A Synthetic Overview of Benzoxazines and Benzoxazepines as Anticancer Agents

One-Pot Synthesis of Tricyclic Benzoxazines and Benzoxazepine by Heterogeneous Biochemo Multienzyme Cascade Reaction

Benzoxazine and benzoxazepine derivatives with tricyclic five-, six-, and seven-membered lactone and lactam rings were synthesized in one-pot conditions by using biochemo multienzyme cascade of lipase M and tyrosinase. The reaction involves tyrosinase-mediated ortho-hydroxylation of the phenolic moiety, followed by 1,6-Michael addition and tandem intramolecular ring closure. The method achieves high atom economy, minimizes purification steps, and provides a sustainable alternative to conventional multistep syntheses. Enzymes showed excellent reusability, further enhancing the green approach.

Carbonyl vs Hydroxy: Rhodium catalyzed carbonyl ylide triggered diastereoselective synthesis of 2,5-methano-1,3-benzoxazepines

A general and efficient rhodium catalyzed chemoselective reaction of N-sulfonyl-1,2,3-triazoles with 2-hydroxyphenyl substituted enone has been successfully accomplished. The reaction occurs through the initial chemoselective reaction of azavinyl carbenes to the carbonyl group of enone followed by rearrangement and cyclization. The reaction tolerated various functional groups and allowed the synthesis of various 2,5-methano-1,3-benzoxazepines in high yield as single diastereomer. Control experiments revealed the formation of potential dihydropyrrole as an intermediate and aided in proposing the plausible mechanism.

Base-Mediated Synthesis of Imidazole-Fused 1,4-Benzoxazepines via 7-exo-dig Cyclizations: Propargyl Group Transformation

Herein, we describe the synthesis of a series of imidazole-fused 1,4-benzoxazepines using 7-exo-dig cyclizations. Two sets of substrates, one containing disubstituted alkyne functional groups and the other featuring terminal alkynes, were synthesized by using O-propargylation, Sonogashira cross-coupling, and condensation reactions between aldehydes and o-diaminobenzene. While the disubstituted substrates yielded exocyclic E/Z configured cyclization products smoothly, the reactions involving terminal alkynes resulted in the formation of isomeric products with altered skeletal structures, in addition to the expected 7-exo-dig cyclization products. Density functional theory (DFT) calculations were used to clarify the mechanisms underlying the formation of these products. It is suggested that these unexpected products are formed through a series of intermolecular O-to-N-propargyl transfer reactions, followed by 7-exo-dig cyclization, in accordance with Baldwin's rules. Furthermore, this study extensively demonstrates the conversion of exocyclic products to endocyclic products through a base-mediated 1,3-H shift.

Electrochemical [3+3] Annulation of Phenol and Hydrazone: Synthesis of 1,3,4-Oxadiazines

A novel [3+3] cyclization reaction between phenol and hydrazone was successfully developed under electrochemically driven conditions. This reaction provided access to a diverse array of 1,3,4-oxadiazinane compounds in consistently high yields, reaching up to 87%. Notably, the reaction exhibited remarkable tolerance toward a broad spectrum of both phenol and hydrazone substrates, underscoring its versatility. Moreover, the protocol distinguished itself by its exceptional atom and step economy, facilitating the efficient construction of functionalized 1,3,4-oxadiazines. The synthetic utility of this approach was further exemplified by its scalability, as demonstrated by gram-scale reactions, and its broad substrate scope.

Investigation of photophysical properties and potential biological applications of substituted tris(polypyridyl)ruthenium(II) complexes

The photophysical properties of tris(polypyridyl)ruthenium(II) complex [Ru(dmbpy)3]2+ [dmbpy = 4,4'-dimethyl-2,2'-bipyridine] were investigated and compared with [Ru(bpy)3]2+ following both experimental and computational approaches. The variations in the electronic properties of the complex in the ground and excited states were determined by density functional theory (DFT) methods, and their effects on the anticancer, antioxidant, and antimicrobial activities were also evaluated by molecular docking and dynamic simulation studies. The potential of these complexes to serve as bioanalytes was investigated by their ability to bind with quinones, the well-known electron mediators in numerous light-driven reactions. Following the above, the anticancer properties were evaluated against breast cancer-related proteins. The results revealed that the complex possesses comparable anticancer and antioxidant potential to that of [Ru(bpy)3]2+. The physical, electronic, and biological properties of this complex depend on the nature of the ligands and the medium of investigation. Herein, the potential applications of [Ru(bpy)3]2+ in clinical diagnostics as antioxidants and therapeutic agents were evaluated.

