4‘- and 1‘-Methyl-Substituted 5‘-Norcarbanucleosides

Structure-Unit-Based Total Synthesis of (-)-Sinulochmodin C

Herein we report a structure-unit-based asymmetric total synthesis of sinulochmodin C, a norcembranoid diterpenoid bearing a transannular strained ether bridge β-keto tetrahydrofuran moiety. Our synthetic route features an intramolecular double Michael addition to construct stereospecifically the [7,6,5,5] tetracyclic skeleton, a vinylogous hydroxylation/oxidation procedure or a stereospecific epoxide opening/oxidation sequence to establish the γ-keto enone intermediate, a Lewis acid/Brønsted acid mediated transannular oxa-Michael addition to fuse the β-keto tetrahydrofuran moiety, a Mukaiyama hydration/Pd-C hydrogenation to reverse the C1-configuration of the isopropenyl unit, and a bioinspired transformation of sinulochmodin C into scabrolide A.

Stereoselective Approach for the Synthesis of Diverse 1'-Modified Carbanucleosides

We describe an efficient and stereoselective synthesis of 1'-substituted-β-carbocylic nucleosides 5 via gem-dichlorooxirane intermediate 7, which directly condensed with weak nucleophiles such as pyrimidines or purines. The formation of gem-dichlorooxirane 7 and direct nucleobase condensation exclusively proceeded in protic polar solvents like MeOH. This method provides a general and modular route for the late-stage diversification of 1'-modified nucleosides.

Chemical Approaches to Carbocyclic Nucleosides

Nucleoside analogues are at the forefront of antiviral therapy for last decades. To circumvent some of their limitations, based on their metabolism, and in order to improve their anti-viral potency and selectivity, several families of nucleoside analogues have been described through structural modifications at the sugar and heterocycles. The replacement of the oxygen of the nucleoside by a methylene has led to the family of carbocyclic (or cyclopentane) nucleoside analogues. Various potent anti-HIV and anti-HBV drugs belong to this family. Main syntheses of carbocyclic analogues of nucleosides used Diels-Alder reactions (in racemic or asymmetric series), but also started from carbohydrates (ribose, glucose), as a source of optically active compounds, which then had to be transformed into carbacycles under various conditions. The growing interest in carbocyclic nucleosides has led several groups, including ours, to develop new analogues and to explore novel routes. This article will review some of the recent chemistry developed on selected five-membered ring carbocyclic nucleosides.

Synthesis of Nucleoside-like Molecules from a Pyrolysis Product of Cellulose and Their Computational Prediction as Potential SARS-CoV-2 RNA-Dependent RNA Polymerase Inhibitors

(1R,5S)-1-Hydroxy-3,6-dioxa-bicyclo[3.2.1]octan-2-one, available by an efficient catalytic pyrolysis of cellulose, has been applied as a chiral building block in the synthesis of seven new nucleoside analogues, with structural modifications on the nucleobase moiety and on the carboxyl- derived unit. The inverted configuration by Mitsunobu reaction used in their synthesis was verified by 2D-NOESY correlations, supported by the optimized structure employing the DFT methods. An in silico screening of these compounds as inhibitors of SARS-CoV-2 RNA-dependent RNA polymerase has been carried out in comparison with both remdesivir, a mono-phosphoramidate prodrug recently approved for COVID-19 treatment, and its ribonucleoside metabolite GS-441524. Drug-likeness prediction and data by docking calculation indicated compound 6 [=(3S,5S)-methyl 5-(hydroxymethyl)-3-(6-(4-methylpiperazin-1-yl)-9H-purin-9-yl)tetrahydrofuran-3-carboxylate] as the best candidate. Furthermore, molecular dynamics simulation showed a stable interaction of structure 6 in RNA-dependent RNA polymerase (RdRp) complex and a lower average atomic fluctuation than GS-441524, suggesting a well accommodation in the RdRp binding pocket.

A Failed Late-Stage Epimerization Thwarts an Approach to Ineleganolide

Significant efforts were made to complete a synthesis of the complex norcembranoid ineleganolide via a seemingly attractive strategy involving late-stage creation of the central seven-membered ring. While the two key enantioenriched building blocks were made via high-yielding sequences and their convergent union was efficient, the critical C4-C5 bond of this sterically congested natural product could never be forged. Several interesting examples of unexpected acid-base behavior and unanticipated proximity-induced reactivity accounted for most of the problems in the execution of the synthesis plan.

Essential reactive intermediates in nucleoside chemistry: cyclonucleoside cations

DFT-based modeling as well as experimental examination of model keto nucleosides have revealed that high susceptibility of these compounds to acids is due to formation of intermediate cyclonucleoside cations of low energy. Theoretically established chemical structures of these previously overlooked intermediates explain the reaction courses for a cluster of nucleoside reactions.

The nitrosocarbonyl hetero-Diels-Alder reaction as a useful tool for organic syntheses

Organic transformations that result in the formation of multiple covalent bonds within the same reaction are some of the most powerful tools in synthetic organic chemistry. Nitrosocarbonyl hetero-Diels-Alder (HDA) reactions allow for the simultaneous stereospecific introduction of carbon-nitrogen and carbon-oxygen bonds in one synthetic step, and provide direct access to 3,6-dihydro-1,2-oxazines. This Review describes the development of the nitrosocarbonyl HDA reaction and the utility of the resulting oxazine ring in the synthesis of a variety of important, biologically active molecules.

Novel synthesis and anti-HIV activity of 4'-branched exomethylene carbocyclic nucleosides using a ring-closing metathesis of triene

The exomethylene of 6 was successfully constructed from the aldehyde 5 using Eschenmoser's reagents. A triene compound 7 was cyclized successfully using Grubbs' II catalyst to give an exomethylene carbocycle nucleus for the target compound. A Mitsunobu reaction was successfully used to condense the natural bases (adenine, thymine, uracil, and cytosine). The synthesized cytosine analogue 20 showed moderate anti-HIV activity (EC(50) = 10.67 microM).

Synthesis and antiviral activity of novel anomeric branched carbocyclic nucleosides

Novel anomeric branched carbocyclic nucleosides were synthesized from 1,3-dihydroxy acetone. 4'-Hydroxymethyl was installed by [3,3]-sigmatropic rearrangement reaction and 1'-methyl group was introduced by carbonyl addition of methylmagnesium bromide. The coupling of nucleosidic bases and desilylation afforded a series of novel nucleosides. The synthesized compounds 16-19 were evaluated for their antiviral activity against HIV-1, HSV-1, HSV-2, and EMCV. Compounds 16 and 19 exhibit toxicity non-related to any anti-HIV-1 activity.

Asymmetric Synthesis of the Carbocyclic Nucleoside Building Block (R)-(+)-4-Aminocyclopentenone Using δ-Amino β-Ketophosphonates and Ring-Closing Metathesis (RCM)

Amino keto-2,7-dienes undergo ring-closing metathesis (RCM) to give 4-aminocyclopentenones, valuable intermediates in the asymmetric construction of carbocyclic nucleosides. The key amino ketodienes were prepared using delta-amino beta-ketophophonates, a new sulfinimine-derived chiral building block, and HWE chemistry. [reaction: see text]