Synthesis and biological activity of some new benzoxazoles

Novel Sulfonylamido Benzoxazole Derivatives: Synthesis, Characterisation, Molecular Docking, DFT, and Antimicrobial Activity Investigations

In this work, numerous novel 2-(p-ethyl/fluorophenyl)-5-[(p-substitutedphenyl)sulfonylamido]benzoxazole derivatives were designed, synthesized, and structurally characterized using 1H-NMR, 13C-NMR, mass spectroscopy, and elemental analysis approaches. The antimicrobial activity against several Gram (+) bacteria, Gram (-) bacteria, and fungal species was determined using the in vitro microdilution technique. A molecular docking analysis was performed on all produced compounds utilizing the S. aureus gyrase complex with ciprofloxacin and DNA. Two of the most effective compounds against S. aureus, N4 and N9, have binding energies of -8.7 kcal/mol and -8.6 kcal/mol, respectively, and their interactions have been demonstrated in 2D and 3D. Furthermore, utilizing the 6-311G(d,p) base set and DFT/B3LYP theory, MEP analysis, geometric optimization, and molecular reactivity analysis (HOMO-LUMO) of N4 and N9 were performed, and the results were presented. All compounds' theoretical ADMET profiles were computed as well. With all of this knowledge, this study could be a pioneer in the development of novel anti-S. aureus compounds.

Similarity searching for anticandidal agents employing a repurposing approach

Fungal infections caused by Candida are still a public health concern. Particularly, the resistance to traditional chemotherapeutic agents is a major issue that requires efforts to develop new therapies. One of the most interesting approaches to finding new active compounds is drug repurposing aided by computational methods. In this work, two databases containing anticandidal agents and drugs were studied employing cheminformatics and compared by similarity methods. The results showed 36 drugs with high similarities to some candicidals. From these drugs, trimetozin, osalmid and metochalcone were evaluated against C. albicans (18804), C. glabrata (90030), and miconazole-resistant strain C. glabrata (32554). Osalmid and metochalcone were the best, with activity in the micromolar range. These findings represent an opportunity to continue with the research on the potential antifungal application of osalmid and metochalcone as well as the design of structurally related derivatives.

Synthesis, Antimicrobial Activity, and Molecular Modeling Studies of Some Benzoxazole Derivatives

Background:

The need to develop novel antimicrobial agents is apparent as infectious diseases are increasing and resistance is rapidly developing against the drugs used in the treatment.

Objective:

This study aimed at the synthesis, antimicrobial susceptibility testing, and computational elucidation of the mechanism of action of benzoxazole derivatives. It also aimed to compare the results obtained in this study with the previous studies by our group. This would pave the way for designing novel molecules with better antimicrobial activity. The other goal was pharmacophore analysis and in silico ADMET analysis of them.

Methods:

In this study, synthesis, antimicrobial susceptibility testing, molecular docking, pharmacophore analysis, and ADMET prediction were carried out.

Results:

The antimicrobial activity studies demonstrated that the synthesized compounds were active against standard strains and clinical isolates at high concentrations. Then, the antimicrobial testing results were compared to similar benzoxazoles tested by our group previously. Benzoxazole derivatives without a methylene bridge between oxazole and phenyl ring were found to be more active than those with the methylene bridge. This was also confirmed by molecular modeling undertaken in this study. The computational results indicated that the antibacterial activity could be achieved by DNA gyrase inhibition. Pharmacophore analysis showed that hydrogen bond acceptor (HBA), hydrogen bond donor (HBD), and hydrophobicity features would contribute to the inhibition. In addition, in silico ADMET property investigation of the compounds exhibited that they had the desired pharmacokinetics.

Conclusion:

Although antibacterial activity by inhibiting DNA gyrase is selective, the synthesized compounds were active at much higher concentrations than the standards. Therefore, in prospective antimicrobial studies, it is better to focus on benzoxazole derivatives without the methylene bridge. Since the compounds had suitable in silico ADMET properties, screening them against the other pharmacologic activities should be carried out. It is recommended to support the molecular modeling results with in vitro or in vivo studies.

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.

Synthesis, antimicrobial activity, density functional modelling and molecular docking with COVID-19 main protease studies of benzoxazole derivative: 2-(p-chloro-benzyl)-5-[3-(4-ethly-1-piperazynl) propionamido]-benzoxazole

This study contains synthesis, antimicrobial activity, density functional modelling and molecular docking studies of benzoxazole derivative: 2-(p-chloro-benzyl)-5-[3-(4-ethly-1-piperazynl) propionamido]-benzoxazole. The synthetic procedure of investigated compound is given in detail. The newly synthesized benzoxazole compound and standard drugs were evaluated for their antimicrobial activity against some Gram-positive, Gram-negative bacteria and fungus C. albicans and their drug-resistant isolates. The benzoxazole compound has been characterized by using 1H-NMR, IR and MASS spectrometry and elemental analysis techniques. The molecular structure of the compound in the ground state has been modelling using density functional theory (DFT) with B3LYP/6-311++g(d,p) level. The molecular docking of 2-(p-chloro-benzyl)-5-[3-(4-ethly-1-piperazynl) propionamido]-benzoxazole with COVID-19 main protease has been also performed by using optimized geometry and the experimentally determined dimensional structure of the main protease (M-pro) of COVID-19.

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.

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.

