Benzoxazoles and oxazolopyridines in medicinal chemistry studies

An updated patent review on PD-1/PD-L1 antagonists (2022-present)

INTRODUCTION

PD-L1, via its interactions with PD-1, constitutes a key immune checkpoint that allows cancer cells to escape immune surveillance. Targeting PD-1/PD-L1 with monoclonal antibodies (mAbs) led to spectacular success in clinical oncology. However, the inherent limitations of mAbs and increasing findings about immune-related adverse events (iRAEs) prompted intense research in the field of small-molecule inhibitors of PD-L1.

AREAS COVERED

This review covers inhibitors of PD-L1 reported in patents published in the online databases of the World Intellectual Property Organization and European Patent Office in the 2022-2023 period. This review provides a landscape of available inhibitors, including their chemical structures, activity, and stage of development.

EXPERT OPINION

Small-molecule inhibitors impairing PD-L1/PD-1 interaction represent an attractive alternative to mAbs. In recent years, the field of small-molecule and macrocyclic inhibitors targeting PD-L1 has grown rapidly. The majority (if not all) of small-molecule inhibitors developed recently, similarly to their predecessors, act through a dimerization mechanism of PD-L1, followed by its internalization into the cytosol. In contrast, macrocyclic peptides act purely through a competition mechanism known as protein-protein interaction inhibitors. The ongoing clinical trials should ultimately reveal which strategy has real clinical potential and may complement or even replace mAbs-based therapies.

1,2,3-Triazol-5-ylidene- vs. 1,2,3-triazole-based tricarbonylrhenium(I) complexes: influence of a mesoionic carbene ligand on the electronic and biological properties

The tricarbonylrhenium complexes that incorporate a mesoionic carbene ligand represent an emerging and promising class of molecules, the solid-state optical properties of which have rarely been investigated. The aim of this comprehensive study is to compare three of these complexes with their 1,2,3-triazole-based analogues. The Hirshfeld surface analysis of the crystallographic data revealed that the triazolylidene derivatives are more prone to π-π interactions than their 1,2,3-triazole-based counterparts. The FT-IR and electrochemical data indicated a stronger electron donor effect from the organic ligand to the rhenium atom for triazolylidene derivatives, which was confirmed by DFT calculations. All compounds were phosphorescent in solution, where the 1,2,3-triazole-based complexes showed unusually strong dependence on dissolved oxygen. All compounds also emitted in the solid state, some of them exhibited marked solid-state luminescence enhancement (SLE) effect. The 1,2,3-triazole based complex Re-Phe even displayed astounding photoluminescence efficiency with quantum yield up to 0.69, and proved to be an excellent candidate for applications linked to aggregation-induced emission (AIE). Interestingly, one triazolylidene-based complex (Re-T-BOP) showed attractive antibacterial activity. This study highlights the potential of these new molecules for applications in the fields of photoluminescent and therapeutic materials, and provides the first bases for the design of efficient molecules in these research areas.

Engineered Phenylalanine Ammonia-Lyases for the Enantioselective Synthesis of Aspartic Acid Derivatives

Biocatalytic hydroamination of alkenes is an efficient and selective method to synthesize natural and unnatural amino acids. Phenylalanine ammonia-lyases (PALs) have been previously engineered to access a range of substituted phenylalanines and heteroarylalanines, but their substrate scope remains limited, typically including only arylacrylic acids. Moreover, the enantioselectivity in the hydroamination of electron-deficient substrates is often poor. Here, we report the structure-based engineering of PAL from Planctomyces brasiliensis (PbPAL), enabling preparative-scale enantioselective hydroaminations of previously inaccessible yet synthetically useful substrates, such as amide- and ester-containing fumaric acid derivatives. Through the elucidation of cryo-electron microscopy (cryo-EM) PbPAL structure and screening of the structure-based mutagenesis library, we identified the key active site residue L205 as pivotal for dramatically enhancing the enantioselectivity of hydroamination reactions involving electron-deficient substrates. Our engineered PALs demonstrated exclusive α-regioselectivity, high enantioselectivity, and broad substrate scope. The potential utility of the developed biocatalysts was further demonstrated by a preparative-scale hydroamination yielding tert-butyl protected l-aspartic acid, widely used as intermediate in peptide solid-phase synthesis.

