3 μM. The cytotoxic potential of the quinones evaluated was also assayed using non-tumor cells, exemplified by peripheral blood mononuclear (PBMC), V79 and L929 cells. Mechanistic role for

NAD(P)H

Quinone Oxidoreductase 1 (NQO1) was also elucidated. These compounds could provide promising new lead derivatives for more potent anticancer drug development and delivery, and represent one of the most active classes of lapachones reported.

Stereocontrolled Construction of Tetrahydropyrano[2,3-c]pyrazole Scaffold via an Organocatalyzed Formal [3 + 3] Annulation

A bifunctional squaramide catalyzed enantioselective formal [3 + 3] annulation reaction with pyrazolin-5-ones and nitroallylic acetates has been developed. Densely substituted tetrahydropyrano[2,3-c]pyrazoles with two adjacent stereogenic centers are obtained in a highly stereocontrolled manner. Representative transformation of the annulation product to a biologically important fused dihydroisoquinoline is achieved without any appreciable loss in the diastereo- and enantioselectivity.

Asymmetric synthesis of cyclopentanes bearing four contiguous stereocenters via an NHC-catalyzed Michael/Michael/esterification domino reaction

An NHC-catalyzed Michael/Michael/esterification domino reaction via homoenolate/enolate intermediates for the asymmetric synthesis of tetrasubstituted cyclopentanes bearing four contiguous stereocenters is described. A variety of α,β-unsaturated aldehydes and 2-nitroallylic acetates react well with good domino yields and high stereoselectivities.

Catalytic asymmetric reactions and synthesis of quinones

Organo- and metal–ligand catalysed asymmetric reactions of quinones lead to complex enantiopure compounds including quinones.

Effective and novel enantioselective preparation of pyranopyrazoles and pyranocoumarins that is catalyzed by a quinine-derived primary amine

In this study, we executed an effective and novel enantioselective Michael/cyclodehydration sequential reaction between pyrazolin-5-one (or 4-hydroxy-2-pyrone) and chalcones that is catalyzed by a quinine-derived primary amine L7 in the presence of Boc-d-Phg-OH.