Oxazole-Based Compounds As Anticancer Agents

Regiodivergent Synthesis of 4- and 5-Sulfenyl Oxazoles from Alkynyl Thioethers

The regiodivergent synthesis of 4- and 5-sulfenyl oxazoles from 1,4,2-dioxazoles and alkynyl thioethers has been achieved. Gold-catalysed conditions are used to favour the formation of 5-sulfenyl oxazoles via β-selective attack of the nitrenoid relative to the sulfenyl group. In contrast, 4-sulfenyl oxazoles are formed by α-selective reaction under Brønsted acid conditions from the same substrates. The nature of stabilising gold-sulfur interactions have been investigated by natural bond orbital analysis, showing that the S→Au interactions are significantly stronger in the intermediate that favours the 5-sulfenyl oxazoles. A kinetic survey identifies catalyst inhibition processes. This study into the regiodivergent methods includes the development of telescoped annulation-oxidation protocols for regioselective access to oxazole sulfoxides and sulfones.

Synthesis, characterization of novel N-(4-cyano-1,3-oxazol-5-yl)sulfonamide derivatives and in vitro screening their activity against NCI-60 cancer cell lines

A novel series of N-(4-cyano-1,3-oxazol-5-yl)sulfonamides have been synthesized and characterized by IR, 1 H NMR, 13 C NMR spectroscopy, elemental analysis and chromato-mass-spectrometry. The anticancer activities of all newly synthesized compounds were evaluated via a single high-dose assay (10 μM) against 60 cancer cell lines by the National Cancer Institute (USA) according to its screening protocol. Among them, compounds 2 and 10 exhibited the highest activity against the 60 cancer cell lines panel in the one-dose assay. Compounds 2 and 10 showed inhibitory activity within the GI50 parameter and in five dose analyses. However, their cytostatic activity was only observed against some cancer cell lines, and cytotoxic concentration was outside the maximum used, i. e., >100 μM. The COMPARE analysis showed that the average graphs of the tested compounds have a moderate positive correlation with compounds with the L-cysteine analog and vinblastine (GI50 ) as well as paclitaxel (TGI), which target microtubules. Therefore, disruption of microtubule formation may be one of the mechanisms of the anticancer activity of the tested compounds, especially since among tubulin inhibitors with antitumor activity, compounds with an oxazole motif are widely represented. Therefore, N-(4-cyano-1,3-oxazol-5-yl)sulfonamides may be promising for further functionalization to obtain more active compounds.

Density Functional Theory Calculations: A Useful Tool to Investigate Mechanisms of 1,3-Dipolar Cycloaddition Reactions

The present review contains a representative sampling of mechanistic studies, which have appeared in the literature in the last 5 years, on 1,3-dipolar cycloaddition reactions, using DFT calculations. Attention is focused on the mechanistic insights into 1,3-dipoles of propargyl/allenyl type and allyl type such as aza-ylides, nitrile oxides and azomethyne ylides and nitrones, respectively. The important role played by various metal-chiral-ligand complexes and the use of chiral eductors in promoting the site-, regio-, diastereo- and enatioselectivity of the reaction are also outlined.

Deciphering Deoxynybomycin Biosynthesis Reveals Fe(II)/α-Ketoglutarate-Dependent Dioxygenase-Catalyzed Oxazoline Ring Formation and Decomposition

The antibacterial agents deoxynybomycin (DNM) and nybomycin (NM) have a unique tetracyclic structure featuring an angularly fused 4-oxazoline ring. Here, we report the identification of key enzymes responsible for forming the 4-oxazoline ring in Embleya hyalina NBRC 13850 by comparative bioinformatics analysis of the biosynthetic gene clusters encoding structurally similar natural products DNM, deoxynyboquinone (DNQ), and diazaquinomycins (DAQs). The N-methyltransferase DnmS plays a crucial role in catalyzing the N-dimethylation of a tricyclic precursor prenybomycin to generate NM D; subsequently, the Fe(II)/α-ketoglutarate-dependent dioxygenase (Fe/αKGD) DnmT catalyzes the formation of a 4-oxazoline ring from NM D to produce DNM; finally, a second Fe/αKGD DnmU catalyzes the C-12 hydroxylation of DNM to yield NM. Strikingly, DnmT is shown to display unexpected functions to also catalyze the decomposition of the 4-oxazoline ring and the N-demethylation, thereby converting DNM back to prenybomycin, to putatively serve as a manner to control the intracellular yield of DNM. Structure modeling, site-directed mutagenesis, and quantum mechanics calculations provide mechanistic insights into the DnmT-catalyzed reactions. This work expands our understanding of the functional diversity of Fe/αKGDs in natural product biosynthesis.