Current Development of Thiazole-Containing Compounds as Potential Antibacterials against Methicillin-Resistant Staphylococcus aureus

The emergence of multi-drug-resistant bacteria is threatening to human health and life around the world. In particular, methicillin-resistant Staphylococcus aureus (MRSA) causes fatal injuries to human beings and serious economic losses to animal husbandry due to its easy transmission and difficult treatment. Currently, the development of novel, highly effective, and low-toxicity antimicrobials is important to combat MRSA infections. Thiazole-containing compounds with good biological activity are widely used in clinical practice, and appropriate structural modifications make it possible to develop new antimicrobials. Here, we review thiazole-containing compounds and their antibacterial effects against MRSA reported in the past two decades and discuss their structure-activity relationships as well as the corresponding antimicrobial mechanisms. Some thiazole-containing compounds exhibit potent antibacterial efficacy in vitro and in vivo after appropriate structural modifications and could be used as antibacterial candidates. This Review provides insights into the development of thiazole-containing compounds as antimicrobials to combat MRSA infections.

Metal-free visible light mediated direct C-H amination of benzoxazole with secondary amines

An efficient visible light mediated, eosin Y catalyzed direct C-H oxidative amination of benzoxazoles with secondary amines has been developed, which providing a straightforward, green, and environmentally benign access to a wide variety of substituted benzoxazole-2-amines under mild reaction conditions. The biological studies such as drug-likeness and molecular docking are also carried out on the molecule.

Application of Vitreoscilla Hemoglobin as a Green and Efficient Biocatalyst for the Synthesis of Benzoxazoles in Water

We report an efficient and eco-friendly method for the Vitreoscilla hemoglobin (VHb)-catalyzed synthesis of benzoxazoles in water at room temperature. tert-Butyl hydroperoxide and 2,2,6,6-tetramethyl-1-piperidinyloxy were used as oxidant and radical scavenger, respectively. A total of 27 functionally diverse benzoxazoles were prepared in moderate to high yields (62 %-94 %) by the annulation reaction of phenols with amines in the presence of VHb in 1 h. Thus, this method is highly viable for practical applications. This work broadens the application of hemoglobin to organic synthesis.

Medicinal-Chemistry-Driven Approach to 2-Substituted Benzoxazole-Estradiol Chimeras: Synthesis, Anticancer Activity, and Early ADME Profile

The efficient synthesis of novel estradiol-based A-ring-fused oxazole derivatives, which can be considered as benzoxazole-steroid domain-integrated hybrids containing a common benzene structural motif, is described. The target compounds were prepared from steroidal 2-aminophenol precursors by heterocycle formation or functional group interconversion (FGI) strategies. According to 2D projection-based t-distributed stochastic neighbor embedding (t-SNE), the novel molecules were proved to represent a new chemical space among steroid drugs. They were characterized based on critical physicochemical parameters using in silico and experimental data. The performance of the compounds to inhibit cell proliferation was tested on four human cancer cell lines and non-cancerous cells. Further examinations were performed to reveal IC50 and lipophilic ligand efficiency (LLE) values, cancer cell selectivity, and apoptosis-triggering features. Pharmacological tests and LLE metric revealed that some derivatives, especially the 2-(4-ethylpiperazin-1-yl)oxazole derivative exhibit strong anticancer activity and trigger the apoptosis of cancer cells with relatively low promiscuity risk similarly to the structurally most closely-related and intensively studied anticancer agent, 2-methoxy-estradiol.