Recent Progress in the Synthesis of Benzoxazin-4-Ones, Applications in N-Directed Ortho-Functionalizations, and Biological Significance

The development of efficient synthetic procedures to access fused N, O-heterocyclic skeletons has been a pivotal research topic in organic synthesis for several years. Owing to the applications of N, O-fused heterocycles in organic synthesis, material sciences, and medicinal chemistry, significant efforts have been dedicated to design novel methods for their construction. To this end, 1,3-benzoxazin-4-ones are privileged candidates for N, O-heterocyclic molecules often found in natural products, agrochemicals, and materials science applications. In this review, we aim to summarize the existing literature on the synthesis of 1,3-benzoxazin-4-ones from 2010 onwards. Moreover, 1,3-benzoxazin-4-ones have also been identified as an excellent native directing group for the ortho-functionalization via C-H activation, which is often a strenuous task requiring pre-functionalized substrates. In the latter part of this report, we compiled several interesting examples of N-directed functionalizations of 1,3-benzoxazin-4-ones. Additionally, to emphasize biological importance, recent developments on the anticancer evaluations of benzoxazine-4-one core are included. We believe that by harnessing the methodologies discussed herein, new possibilities could be unlocked for the synthesis of fused N, O-heterocycles, leading to the development of novel biologically active compounds and functional materials.

InCl3-Catalyzed One-Pot Synthesis of Pyrrolo/Indolo- and Benzooxazepino-Fused Quinoxalines

In this paper, we describe an efficient InCl3-catalyzed two-component reaction of 1-(2-aminophenyl)pyrroles/indoles and 2-propargyloxybenzaldehydes for the direct synthesis of 12bH-benzo[6,7]1,4-oxazepino[4,5-a]pyrrolo/indolo[2,1-c]quinoxalines. This high atom- and step-economical one-pot process generates three new C/N-C bonds in a single synthetic operation, resulting in the formation of new six- and seven-membered heterocyclic rings. The easy availability of the starting materials, the use of the relatively inexpensive indium catalyst, and the good substrate scope are the salient features of this strategy. The proposed mechanistic pathway involves imine formation, two consecutive cyclizations via electrophilic aromatic substitution and nucleophilic addition reactions, and the H shift step.

Design and Synthesis of Novel Antioxidant 2-Substituted-5,7,8-Trimethyl-1,4-Benzoxazine Hybrids: Effects on Young and Senescent Fibroblasts

The exponential growth of the aged population worldwide is followed by an increase in the prevalence of age-related disorders. Oxidative stress plays central role in damage accumulation during ageing and cell senescence. Thus, a major target of today's anti-ageing research has been focused on antioxidants counteracting senescence. In the current work, six novel 5,7,8-trimethyl-1,4-benzoxazine/catechol or resorcinol hybrids were synthesized connected through a methoxymethyl-1,2,3-triazolyl or a 1,2,3-triazoly linker. The compounds were evaluated for their antioxidant capacity in a cell-free system and for their ability to reduce intracellular ROS levels in human skin fibroblasts, both young (early-passage) and senescent. The most efficient compounds were further tested in these cells for their ability to induce the expression of the gene heme oxygenase-1 (ho-1), known to regulate redox homeostasis, and cellular glutathione (GSH) levels. Overall, the two catechol derivatives were found to be more potent than the resorcinol analogues. Furthermore, these two derivatives were shown to act coordinately as radical scavengers, ROS inhibitors, ho-1 gene expression inducers, and GSH enhancers. Interestingly, one of the two catechol derivatives was also found to enhance human skin fibroblast viability. The properties of the synthesized compounds support their potential use in cosmetic applications, especially in products targeting skin ageing.

Biocatalytic Generation of o-Quinone Imines in the Synthesis of 1,4-Benzoxazines and Its Comparative Green Chemistry Metrics

1,4-Benzoxazines are important motifs in many pharmaceuticals and can be formed by a reaction sequence involving the oxidation of o-aminophenols to their corresponding quinone imine followed by an in situ inverse electron demand Diels-Alder (IEDDA) cycloaddition with a suitable dienophile. Reported herein is the development of a reaction sequence that employs horseradish peroxidase to catalyze the oxidation of the aminophenols prior to the IEDDA as a more sustainable alternative to the use of conventional stoichiometric oxidants. The synthesis of 10 example benzoxazines is demonstrated in this "one-pot, two-step" procedure with yields between 42% and 92%. The green chemistry metrics, including the E-factor and generalized reaction mass efficiency, for this biocatalytic reaction were compared against the conventional chemical approach. It was found that the reported biocatalytic route was approximately twice as green by these measures.

Access to a Diverse Array of Bridged Benzo[1,5]oxazocine and Benzo[1,4]diazepine Structures

The preparation of bridged benzo[1,5]oxazocines and benzo[1,4]diazepines is demonstrated from simple aniline and aldehyde starting materials. A one-pot condensation/6π electrocyclization is followed by an intramolecular trapping of the 2,3-dihydroquinoline intermediate by nitrogen or oxygen nucleophiles to give bridged seven- and eight-membered products. Using 3-hydroxypyridinecarboxaldehydes results in a stable zwitterionic structure that can undergo a diastereoselective reduction under hydrogenative conditions. A similar cyclization/hydrogenation pathway with excellent diastereoselectivity is also demonstrated from 2-pyridyl-substituted 1,2,3,4-tetrahydroquinolines.