Synthesis of C-4′Truncated Phosphonated Carbocyclic 2′-Oxa-3′-azanucleosides as Antiviral Agents

Novel Isoxazolidine and γ-Lactam Analogues of Homonucleosides

Homonucleoside analogues cis-16 and trans-17 having a (5-methoxycarbonyl)isoxazolidine framework were synthesized via the 1,3-dipolar cycloaddition of nucleobase-derived nitrones with methyl acrylate. Hydrogenolysis of the isoxazolidines containing thymine, dihydrouracil, theophylline and adenine moieties efficiently led to the formation of the respective γ-lactam analogues. γ-Lactam analogues having 5-bromouracil and 5-chlorouracil fragments were synthesized by treatment of uracil-containing γ-lactams with NBS and NCS. Isoxazolidine and γ-lactam analogues of homonucleosides obtained herein were evaluated for activity against a broad range of DNA and RNA viruses. None of the compounds that were tested exhibited antiviral or cytotoxic activity at concentrations up to 100 µM. The cytostatic activities of all compounds toward nine cancerous cell lines was tested. γ-Lactams trans-15e (Cl-Ura) and cis-15h (Theo) appeared the most active toward pancreatic adenocarcinoma cells (Capan-1), showing IC50 values 21.5 and 18.2 µM, respectively. Isoxazolidine cis-15e (Cl-Ura) inhibited the proliferation of colorectal carcinoma (HCT-116).

(Z)-1-(1,3-Diphenyl-1H-pyrazol-4-yl)-N-phenylmethanimineN-oxide

In the title nitrone, C22H17N3O, the dihedral angles between the central pyrazole ring and pendant N-bound, C-bound and nitrone-bound phenyl rings are 20.93 (6), 41.27 (6), and 32.57 (6)°, respectively. In the crystal, (101) layers are generated by C—H...O hydrogen bonds coupled with C—H...π(ring) and offset π–π stacking interactions.

Molecular modeling studies of pseudouridine isoxazolidinyl nucleoside analogues as potential inhibitors of the pseudouridine 5'-monophosphate glycosidase

In this paper, we investigated the hypothesis that pseudouridine isoxazolidinyl nucleoside analogues could act as potential inhibitors of the pseudouridine 5'-monophosphate glycosidase. This purpose was pursued using molecular modeling and in silico ADME-Tox profiling. From these studies emerged that the isoxazolidinyl derivative 1 5'-monophosphate can be effectively accommodated within the active site of the enzyme with a ligand efficiency higher than that of the natural substrate. In this context, the poor nucleofugality of the N-protonated isoxazolidine prevents or slows down, the first mechanistic step proposed for the degradation of the pseudouridine 5'-monophosphate glycosidase, leading to the enzyme inhibition. Finally, the results of the physicochemical and ADME-Tox informative analysis pointed out that compound 1 is weakly bounded to plasma protein, only moderately permeate the blood-brain barrier, and is non-carcinogen in rat and mouse. To the best of our knowledge, this is the first paper that introduces the possibility of inhibition of pseudouridine 5'-monophosphate glycosidase by a molecule that competing with the natural substrate hinders the glycosidic C-C bond cleavage.

Alternative Route Toward Nitrones: Experimental and Theoretical Findings

Nitrones are important building blocks for natural and biologically active compounds, used as spin-trap reagents and therapeutic agents. All this makes nitrones intriguing and valuable compounds for fundamental studies and as useful chemicals in various synthetic strategies. Therefore, nitrones are still of great interest and in the limelight of researches. With our initial goal to solve synthetic problems toward 5-phenyl-2,2'-bipyridine (Phbpy), we found that this reaction can proceed through the formation of 6-phenyl-3-(pyridin-2-yl)-1,2,4-triazin-4(3H)-ol (4-OH), which rapidly isomerizes to a 3,4-dihydro-1,2,4-triazine-based nitrone, namely 6-phenyl-3-pyridin-2-yl-2,3-dihydro-1,2,4-triazin-4-oxide (4'), This encouraged us to study condensation of hydrazonophenylacetaldehyde oxime (2), obtained from 2-isonitrosoacetophenone (1), with other aldehydes. The reaction with both salicylaldehyde and p-tolualdehyde leads to the open-chain isomers, namely (2-hydroxybenzylidene)hydrazono-2-phenylacetaldehyde oxime (5) and (4-methylbenzylidene)hydrazono-2-phenylacetaldehyde oxime (6), respectively. The latter product exists in solution in equilibrium with its cyclic isomer 6-phenyl-3-(4-methylphenyl)-2,3-dihydro-1,2,4-triazin-4-oxide (6'), while the former one exists in solution exclusively in the open-chain form. It was also found that 2 reacts with acetone with the formation of 3,3-dimethyl-6-phenyl-2,3-dihydro-1,2,4-triazin-4-oxide (7'), which also exists in solution in equilibrium with its open-chain isomer 2-phenyl-2-(propan-2-ylidenehydrazono)acetaldehyde oxime (7). The static DFT as well as ab initio molecular dynamics simulations have corroborated the experimental findings.

