Design, synthesis, antiviral and cytostatic evaluation of novel isoxazolidine nucleotide analogues with a 1,2,3-triazole linker

Phosphorylated Nitrones-Synthesis and Applications

Phosphorylated nitrones belong to an important class of compounds with several applications, such as their therapeutic potency to reduce oxidative stress or as spin-trapping agents. This review covers available synthetic methods for the preparation of both non-cyclic and cyclic phosphorylated nitrones, including the possibilities of the modification of structures with selected functional groups, as well as examples of their application. As reported, the incorporation of diethoxyphosphoryl function into the structure of PBN and DMPO resulted in obtaining their phosphorylated analogs, i.e., N-benzylidene-1-diethoxyphosphoryl-1-methylethylamine N-oxide (PPN) and 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO), respectively, both forming spin adducts of improved stability in comparison to the reference non-phosphorus nitrones. Moreover, antioxidant and neuroprotective activity observed in the group of phosphorylated nitrones makes them promising candidates for therapeutics.

New 3-(Dibenzyloxyphosphoryl)isoxazolidine Conjugates of N1-Benzylated Quinazoline-2,4-diones as Potential Cytotoxic Agents against Cancer Cell Lines

In this study, a new series of cis and trans 5-substituted-3-(dibenzyloxyphosphoryl)isoxazolidines 16a-g were synthesized by the 1,3-dipolar cycloaddition reaction of N-benzyl-C-(dibenzyloxyphosphoryl)nitrone and selected N1-allyl-N3-benzylquinazoline-2,4-diones. All the obtained trans-isoxazolidines 16a-g and the samples enriched in respective cis-isomers were evaluated for anticancer activity against three tumor cell lines. All the tested compounds exhibited high activity against the prostate cancer cell line (PC-3). Isoxazolidines trans-16a and trans-16b and diastereoisomeric mixtures of isoxazolidines enriched in cis-isomer using HPLC, namely cis-16a/trans-16a (97:3) and cis-16b/trans-16b (90:10), showed the highest antiproliferative properties towards the PC-3 cell line (IC50 = 9.84 ± 3.69-12.67 ± 3.45 μM). For the most active compounds, induction apoptosis tests and an evaluation of toxicity were conducted. Isoxazolidine trans-16b showed the highest induction of apoptosis. Moreover, the most active compounds turned out safe in vitro as none affected the cell viability in the HEK293, HepG2, and HSF cellular models at all the tested concentrations. The results indicated isoxazolidine trans-16b as a promising new lead structure in the search for effective anticancer drugs.

1,3-Dipolar cycloaddition of nitrones: synthesis of multisubstituted, diverse range of heterocyclic compounds

The 1,3-dipolar cycloaddition reaction of nitrone is one of the most important methods for the synthesis of different sizes of heterocycles which have enormous applications in natural products, biologically active molecules and pharmaceuticals.

Catalyst-Free Regioselective [3+2] Cycloadditions of α,β-unsaturated N-arylnitrones with Alkenes to Access Functionalized Isoxazolidines: A DFT Study

The catalyst-free regioselective [3+2]-cycloaddition of α,β-unsaturated N-arylnitrones with alkenes are developed. The series of synthetically important functionalized isoxazolidines are prepared in good to excellent yields by step economic pathway under ligand and transition-metal-free conditions. The regioselective cycloaddition pathway supported by control experiment and computational study.

Oxazole-Based Compounds As Anticancer Agents

Heterocyclic compounds represent a significant target for anti-cancer research and drug discovery, due to their structural and chemical diversity. Oxazoles, with oxygen and nitrogen atoms present in the core structure, enable various types of interactions with different enzymes and receptors, favoring the discovery of new drugs. Aim of this review is to describe the most recent reports on the use of oxazole-based compounds in anticancer research, with reference to the newly discovered iso/oxazole-based drugs, to their synthesis and to the evaluation of the most biologically active derivatives. The corresponding dehydrogenated derivatives, i.e. iso/oxazolines and iso/oxazolidines, are also reported.