Design, Synthesis, and Evaluation of a New Series of Hydrazones as Small-Molecule Akt Inhibitors for NSCLC Therapy

In an endeavor to identify small molecules for the management of non-small-cell lung carcinoma, 10 new hydrazone derivatives (3a-j) were synthesized. MTT test was conducted to examine their cytotoxic activities against human lung adenocarcinoma (A549) and mouse embryonic fibroblast (L929) cells. Compounds 3a, 3e, 3g, and 3i were determined as selective antitumor agents on A549 cell line. Further studies were conducted to figure out their mode of action. Compounds 3a and 3g markedly induced apoptosis in A549 cells. However, both compounds did not show any significant inhibitory effect on Akt. On the other hand, in vitro experiments suggest that compounds 3e and 3i are potential anti-NSCLC agents acting through Akt inhibition. Furthermore, molecular docking studies revealed a unique binding mode for compound 3i (the strongest Akt inhibitor in this series), which interacts with both hinge region and acidic pocket of Akt2. However, it is understood that compounds 3a and 3g exert their cytotoxic and apoptotic effects on A549 cells via different pathway(s).

Discovery of N-methylbenzo[d]oxazol-2-amine as new anthelmintic agent through scalable protocol for the synthesis of N-alkylbenzo[d]oxazol-2-amine and N-alkylbenzo[d]thiazol-2-amine derivatives

We discovered a lead compound, N-methylbenzo[d]oxazol-2-amine (2a), which had comparable potency to albendazole, an orally administered anthelminticdrug, against Gnathostoma spinigerum, Caenorhabditis elegans and Trichinella spiralis. Compound 2a showed about 10 times lower cytotoxicity towards normal human cell line (HEK293) than albendazole. Moreover, we have developed new processes for the synthesis of N-alkylbenzo[d]oxazol-2-amine and N-alkylbenzo[d]thiazol-2-amine derivatives via metal-free conditions. This protocol could serve as a robust and scalable method, especially, to synthesize N-methylbenzo[d]oxazol-2-amine and N-methylbenzo[d]thiazol-2-amine derivatives which were difficult to prepare using other metal-free conditions. The method employed benzoxazole-2-thiol or benzothiazole-2-thiol as the substrate. The reaction was triggered by methylation of the thiol functional group to form the methyl sulfide intermediate, a crucial tactic, which facilitated in a smooth nucleophilic addition-elimination reaction with gaseous methylamine generated in situ from N-methylformamide. In addition, the proteomic analysis of compound 2a was also studied in this work.

Synthesis of 2-Aminofurans and 2-Aminothiophenes through Elemental Sulfur-Promoted Switchable Redox Condensation Reaction of Enaminones with Methylene Nitriles

Herein, we report an elemental sulfur-promoted switchable redox condensation reaction that can selectively prepare 2-aminofurans and 2-aminothiophenes from the corresponding enaminones and methylene nitriles, respectively. Mechanistic studies demonstrated that the enaminones, as dual nucleophiles, reacted with nitrile acetate to produce 2-aminofurans via 3,5-annulation under promotion by elemental sulfur. These reactions used readily available starting materials, transition metal-free, eco-friendly procedures, gram-scale syntheses, and wide functional group tolerance. The methodology may be useful for the construction of 2-aminofuran and 2-aminothiophene derivatives with potential biological activity.

New Triazinoindole Bearing Benzimidazole/Benzoxazole Hybrids Analogs as Potent Inhibitors of Urease: Synthesis, In Vitro Analysis and Molecular Docking Studies

