Synthesis of 4′-thionucleosides by 1,3-dipolar cycloadditions of the simplest thiocarbonyl ylide with alkenes bearing electron-withdrawing groups

Cucurbit[7]uril as a catalytic nanoreactor for one-pot synthesis of isoxazolidines in water

The main objective of supramolecular chemistry is to mimic the macrosystems present in nature, a goal that fits perfectly with the green chemistry guidelines. The aim of our work is to use the hydrophobic cavity of cucurbit[7]uril (CB[7]) to mimic nature for performing different dehydration and cycloaddition reactions in water. The hydrophobic cavity of CB[7] made it possible to synthesize nitrones and isoxazolidines in a one-pot fashion using water as a reaction solvent. Substituted isoxazolidines were obtained from the cycloaddition of nitrones with various styrenes and cinnamates, under microwave irradiation, with a catalytic amount of CB[7], and a moderate increase in the formation of the trans adduct was observed, compared to the reaction being carried out in toluene. The mechanism of the reaction and the inclusion of reagents and products in the CB[7] cavity have been studied and rationalized by NMR spectroscopy, ESI-MS experiments, and molecular modeling calculations.

Tandem four-component reaction for efficient synthesis of dihydrothiophene with substituted amino acid ethyl esters

The one-pot four-component reaction of aromatic aldehydes, malononitrile, 1,3-thiazolidinedione and ethyl glycinate hydrochloride in ethanol in the presence of triethylamine afforded trans-dihydrothiophene ureidoformamide derivatives in moderate to good yields. The other α-amino acid ethyl esters resulted in the corresponding diastereoisomeric dihydrothiophene derivatives with various molecular ratios. The functionalized thiophene derivatives were also successfully prepared by sequential dehydrogenation reaction with DDQ.

The one-pot four-component reaction of aromatic aldehydes, malononitrile, 1,3-thiazolidinedione and ethyl glycinate hydrochloride in ethanol in the presence of triethylamine afforded trans-dihydrothiophene.

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.

γ-Cyclodextrin as a Catalyst for the Synthesis of 2-Methyl-3,5-diarylisoxazolidines in Water

A green and efficient 1,3-dipolar cycloaddition of nitrones with different styrenes and cinnamates using a catalytic amount of γ-cyclodextrin (γ-CD) in water has been developed to give substituted isoxazolidines. γ-CD was found to be highly efficacious in carrying out this reaction under an eco-friendly environment, affording moderate to excellent yields and, in some cases, excellent diastereomeric excess (up to >95%) at 100 °C in 8-12 h. The catalyst can be easily recuperated and recycled for several times without loss of activity. Water, an eco-friendly reaction medium, has been utilized for the first time, to the best of our knowledge, in this reaction. The credit of the presented protocol includes high yields and catalyst reusability, and precludes the use of organic solvents. The use of in silico calculations allowed us to rationalize the obtained results and to improve the stereoselectivity.

Nucleosides with Transposed Base or 4'-Hydroxymethyl Moieties and Their Corresponding Oligonucleotides

This review focuses on 4'-hydroxymethyl- or nucleobase-transposed nucleosides, nucleotides, and nucleoside phosphonates, their stereoisomers, and their close analogues. The biological activities of all known 4'-hydroxymethyl- or nucleobase-transposed nucleosides, nucleotides, and nucleoside phosphonates as potential antiviral or anticancer agents are compiled. The routes that have been taken for the chemical synthesis of such nucleoside derivatives are described, with special attention to the innovative strategies. The enzymatic synthesis, base-pairing properties, structure, and stability of oligonucleotides containing nucleobase- or 4'-hydroxymethyl-transposed nucleotides are discussed. The use of oligonucleotides containing nucleobase- or 4'-hydroxymethyl-transposed nucleotides as small oligonucleotide (e.g., human immunodeficiency virus integrase) inhibitors, in applications such as antisense therapy, silencing RNA (siRNA), or aptamer selections, is detailed.

Synthetic scope, computational chemistry and mechanism of a base induced 5-endo cyclization of benzyl alkynyl sulfides

We present an experimental and computational study of the reaction of aryl substituted benzyl 1-alkynyl sulfides with potassium alkoxide in acetonitrile, which produces 2-aryl 2,3-dihydrothiophenes in poor to good yields. The cyclization is most efficient with electron withdrawing groups on the aromatic ring. Evidence indicates there is rapid exchange of protons and tautomerism of the alkynyl unit prior to cyclization. Theoretical calculations were also conducted to help rationalize the base induced 5-endo cyclization of benzyl 1-propynyl sulfide (1a). The potential energy surface was calculated for the formation of 2,3-dihydrothiophene in a reaction of benzyl 1-propynyl sulfide (1a) with potassium methoxide. Geometries were optimized with CAM-B3LYP/6-311+G(d,p) in acetonitrile with the CPCM solvent model. It is significant that the benzyl propa-1,2-dien-1-yl sulfane (6) possessed a lower benzylic proton affinity than the benzyl prop-2-yn-1-yl sulfane (8) thus favoring the base induced reaction of the former. From benzyl(propa-1,2-dien-1-yl sulfane (6), 2,3-dihydrothiophene can be formed via a conjugate base that undergoes 5-endo-trig cyclization followed by a protonation step.

Stereoselective synthesis of 4'-selenonucleosides using the Pummerer glycosylation reaction

The syntheses of four selenonucleosides, namely 4'-beta-selenoadenosine, -cytidine, -thymidine, and -uridine are described. Commercially available D-ribonolactone was converted to the key intermediate 1,4-anhydro-4-seleno-D-ribitol in seven steps in overall excellent yield. Oxidation of the seleno-d-ribitol with MCPBA gave a single diastereomeric selenoxide in excellent yield, which upon Pummerer reaction in the presence of silylated purine or pyrimidine bases gave stereoselectively the corresponding 4'-beta-selenonucleosides. The stereochemistry at the anomeric center was determined by means of 1D-NOE experiments.