Diastereoselective synthesis of atropisomeric pyrazolyl pyrrolo[3,4-d]isoxazolidines via pyrazolyl nitrone cycloaddition to facially divergent maleimides: intensive NMR and DFT studies

A pyrazolyl nitrone (2) underwent 1,3-dipolar cycloadditions to afford some N-substituted maleimides (3a-o). An atropisomeric character was introduced into the formed cycloadducts by using maleimides that have a restricted rotation around the C-N bond. Also, facial selectivity of both endo and exo cycloaddition was observed where the major atropisomer was one that is formed by attacking the nitrone from the less hindered face of the dipolarophile. On the other hand, maleimides with free rotation around the C-N bond led to endo and exo cycloadducts without atropisomerism. The presence of atropisomerism in the formed cycloadducts was confirmed by extensive NMR studies and DFT calculations.

Chemo-, regio-, and stereoselectivity in 1,3-dipolar cycloaddition of piperine with nitrones. A cycloadditive route to aminoalcohols

The chemoselective 1,3-dipolar cycloaddition between piperine and nitrones and further transformation of the cycloadducts to novel acyclic 1,3-amino alcohols.

Design, Synthesis and Bioactivities of Novel Isoxazole-Containing Pyrazole Oxime Derivatives

In this study, in order to find novel biologically active pyrazole oxime derivatives, twenty-eight new pyrazole oxime compounds containing a substituted isoxazole ring were synthesized and evaluated for their acaricidaland insecticidal activities. Bioassays exhibited that some target compounds indicated good acaricidal and insecticidal activities against Tetranychus cinnabarinus, Aphis medicaginis, Mythimna separata, and Nilaparvata lugens. Especially, compounds 9c, 9h, 9u, and 9v showed 100.00%, 90.56%, 90.78%, and 90.62% insecticidal activities against A. medicaginis at the concentration of 20 μg/mL, respectively, compounds 9k and 9u had 70.86% and 100.00% insecticidal activities against M. separata at 20 μg/mL, respectively.

Design, Synthesis, and the Biological Evaluation of a New Series of Acyclic 1,2,3-Triazole Nucleosides

A new strategy for the synthesis of N3 -benzoylated- and N3 -benzylated N1 -propargylquinazoline-2,4-diones 30a-d and 31a-d from isatoic anhydride 41 is reported. The alkynes 30a-d and 31a-d were applied in the 1,3-dipolar cycloadditions with azides 27 and 28 to synthesize acyclic 1,2,3-triazole nucleosides. The obtained alkynes and 1,2,3-triazole were evaluated for antiviral activity against a broad range of DNA and RNA viruses. The alkyne 30d showed activity against adenovirus-2 (EC50  = 8.3 μM), while compounds 37a and 37d were also active toward herpes simplex virus-1 wild-type and thymidine kinase deficient (HSV-1 TK- ) strains (EC50 values in the range of 4.6-13.8 μM). In addition, compounds 30a, 30b, 37b, and 37c exhibited activity toward varicella-zoster virus (VZV) TK+ and TK- strains (EC50  = 2.1-9.5 μM). The compound 30b proved to be the most selective against VZV and displayed marginal activity against human cytomegalovirus (HCMV). Although the compound 30a had improved anti-HCMV activity, the increase in anti-HCMV activity was accompanied by significant toxicity. Compounds 37a and 37d showed inhibitory effects toward the human T lymphocyte (CEM) cell line (IC50  = 21 ± 7 and 22 ± 1 μM, respectively), while compound 35 exhibited cytostatic activity toward HMEC-1 cells (IC50  = 28 ± 2 μM).

Lewis base-catalyzed diastereoselective [3 + 2] cycloaddition reaction of nitrones with electron-deficient alkenes: an access to isoxazolidine derivatives

A Lewis base-catalyzed [3 + 2] cycloaddition reaction of nitrones with electron-deficient alkenes has been achieved under mild reaction conditions, affording functionalized isoxazolidines as single diastereomers in moderate to excellent yields.

Isoxazolidine: A Privileged Scaffold for Organic and Medicinal Chemistry

The isoxazolidine ring represents one of the privileged structures in medicinal chemistry, and there have been an increasing number of studies on isoxazolidine and isoxazolidine-containing compounds. Optimization of the 1,3-dipolar cycloaddition (1,3-DC), original methods including electrophilic or palladium-mediated cyclization of unsaturated hydroxylamine, has been developed to obtain isoxazolidines. Novel reactions involving the isoxazolidine ring have been highlighted to accomplish total synthesis or to obtain bioactive compounds, one of the most significant examples being probably the thermic ring contraction applied to the total synthesis of (±)-Gelsemoxonine. The unique isoxazolidine scaffold also exhibits an impressive potential as a mimic of nucleosides, carbohydrates, PNA, amino acids, and steroid analogs. This review aims to be a comprehensive and general summary of the different isoxazolidine syntheses, their use as starting building blocks for the preparation of natural compounds, and their main biological activities.