Photoredox-catalyzed coupling of aryl sulfonium salts with CO2 and amines to access O-aryl carbamates

An efficient photoredox-catalyzed three-component coupling reaction of aryl sulfonium salts, carbon dioxide and amines has been developed for the first time. This reaction provides a new strategy for the synthesis of a range of valuable O-aryl carbamates from readily available arenes via a site-selective thianthrenation/carbamoyloxylation two-step process. Mild conditions, broad substrate scope and good functional group tolerance are the features of the transformation. The synthetic utility of the method was demonstrated by the late-stage modification of bioactive molecules and pharmaceuticals.

Iodine-Promoted Oxidative Cyclization of Methyl Azaarenes and α-Amino Ketones for One-Pot Synthesis of 2-Azaaryl-5-aryl Oxazoles

A high efficiency protocol was developed for the synthesis of 2,5-disubstituted oxazoles via iodine-promoted oxidative domino cyclization. These reactions were performed with readily available methyl azaarenes and α-amino ketones under metal-free conditions. This protocol is a simple method with high functional group compatibility, a wide range of substrates, and excellent yield, providing a new way to synthesize azaarene-attached oxazoles.

Synthesis and evaluation of novel almazole D analogs as anticancer agents

Novel almazole D-amide conjugates, esters, and N-alkylated analogs were synthesized and investigated for their anticancer activity against seven cancer cell lines. Among the series, compounds 5g and 5m showed significant anticancer activities against multiple cell lines with moderate selectivity indices. Compound 5g had IC₅₀ values of 5.86 ± 0.31, 9.94 ± 0.06, 12.74 ± 0.12, and 9.40 ± 0.03 μM against the B16-F10, DU145, HeLa, and LC-540 cell lines, respectively, while compound 5m showed IC₅₀ values of 6.35 ± 0.09, 9.17 ± 0.11, 9.00 ± 0.011, 19.65 ± 0.63, 8.13 ± 0.04, and 11.56 ± 0.01 μM against B16-F10, DU145, HeLa, HepG2, LC-540, and SK-BR-3 cells, respectively. Compared to almazole D, which only showed significant activity against B16-F10 cells (IC₅₀  = 9.05 ± 0.008 μM), the synthesized analogs showed improved anticancer activity against multiple cell lines. The kinase inhibition assay coupled with the docking studies revealed that epidermal growth factor receptor (EGFR) kinase inhibition via interaction with amino acid residue T790 on the EGFR is one of the possible mechanisms by which 5g exerts its anticancer potential. The ADMET prediction and drug-likeness of the analogs project the synthesized analogs as promising agents, which can be further developed for application in cancer therapy.

New antiproliferative agents derived from tricyclic 3,4-dihydrobenzo[4,5]imidazo[1,2-a][1,3,5]triazine scaffold: Synthesis and pharmacological effects

A series of novel 3,4-dihydrobenzo[4,5]imidazo[1,2-a][1,3,5]triazine (BIT) derivatives were designed and synthesized. In vitro antiproliferative activity was detected toward two human colorectal adenocarcinoma cell lines (CaCo-2 and HT-29) and one human dermal microvascular endothelial cell line (HMVEC-d). The most active compounds, namely 2-4 and 8, were further investigated to clarify the mechanism behind their biological activity. Through immunofluorescence assay, we identified the target of these molecules to be the microtubule cytoskeleton with subsequent formation of dense microtubule accumulation, particularly at the periphery of the cancer cells, as observed in paclitaxel-treated cells. Overall, these results highlight BIT derivatives as robust and feasible candidates deserving to be further developed in the search for novel potent antiproliferative microtubule-targeting agents.

