A new general synthesis of isomeric nucleosides

Synthesis of glucopyranos-6′-yl purine and pyrimidine isonucleosides as potential cholinesterase inhibitors. Access to pyrimidine-linked pseudodisaccharides through Mitsunobu reaction

The synthesis of new isonucleosides comprising purine and pyrimidine-derived systems linked to methyl glucopyranosidyl units at C-6 and evaluation of their cholinesterase inhibitory profiles is reported. Their access was based on the Mitsunobu coupling of partially acetylated and benzylated methyl glucopyranosides with purine and pyrimidine derivatives. While the reactions with purines and theobromine proceeded with complete regioselectivity, affording exclusively N9- or N1-linked 6′-isonucleosides, respectively, the use of pyrimidine nucleobases led to N1 and/or N3-glucopyranosid-6′-yl pyrimidines and/or to N1,N3/2-O,4-O-pyrimidine-linked pseudodisaccharides through bis-coupling, depending on the substitution pattern of the sugar precursor and on the nature of the nucleobase. From this series of compounds, four were shown to be effective and selective inhibitors of acetylcholinesterase with inhibition constants in the micromolar concentration range. A tri-O-acetylated N1-glucopyranosid-6′-yl theobromine and a benzylated N1,N3-bis-glucopyranosid-6-yl thymine were the most active molecules with Ki values of 4 μM. A tri-O-benzylated glucopyranosid-6′-yl uracil displayed good and selective inhibition of butyrylcholinesterase (Ki=8.4±1.0 μM), similar to that exhibited by the standard galantamine. Molecular docking simulations, performed with the two most effective acetylcholinesterase inhibitors, showed interactions with key amino acid residues located at the enzyme’s active site gorge, which explain the competitive component of their inhibitory activities.

Nucleosides with Transposed Base or 4'-Hydroxymethyl Moieties and Their Corresponding Oligonucleotides

This review focuses on 4'-hydroxymethyl- or nucleobase-transposed nucleosides, nucleotides, and nucleoside phosphonates, their stereoisomers, and their close analogues. The biological activities of all known 4'-hydroxymethyl- or nucleobase-transposed nucleosides, nucleotides, and nucleoside phosphonates as potential antiviral or anticancer agents are compiled. The routes that have been taken for the chemical synthesis of such nucleoside derivatives are described, with special attention to the innovative strategies. The enzymatic synthesis, base-pairing properties, structure, and stability of oligonucleotides containing nucleobase- or 4'-hydroxymethyl-transposed nucleotides are discussed. The use of oligonucleotides containing nucleobase- or 4'-hydroxymethyl-transposed nucleotides as small oligonucleotide (e.g., human immunodeficiency virus integrase) inhibitors, in applications such as antisense therapy, silencing RNA (siRNA), or aptamer selections, is detailed.

Construction of an isonucleoside on a 2,6-dioxobicyclo[3.2.0]-heptane skeleton

We have built a new isonucleoside derivative on a 2,6-dioxobicyclo[3.2.0]heptane skeleton as a potential anti-HIV agent. To synthesize the target compound, an acetal-protected dihydroxyacetone was first converted to a 2,3-epoxy-tetrahydrofuran derivative. Introduction of an azide group, followed by the formation of an oxetane ring, gave a pseudosugar derivative with a 2,6-dioxobicyclo[3.2.0]heptane skeleton. The desired isonucleoside was obtained by constructing a purine base moiety on the scaffold, followed by amination.

Enzymatic recognition of 2'-modified ribonucleoside 5'-triphosphates: towards the evolution of versatile aptamers

The quest for effective, selective and nontoxic nucleic-acid-based drugs has led to designing modifications of naturally occurring nucleosides. A number of modified nucleic acids have been made in the past decades in the hope that they would prove useful in target-validation studies and therapeutic applications involving antisense, RNAi, aptamer, and ribozyme-based technologies. Since their invention in the early 1990s, aptamers have emerged as a very promising class of therapeutics, with one drug entering the market for the treatment of age-related macular degeneration. To combat the limitations of aptamers containing naturally occurring nucleotides, chemically modified nucleotides have to be used. In order to apply modified nucleotides in aptamer drug development, their enzyme-recognition capabilities must be understood. For this purpose, several modified nucleoside 5'-triphosphates were synthesized and investigated as substrates for various enzymes. Herein, we review studies on the enzyme-recognition of various 2'-sugar-modified NTPs that were carried out with a view to their effective utilization in SELEX processes to generate versatile aptamers.

