Synthesis of some novel 2-substituted benzoxazoles as anticancer, antifungal, and antimicrobial agents

Recent advances on anticancer and antimicrobial activities of directly-fluorinated five-membered heterocycles and their benzo-fused systems

Due to the importance of the fluorinated heterocycles as main components of marketed drugs where 20% of the anticancer and antibiotic drugs contain fluorine atoms, this review describes the reported five-membered heterocycles and their benzo-fused systems having directly connected fluorine atom(s). The in vivo and in vitro anticancer and antimicrobial activities of these fluorinated heterocycles are well reported. Some fluorinated heterocycles were found to be lead structures for drug design developments where their activities were almost equal to or exceeded the potency of the reference drugs. In most cases, the fluorine-containing heterocycles showed promising safety index via their reduced cytotoxicity in non-cancerous cell lines. SAR study assigned that fluorinated heterocycles having various electron-donating or electron-withdrawing substituents significantly affected the anticancer and antimicrobial activities.

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.

Immobilization and Release Studies of Triazole Derivatives from Grafted Copolymer Based on Gellan-Carrying Betaine Units

New polymer-bioactive compound systems were obtained by immobilization of triazole derivatives onto grafted copolymers and grafted copolymers carrying betaine units based on gellan and N-vinylimidazole. For preparation of bioactive compound, two new types of heterocyclic thio-derivatives with different substituents were combined in a single molecule to increase the selectivity of the biological action. The 5-aryl-amino-1,3,4 thiadiazole and 5-mercapto-1,2,4-triazole derivatives, each containing 2-mercapto-benzoxazole nucleus, were prepared by an intramolecular cyclization of thiosemicarbazides-1,4 disubstituted in acidic and basic medium. The structures of the new bioactive compounds were confirmed by elemental and spectral analysis (FT-IR and 1H-NMR). The antimicrobial activity of 1,3,4 thiadiazoles and 1,2,4 triazoles was tested on gram-positive and gram-negative bacteria. The triazole compound was chosen to be immobilized onto polymeric particles by adsorption. The Langmuir, Freundlich, and Dubinin-Radushkevich adsorption isotherm were used to describe the adsorption equilibrium. Also, the pseudo-first and pseudo-second models were used to elucidate the adsorption mechanism of triazole onto grafted copolymer based on N-vinylimidazole and gellan (PG copolymer) and grafted copolymers carrying betaine units (PGB1 copolymer). In vitro release studies have shown that the release mechanism of triazole from PG and PGB1 copolymers is characteristic of an anomalous transport mechanism.

Importance of Fluorine in Benzazole Compounds

Fluorine-containing heterocycles continue to receive considerable attention due to their unique properties. In medicinal chemistry, the incorporation of fluorine in small molecules imparts a significant enhancement their biological activities compared to non-fluorinated molecules. In this short review, we will highlight the importance of incorporating fluorine as a basic appendage in benzothiazole and benzimidazole skeletons. The chemistry and pharmacological activities of heterocycles containing fluorine during the past years are compiled and discussed.

TEMPO-Mediated C-H Amination of Benzoxazoles with N-Heterocycles

The direct amination of benzoxazoles at C2 using N-heterocycles as nitrogen sources has been developed for the first time. Several kinds of inexpensive oxidants and also electricity were effective for this transformation in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl. This metal-free and operationally simple reaction can afford a variety of important C,N'-linked bis-heteocycles in moderate to good yields under very mild reaction conditions. The in situ generated oxoammonium salt was proved to be important for this transformation.

Design, synthesis, DFT study and antifungal activity of the derivatives of pyrazolecarboxamide containing thiazole or oxazole ring

Pyrazolecarboxamide fungicides are one of the most important classes of agricultural fungicides, which belong to succinodehydrogenase inhibitors (SDHIS). To discover new pyrazolecarboxamide analogues with broad spectrum and high activity, a class of new compounds of pyrazole carboxamide derivatives containing thiazole or oxazole ring were designed by scaffold hopping and bioisosterism, and 36 pyrazole carboxamide derivatives with antifungal activity were synthesized. Those compounds were evaluated against five phytopathogenic fungi, Gibberella zeae, Phytophythora capsici, Sclerotonia sclerotiorum, Erysiphe graminis and Puccinia sorghi. The results indicated that most of the compounds displayed good fungicidal activities, especially against E. graminis. Theoretical calculations were carried out at the B3LYP/6-31G (d, p) level and the full geometry optimization was carried out using the 6-31G (d, p) basis set, and the frontier orbital energy, atomic net charges, molecular docking were discussed, and the structure-activity relationships were also studied.

Antifungal Activity of New Eugenol-Benzoxazole Hybrids against Candida spp

Eugenol is a natural allylphenol responsible for a wide range of biological activities, especially antimicrobial. Benzoxazoles are heterocycles with recognized antimicrobial activities. This paper describes the design, synthesis, and the biological results for benzoxazole type derivatives of eugenol as antifungal agents. The products were obtained in good yields by a four-step synthetic sequence involving aromatic nitration, nitroreduction, amide formation, and cycle condensation. They were evaluated against species of Candida spp. in microdilution assays, and four products (5a, 5b′, 5c, and 5d′) were about five times more active than eugenol against C. albicans and C. glabrata. Two of them (5b′ and 5d′) showed good activity against C. krusei, a species which is naturally resistant to fluconazole. Furthermore, the active products were more selective than eugenol against human blood cells, showing that they are interesting substances for further optimization.

Synthesis, characterization, and pharmacological evaluation of novel azolo- and azinothiazinones containing 2,4-dihydroxyphenyl substituent as anticancer agents

ABSTRACT

We reported the synthesis and characterization of a series of azolo- and azino[1,3]thiazinones containing the 2,4-dihydroxyphenyl substituent. The compounds were prepared by a new one-step reaction of aryl-modified sulfinylbis[(2,4-dihydroxyphenyl)methanethione]s and the corresponding aminoazolo(azino)carboxamides. Their chemical structures were confirmed by IR, NMR: 1H, 13C, HSQC, and EI-MS spectral data. The compounds inhibited proliferation and viability of lung cancer A549, colon cancer HT-29, and glioma C6 cells in a structure- and concentration-dependent manner. The activity of some analogues was below 10 μmol dm-3 (IC50). Glioma C6 cells were the most sensitive to tested compounds. Generally, the derivatives were not toxic for the skin fibroblast HSF culture. Moreover, some of them exerted a protective effect on the treated normal cells. Evaluation of compound properties in silico showed that they possess significant drug-like characteristics and most of them display a low toxicity.

GRAPHICAL ABSTRACT

Synthesis and Biological Evaluation of Novel 5,7-Dichloro-1,3-benzoxazole Derivatives

A new class of 5,7-dichloro-1,3-benzoxazole derivatives4–11were synthesized by fusing 5,7-dichloro-2-hydrazino-1,3-benzoxazole3nucleus with aliphatic acids, active methylene compounds, and with selected esters to form heterocyclic ring systems like 1,2,4-triazoles, pyrazoles, and triazine moieties. The compound3on diazotization reaction affords the tetrazole compound. The synthesized compounds were characterized by1H NMR, IR, Mass, and13C NMR spectral data and screened for cytotoxic, antimicrobial, antioxidant, and antilipase activities. The compounds4,5, and8have shown significant antimicrobial activities, whereas compounds6and8have been emerged as leading cytotoxic agents. The compounds9,10, and11were found to be strong enzyme inhibitors.