Twenty-four analogs based on triazinoindole bearing benzimidazole/benzoxazole moieties (1-25) were synthesized. Utilizing a variety of spectroscopic methods, including ¹H-, ¹³C-NMR, and HREI-MS, the newly afforded compounds (1-25) were analyzed. The synthesized analogs were tested against urease enzyme (in vitro) as compared to the standard thiourea drug. All triazinoindole-based benzimidazole/benzoxazole analogs (1-25) exhibited moderate to excellent inhibition profiles, having IC₅₀ values of 0.20 ± 0.01 to 36.20 ± 0.70 μM when evaluated under the positive control of thiourea as a standard drug. To better understand the structure-activity relationship, the synthesized compounds were split into two groups, "A" and "B." Among category "A" analogs, analogs 8 (bearing tri-hydroxy substitutions at the 2,4,6-position of aryl ring C) and 5 (bearing di-hydroxy substitutions at the 3,4-position of aryl ring C) emerged as the most potent inhibitors of urease enzyme and displayed many times more potency than a standard thiourea drug. Besides that, analog 22 (which holds di-hydroxy substitutions at the 2,3-position of the aryl ring) and analog 23 (bearing ortho-fluoro substitution) showed ten-fold-enhanced inhibitory potential compared to standard thiourea among category "B" analogs. Molecular docking studies on the active analogs of each category were performed; the results obtained revealed that the presence of hydroxy and fluoro-substitutions on different positions of aryl ring C play a pivotal role in binding interactions with the active site of the targeted urease enzyme.

Insights into development of Decaprenyl-phosphoryl-β-D-ribose 2'-epimerase (DprE1) inhibitors as antitubercular agents: A state of the art review

Mycobacterium tuberculosis is a causative agent for the world threatening infectious disease known as tuberculosis. M. tuberculosis is also referred as Koch's bacillus as it was first defined by Robert Koch in 1821. In the entire history of M. tuberculosis infection, several different targets were identified and explored with a hope of effective therapeutic treatment against tuberculosis. Drug-resistant tuberculosis is the major obstacle for researchers and letting them fail continuously to discover new drug candidates. Among the numerous antitubercular targets, Decaprenyl-phosphoryl-β-D-ribose-2'-epimerase (DprE1) is novel target identified in the year 2009. The present article portrays insights of DprE1 enzyme in all the aspects i.e., identification, structural elucidation to designing strategies and synthesis of potential drug candidates to combat resistant strains. Along with the synthesis and biological activity of novel compounds, structure-activity relationship (SAR) data is given to help medicinal chemists and researchers working in this area for the development of new inhibitors to fight against M. tuberculosis. DprE1 is new ray of hope for antitubercular treatment. No single drug candidate (DprE1 inhibitor) has passed clinical trial yet and hence it nullifies the risk of development of resistance or mutations at specific residues. Researchers working in this area have to design and come up with new potent candidates with less dose, no toxicity to combat this deadly infection. This review emphasized on year wise systematic development and progress of DprE1 inhibitors.

Tandem cyclization/arylation of diaryliodoniums via in situ constructed benzoxazole as a directing group for atom-economical transformation

Linear diaryliodoniums often undergo only single arylation and leave equivalent aryl iodide as waste.

Iodine-catalyzed synthesis of benzoxazoles using catechols, ammonium acetate, and alkenes/alkynes/ketones via C–C and C–O bond cleavage

An efficient metal-free synthesis strategy of benzoxazoles was developed via coupling catechols, ammonium acetate, and alkenes/alkynes/ketones. The developed methodology represents an operationally simple, one-pot and large-scale procedure for the preparation of benzoxazole derivatives using molecular iodine as the catalyst.

A metal-free one-pot multi-component method for the efficient synthesis of 2-aryl benzoxazoles via coupling of catechols, ammonium acetate and alkenes/alkynes/ketones using an I₂–DMSO catalyst system is illustrated.

DMF-Assisted Radical Cyclization of o-Isocyanodiaryl Ethers via 1,5-Aryl Migration: Construction of 2-Arylbenzoxazoles

A novel DMF-assisted radical cyclization of o-isocyanodiaryl ethers via 1,5-aryl migration has been developed for the synthesis of a series of 2-arylbenzoxazoles by the FeCl₃/TBHP/Et₃N catalytic system in DMF. However, N,N-dimethylbenzo[d]thiazole-2-carboxamide and N,N-dimethylbenzo[d]selenazole-2-carboxamide were obtained from the corresponding substrate 2-isocyanophenyl p-methoxyphenyl thioether and 2-isocyanodiphenyl selenoether under the same conditions. A possible mechanism may involve aryl 1,5-migration and DMF-assisted radical cyclization of o-isocyanodiaryl ethers.

