A remarkably simple chemicoenzymatic approach to structurally complex bicyclo[3.1.0]hexane carbocyclic nucleosides

A survey of enoldiazo nucleophilicity in selective C-C bond forming reactions for the synthesis of natural product-like frameworks

A survey of in situ, catalytically generated carbocations for coupling with enoldiazoacetate nucleophiles was performed. These couplings facilitate the rapid assembly of complex organodiazo compounds that provide a template for the synthesis of a variety of carbocyclic and heterocyclic ring systems.

Methanocarba ring as a ribose modification in ligands of G protein-coupled purine and pyrimidine receptors: synthetic approaches

Adenosine receptors (ARs) and P2Y receptors for purine and pyrimidine nucleotides have widespread distribution and regulate countless physiological processes. Various synthetic ligands are in clinical trials for treatment of inflammatory diseases, pain, cancer, thrombosis, ischemia, and other conditions. The methanocarba (bicyclo[3.1.0]hexane) ring system as a rigid substitution for ribose, which maintains either a North (N) or South (S) conformation, tends to preserve or enhance the potency and/or selectivity for certain receptor subtypes. This review summarizes recent developments in the synthetic approaches to these biologically important nucleoside and nucleotide analogues.

New bicyclo[3.1.0]hexane unit ent-kaurane diterpene and its seco-derivative from Isodon eriocalyx var. laxiflora

Neolaxiflorin A (1), an unprecedented ent-kaurane diterpenoid with a bicyclo[3.1.0]hexane unit, and its seco-derivative, neolaxiflorin B (2), along with two known compounds 3 and 4 were isolated from the leaves of Isodon eriocalyx var. laxiflora. The absolute configuration of 1 was determined by spectral methods and single crystal X-ray diffraction analysis. Compound 4 and the synthesized compound 5 exhibited significant cytotoxicity.

Synthesis of enantiomerically pure D- and L-bicyclo[3.1.0]hexenyl carbanucleosides and their antiviral evaluation

Based upon the fact that l-nucleosides have been generally known to be less cytotoxic than d-counterparts, l-bicyclo[3.1.0]hexenyl carbanucleoside derivatives with a fixed north conformation were designed and synthesized by employing a novel synthetic strategy starting from (R)-epichlorohydrin in order to search for new anti-HIV agents with high potency and less cytotoxicity. A tandem alkylation, γ-lactonization, a chemoselective reduction of ester in the presence of γ-lactone functional group, a RCM reaction, and a Mitsunobu coupling reaction were used as key reactions. d-Counterpart nucleosides were also prepared according to the same synthetic method. Among the synthesized carbanucleosides, d-thymine nucleoside, d-2 and l-thymine nucleoside, l-2 exhibited excellent anti-HIV-1 and -2 activities, in MT-4 cells, which were higher than those of ddI, an anti-AIDS drug. Whereas d-2 exhibited high cytotoxicity in MT-4 cell lines, l-2 did not show any discernible cytotoxicity in all cell lines tested, reflecting that l-2 may be a good candidate for an anti-AIDS drug. l-2 also showed weak anti-HSV-2 activity without cytotoxicity. However, none of the synthesized nucleosides exhibited antiviral activities against RNA viruses including coxsakie, influenza, corona and polio viruses, maybe due to their 2′,3′-dideoxy structure. Potent antiviral effects of d-2 and l-2 indicate that nucleosides belonging to a class of D4Ns can be an excellent candidate for anti-DNA virus agents. This research strongly supports l-nucleosides of a class of D4Ns to be a very promising candidate for antiviral agents due to its low cytotoxicity and a good antiviral activity.

Total syntheses of a conformationally locked North-type methanocarba puromycin analogue and a dinucleotide derivative

An original synthetic approach for the first synthesis of an enantiopure methanocarba puromycin (3'-alpha-aminoacylamino-3'-deoxyadenosine) analogue and its cytidine dinucleotide derivative is described. Each compound is conformationally locked in a North-type pucker and exhibits both a pseudoaxial hydroxy group and a pseudoequatorial aminoacyl group. The syntheses were accomplished from D-ribose in 18 and 19 steps, respectively, with key steps being a ring-closing metathesis, a Luche reduction, a Simmons-Smith cyclopropanation, a Mitsunobu coupling, a Mattocks bromoacetylation, a regioselective and a stereoselective nucleophilic substitution, a chemoselective phosphoramidite coupling and a Staudinger-Vilarrasa coupling. Both molecules are being tested for peptidyl transfer efficiency in ribosomes for comparison with the peptidyl transfer kinetics of natural puromycin and other natural and synthetic ribosomal A site substrates.

Asymmetric synthesis and biological activity of L-bicyclocarba-d4T

Novel L-bicyclocarba-d4T (1), an enantiomer of D-N-MCd4T has been enantiopurely synthesized as a potent anti-HIV agent starting from (R)-epichlorohydrin using tandem alkylation, chemoselective reduction of ester in the presence of lactone functional group, Grignard reaction, RCM reaction, and Mitsunobu reaction as key steps. L-N-MCd4T (1) was found to be very potent anti-HIV-1 (EC(50) = 6.76 microg/mL) agent with no cytotoxicity.