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).

New developments of ketonitrones in organic synthesis

Various vinyl ketonitrones are prepared using new strategies and were applied to synthesize heterocycles in organic synthesis.

Synthesis and biological properties of 5-(1H-1,2,3-triazol-4-yl)isoxazolidines: a new class of C-nucleosides

A novel series of C-nucleosides, featuring the presence of a 1,2,3-triazole ring linked to an isoxazolidine system, has been designed as mimetics of the pyrimidine nucleobases. An antiproliferative effect was observed for compounds 17a and 17b: the growth inhibitory effect reaches the 50% in HepG2 and HT-29 cells and increases up to 56% in the SH-SY5Y cell line after 72 h of incubation at a 100 µM concentration.

C-5'-Triazolyl-2'-oxa-3'-aza-4'a-carbanucleosides: Synthesis and biological evaluation

A novel series of 2’-oxa-3’-aza-4’a-carbanucleosides, featured with a triazole linker at the 5’-position, has been developed by exploiting a click chemistry reaction of 5’-azido-2’-oxa-3’-aza-4’a-carbanucleosides with substituted alkynes. Biological tests indicate an antitumor activity for the synthesized compounds: most of them inhibit cell proliferation of Vero, BS-C-1, HEp-2, MDCK, and HFF cells with a CC₅₀ in the range of 5.0–40 μM. The synthesized compounds do not show any antiviral activity.

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.

A bonding evolution theory study of the mechanism of [3+2] cycloaddition reactions of nitrones with electron-deficient ethylenes

BET study of the mechanism of zw-type [3+2] cycloaddition reactions of nitrones with electron-deficient ethylenes.

G, Malik A, Kumar V, Chatterjee A, Roy BG, Banerjee M. In situ mechanochemical synthesis of nitrones followed by 1,3-dipolar cycloaddition: a catalyst-free, “green” route to cis-fused chromano[4,3-c]isoxazoles

An efficient, catalyst free mechanochemical route to cis-fused chromano[4,3-c]isoxazoles has been developed via a simple mortar-pestle grinding method.

Enantiomerically pure phosphonated carbocyclic 2'-oxa-3'-azanucleosides: synthesis and biological evaluation

Starting from enantiomeric pure 1-[(3S,5R)- and 1-[(3R,5S)-3-(hydroxymethyl)-2-methylisoxazolidin-5-yl]-5-methylpyrimidine-2,4(1H,3H)-diones (-)7a and (+)7b, obtained by lipase-catalyzed resolution, pure diethyl{[(3S,5R)-2-methyl-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)isoxazolidin-3-yl]methyl}phosphonate (-)12a and diethyl{[(3R,5S)-2-methyl-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)isoxazolidin-3-yl]methyl}phosphonate (+)12b have been synthesized. The obtained compounds showed no cytotoxic activity versus the U937 cell line in comparison with AZT, and were poorly able to inhibit HIV infection in vitro.

1-Amino-3-(1H-1,2,3-triazol-1-yl)propylphosphonates as acyclic analogs of nucleotides

A new series of 1-amino-3-(1H-1,2,3-triazol-1-yl)propylphosphonates (R)- and (S)-16 were obtained from enantiomerically pure (R)- and (S)-1-tert-butoxycarbonyl (Boc)-amino-3-azidopropylphosphonates and N-propargylated nucleobases in good yields. All 1,2,3-triazolylphosphonates (R)- and (S)-16 were evaluated for their activities against a broad range of DNA and RNA viruses. Compound (R)-16g (B = 3-acetylindole) was moderately active against vesicular stomatitis virus in HeLa cell cultures (EC50 = 45 µM). In addition, (S)-16c (B = adenine), (R)-16f (B = N(3)-Bz-benzuracil), (R)-16g (B = 3-acetylindole), and (R)-16h (B = 5,6-dimethylbenzimidazole) were cytotoxic toward Crandell-Rees feline kidney (CRFK) cells (CC50 = 2.9, 45, 72, and 96 µM, respectively). Compounds (R)-16g, (S)-16g, and (S)-16h were slightly cytostatic to different tumor cell lines.

