Photoredox-catalyzed diastereoselective dearomative prenylation and reverse-prenylation of electron-deficient indole derivatives

In Vitro Enzymatic and Computational Assessments of Pyrazole-Isatin and Pyrazole-Indole Conjugates as Anti-Diabetic, Anti-Arthritic, and Anti-Inflammatory Agents

Background/Objectives: Recently, the prevalence of diseases such as diabetes, arthritis, and inflammatory diseases, along with their complications, has become a significant health problem. This is in addition to the various biomedical applications of pyrazole, isatin, and indole derivatives. Accordingly, cooperation will continue between chemistry scientists, pharmaceutical scientists, and human doctors to produce hybrid compounds from pyrazole with isatin or indole possessing biological activities as anti-diabetic, anti-arthritic, and anti-inflammatory agents. Methods: The two series of pyrazole-isatin conjugates 12a-h and pyrazole-indole conjugates 14a-d were prepared from our previous works via the direct reaction of 5-amino-pyrazoles 10a-d with N-alkyl isatin 11a,b, and 1H-indole-3-carbaldehyde (13), respectively, using the previously reported procedure. The potential biological activities of 12a-h and 14a-d as anti-diabetic, anti-arthritic, and anti-inflammatory agents were assessed through estimated inhibition percentage (%) and the median inhibitory concentrations (IC50) using methods described in the literature. Further, the computational assessments of 12a-h and 14a-d such as toxic doses (the median lethal dose, LD50), toxicity classes, drug-likeness model scores (DLMS), molecular lipophilicity potential (MLP) maps, polar surface area (PSA) maps, and topological polar surface area (TPSA) values were predicted using available free websites. Results: The in vitro enzymatic assessment results showed that pyrazole-indole conjugate 14b possesses powerful activities against (i) α-amylase (% = 65.74 ± 0.23, IC50 = 4.21 ± 0.03 µg/mL) and α-glucosidase (% = 55.49 ± 0.23, IC50 = 2.76 ± 0.01 µg/mL); (ii) the protein denaturation enzyme (% = 49.30 ± 0.17) and against the proteinase enzyme (% = 46.55 ± 0.17) with an IC50 value of 6.77 ± 0.01 µg/mL; (iii) the COX-1, COX-2, and 5-LOX enzymes with an IC50 of 5.44 ± 0.03, 5.37 ± 0.04, and 7.52 ± 0.04, respectively, which is almost close to the IC50 of the indomethacin and zileuton drugs. Also, the computational assessment results showed (i) the conjugate 14b possesses lipophilic surface properties thus can cross cell membranes, and is effective for treatment; (ii) all the conjugates possess a TPSA value of more than 140 Å2 thus possess good intestinal absorption. Conclusions: The two series of pyrazole-isatin conjugates 12a-h and pyrazole-indole conjugates 14a-d were synthesized from our previous works. The results of these in vitro enzymatic and computational assessments concluded that the pyrazole-indole conjugate 14b possesses powerful activities against various studied enzymes and possesses good computational results. In the future, our research team will present in vitro, in vivo biological, and computational assessments to hopefully obtain effectual agents such as anti-diabetic, anti-arthritic, and anti-inflammatory.

Terpenylation of Ketones and a Secondary Alcohol under Hydrogen-Borrowing Manganese Catalysis

An Earth-abundant Mn-PNP pincer complex-catalyzed terpenylation of cyclic and acyclic ketones and secondary alcohol 1-phenylethanol using isoprenoid derivatives prenol, nerol, phytol, solanesol, and E-farnesol as allyl surrogates is reported. The C-C coupling reactions are green and atom-economic, proceeding via dehydrogenation of alcohols following a hydrogen autotransfer methodology aided by metal-ligand cooperation.

Visible-Light-Induced Dearomative Annulation of Indoles toward Stereoselective Formation of Fused- and Spiro Indolines

Dearomatization approaches are attractive for their abilities to transform simple, planar arenes into complex, three-dimensional architectures. In particular, visible-light driven dearomatization strategies are significant because of their mild, green, and sustainable nature, enabling the fabrication of new chemical bonds via an electron transfer or energy transfer process. Indole compounds, being potentially bioactive and readily accessible, can be employed efficiently as building blocks for constructing diverse annulated frameworks under photocatalysis. Highly stereoselective radical cascade reactions of appropriate indole systems can provide complex cyclic scaffolds bearing multiple stereocenters. In fact, the past few years have witnessed the renaissance of dearomative cycloadditions of indoles via visible-light-induced photocatalysis. The present review highlights recent advances (2019-mid 2024) in visible-light-driven dearomative annulation of indoles leading to formation of polycyclic indolines, including angularly fused and spiro indolines. Most of the reactions described in this review are simple, providing quick access to the desired products. Additionally, characteristic reaction mechanisms are offered to provide an understand of how indole scaffolds show distinctive reactivity under photocatalytic conditions.

Photochemical dearomative skeletal modifications of heteroaromatics

Dearomatization has emerged as a powerful tool for rapid construction of 3D molecular architectures from simple, abundant, and planar (hetero)arenes. The field has evolved beyond simple dearomatization driven by new synthetic technology development. With the renaissance of photocatalysis and expansion of the activation mode, the last few years have witnessed impressive developments in innovative photochemical dearomatization methodologies, enabling skeletal modifications of dearomatized structures. They offer truly efficient and useful tools for facile construction of highly complex structures, which are viable for natural product synthesis and drug discovery. In this review, we aim to provide a mechanistically insightful overview on these innovations based on the degree of skeletal alteration, categorized into dearomative functionalization and skeletal editing, and to highlight their synthetic utilities.

Tunable C-H functionalization and dearomatization enabled by an organic photocatalyst

C-H functionalization and dearomatization constitute fundamental transformations of aromatic compounds, which find wide applications in various research areas. However, achieving both transformations from the same substrates with a single catalyst by operating a distinct mechanism remains challenging. Here, we report a photocatalytic strategy to modulate the reaction pathways that can be directed toward either C-H functionalization or dearomatization under redox-neutral or net-reductive conditions, respectively. Two sets of indoles and indolines bearing tertiary alcohols are divergently furnished with good yields and high selectivity. The key to success is the introduction of isoazatruxene ITN-2 as a novel photocatalyst (PC), which outperforms the commonly used PCs. The ready synthesis and high modulability of isoazatruxene type PCs indicate their great application potential.

Visible-Light Photoredox-Catalyzed Intermolecular α-Aminomethyl/Carboxylative Dearomatization of Indoles with CO2 and α-Aminoalkyl Radical Precursors

Disclosed here is a visible-light photoredox-catalyzed intermolecular sequential α-aminomethyl/carboxylative dearomatization of indoles with CO2 and α-aminoalkyl radical precursors, affording a series of functionalized indoline-3-carboxylic acids and lactams in good yields with high regioselectivity. This multicomponent reaction provides a green and facile method for the synthesis of diverse functionalized indolines by using CO2 as the carboxylic and carbonyl source.