Synthesis, Structures and Properties of Trioxa[9]circulene and Diepoxycyclononatrinaphthalene

This article presents trioxa[9]circulene (3) as a novel member of hetero[n]circulenes. Its synthesis began with the synthesis of dimethoxydioxa[8]helicene (5) and used dimethoxydiepoxycyclononatrinaphthalene (4) as a key intermediate, despite the condensation reaction predominantly yielding a 1,4-addition byproduct. The structures and properties of 3-5 were extensively investigated using experimental and computational methods. Analysis of the crystal structures reveal elongation of the internal C-C bonds in the nine-membered ring of 3 compared to 4 and 5. Computational studies demonstrate the remarkable flexibility of trioxa[9]circulene's saddle-shaped polycyclic framework, while the other two compounds are rigid with large racemization barriers. Optically pure forms of 4 and 5 exhibit absorption and luminescence dissymmetry factors on the order of 10-2, with smaller values observed for compound 4. In the crystal structures, molecules of 3 stack to form columns with remarkable π-π overlap, and the π-π interactions of 4 exhibit short intermolecular C-to-C contacts. Consequently, the solution-processed film of 4 functioned as a p-type organic semiconductor in field effect transistors.

Oxime Esters: Flexible Building Blocks for Heterocycle Formation

Oxime esters as the applicable building blocks, internal oxidizing agents, and directing groups in the synthesis of -, S-, and O-containing heterocycle scaffolds have gained great attention in the last decade. This review provides an overview of recent advances in the cyclization of oxime esters with various functional group reagents under transition metal and transition metal-free catalyzed conditions. Moreover, the mechanistic aspects of these protocols are explained in detail.

Design of Aurone-Based Dual-State Emissive (DSE) Fluorophores

The development of dual-state emissive (DSE) fluorophores, i. e. organic molecules showing balanced emission in both solution and as molecular solids, has recently become an emerging approach in material science, biology, sensing, and optoelectronics. However, the majority of existing DSE fluorophores represents structural modifications of the scaffolds known for their aggregation-induced emission (AIE) properties, e. g., tetraphenylethylenes (TFE), triphenylamines (TFA), and others. In this study, we introduce aurones as an easily accessible scaffold for the construction of DSE fluorophores and describe the main design principles allowing to achieve the balanced emission in both solution and solid state. Herein, we present the solid-state fluorescence in a systematic series of aurone derivatives for the first time. We propose that the newly found DSE properties of aurones in combination with their established biological activity can be applied efficiently in biomedical studies and diagnostic tools.

Naturally Occurring O-heterocycles as Anticancer Agents

Cancer is a leading cause of death worldwide. Proper efficient drugs are required to treat this deadly disease. Natural products have long been a vital source of anticancer agents and they have generated various "lead compounds" suitable for drug developments. With the recent advancement of chemical synthesis and bioevaluation techniques these lead compounds of natural origins have been utilized for production of useful anticancer drugs. Among the naturally occurring bioactive compounds various O-heterocycles have been evaluated as remarkable cancer therapeutic agents. These compounds generally possess unique structures and novel mechanism of action. In the present review article, some selected O-heterocycles as promoting anticancer agents have been discussed in brief. Various natural sources and chemistry as well as bioactivities of these compounds have been described. The development of improved analogues of these compounds through synthetic modifications and efficient bioevaluation along with proper studies on structure-activity relationship and mechanism of actions has been mentioned. The article has demonstrated the recent relevance of naturally occurring O-heterocyclic compounds in current anticancer drug discovery and development scenario.

New Alkoxy Flavone Derivatives Targeting Caspases: Synthesis and Antitumor Activity Evaluation

The antitumor activity of natural flavonoids has been exhaustively reported. Previously it has been demonstrated that prenylation of flavonoids allows the discovery of new compounds with improved antitumor activity through the activation of caspase-7 activity. The synthesis of twenty-five flavonoids (4–28) with one or more alkyl side chains was carried out. The synthetic approach was based on the reaction with alkyl halide in alkaline medium by microwave (MW) irradiation. The in vitro cell growth inhibitory activity of synthesized compounds was investigated in three human tumor cell lines. Among the tested compounds, derivatives 6, 7, 9, 11, 13, 15, 17, and 18 revealed potent growth inhibitory activity (GI₅₀ < 10 μM), being the growth inhibitory effect of compound 13 related with a pronounced caspase-7 activation on MCF-7 breast cancer cells and yeasts expressing human caspase-7. A quantitative structure-activity relationship (QSAR) model predicted that hydrophilicity, pattern of ring substitution/shape, and presence of partial negative charged atoms were the descriptors implied in the growth inhibitory effect of synthesized compounds. Docking studies on procaspase-7 allowed predicting the binding of compound 13 to the allosteric site of procaspase-7.

The Current Status of O-Heterocycles: A Synthetic and Medicinal Overview

O-Heterocycles have been explored in the field of medicinal chemistry for a long time, but their significance has not been duly recognised and they are often shunned in favour of N-heterocycles. The design of bioactive molecules for nearly every pathophysiological condition is primarily focused on novel N-heterocycles. The main reasons for such bias include the ease of synthesis and possible mimicking of physiological molecules by N-heterocycles. But considering only this criterion rarely provides breakthrough molecules for a given disease condition, and instead the risks of toxicity or side effects are increased with such molecules. On the other hand, owing to improved synthetic feasibility, O-heterocycles have established themselves as equally potent lead molecules for a wide range of pathophysiological conditions. In the last decade there have been hundreds of reports validating the fact that equally potent molecules can be designed and developed by using O-heterocycles, and these are also expected to have comparably low toxicity. Even so, researchers tend to remain biased toward the use of N-heterocycles over O-heterocycles. Thus, this review provides a critical analysis of the synthesis and medicinal attributes of O-heterocycles, such as pyrones, oxazolones, furanones, oxetanes, oxazolidinones, and dioxolonones, and others, reported in the last five years, underlining the need for and the advantages guiding researchers toward them.