Conformationally locked bicyclo[4.3.0]nonane carbanucleosides: synthesis and bio-evaluation

Design and Synthesis of Bicyclo[4.3.0]nonene Nucleoside Analogues

Nucleoside analogues are effective antiviral agents, and the continuous emergence of pathogenic viruses demands the development of novel and structurally diverse analogues. Here, we present the design and synthesis of novel nucleoside analogues with a carbobicyclic core, which mimics the conformation of natural ribonucleosides. Employing a divergent synthetic route featuring an intermolecular Diels-Alder reaction, we successfully synthesized carbobicyclic nucleoside analogues with high antiviral efficacy against respiratory syncytial virus.

From Heterocycles to Carbacycles: Synthesis of Carbocyclic Nucleoside Analogues from Enals and Hydroxylamines

Substituted and stereochemically dense carbacycles can be prepared by sequential dipolar cycloaddition and reductive cleavage from enals and hydroxylamines. The reaction sequence proceeds with high efficiency for a wide variety of enals and hydroxylamines. The reaction is regio- and diastereoselective for the initial formation of a bridged bisisoxazolidine intermediate, which then undergoes quantitative double N-O cleavage to produce carbacycles as single diastereomers.

Catalytic reductive [4 + 1]-cycloadditions of vinylidenes and dienes

Cycloaddition reactions provide direct and convergent routes to cycloalkanes, making them valuable targets for the development of synthetic methods. Whereas six-membered rings are readily accessible from Diels-Alder reactions, cycloadditions that generate five-membered rings are comparatively limited in scope. Here, we report that dinickel complexes catalyze [4 + 1]-cycloaddition reactions of 1,3-dienes. The C₁ partner is a vinylidene equivalent generated from the reductive activation of a 1,1-dichloroalkene in the presence of stoichiometric zinc. Intermolecular and intramolecular variants of the reaction are described, and high levels of asymmetric induction are achieved in the intramolecular cycloadditions using a C ₂-symmetric chiral ligand that stabilizes a metal-metal bond.

Cycloaddition reactions for antiviral compounds

Prominent in the current stage of drug development, antiviral compounds can be efficiently prepared through cycloaddition reactions. The chapter reports the use of classical Diels–Alder and their hetero version for the design and synthesis of compounds that were tested for their antiviral activities against a variety of viruses. Furthermore, 1,3-dipolar cycloaddition reactions of selected 1,3-dipoles, such as azides, nitrones, and nitrile oxides, are reviewed in the light of their application in the preparation of key intermediates for antiviral synthesis. A few examples of [2+2] cycloaddition reactions are also presented. The products obtained from these pericyclic reaction approaches were all tested for their activities in terms of blocking the virus replication, and the relevant biological data are highlighted.