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.

Crystal structure of methyl 1,3-benzoxazole-2-carboxyl-ate

The title compound, C9H7NO3, crystallizes in the monoclinic (P21) space group. In the crystal, the almost planar mol-ecules display a flattened herringbone arrangement. Stacking mol-ecules are slipped in the lengthwise and widthwise directions and are linked by π-π inter-actions [d(Cg⋯Cg = 3.6640 (11) Å]. The structure is characterized by strong C-H⋯N and weak C-H⋯O hydrogen bonds, and further stabilized by C-O⋯π inter-actions.

Recent Trends in the Design, Synthesis, Spectroscopic Behavior, and Applications of Benzazole-Based Molecules with Solid-State Luminescence Enhancement Properties

Molecules that exhibit solid-state luminescence enhancement, i.e. the rare property to be more strongly emissive in the solid state than in solution, find an increasing number of applications in the fields of optoelectronic and nanophotonic devices, sensors, security papers, imaging, and theranostics. Benzazole (BZ) heterocycles are of particular value in this context. The simple enlargement of their π-electron system using a -C=C-Ar or -N=C-Ar moiety is enough for intrinsic solid-state luminescence enhancement (SLE) properties to appear. Their association with a variety of polyaromatic motifs leads to SLE-active molecules that frequently display attractive electroluminescent properties and are sensitive to mechanical stimuli. The excited-state intramolecular proton transfer (ESIPT) process that takes place in some hydroxy derivatives reinforces the SLE effect and enables the development of new sensors based on a protection/deprotection strategy. BZ may also be incorporated into frameworks that are prototypical aggregation-induced enhancement (AIE) luminogens, such as the popular tetraphenylethene (TPE), leading to materials with excellent optical and electroluminescent performance. This review encompasses the various ways to use BZ units in SLE systems. It underlines the significant progresses recently made in the understanding of the photophysical mechanisms involved. A brief overview of the synthesis shows that BZ units are robust building blocks, easily incorporated into a variety of structures. Generally speaking, we try to show how these small heterocycles may offer advantages for the design of increasingly efficient luminescent materials.

Biological activity of 3-(2-benzoxazol-5-yl)alanine derivatives

Searching for new drugs is still a challenge for science, mainly because of civilization development and globalization which promote the rapid spread of diseases, which is particularly dangerous in the case of infectious ones. Moreover, readily available already known antibiotics are often overused or misused, possibly contributing to the increase in the number of multidrug-resistant microorganisms. A consequence of this is the need for new structures of potential drugs. One of them is a benzoxazole moiety, a basic skeleton of a group of fluorescent heterocyclic compounds already widely used in chemistry, industry, and medicine, which is also present in naturally occurring biologically active compounds. Moreover, synthetic benzoxazoles are also biologically active. Considering all of that, a large group of non-proteinogenic amino acids based on 3-(2-benzoxazol-5-yl)alanine skeleton was studied in search for new antimicrobial and anticancer agents. Screening tests revealed that antibacterial potential of 41 compounds studied is not very high; however, they are selective acting only against Gram-positive bacteria (B. subtilis). Moreover, almost half of the studied compounds have antifungal properties, also against pathogens (C. albicans). Most of studied compounds are toxic to both normal and cancer cells. However, in a few cases, toxicity to normal cells is much lower than for cancer cells indicating these compounds as future anticancer agents. The research carried out on such a large group of compounds allowed to establish a structure–activity relationship which enables to select candidates for further modifications, necessary to improve their biological activity and obtain a new lead structure with potential for therapeutic use.

