Isoxazole/Isoxazoline Skeleton in the Structural Modification of Natural Products: A Review

Access to Isoxazoles via Photo-oxygenation of Furan Tethered α-Azidoketones

Photocatalyst-free visible light-enabled direct oxygenation of furan-tethered α-azidoketones was studied. The reaction yielded various products depending on the substituents, with isoxazoles forming as the major products. The findings suggest that singlet oxygen was generated during the reaction and reacted with α-azidoketones in a [4 + 2] fashion to yield endoperoxides, which rearranged in multiple ways to generate isoxazoles. Some of the synthesized isoxazoles were evaluated as α-glucosidase inhibitors, and three of them 5bi, 5bj, and 5bl exhibited good activity with IC50 values of 454.57 ± 29.34, 147.84 ± 2.28, and 272.58 ± 42.06 μM, respectively, when compared with the standard drug acarbose (IC50 = 1224.33 ± 126.72 μM).

In Silico Exploration of Isoxazole Derivatives of Usnic Acid: Novel Therapeutic Prospects Against α-Amylase for Diabetes Treatment

Diabetes mellitus (DM) a metabolic disorder characterized by high blood sugar levels causing damage to various organs over time. Current anti-diabetic drugs have limitations and side effects, prompting a search for new inhibitors targeting the α-amylase enzyme. This study aims to discover such inhibitors from thirty isoxazole derivatives of usnic acid using in silico approaches. The potential inhibitory effects of compounds were investigated using ADMET, molecular docking, molecular dynamic simulation, principal component analysis and density functional theory studies. ADMET analysis exhibited a wide range of physicochemical, pharmacokinetic, and drug-like qualities with no significant side effects which were then investigated using molecular docking experiment to determine the lead compound with the best binding affinity for the α-amylase enzyme. All compounds showed good binding affinity against α-amylase enzyme (-7.9 to -9.2 kcal/mol) where compound-13 showed the best binding affinity of -9.2 kcal/mol forming hydrogen bonds with Leu162, Tyr62, Glu233 and Asp300 amino acids. Furthermore, the binding posture and the stability of the compound-13-α-amylase enzyme complex was confirmed by molecular dynamic simulation experiment. Moreover, compound-13 showed binding energy value of -27.92 ± 5.61 kcal/mol, which indicated it could be an α-amylase inhibitor. Additionally, the reactivity of compound-13 was further confirmed by density functional theory analysis. The above findings suggest compound-13 to be a potential α-amylase inhibitor in DM. And setting the stage for further in vitro and in vivo experimental validation.

Acridine-Isoxazole and Acridine-Azirine Hybrids: Synthesis, Photochemical Transformations in the UV/Visible Radiation Boundary Region, and Anticancer Activity

Easy-to-handle N-hydroxyacridinecarbimidoyl chloride hydrochlorides were synthesized as convenient nitrile oxide precursors in the preparation of 3-(acridin-9/2-yl)isoxazole derivatives via 1,3-dipolar cycloaddition with terminal alkynes, 1,1-dichloroethene, and acrylonitrile. Azirines with an acridin-9/2-yl substituent attached directly or via the 1,2,3-triazole linker to the azirine C2 were also synthesized. The three-membered rings of the acridine-azirine hybrids were found to be resistant to irradiation in the UV/visible boundary region, despite their long-wave absorption at 320-420 nm, indicating that the acridine moiety cannot be used as an antenna to transfer light energy to generate nitrile ylides from azirines for photoclick cycloaddition. The acridine-isoxazole hybrids linked at the C9-C3 or C2-C3 atoms under blue light irradiation underwent the addition of such hydrogen donor solvents, such as, toluene, o-xylene, mesitylene, 4-chlorotoluene, THF, 1,4-dioxane, or methyl tert-butyl ether (MTBE), to the acridine system to give the corresponding 9-substituted acridanes in good yields. The synthesized acridine-azirine, acridine-isoxazole, and acridane-isoxazole hybrids exhibited cytotoxicity toward both all tested cancer cell lines (HCT 116, MCF7, and A704) and normal cells (WI-26 VA4).

New thiazolyl-isoxazole derivatives as potential anti-infective agents: design, synthesis, in vitro and in silico antimicrobial efficacy