Synthesis, Structure Revision, and Cytotoxicity of Nocarbenzoxazole G

The total synthesis of nocarbenzoxazoles F (1) and G (2), originally obtained from the marine-derived halophilic bacterial strain Nocardiopsis lucentensis DSM 44048, was achieved via a simple and versatile route involving microwave-assisted construction of a benzoxazole skeleton, followed by carbon-carbon bond formation with the corresponding aryl bromides. Unfortunately, the ¹H and ¹³C NMR spectra of natural nocarbenzoxazole G did not agree with those of the synthesized compound. In particular, the spectra of the isolated and synthesized compounds showed considerable differences in the signals from the protons and carbons in the aryl group. The revised structure was validated by the total synthesis of the actual nocarbenzoxazole G (8c) molecule, which is a regioisomer of the compound that was reported earlier as nocarbenzoxazole G. The synthesized derivatives showed specific cytotoxicity to the human cervical carcinoma cell line, HeLa, but did not have any remarkable effect on the other cell lines.

Synthesis, Molecular Modeling and Biological Evaluation of 5-arylidene-N,N-diethylthiobarbiturates as Potential α-glucosidase Inhibitors

BACKGROUND

Barbituric acid derivatives are a versatile group of compounds which are identified as potential pharmacophores for the treatment of anxiety, epilepsy and other psychiatric disorders. They are also used as anesthetics and have sound effects on the motor and sensory functions. Barbiturates are malonylurea derivatives with a variety of substituents at C-5 position showing resemblance with nitrogen and sulfur containing compounds like thiouracil which exhibited potent anticancer and antiviral activities. Recently, barbituric acid derivatives have also received great interest for applications in nanoscience.

OBJECTIVE

Synthesis of 5-arylidene-N,N-diethylthiobarbiturates, biological evaluation as potential α-glucosidase inhibitors and molecular modeling.

METHODS

In the present study, N,N-Diethylthiobarbituric acid derivatives were synthesized by refluxing of N,N-diethylthiobarbituric acid and different aromatic aldehydes in distilled water. In a typical reaction; a mixture of N,N-diethylthiobarbituric acid 0.20 g (1 mmol) and 5-bromo-2- hydroxybenzaldehyde 0.199 g (1 mmol) mixed in 10 mL distilled water and reflux for 30 minutes. After completion of the reaction, the corresponding product 1 was filtered and dried and yield calculated. It was crystallized from ethanol. The structures of synthesized compounds 1-25 were carried out by using 1H, 13C NMR, EI spectroscopy and CHN analysis used for the determination of their structures. The α-glucosidase inhibition assay was performed as given by Chapdelaine et al., with slight modifications and optimization.

RESULTS

Our newly synthesized compounds showed a varying degree of α-glucosidase inhibition and at least four of them were found as potent inhibitors. Compounds 6, 5, 17, 11 exhibited IC50 values (Mean±SEM) of 0.0006 ± 0.0002, 18.91 ± 0.005, 19.18 ± 0.002, 36.91 ± 0.003 µM, respectively, as compared to standard acarbose (IC50, 38.25 ± 0.12 µM).

CONCLUSION

Our present study has shown that compounds 6, 5, 17, 11 exhibited IC50 values of 0.0006 ± 0.0002, 18.91 ± 0.005, 19.18 ± 0.002, 36.91 ± 0.003 µM, respectively. The studies were supported by in silico data analysis.

A base promoted multigram synthesis of aminoisoxazoles: valuable building blocks for drug discovery and peptidomimetics

An easy access to a large panel of aminoisoxazoles starting from commonly available amino acids.

Synthesis and different biological activities of novel benzoxazoles

A series of 2-[4-(4-substitutedbenzamido/phenylacetamido/butanamido)phenyl]-5-ethylsulphonyl-benzoxazole derivatives were synthesized and biologically evaluated as possible antimicrobial agents and inhibitors of tyrosinase, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE). The results demonstrated that the synthesized compounds exhibited a broad spectrum of activity with minimum inhibitory concentration (MIC) values of 128-16 μg/ml against some Gram-positive, Gram-negative bacteria as well as Candida albicans and C. krusei. The compound 10 displayed higher activity in this series against methicilline resistant Staphylococcus aureus (MRSA) with a MIC value of 16 μg/ml than the compared control drugs ampicillin and ceftriaxone. Compound 14 showed moderate tyrosinase inhibition, however, none of the compounds showed effect as inhibitor of AChE and BChE.

FT-IR, FT-Raman, SERS and computational study of 5-ethylsulphonyl-2-(o-chlorobenzyl)benzoxazole

FT-IR, FT-Raman and surface-enhanced Raman scattering spectra of 5-ethylsulphonyl-2-(o-chlorobenzyl)benzoxazole were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian09 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution calculations. The presence of CH(2), SO(2) and CH(3) modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface which affects the orientation and metal molecule interaction. The synthesis, NMR spectra and antibacterial properties are reported. The title compound shows more inhibitory effect against Pseudomonas aeruginosa than ampicillin and found to be more potent against Klebsiella pneumoniae and drug-resistant Bacillus subtilis than the other microorganisms. A computation of the first hyperpolarizability indicates that the compound may be a good candidate as a NLO material. The RMS errors of the observed Raman and IR bands are found to be 30.93, 29.77 for HF and 9.57, 6.75 for DFT methods, respectively.