Novel isoxazolidine analogues of homonucleosides and homonucleotides

Isoxazolidine analogues of homonucleos(t)ides were synthesized from nucleobase-derived nitrones 20a-20e (uracil, 5-fluorouracil, 5-bromouracil, thymine, adenine) employing 1,3-dipolar cycloadditions with allyl alcohol as well as with alkenylphosphonates (allyl-, allyloxymethyl- and vinyloxymethyl- and vinylphosphonate). Besides reactions with vinylphosphonate the additions proceeded regioselectively to produce mixtures of major cis and minor trans 3,5-disubstituted isoxazolidines (d.e. 28–82%). From vinylphosphonate up to 10% of 3,4-disubstituted isoxazolidines was additionally produced. Vicinal couplings, shielding effects and 2D NOE correlations were employed in configurational assignments as well as in conformational analysis to find out preferred conformations for several isoxazolidines and to observe anomeric effects (pseudoaxial orientation of phosphonylmethoxy groups) for those obtained from vinyloxymethylphosphonate. None of the tested compounds were endowed in vitro with antiviral activity against a variety of DNA and RNA viruses at subtoxic concentrations (up to 250 μM) nor exhibited antiproliferative activity towards L1210, CEM, and HeLa cells (IC₅₀ = ≥100 μM).

A Green Ultrasound Synthesis, Characterization and Antibacterial Evaluation of 1,4-Disubstituted 1,2,3-Triazoles Tethering Bioactive Benzothiazole Nucleus

The synthesis of N-(benzo[d]thiazol-2-yl)-2-(4-substituted-1H-1,2,3-triazol-1-yl)acetamides 5a–r via the 1,3-dipolar cycloaddition reaction between 2-azido-N-(benzo[d]thiazol-2-yl)acetamide derivatives 3a–c and different alkynes were performed in the presence and absence of ultrasound irradiation. The synthesis was carried out using t-BuOH/H₂O (1:1, v/v) as reaction solvents and CuSO₄·5H₂O/sodium ascorbate as the catalyst. The copper catalyst was implemented to provide the regioselective 1,4-disubstituted 1,2,3-triazoles 5a–r. Significant reductions in reaction times with comparably higher yields were observed when the reactions were carried out under ultrasound irradiation. The structures of the newly synthesized 1,2,3-triazoles were elucidated by IR, NMR, MS, and elemental analyses. They were also screened for their antimicrobial activity against three gram-positive (Streptococcus pneumonia, Bacillus subtilis, and Staphylococcus aureus), three gram-negative (Pseudomonasaeuroginosa, Escherichia coli, and Klebsiella pneumonia), and two fungal strains (Aspergillus fumigates and Candida albicans). Most of the tested compounds displayed promising antimicrobial activities at a Minimum Inhibition Concentration (MIC) of 4–16 μg/mL.

Pronounced Inhibition Shift from HIV Reverse Transcriptase to Herpetic DNA Polymerases by Increasing the Flexibility of α-Carboxy Nucleoside Phosphonates

Alpha-carboxynucleoside phosphonates (α-CNPs) are novel viral DNA polymerase inhibitors that do not need metabolic conversion for enzyme inhibition. The prototype contains a cyclopentyl linker between nucleobase and α-carboxyphosphonate and preferentially (50- to 100-fold) inhibits HIV-1 RT compared with herpetic DNA polymerases. A synthesis methodology involving three steps has been developed for the synthesis of a series of novel α-CNPs, including a Rh(II)-catalyzed O-H insertion that connects the carboxyphosphonate group to a linker moiety and an attachment of a nucleobase to the other end of the linker by a Mitsunobu reaction followed by final deprotection. Replacing the cyclopentyl moiety in the prototype α-CNPs by a more flexible entity results in a selectivity shift of ∼ 100-fold in favor of the herpetic DNA polymerases when compared to selectivity for HIV-1 RT. The nature of the kinetic interaction of the acyclic α-CNPs against the herpetic DNA polymerases differs from the nature of the nucleobase-specific kinetic interaction of the cyclopentyl α-CNPs against HIV RT.