Synthesis of 4-(organoselenyl) oxazolones via cyclization of N-alkynyl ethylcarbamates promoted by organoselenium

Organoselenyl iodide promoted the intramolecular nucleophilic cyclization of N-alkynyl ethylcarbamates in the synthesis of 4-(organoselenyl) oxazolones. The reaction was regioselective, giving the five-membered oxazolone products as the unique regioisomer via an initial activation of the carbon-carbon triple bond through a seleniranium intermediate, followed by an intramolecular 5-endo-dig cyclization mode. The generality of the methodology has been proven by applying the optimized reaction conditions to different organoselenyl iodides and N-alkynyl ethylcarbamates having different substituents directly bonded to the nitrogen atom and in the terminal position of the alkyne.

Recent Developments in Nanocatalyzed Green Synthetic Protocols of Biologically Potent Diverse O-Heterocycles—A Review

The dynamic growth in green organic synthetic methodologies for diverse heterocyclic scaffolds has substantially contributed to the field of medicinal chemistry over the last few decades. The use of hybrid metal nanocatalysts (NCs) is one such benign strategy for ensuring the advancement of modern synthetic chemistry by adhering to the principles of green chemistry, which call for a sustainable catalytic system that converts reacting species into profitable chemicals at a faster rate and tends to reduce waste generation. The metal nanoparticles (NPs) enhance the exposed surface area of the catalytic active sites, thereby making it easier for reactants and metal NCs to have an effective interaction. Several review articles have been published on the preparation of metal NCs and their uses for various catalytic heterocyclic transformations. This review will summarize different metal NCs for the efficient green synthesis of various O-heterocycles. Furthermore, the review will provide a concise overview of the role of metal NCs in the synthesis of O-heterocycles and will be extremely useful to researchers working on developing novel green and simple synthetic pathways to various O-heterocyclic-derived molecules.

Time-economical synthesis of selenofunctionalized heterocycles via I2O5-mediated selenylative heterocyclization

A time-economical and robust synthesis of various selenofunctionalized heterocycles was accomplished via I₂O₅-mediated selenocyclizations of olefins with diselenides. Using this method, 116 selenomethyl-substituted heterocycles were synthesized with up to 97% isolated yield in minutes. Additional features of this new protocol include the use of an inorganic oxidant, mild conditions, and easy operation. Preliminary investigations suggest that the transformation operates through selenenyl iodide-induced electrophilic cyclization.

A new anti-proliferative compound from an endophytic fungus, Phoma sp

A new oxazole-type compound (1), named macrooxazole E, and three known macrooxazoles A-C (2-4), were isolated from ethyl acetate (EtOAc) extracts of Phoma sp. JS0228 cultures, an endophytic fungus of Morus alba (M. alba). Structures of the isolated compounds were determined using spectroscopic methods, such as 1 D- and 2 D-nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). Macrooxazole E (1) differed from macrooxazole C only in the presence of methyl carboxylate instead of free carboxylic acid. Macrooxazole C showed moderate anti-proliferative activities against human breast cancer (MCF-7) and prostate cancer (LNCaP) cell lines with IC₅₀ values of 0.29 mM and 0.36 mM, respectively. This study presents the possibility of the endophytic fungus Phoma sp. JS0228 to produce new bioactive natural compounds.

An Overview of Bioactive 1,3-Oxazole-Containing Alkaloids from Marine Organisms

1,3-Oxazole chemicals are a unique class of five-membered monocyclic heteroarenes, containing a nitrogen atom and an oxygen. These alkaloids have attracted extensive attention from medicinal chemists and pharmacologists owing to their diverse arrays of chemical structures and biological activities, and a series of 1,3-oxazole derivatives has been developed into therapeutic agents (e.g., almoxatone, befloxatone, cabotegravir, delpazolid, fenpipalone, haloxazolam, inavolisib). A growing amount of evidence indicates that marine organisms are one of important sources of 1,3-oxazole-containing alkaloids. To improve our knowledge regarding these marine-derived substances, as many as 285 compounds are summarized in this review, which, for the first time, highlights their sources, structural features and biological properties, as well as their biosynthesis and chemical synthesis. Perspective for the future discovery of new 1,3-oxazole compounds from marine organisms is also provided.