2-(2-(Fluorosulfonyloxy)phenyl)benzoxazole

The fluorosulfate derivatives of benzoxazole attract attention since benzoxazole-based compounds have a wide range of biological activities, and the ability of the –SO2F group to react with various functional groups makes it possible to synthesize various new derivatives. The new 2-(2-(fluorosulfonyloxy)phenyl)benzoxazole (2) has been synthesized by the SuFEx click reaction in a two-chamber reactor. Compound 2 is the first example of a benzoxazole derivative with a fluorosulfate-containing substituent at position two of the benzoxazole heterocycle. The anti-cancer potency of 2 was evaluated in silico using molecular docking. The docking results suggest that title compound 2 is of great interest for further studies as a possible anaplastic lymphoma kinase inhibitor.

Base-Catalyzed Three-Component Reaction of α-Cyanoacetates with Chalcones and Elemental Sulfur: Access to 2-Aminothiophenes Unobtainable via the Gewald Reaction

Although the Gewald reaction was well-known for more than half a century as an excellent method providing bioactive 2-aminothiophenes from reactions of α-cyanoacetates and carbonyl compounds and elemental sulfur, its application to dibenzoylmethanes as the carbonyl substrates was, however, unknown and experimentally proven unsuccessful. We propose here a convenient approach to such a series of compounds by a DABCO-catalyzed, one-pot, two-step, three-component reaction of α-cyanoacetate with chalcones and elemental sulfur. This catalytic strategy is highlighted by its excellent atom/step efficiency and high degree of structural diversification by simply choosing the suitable starting chalcones, which are unarguably much more readily available than dibenzoylmethanes.

Synthesis, Characterization, and Preliminary In Vitro Cytotoxic Evaluation of a Series of 2-Substituted Benzo [d] [1,3] Azoles

A series of benzo [d] [1,3] azoles 2-substituted with benzyl- and allyl-sulfanyl groups were synthesized, and their cytotoxic activities were in vitro evaluated against a panel of six human cancer cell lines. The results showed that compounds BTA-1 and BMZ-2 have the best inhibitory effects, compound BMZ-2 being comparable in some cases with the reference drug tamoxifen and exhibiting a low cytotoxic effect against healthy cells. In silico molecular coupling studies at the tamoxifen binding site of ERα and GPER receptors revealed affinity and the possible mode of interaction of both compounds BTA-1 and BMZ-2.

Copper-catalyzed oxidative cyclization of glycine derivatives toward 2-substituted benzoxazoles

A novel and straightforward intramolecular cyclization of glycine derivatives to 2-substituted benzoxazoles through copper-catalyzed oxidative C-H/O-H cross-coupling was described. A variety of glycine derivatives involving short peptides underwent cross-dehydrogenative-coupling readily to afford diverse 2-substituted benzoxazoles. The synthetic method has the advantages of simple operation, broad substrate scope and mild reaction conditions, thus providing an alternative effective approach for benzoxazole construction.

Chemoselective Rearrangement Reactions of Sulfur Ylide Derived from Diazoquinones and Allyl/Propargyl Sulfides

Here, we describe three types of rearrangement reactions of sulfur ylide derived from diazoquinones and allyl/propargyl sulfides. With Rh₂(esp)₂ as the catalyst, diazoquinones react with allyl/propargyl sulfides to form a sulfur ylide, which undergoes a chemoselective tautomerization/[2,3]-sigmatropic rearrangement reaction, a Doyle-Kirmse rearrangement/Cope rearrangement cascade reaction, or a Doyle-Kirmse rearrangement/elimination reaction, depending on the substituent of the sulfides. The protocol provides alkenyl and allenyl sulfides and multisubstituted phenols with moderate and high yields.

A new series of benzoxazole-based SIRT1 modulators for targeted therapy of non-small-cell lung cancer

