Synthesis of Protected Amino Hexitol Nucleosides as Building Blocks for Oligonucleotide Synthesis.

A new synthesis protocol for the preparation of hitherto unknown 1',5'-anhydro-4'-amino-trityl/MMTr hexitol nucleosides has been developed. Key steps in the synthesis of the pyrimidine analogues (U and C) include the regioselective d- allo-hexitol oxirane and 2',4'-anhydronucleoside ring opening by uracil and azide, respectively. A different strategy using a regioselective epoxide ring opening of d- gulo-oxirane, followed by a SN2 type of azidation reaction, has been adopted for the purine analogues (A and G). These compounds can be easily converted to 6'-phosphoramidites for the solid-phase synthesis of N4' → P6' phosphoramidates of amino hexitol nucleic acids (AHNA).

Synthesis of a 3'-Fluoro-3'-deoxytetrose Adenine Phosphonate.

A new synthetic route to a 3'-fluoro-3'-deoxytetrose adenine phosphonate has been developed. The synthesis starts from l-xylose and key steps include the stereospecific introduction of the phosphonomethoxy group and adenine. In addition, a regioselective fluorination reaction allows access to the desired 3'-fluoro-3'-deoxytetrose moiety. This methodology allows the straightforward synthesis of a 3'-fluoro-3'-deoxytetrose adenine phosphonate and can be expanded toward the synthesis of other types of 3'-fluoro nucleoside phosphonates.

Syntheses of 5'-Nucleoside Monophosphate Derivatives with Unique Aminal, Hemiaminal, and Hemithioaminal Functionalities: A New Class of 5'-Peptidyl Nucleotides.

A number of synthetically useful transformations have been developed to generate novel 5'-peptidyl nucleoside monophosphate analogues that incorporate sensitive phosphoaminal, -hemiaminal or -hemithioaminal functionalities. The strategies adopted entailed the coupling between dipeptides, which enclose a reactive Cα-functionalized glycine residue and phosphate or phosphorothioate moieties. These developments led to potentially powerful and general methodologies for the preparation of α-phosphorylated pseudopeptides as well as nucleoside monophosphate mimics. The resulting conjugates are of interest for a variety of important applications, which range from drug development to synthetic biology, as pronucleotides or artificial building blocks for the enzymatic synthesis of xenobiotic information systems. The potential of all dipeptide-TMP conjugates as pyrophosphate mimics in the DNA polymerization reaction was tested, and the influence of the nature of the linker was evaluated by in vitro chain elongation assay in the presence of wild-type microbial DNA polymerases.