Novel epimerization of aromatic C-nucleosides with electron-withdrawing substituents with trifluoroacetic acid–benzenesulfonic acid using mild conditions

Highly Stereoselective Glycosylation Reactions of Furanoside Derivatives via Rhenium (V) Catalysis

A novel approach for the formation of anomeric carbon-functionalized furanoside systems was accomplished through the employment of an oxo-rhenium catalyst. The transformation boasts a broad range of nucleophiles including allylsilanes, enol ethers, and aromatics in addition to sulfur, nitrogen, and hydride donors, able to react with an oxocarbenium ion intermediate derived from furanosidic structures. The excellent stereoselectivities observed followed the Woerpel model, ultimately providing 1,3-cis-1,4-trans systems. In the case of electron-rich aromatic nucleophiles, an equilibration occurs at the anomeric center with the selective formation of 1,3-trans-1,4-cis systems. This anomalous result was rationalized through density functional theory calculations. Different oxocarbenium ions such as those derived from dihydroisobenzofuran, pyrrolidine, and oxazolidine heterocycles can also be used as a substrate for the oxo-Re-mediated allylation reaction.

Synthetic Approaches for the Preparation of Phosphoramidate Prodrugs of 2'-Deoxypseudoisocytidine

A synthetic procedure for the preparation of phosphoramidate prodrugs of C-nucleosides is reported. Different phosphorochloridates were reacted with 3'-O-protected N-acetyl-2'-deoxypseudoisocytidine or 3'-O-protected 2'-deoxypseudoisocytidine, followed by acidic hydrolysis of the protecting group. In the presence of the N-acetyl moiety, the enolisable keto group of the nucleobase was able to react (like the 5'-OH) with the phosphorochloridates to give bisphosphorylated derivatives. Epimerisation (β to α) occurred if the amino group of the nucleobase was unprotected. These side reactions demonstrate the peculiar behaviour of C-nucleosides compared to their nucleoside analogues. It was demonstrated that the first enzymatic activation step for this new class of prodrugs can be mediated by carboxypeptidase and that it follows the same pathway and rate reported for ProTides of more conventional nucleoside analogues. These new phosphoramidate derivatives deserve further investigation for their therapeutic potential as anti-cancer agents.

FeCl3-promoted and ultrasound-assisted synthesis of resveratrol O-derived glycoside analogs

Phenol derived O-glycosides were synthesized using a direct and convenient O-glycosidation, starting from acetylated sugars in the presence of FeCl3, an inexpensive, mild and benign Lewis acid catalyst. The reactions were carried out under both conventional and ultrasonic irradiation conditions. In general, improvement in rates and yields were observed when reactions were carried out under sonication compared with conventional conditions leading to the corresponding β-O-glycosides as the major anomer. Post-synthetic transformations of iodophenol intermediates led to new resveratrol O-glycoside analogs in good overall yields.

Synthesis and characterization of a DNA analogue stabilized by mercapto C-nucleoside induced disulfide bonding

A redox-active nucleobase analogue of a nucleotide was synthesized and incorporated into DNA using phosphoramidite chemistry. An analogue-containing oligonucleotide in the absence of a reducing reagent formed a stable duplex with a substantially higher melting temperature compared to that of a standard DNA duplex of the same length.