Facile synthesis of 2′,3′-unsaturated nucleosides from 2-deoxyribose

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

Structure-activity relationships of 2'-fluoro-2',3'-unsaturated D-nucleosides as anti-HIV-1 agents

We studied the structure-activity relationships of a series of 2'-fluoro-2',3'-unsaturated D-nucleosides against HIV-1 in human peripheral blood mononuclear (PBM) cells. The target compounds 10-21 and 28-33 were prepared by N-glycosylation of the acetate 4, which was readily prepared from 2,3-O-isopropylidene-D-glyceraldehyde in five steps. Among the newly synthesized nucleosides, 2-amino-6-chloropurine (11), adenine (14), inosine (16), guanine (18), 2,6-diaminopurine (20), and 5-fluorocytosine (30) derivatives were found to exhibit interesting anti-HIV activities with EC(50) values of 4.3, 0.44, 1.0, 2.6, 3.0, and 0.82 microM, respectively. The implications for drug resistance of the titled nucleosides with respect to lamivudine-resistant variants (M184V) were also examined, and no significant cross-resistance with the variants was observed with the D-series.

Synthesis and anti-HIV and anti-HBV activities of 2'-fluoro-2', 3'-unsaturated L-nucleosides

The synthesis of L-nucleoside analogues containing 2'-vinylic fluoride was accomplished by direct condensation method, and their anti-HIV and anti-HBV activities were evaluated in vitro. The key intermediate 8, the sugar moiety of our target compounds, was prepared from 1,2-O-isopropylidene-L-glyceraldehyde via (R)-2-fluorobutenolide intermediate 5 in five steps. Coupling of the acetate 8 with the appropriate heterocycles (silylated uracil, thymine, N4-benzoylcytosine, N4-benzoyl-5-fluorocytosine, 6-chloropurine, and 6-chloro-2-fluoropurine) in the presence of Lewis acid afforded a series of 2'-fluorinated L-nucleoside analogues (15-18, 23-26, 36-45). The newly synthesized compounds were evaluated for their antiviral activities against HIV-1 in human peripheral blood mononuclear (PBM) cells and HBV in 2.2.15 cells. Cytosine 23, 5-fluorocytosine 25, and adenine 36 derivatives exhibited moderate to potent anti-HIV (EC50 0.51, 0.17, and 1.5 microM, respectively) and anti-HBV (EC50 0.18, 0.225, and 1.7 microM, respectively) activities without significant cytotoxicity up to 100 microM in human PBM, Vero, CEM, and HepG2 cells.

Stereoselective Synthesis of 2'-Amino-2',3'-dideoxynucleosides by Nitrone 1,3-Dipolar Cycloaddition: A New Efficient Entry Toward d4T and Its 2-Methyl Analogue

An efficient access to 2'-(dimethylamino)-2',3'-dideoxynucleosides is reported. The synthetic strategy relies on the 1,3-dipolar cycloaddition of C-alkoxycarbonyl nitrones to allyl acetate, followed by reductive ring opening to substituted lactones, DIBALH reduction to the corresponding 3-(dimethylamino)tetrahydro-2-furanols, and coupling with silylated thymine. The removal of the dimethylamino group by Cope elimination affords a new formal synthesis of d4T and analogous unsaturated 2',3'-dideoxynucleosides.