Efficacious One-pot Synthesis of 2-thiazolines and 2-oxazolines Under Solvent and Metal-Free Conditions

Background:

2-oxazolines and 2-thiazolines are important heterocycles due to their extensive applications in chemistry, biochemistry, and pharmacology. Most of the precedent methods for preparing these heterocycles involve one or more drawbacks, including harsh reaction conditions, long reaction times, low yields of products, high temperature, and toxic solvents.

Objective:

The aim of this study was to develop a new and eco-efficient method for the preparation of 2-oxazolines and 2-thiazolines.

Methods:

Amino alcohols were condensed with nitriles in a sealed tube under solvent-free and metal- free conditions.

Results:

Our procedure appears to be highly eco-efficient and promotes quantitative access to 2-oxazolines and 2-thiazolines using simple and minimum manipulation.

Conclusion:

This simple approach allows high conversion for different nitriles yielded from 78 to 99% and easy isolation of the targeted products without further purification. To the best of our knowledge, our procedure is the most efficient and fast method reported to date in terms of chemical yields, number of steps, and atom economy.

Biomaterials from the sea: Future building blocks for biomedical applications

Marine resources have tremendous potential for developing high-value biomaterials. The last decade has seen an increasing number of biomaterials that originate from marine organisms. This field is rapidly evolving. Marine biomaterials experience several periods of discovery and development ranging from coralline bone graft to polysaccharide-based biomaterials. The latter are represented by chitin and chitosan, marine-derived collagen, and composites of different organisms of marine origin. The diversity of marine natural products, their properties and applications are discussed thoroughly in the present review. These materials are easily available and possess excellent biocompatibility, biodegradability and potent bioactive characteristics. Important applications of marine biomaterials include medical applications, antimicrobial agents, drug delivery agents, anticoagulants, rehabilitation of diseases such as cardiovascular diseases, bone diseases and diabetes, as well as comestible, cosmetic and industrial applications.

Bioactivity of Serratiochelin A, a Siderophore Isolated from a Co-Culture of Serratia sp. and Shewanella sp

Siderophores are compounds with high affinity for ferric iron. Bacteria produce these compounds to acquire iron in iron-limiting conditions. Iron is one of the most abundant metals on earth, and its presence is necessary for many vital life processes. Bacteria from the genus Serratia contribute to the iron respiration in their environments, and previously several siderophores have been isolated from this genus. As part of our ongoing search for medicinally relevant compounds produced by marine microbes, a co-culture of a Shewanella sp. isolate and a Serratia sp. isolate, grown in iron-limited conditions, was investigated, and the rare siderophore serratiochelin A (1) was isolated with high yields. Compound 1 has previously been isolated exclusively from Serratia sp., and to our knowledge, there is no bioactivity data available for this siderophore to date. During the isolation process, we observed the degradation product serratiochelin C (2) after exposure to formic acid. Both 1 and 2 were verified by 1-D and 2-D NMR and high-resolution MS/MS. Here, we present the isolation of 1 from an iron-depleted co-culture of Shewanella sp. and Serratia sp., its proposed mechanism of degradation into 2, and the chemical and biological characterization of both compounds. The effects of 1 and 2 on eukaryotic and prokaryotic cells were evaluated, as well as their effect on biofilm formation by Staphylococcus epidermidis. While 2 did not show bioactivity in the given assays, 1 inhibited the growth of the eukaryotic cells and Staphylococcus aureus.

Recent Advances in the Synthesis of Oxazole-Based Molecules via van Leusen Oxazole Synthesis

Oxazole compounds, including one nitrogen atom and one oxygen atom in a five-membered heterocyclic ring, are present in various biological activities. Due to binding with a widespread spectrum of receptors and enzymes easily in biological systems through various non-covalent interactions, oxazole-based molecules are becoming a kind of significant heterocyclic nucleus, which have received attention from researchers globally, leading them to synthesize diverse oxazole derivatives. The van Leusen reaction, based on tosylmethylisocyanides (TosMICs), is one of the most appropriate strategies to prepare oxazole-based medicinal compounds. In this review, we summarize the recent advances of the synthesis of oxazole-containing molecules utilizing the van Leusen oxazole synthesis from 1972, aiming to look for potential oxazole-based medicinal compounds, which are valuable information for drug discovery and synthesis.