Regio- and stereoselective synthesis of truncated 3'-aminocarbanucleosides and their binding affinity at the A3 adenosine receptor

The stereoselective synthesis of truncated 3'-aminocarbanucleosides 4a-d via a stereo- and regioselective conversion of a diol 9 to bromoacetate 11a and their binding affinity towards the human A(3) adenosine receptor are described.

Incorporation of 2'-deoxy-2'-isonucleoside 5'-triphosphates (iNTPs) into DNA by A- and B-family DNA polymerases with different recognition mechanisms

Recently, α-L-threofuranosyl nucleoside 3'-triphosphates (tNTPs) have been reported to be incorporated into DNA by DNA polymerases. Isonucleosides especially the 2'-deoxy-2'-isonucleosides, would be considered regioisomers of α-L-threofuranosyl nucleosides. Therefore, we investigated the synthesis of 2'-deoxy-2'-isonucleoside 5'-triphosphates (iNTPs) having the four natural nucleobases and their incorporation into primer-template duplexes consisting of oligonucleotides containing natural 2'-deoxyribonucleosides and 2'-deoxy-2'-isonucleosides by using primer-extension reactions. We found that Klenow fragment (exo-; an A-family DNA polymerase) has strict recognition of the shape of nucleoside 5'-triphosphates and Therminator (a B-family DNA polymerase) has strict recognition of the shape of primer-template complexes, especially two base pairs upstream of the primer 3' terminus.

Synthetic approaches to nuclease-resistant, nonnatural dinucleotides of anti-HIV integrase interest

New, nonnatural dinucleotide 5'-monophosphates with a surrogate isonucleoside component of L-related stereochemistry, have been synthesized. Structures of the target compounds were confirmed by multinuclear NMR spectra (1H, 13C, 31P, COSY), UV hypochromicity, FAB HRMS data and X-ray crystallography. These compounds are totally resistant to cleavage by 3'- and 5'-exonucleases. Dinucleotides of this study with a terminal L-isonucleoside component showed remarkable selectivity for inhibition of the strand transfer step of HIV-1 integrase. To the best of our knowledge, these compounds represent only the second example of this type of selectivity of inhibition of the strand transfer step.

Convenient Synthesis of Nucleoside and Isonucleoside Analogues

[reaction: see text]. A very simple methodology to stereoselectively achieve tricyclic isonucleosides (nucleobase = thymine, uracil, and 5-fluoruracil) and 3'-C-branched nucleosides (nucleobase = theophylline) was performed by means of a DBU-mediated addition process using a readily available 2-bromo sugar. The mechanism for these transformations implies the loss of both substituents at C-2 and C-3 on the sugar moiety, and although it seems that DBU is probably involved, its involvement has not yet been ascertained. Cytosine did not react under these conditions.

Inhibition of the strand transfer step of HIV-1 integrase by non-natural dinucleotides

New, non-natural dinucleotide 5'-monophosphates, with a surrogate isonucleoside component of l-related stereochemistry at the 'terminal' position, have been synthesized. Structures of 2a-c were confirmed by multinuclear NMR spectra ((1)H, (13)C, (31)P, COSY), UV hypochromicity and FAB HRMS data. These compounds are totally resistant to cleavage by 3'- and 5'-exonucleases. The dinucleotides showed remarkable selectivity for inhibition of the strand transfer step of HIV-1 integrase. To the best of our knowledge, these compounds represent only the second example of selective strand transfer inhibitors of HIV integrase.

A new approach for the synthesis of novel 5-substituted isodeoxyuridine analogs

Cyclic sulfates of carbohydrates provide excellent synthons for the preparation of isodeoxyuridines through direct nucleophilic substitution reactions. These substitution reactions have exceptional regioselectivity. The products of the reactions served as key precursors for the synthesis of 5-substituted isodeoxyuridines via the Stille and Heck coupling reactions. Interestingly, unprotected nucleosides could be used in these metal-mediated functionalizations. The methodologies are general and allow ready access to a variety of C-5 functionalized isomeric deoxyuridines, but also have the potential to be extended to other nucleoside analogs.