In an attempt to identify potential anticancer agents for non-small-cell lung cancer (NSCLC) targeting sirtuin 1 (SIRT1), the synthesis of a new series of benzoxazoles (3a - i) was carried out through a facile and versatile synthetic route. The compounds were evaluated for their cytotoxic effects on A549 human lung adenocarcinoma and NIH/3T3 mouse embryonic fibroblast cells using the MTT assay. 2-[(5-Nitro-1H-benzimidazol-2-yl)thio]-N-(2-methylbenzoxazol-5-yl)acetamide (3e) and 2-[(5-chloro-1H-benzimidazol-2-yl)thio]-N-(2-methylbenzoxazol-5-yl)acetamide (3g) were the most potent and selective anticancer agents in this series against the A549 cell line, with IC₅₀ values of 46.66 ± 11.54 and 55.00 ± 5.00 µM, respectively. The flow cytometry-based apoptosis detection assay was performed to determine their effects on apoptosis in A549 cells. Both compounds induced apoptosis in a dose-dependent manner. The effects of compounds 3e and 3g on SIRT1 activity were determined. On the basis of in vitro studies, it was observed that compound 3g caused a significant decrease in SIRT1 levels in a dose-dependent manner, whereas compound 3e increased the SIRT1 levels. According to molecular docking studies, the substantial alteration in the type of action could be attributed to the difference between the interactions of compounds 3e and 3g with the same residues in the active site of SIRT1 (PDB code: 4IG9). On the basis of in silico ADME (absorption, distribution, metabolism, and excretion) studies, these compounds are predicted to possess favorable ADME profiles. According to the in vitro and in silico studies, compounds 3e and 3g, small-molecule SIRT1 modulators, were identified as potential orally bioavailable anticancer agents for the targeted therapy of NSCLC.

Semisynthesis and insecticidal bioactivities of benzoxazole and benzoxazolone derivatives of honokiol, a naturally occurring neolignan derived from Magnolia officinalis

Honokiol, a natural bioactive neolignan isolated from the bark and leaf of Magnolia officinalis and Magnolia obovata, exhibits many important biological properties. In continuation of our interest in discovery of the agrochemicals derived from the natural sources, thirty-seven new 8/8'-alkylthiol-benzoxazole and N-alkyl/sulfonyl-benzoxazolone derivatives of honokiol were prepared and their insecticidal activities were evaluated against the larvae of Mythimna separata Walker and Plutella xylostella Linnaeus. The results showed that eleven derivatives exhibited potent insecticidal activity against M. separata when compared with the positive control. Particularly, compound 5h displayed the most promising insecticidal activity against M. separata with the final mortality rate (FMR) of 58.6%. Meanwhile, compounds 7n (FMR = 65.3%), 7p (FMR = 61.5%), and 8c (FMR = 65.3%) demonstrated a greater insecticidal activity against P. xylostella than toosendanin, a well-known botanical insecticide. Additionally, the preliminary structure-activity relationships (SARs) were also discussed. This study indicates that these honokiol derivatives could be used as leads for the further derivation and development of the potential pesticide candidates for crop protection.

Tryptoline-based benzothiazoles re-sensitize MRSA to β-lactam antibiotics

Resistance-modifying agents (RMAs) offer a promising solution to combat bacterial antibiotic resistance. Here we report the discovery and structure-activity relationships of a new class of RMAs with a novel tryptoline-based benzothiazole scaffold. Our most potent compound in this series (4ad) re-sensitizes multiple MRSA strains to cephalosporins at low concentrations (2 μg/mL) and has low mammalian cytotoxicity with a half growth inhibitory concentration (GI₅₀) > 100 μg/mL in human cervical carcinoma (HeLa) cells. In addition, the same core scaffold with different substitutions also gives good antibacterial activity against MRSA.

Diastereo- and Enantioselective 1,6-Conjugate Addition of 2-Azaarylacetamides to para-Quinone Methides

A chiral Mg(II)/N,N'-dioxide complex was found to be highly effective in promoting the diastereo- and enantioselective 1,6-conjugate addition of various azaarylacetamides to p-quinone methides under mild reaction conditions. Various chiral azaarene derivatives containing gem(1,1)-diaryl skeletons were obtained in good yields, dr, and excellent ee values. Meanwhile, on the basis of insight gained from the control experiments as well as the single-crystal structure of the Mg(II)/N,N'-dioxide complex and product, a possible transition state was proposed to explain the origin of coordination and stereoinduction.