Antimicrobial resistance threatens the efficacious prevention and treatment of infectious diseases caused by microorganisms. To combat microbial infections, the need for new drug candidates is essential. In this context, the design, synthesis, antimicrobial screening, and in silico study of a new series of 5-aryl-3-(2-arylthiazol-4-yl)isoxazole (9a-t) have been reported. The structure of new compounds was confirmed by spectrometric methods. Compounds 9a-t were evaluated for in vitro antitubercular and antimicrobial activity. Against M. tuberculosis H37Rv, fourteen compounds showed good to excellent antitubercular activity with MIC 2.01-9.80 µM. Compounds 9a, 9b, and 9r showed four-fold more activity than the reference drug isoniazid. Nine compounds, 9a, 9b, 9d, 9e, 9i, 9q, 9r, 9s, and 9t, showed good antibacterial activity against E. coli with MIC 7.8-15.62 µg/mL. Against A. niger, four compounds showed good activity with MIC 31.25 µg/mL. Against C. albicans, all twenty compounds reported excellent to good activity with MIC 7.8-31.25 µg/mL. Compounds 9c-e, 9g-j, and 9q-t showed comparable activity concerning the reference drug fluconazole. The compounds 9a-t were screened for cytotoxicity against 3t3l1 cell lines and found to be less or non-cytotoxic. The in silico study exposed that these compounds displayed high affinity towards the M. tuberculosis targets PanK, DprE1, DHFR, PknA, KasA, and Pks13, and C. albicans targets NMT, CYP51, and CS. The compound 9r was evaluated for structural dynamics and molecular dynamics simulations. The potent antitubercular and antimicrobial activity of 5-aryl-3-(2-arylthiazol-4-yl)isoxazole (9a-t) derivatives has recommended that these compounds could assist in treating microbial infections.Communicated by Ramaswamy H. Sarma.

A Convenient Synthesis of Novel Isoxazolidine and Isoxazole Isoquinolinones Fused Hybrids

Isoxazolidine, isoxazole, and isoquinolinone rings are present in the structure of several natural products and/or pharmaceutically interesting compounds. In this work, facile and efficient pathways have been developed for the preparation of fused frameworks bearing those heterocycles. The successful approaches for both isoxazolidine/isoquinolinone and isoxazole/isoquinolinone hybrid syntheses relied initially on 1,3-dipolar cycloadditions of nitrones and nitrile oxides to indenone and 2-propargylbenzamide, respectively. The construction of the isoquinolinone lactam system followed by performing a selective Schmidt reaction for isoxazolidine derivatives (two steps overall), whereas the isoxazole lactams were reached via an Ullmann-type cyclisation (three steps overall). Key observations were made regarding the stereo- and regioselectivities of the reactions employed, and small libraries of the targeted hybrids were prepared, demonstrating the general applicability of these strategies.

3-[N,N-Bis(sulfonyl)amino]isoxazolines with Spiro-Annulated or 1,2-Annulated Cyclooctane Rings Inhibit Reproduction of Tick-Borne Encephalitis, Yellow Fever, and West Nile Viruses

Spirocyclic compounds containing heterocyclic moieties represent promising 3D scaffolds for modern drug design. In the search for novel anti-flaviviral agents, we have obtained a series of 3-[N,N-bis(sulfonyl)amino]isoxazolines containing spiro-annulated cyclooctane rings and assessed their antiviral activity against tick-borne encephalitis (TBEV), yellow fever (YFV), and West Nile (WNV) viruses. The structural analogs of spirocyclic compounds with a single sulfonyl group or 1,2-annulated cyclooctane ring were also investigated. Almost all the studied 3-[N,N-bis(sulfonyl)amino]isoxazolines revealed antiviral activity against TBEV and WNV. The most active against TBEV was spiro-isoxazoline derivative containing p-nitrophenyl groups in the sulfonyl part (EC₅₀ 2.0 ± 0.5 μM), while the highest potency against WNV was found for the compounds with lipophilic substituents in sulfonyl moiety, naphtyl being the most favorable one (EC₅₀ 1.3 ± 0.5 μM). In summary, two novel scaffolds of anti-flaviviral agents based on N,N-bis(sulfonyl)amino]isoxazoline were proposed, and the compounds of this type demonstrated activity against TBEV and WNV.

Antioxidant activity of novel nitrogen scaffold with docking investigation and correlation of DFT stimulation

Heterocyclic scaffolds are frequently employed in drug development to treat a variety of conditions, including cancers. These substances have the ability to engage covalently or non-covalently with particular residues in the target proteins, inhibiting them. In this study, the formation of N-, S-, and O-containing heterocycles by the interaction of chalcone with nitrogen-containing nucleophiles such as hydrazine, hydroxyl amine, guanidine, urea, and aminothiourea was explored. FT-IR, UV-visible, NMR, and mass spectrometric studies were used to confirm the heterocyclic compounds that were produced. These substances were tested for their antioxidant activity by their capacity to scavenge the artificial radicals 2,2-diphenyl-1-picrylhydrazyl (DPPH). The strongest antioxidant activity was demonstrated by compound 3 (IC50 = 93.4 μM), whereas compound 8 (IC50 = 448.70 μM) had the lowest activity when compared to vitamin C (IC50 141.9 μM). Also, the experimental findings and the docking estimation of these heterocyclic compounds with PDBID:3RP8 were in agreement. Additionally, the compounds' global reactivity characteristics, such as HOMO-LUMO gaps, electronic hardness, chemical potential, electrophilicity index, and Mulliken charges, were identified using DFT/B3LYP/6-31G(d,p) basis sets. The two chemicals that displayed the best antioxidant activity also had their molecular electrostatic potential (MEP) ascertained using DFT simulations.