Synthesis of Bicyclo[3.1.0]hexanes Functionalized at the Tip of the Cyclopropane Ring. Application to the Synthesis of Carbocyclic Nucleosides

[reaction: see text] A general synthetic strategy for the preparation of functionalized bicyclo[3.1.0]hexanes is described. The new approach employs a cross metathesis step designed to functionalize the appropriate terminal olefin of the bicyclo[3.1.0]hexane precursor and a carbene-mediated intramolecular cyclopropanation reaction on the corresponding diazo intermediate. This combined methodology allowed the diastereoselective introduction of chemically diverse substituents at the tip of the cyclopropane group, except in cases where the substituents consisted of electron-withdrawing groups where a competing [3 + 2] cycloaddition predominated.

Synthesis of novel l-N-MCd4T as a potent anti-HIV agent

L-N-MCd4T (1) has been synthesized as a potent anti-HIV agent starting from (R)-epichlorohydrin using tandem alkylation, chemoselective reduction of ester in the presence of lactone functional group, RCM reaction and Mitsunobu reaction as key steps and was found to be a very potent anti-HIV-1 (EC50 = 6.76 microg mL(-1)) agent without cytotoxicity up to 100 microg mL(-1), indicating that the anti-HIV-1 activity found is similar to that of ddI (EC50 = 4.95 microg mL(-1)), which is used clinically for the treatment of AIDS patients.

Conformationally Constrained Purine Mimics. Incorporation of Adenine and Guanine into Spirocyclic Nucleosides

Directed syntheses of spirocyclic nucleosides featuring adenine and guanine as the nucleobases have been successfully developed. The key starting materials are the enantiomerically pure spiro lactones 4, 15, and 28, which have proven amenable to conversion to anomeric mixtures of chloro sugars. The latter can enter into glycosidation by SN2 displacement with the sodium salts of 6-chloropurine or 2-amino-6-chloropurine. In the saturated series, the chromatographic separation of 18 from 19 was possible. Where 33 and 34 are concerned, their relatively rapid rate of epimerization precluded this. Mimics 35-37 resisted isolation as pure anomers. The configurational assignments are based on the thermal interconversions and supporting MM3 steric energy calculations. Added corroboration was gained from a crystallographic analysis of 8. Although removal of the TBS protecting groups in all late-stage guanine intermediates proved to be problematical, the pair of hydroxyl groups in 37 could be introduced by proper recourse to the oxidation of 36 with ruthenium tetraoxide.

Recent advances in the synthesis of conformationally locked nucleosides and their success in probing the critical question of conformational preferences by their biological targets

The present work describes some recent approaches to the syntheses of three classes of locked-North nucleosides: beta-D-ribo-, beta-D-deoxyribo-, and beta-D-dideoxyribonucleosides. The method developed for the latter class permitted access to a novel bicyclo[3.1.0]hexene-type nucleosides structurally similar to D4T and carbovir. A structural analysis and biological activities are discussed.

Synthesis and biological evaluation of endocyclic 2',3'-didehydro-2',3'-dideoxymethanocarba adenosine

This is the first report describing the synthesis and conformation of methanocarba nucleosides incorporating an endo (beta-face) cyclopropyl at the 2',3' position of 2',3'-didehydro-2',3'-dideoxy carbocyclic nucleosides. These nucleoside isosteres have been shown to exist in a unique extreme eastern conformation. This prediction was confirmed by x-ray crystallography and high resolution NMR spectroscopy. As expected, the methanocarba adenosine compound was neither a substrate nor an inhibitor of adenosine deaminase. However, some of the compounds synthesized demonstrated moderate antiviral activity against HSV-1. The methanocarba adenosine and its triphosphate form were evaluated as inhibitors of HIV-1 reverse transcriptase.

Synthesis of a conformationally locked version of puromycin amino nucleoside

[reaction: see text] A conformationally locked carbocyclic version of puromycin amino nucleoside was synthesized via Mitsunobu coupling of a 3-azido-substituted carbocyclic moiety with 6-chloropurine without interference from the azido group reacting with triphenylphosphine. The requisite 3-azido-substituted carbocyclic pseudosugar was prepared by a double inversion of configuration at C3' (nucleoside numbering) involving a nucleophilic displacement with azide.

Spirocyclic restriction of nucleosides. Synthesis of the first exemplary syn-1-oxaspiro[4.4]nonanyl member

[reaction: see text] The potential benefits associated with the spirocyclic restriction of nucleosides are summarized. Following exploration of a pi-allylpalladium route to 5'-alpha- or syn-dideoxy examples, we evaluated MOM protection of the 5'-hydroxyl as being suited to the synthesis of the first member of this new class of nucleoside mimic.