Design, synthesis, antiviral, and cytostatic evaluation of novel isoxazolidine analogs of homonucleotides

Moderate diastereoselectivities (d.e. 2-62%) of isoxazolidine homonucleotides were observed for cycloadditions between N-methyl-C-(diethoxyphosphoryl)nitrone and N-allyl nucleobases, with trans-isoxazolidines predominating. The stereochemistry of the substituted isoxazolidines was established based on 2D NOE experiments performed for uracil-containing cycloadducts. The cis- and trans-isoxazolidine phosphonates obtained herein were evaluated in vitro for activity against a broad range of DNA and RNA viruses. None of the compounds were endowed with antiviral activity at subtoxic concentrations, but some of them were found to inhibit the proliferation of L1210 cells with IC50 values in the range of 33-100 µM.

Synthesis and biological evaluation of furopyrimidine N,O-nucleosides

A series of modified N,O-nucleosides, characterized by the presence of a furopyrimidine moiety, has been synthesized by exploiting a Sonogashira cross coupling reaction of 1-isoxazolidinyl-5-iodouracil with alkynes, followed by treatment with CuI in refluxing TEA/MeOH mixture. The obtained compounds were screened against both RNA and DNA viruses. None of the compounds were endowed with antiviral activity at subtoxic concentrations. However, some of them were able to inhibit proliferation of MRC-5, Vero, BS-C-1 cells by 50% (CC50) at concentrations ranging from 0.7 to 62.5 mM.

Self-catalyzed Mannich-type reaction of enolizable cyclic 1,3-dicarbonyls to acyclic nitrones: an entry to functionalized β-enamino diones

A new method for the preparation of highly functionalized β-enamino diones has been developed. The protocol involves an initial self-catalyzed Mannich-type reaction of enolizable cyclic 1,3-dicarbonyls to nitrones, followed by a spontaneous intramolecular reorganization of the resulting nonisolated hydroxylamine to enamino derivatives. These compounds retain the features of unnatural α-amino acids. The ease of preparation makes them attractive intermediates for the synthesis of peptidomimetics, polyheterocycles, and other multifunctional compounds. All experimental results have been efficiently rationalized by in silico studies at the M06-2X level of theory, and a valid mechanistic pathway has been proposed.

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.

Synthesis of azanucleosides through regioselective ring-opening of epoxides catalyzed by sulphated zirconia under microwave and solvent-free conditions

New azanucleosides were obtained using sulphated zirconia (ZS) as catalyst in the nucleophilic oxirane ring opening reaction of 1-allyl-3-(oxiran-2-ylmethyl) pyrimidine-2,4(1H,3H)-dione and 1-allyl-5-methyl-3-(oxiran-2-ylmethyl)-pyrimidine-2,4(1H,3H)-dione, with (S)-prolinol. The new templates were obtained with good yields following a route which exploits the reactivity of epoxides in the presence of sulphated zirconia as catalyst. The key step was carried out using microwave and solvent-free conditions and proceeds with high selectivity.

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

Azidation (TMSN(3), SnCl(4)) of a 9:1 mixture of trans- and cis-5-acetoxy-2-methylisoxazolidin-3-yl-3-phosphonates at the anomeric carbon atom led to the formation of the equimolar mixture of cis- and trans-5-azido-2-methylisoxazolidin-3-yl-3-phosphonates, which were efficiently separated. The 1,3-dipolar cycloaddition of pure trans- and cis-5-azidoisoxazolidin-3-yl-3-phosphonates with selected alkynes gave the respective nucleoside mimetics containing a 1,2,3-triazole linker. The (1,2,3-triazolyl)isoxazolidine phosphonates obtained herein were evaluated in vitro for activity against a variety of DNA and RNA viruses. None of the compounds were endowed with antiviral activity at subtoxic concentrations. Compounds 15f-j and 16f-j were cytostatic in the higher micromolar range.

Tetrofuranose nucleoside phosphonic acids: Synthesis and properties

New isoelectronic, non-isosteric phosphonate analogues of nucleoside 5′-phosphates featuring the phosphorus moiety directly attached on the sugar ring in the C4′ position are described. The analogues were synthesised by a nucleosidation reaction from tetrofuranosyl phosphonate synthons and silylated nucleobases. The pyrimidine compounds with erythro and threo configuration in both D- and L-series were prepared, and the structures were assigned by NMR spectroscopy. The results of NMR conformational studies show that all calculated conformers have a maximum pucker in the range typical for nucleosides. In all compounds, the S-type conformer is preferred and is more significant in α-D-threo-compounds. Studies on inhibition of thymidine phosphorylase revealed that one of the prepared phosphonic acids was a competitive inhibitor of the enzyme (Ki = 4 μM).