Novel 5-arylcarbamoyl-2-methylisoxazolidin-3-yl-3-phosphonates as nucleotide analogues

A series of 5-substituted 3-phosphonylated isoxazolidines have been obtained via cycloaddition of N-methyl-C-(diethoxyphosphoryl)nitrone with N-heteroaromatic acrylamides. Good trans/cis diastereoselectivities (d.e. 58-76%) of isomeric (3-diethoxyphosphoryl)isoxazolidines were observed. cis- and trans-Isoxazolidine phosphonates were evaluated for their antiviral activity against a broad range of DNA and RNA viruses but were found inactive. Their cytostatic activity toward L1210, CEM, and HeLa cells was also established, and compounds cis-12r and trans-11r having a 2,2-difluorobenzo[d][1,3]dioxole moiety slightly inhibited proliferation of HeLa cells at IC50 values of 186 and 179 μM, respectively.

Chemistry of phosphorylated formaldehyde derivatives. Part I

The underinvestigated derivatives of unstable phosphorylated formaldehyde acetals and some of the structurally related compounds, such as thioacetals, aminonitriles, aminomethylphosphinoyl compounds, are considered. Separately considered are halogen aminals of phosphorylated formaldehyde, acetals of phosphorylated formaldehyde of H-phosphinate-type and a phosphorylated gem-diol of formaldehyde. Synthetic methods, chemical properties and examples of practical applications are given.

Design, synthesis, antiviral and cytostatic activity of ω-(1H-1,2,3-triazol-1-yl)(polyhydroxy)alkylphosphonates as acyclic nucleotide analogues

The efficient synthesis of a new series of polyhydroxylated dibenzyl ω-(1H-1,2,3-triazol-1-yl)alkylphosphonates as acyclic nucleotide analogues is described starting from dibenzyl ω-azido(polyhydroxy)alkylphosphonates and selected alkynes under microwave irradiation. Selected O,O-dibenzylphosphonate acyclonucleotides were transformed into the respective phosphonic acids. All compounds were evaluated in vitro for activity against a broad variety of DNA and RNA viruses and for cytostatic activity against murine leukemia L1210, human T-lymphocyte CEM and human cervix carcinoma HeLa cells. Compound (1S,2S)-16b exhibited antiviral activity against Influenza A H3N2 subtype (EC50=20μM-visual CPE score; EC50=18μM-MTS method; MCC >100μM, CC50 >100μM) in Madin Darby canine kidney cell cultures (MDCK), and (1S,2S)-16k was active against vesicular stomatitis virus and respiratory syncytial virus in HeLa cells (EC50=9 and 12μM, respectively). Moreover, compound (1R,2S)-16l showed activity against both herpes simplex viruses (HSV-1, HSV-2) in HEL cell cultures (EC50=2.9 and 4μM, respectively) and feline herpes virus in CRFK cells (EC50=4μM) but at the same time it exhibited cytotoxicity toward uninfected cell (MCC⩾4μM). Several other compounds have been found to inhibit proliferation of L1210, CEM as well as HeLa cells with IC50 in the 4-50μM range. Among them compounds (1S,2S)- and (1R,2S)-16l were the most active (IC50 in the 4-7μM range).

Multicomponent click synthesis of new 1,2,3-triazole derivatives of pyrimidine nucleobases: promising acidic corrosion inhibitors for steel

A series of new mono-1,2,3-triazole derivatives of pyrimidine nucleobases were synthesized by one-pot copper(I)-catalyzed 1,3-dipolar cycloaddition reactions between N-1-propargyluracil and thymine, sodium azide and several benzyl halides. The desired heterocyclic compounds were obtained in good yields and characterized by NMR, IR, and high resolution mass spectrometry. These compounds were investigated as corrosion inhibitors for steel in 1 M HCl solution, using electrochemical impedance spectroscopy (EIS) technique. The results indicate that these heterocyclic compounds are promising acidic corrosion inhibitors for steel.

