α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

It Takes Two to Tango, Part II: Synthesis of A-Ring Functionalised Quinones Containing Two Redox-Active Centres with Antitumour Activities

In 2021, our research group published the prominent anticancer activity achieved through the successful combination of two redox centres (ortho-quinone/para-quinone or quinone/selenium-containing triazole) through a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The combination of two naphthoquinoidal substrates towards a synergetic product was indicated, but not fully explored. Herein, we report the synthesis of 15 new quinone-based derivatives prepared from click chemistry reactions and their subsequent evaluation against nine cancer cell lines and the murine fibroblast line L929. Our strategy was based on the modification of the A-ring of para-naphthoquinones and subsequent conjugation with different ortho-quinoidal moieties. As anticipated, our study identified several compounds with IC₅₀ values below 0.5 µM in tumour cell lines. Some of the compounds described here also exhibited an excellent selectivity index and low cytotoxicity on L929, the control cell line. The antitumour evaluation of the compounds separately and in their conjugated form proved that the activity is strongly enhanced in the derivatives containing two redox centres. Thus, our study confirms the efficiency of using A-ring functionalized para-quinones coupled with ortho-quinones to obtain a diverse range of two redox centre compounds with potential applications against cancer cell lines. Here as well, it literally takes two for an efficient tango!

The Anti-Glioma Effect of Juglone Derivatives through ROS Generation

Juglone has been extensively reported as a natural antitumor pigment. However, it is easy to be oxidized due to active hydroxy in the quinone. Here, we designed some new juglone derivatives, as the hydroxy was replaced by methyl (D1), allyl (D2), butyl (D3), and benzyl (D4) groups. Nuclear magnetic resonance spectra and mass spectrometry were applied to confirm the derivatives and oxidative products of juglone. U87 and U251 cell lines were used for tests in vitro, and primary human glioblastoma cells were applied for in vivo experiments. The CCK8 and EdU assay demonstrated the anti-tumor effect of the four derivatives, and IC50 for U87 was 3.99, 3.28, 7.60, and 11.84 μM, respectively. In U251, IC50 was 7.00, 5.43, 8.64, and 18.05 μM, respectively. D2 and D3 were further selected, and flow cytometry showed that apoptosis rates were increased after D2 or D3 treatment via ROS generation. Potential targets were predicted by network pharmacology analysis, most of which were associated with apoptosis, cell cycle, and metabolism pathway. CDC25B and DUSP1 were two of the most likely candidates for targets. The orthotopic glioblastoma model was established to evaluate the anti-glioma effect and side-effect of juglone derivatives, and the in vivo experiments confirmed the anti-glioma effects of juglone derivatives. In conclusion, new derivatives of juglone were created via chemical group substitution and could inhibit glioma cell viability and proliferation and induce apoptosis rate via ROS generation.

Organophotoredox-catalyzed cyanoalkylation of 1,4-quinones

A visible-light-induced metal-free cyanoalkylation of 1,4-quinones under mild and redox-neutral conditions is described. This reaction proceeds at room temperature without the need of extra base or additive and is suitable for a variety of 1,4-quinones and differently substituted cyclobutanone oxime esters. Further transformation of cyano functionality to tetrazole and amine has also been demonstrated to showcase the advantage of this method to prepare drug-like molecules.

Menadione: a platform and a target to valuable compounds synthesis

Naphthoquinones are important natural or synthetic compounds belonging to the general class of quinones. Many compounds in this class have become drugs that are on the pharmaceutical market for the treatment of various diseases. A special naphthoquinone derivative is menadione, a synthetic naphthoquinone belonging to the vitamin K group. This compound can be synthesized by different methods and it has a broad range of biological and synthetic applications, which will be highlighted in this review.

Perfluoroalkylation of Terminal Alkynes with Perfluoroalkyl Iodides Catalyzed by an Iron Salt

The one-step, direct perfluoroalkylation of terminal alkynes with perfluoroalkyl iodides has been developed in which a simple ligandless iron salt is employed as the catalyst. Various perfluoroalkylated alkynes could be afforded in good to excellent yields with good functional group compatibility. Preliminary mechanistic studies suggest the involvement of the perfluoroalkyl radical in the catalytic cycle and the perfluoroalkylated alkenyl iodides as intermediates. The method provides straight, streamlined, and sustainable access to perfluoroalkylated acetylenes.

Silver-catalyzed cascade cyclization and functionalization of N-aryl-4-pentenamides: an efficient route to γ-lactam-substituted quinone derivatives

The synthesis of γ-lactam-substituted quinone derivatives through a Ag₂O-catalyzed cascade cyclization and functionalization of N-aryl-4-pentenamides has been developed. Related 2-oxazolidinone substituted quinone products can be also obtained with N-aryl allyl carbamates. The reactions proceed through an amidyl radical-initiated 5-exo-trig cyclization and followed radical addition to quinones. They provide an efficient route to various γ-lactam-substituted quinone derivatives with a wide range of substrate scope.

The synthesis of γ-lactam and related 2-oxazolidinone substituted quinone derivatives through a Ag₂O-catalyzed cascade cyclization and functionalization of N-ary-4-pentenamides and N-aryl allyl carbamates has been developed.

Bioinspired Photoredox Benzylation of Quinones

3-Benzylmenadiones were obtained in good yield by using a blue-light-induced photoredox process in the presence of Fe(III), oxygen, and γ-terpinene acting as a hydrogen-atom transfer agent. This methodology is compatible with a wide variety of diversely substituted 1,4-naphthoquinones as well as various cheap, readily available benzyl bromides with excellent functional group tolerance. The benzylation mechanism was investigated and supports a three-step radical cascade with the key involvement of the photogenerated superoxide anion radical.

Copper-Catalyzed Alkylation of Silyl Enol Ethers with Sterically Hindered α-Bromocarbonyls: Access to the Histamine H3 Receptor Antagonist

A general and efficient copper-catalyzed alkylation of silyl enol ethers with functionalized alkyl bromides has been developed for the synthesis of the sterically hindered γ-ketoesters. The transformation was induced through C(sp³)-halogen activation of commercially available sterically hindered alkyl bromides under mild conditions in good results. The strategy could be used for the synthesis of biologically active histamine H₃ receptor (H₃R) antagonist for medicinal purposes.

2-Propargylamino-naphthoquinone derivatives as multipotent agents for the treatment of Alzheimer's disease

Alzheimer's disease is a progressive brain disorder with characteristic symptoms and several pathological hallmarks. The concept of "one drug, one target" has not generated any new drugs since 2004. The new era of drug development in the field of AD builds upon rationally designed multi-target directed ligands that can better address the complexity of AD. Herewith, we designed ten novel derivatives of 2-propargylamino-naphthoquinone. The biological evaluation of these compounds includes inhibition of monoamine oxidase A/B, inhibition of amyloid-beta aggregation, radical-scavenging, and metal-chelating properties. Some of the compounds possess low cytotoxicity profile with an anti-inflammatory ability in the lipopolysaccharide-stimulated cellular model. All these features warrant their further testing in the field of AD.

The silver catalyzed direct C-H functionalization of quinones with dialkyl amides

DMA and other dialkylamides were successfully used as synthons for the C-H functionalization of quinones. This novel amidoalkylation reaction works with a variety of substituted quinones and dialkyl/alkyl amides, such as DMF, NMP and NMA, and the corresponding products were obtained in moderate to good yields. The amidoalkylation of quinones is demonstrated for the first time. A suitable mechanism and the synthetic utility of these compounds are demonstrated. The molecular docking of compound 5 with an Alzheimer's disease (AD) associated AChE target site was studied.