A New stereospecific synthesis of [3.1.0]bicyclic cyclopropano analog of 2'3'-dideoxyuridine

Modern Synthetic Strategies with Organoselenium Reagents: A Focus on Vinyl Selenones

In recent years, vinyl selenones were rediscovered as useful building blocks for new synthetic transformations. This review will highlight these advances in the field of multiple-bond-forming reactions, one-pot synthesis of carbo- and heterocycles, enantioselective construction of densely functionalized molecules, and total synthesis of natural products.

Synthesis of 1',2'-methano-2',3'-dideoxynucleosides as potential antivirals

The synthesis of constrained nucleosides has become an important tool to understand the SAR in the interaction between biological and synthetic nucleotides in the context of antisense oligonucleotide therapy. The incorporation of a cyclopropane into a furanose ring of a nucleoside induces some degree of constrain without affecting significantly the steric environment of a nucleoside. Here, we report a new, short and stereocontrolled synthesis of two constrained nucleosides analogues, 1',2'- methano-2',3'-dideoxyuridine 9, and the corresponding cytidine analog 12. X-ray crystallography revealed that the furanose ring in the constrained uridine and cytidine analogues was flattened with virtual loss of pseudorotation. The phosphoramidate esters of the novel constrained uridine and cytidine nucleosides, intended as prodrugs, were tested in cell-based assays for viral replication across the herpes virus family and HIV inhibition courtesy of Merck laboratories, Rahway. They were also tested in antiproliferative assays against colorectal and melanoma cell lines. Unfortunately, none of the compounds showed activity in these assays.

Synthesis of Oxazolidin-2-ones by Oxidative Coupling of Isonitriles, Phenyl Vinyl Selenone, and Water

Reaction of alkyl isocyanides, phenyl vinyl selenone, and water in the presence of a catalytic amount of Cs2 CO3 afforded oxazolidin-2-ones in good yields. This unprecedented heteroannulation process created four chemical bonds in a single operation with the isocyano group acting formally as a polarized double bond and phenyl vinyl selenone as a latent 1,3-dipole. The phenylselenonyl group played a triple role as an electron-withdrawing group to activate the 1,4-addition, a leaving group, and a latent oxidant in this transformation.

Enantiopure 1,4,5-trisubstituted 1,2,3-triazoles from carbohydrates: applications of organoselenium chemistry

A wide range of stable vinyl selenone-modified furanosides has been synthesized for the first time. These 2π-partners undergo 1,3-dipolar cycloaddition reactions with a wide range of organic azides to afford enantiopure trisubstituted triazoles. Furanosyl rings opened up during triazole synthesis to generate polyfunctionalized molecules, ready to undergo further transformations. This strategy is one of the most convenient methods for the synthesis of enantiopure 1,4,5-trisubstituted 1,2,3-triazoles where the chiral components are attached to C-4 or C-5 position of triazole ring. These triazoles are formed in a regioselective manner, and several pairs of regioisomeric triazoles have also been synthesized. The approach affords densely functionalized triazoles, which are amenable to further modifications because of the presence of aldehyde and hydroxyl groups. This powerful and practical route adds to the arsenals of chemists and biologists interested in the synthesis and applications of triazoles.

Synthesis and anti-HIV activity of conformationally restricted bicyclic hexahydroisobenzofuran nucleoside analogs

A chiral synthesis of a series of hexahydroisobenzofuran (HIBF) nucleosides has been accomplished via glycosylation of a stereo-defined (syn-isomer) sugar motif 16 with the appropriate silylated bases. All nucleoside analogs were obtained in 52-71% yield as a mixture of alpha- and beta-anomeric products increasing the breadth of the novel nucleosides available for screening. The structure of the novel bicyclic HIBF nucleosides was established by a single crystal X-ray structure of the beta-HIBF thymine analog 22b. Furthermore, the sugar conformation for these nucleosides was established as N-type. Among the novel HIBF nucleosides synthesized, twenty-five compounds were tested as inhibitor of HIV-1 in human peripheral blood mononuclear (PBM) cells and seven were found to be active (EC(50) = 12.3-36.2 microM). Six of these compounds were purine analogs with beta-HIBF inosine analog 22o being the most potent (EC(50) = 12.3 microM) among all compounds tested. The striking resemblance between didanosine (ddI) and 22o may explain the potent anti-HIV activity.

First Organocatalyzed Asymmetric Michael Addition of Aldehydes to Vinyl Sulfones

[reaction: see text] The first asymmetric direct Michael addition of aldehydes to vinyl sulfones catalyzed by N-iPr-2,2'-bipyrrolidine is described. 1,4-Adducts are obtained in good yields and enantioselectivities. The determination of absolute configuration allowed us to postulate a Si,Si transition state model, as shown previously for nitroolefins.

Enantiomeric syntheses of conformationally restricted D- and L-2', 3'-dideoxy-2',3'-endo-methylene nucleosides from carbohydrate chiral templates

D- and L-2',3'-dideoxy-2',3'-endo-methylene nucleosides were synthesized as potential antiviral agents. The key intermediates 5-O-tert-butyldiphenylsilyl-D- and L-2,3-dideoxy-2, 3-endo-methylenepentofuranoses (20 and 33, respectively) were obtained by selective protection of the D- and L-2,3-dideoxy-2, 3-endo-methylenepentose derivatives 19 and 32 which were prepared from 1,2:5,6-di-O-isopropylidene-D-mannitol and L-gulonic gamma-lactone, respectively, and converted to 5-O-tert-butyldiphenylsilyl-D- and L-2,3-dideoxy-2, 3-endo-methylenepentofuranosyl acetates (21 and 34, respectively) or the chlorides 22 and 35. The acetates and chlorides were condensed with pyrimidine and purine bases by Vorbrüggen conditions or S(N)2-type condensation. Vorbrüggen conditions using the acetates gave mostly alpha-isomers. In contrast, S(N)2-type condensation using the chlorides greatly improved the beta/alpha ratio. From the synthesis, several D- and L-2',3'-dideoxy-2',3'-endo-methylene nucleoside analogues have been obtained, and their structures have been elucidated by NMR spectroscopy and X-ray crystallography. The synthesized D- and L-adenine derivatives were tested as substrates of adenosine deaminase, which indicated that the D-adenosine derivative 4a was a good substrate of a mammalian adenosine deaminase from calf intestinal mucosa (EC 3.5.4.4) while its L-enantiomer 10a was a poor substrate. Either the D-adenine derivative 4a or its L-enantiomer 10a did not serve as an inhibitor of the enzyme.