The synthesis, antiviral, cytostatic and cytotoxic evaluation of a new series of acyclonucleotide analogues with a 1,2,3-triazole linker

The efficient synthesis of a new series of acyclonucleotide analogues with a 1,2,3-triazole linker is described starting from diethyl azidomethyl-, 2-azidoethyl-, 3-azidopropyl-, 4-azidobutyl-, 2-azido-1-hydroxyethyl-, 3-azido-2-hydroxypropyl- and 3-azido-1-hydroxypropylphosphonates and selected alkynes under microwave irradiation. Several O,O-diethylphosphonate acyclonucleotides were transformed into the respective phosphonic acids. All compounds were evaluated in vitro for activity against a broad variety of DNA and RNA viruses and cytostatic activity against murine leukaemia L1210, human T-lymphocyte CEM and human cervix carcinoma HeLa cells. Acyclonucleotide 22e exhibited activity against both herpes simplex viruses (HSV-1, HSV-2) in HEL cell cultures (EC₅₀ = 17 μM) and feline herpes virus (EC₅₀ = 24 μM) in CRFK cell cultures, while compounds 20k, 21k, 22k and 23k preferentially inhibited proliferation of human T-lymphocyte CEM cells at IC₅₀ in the 2.8–12 μM range.

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Nucleotide analogues with aliphatic linker between phosphorus and 1,2,3-triazole.

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Efficient synthesis of 1,2,3-triazole analogues of nucleotides.

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Antiviral activity and inhibitory effect on the proliferation of CEM cells.

Synthesis, Antimicrobial and cytotoxic activity of New Heterocyclic Hybrids Based on 2,5-Dimethylpyrrole and Pyrrole Scaffolds

A series of 4-(2,5-dimethylpyrrol-1-yl)/4-pyrrol-1-yl benzoic acid hydrazide analogs, some derived triazoles, azetidinones, thiazolidinones, and pyrroles have been synthesized in good yields and structures of these compounds were established by IR, ¹H NMR, ¹³C NMR, mass spectral, and elemental analysis. These compounds were evaluated for their preliminary in vitro antibacterial, antifungal, and antitubercular activity against Mycobacterium tuberculosis H₃₇ Rv strain by the broth dilution assay method. Twenty one of these compounds displayed good antimicrobial activity, with a MIC value of 1-4 μg/ml. Several compounds 4c, 8-10, 15b-15h, and 16b-16d exhibited good in vitro antitubercular activity with MIC value 1-2 μg/ml. Further, some title compounds were also assessed for their cytotoxic activity (IC₅₀) against mammalian Vero cell lines and A₅₄₉ (lung adenocarcinoma) cell lines using the MTT assay method. The results revealed that these compounds exhibit antitubercular activity at non-cytotoxic concentrations.

Synthesis and biological evaluation of novel 1,2,3-triazolonucleotides

A general procedure for the preparation of 1,2,3-triazole analogs of nucleosides from diethyl 2-azidoethoxymethyl- and 2-azidoethoxyethylphosphonates was elaborated. The application of microwave irradiation shortened the reaction time to 10 min in comparison to ca. 48 h when 1,3-dipolar cycloadditions were performed under standard conditions. All compounds were evaluated in vitro for inhibitory activity against a broad variety of DNA and RNA viruses. None of the compounds were antivirally active at subtoxic concentrations. Compound 17k exhibited moderate inhibitory effects on the proliferation of human T-lymphocyte cells (IC50=64 µM for CEM).

Design, synthesis, antiviral and cytostatic evaluation of novel isoxazolidine nucleotide analogues with a carbamoyl linker

5-Arylcarbamoyl-2-methylisoxazolidin-3-yl-3-phosphonates have been synthesised from N-methyl-C-diethoxyphosphorylnitrone and N-arylacrylamides in good yields. cis- and trans-isoxazolidine phosphonates obtained herein were evaluated for activity against a broad range of DNA and RNA viruses. None of the compounds were endowed with antiviral activity at subtoxic concentrations. Isoxazolidines having phenyl substituted with halogen (Ar = 2-F-C₆H₄; 3-Br-C₆H₄; and 4-Br-C₆H₄) have been found to inhibit proliferation of L1210, CEM as well as HeLa cells with IC₅₀ in the 100–170 μM range.