Nucleoside nucleobase modifications

Nucleobase Modifications In the search for new therapeutic derivatives, substituted triazole rings have been introduced on both pyrimidines [2] and purine nucleosides [3-5] (Figure 10.1). Among all the synthesized compounds, some... 

As mentioned in the Introduction, we are especially interested in the effect of nucleoside modifications on RNA structure. The equilibrium sequences introduced above were selected for this reason. The position of the conformational equilibrium of the sequence constructs is expected to be highly sensitive to chemical alteration, e.g. methylation of nucleobases. 

The first category of modifications involved substitutions at C5 of the pyrimidine nucleobase (Figures 14 and 15) [47]. It is well known that C5 substitutions control the pAa of the N3 of C in nucleosides and drastically alter the hydrophobic driving force, base stacking and electronic complementarity... 

As demonstrated in Figs 22 and 23, phosphoramidites of convertible nucleosides allow introduction of non-natural modifications of nucleobases after solid-phase synthesis. 

All transfer RNAs (tRNAs) contain a number of modified nucleobases and typically 2 -D-methylated nucleosides. DNA also contains a more limited number of such species. Some of these modifications, for example, N-7 methylation of guanosine, diminish the metal-binding ability of the bases. A few functional groups, such as the exocyclic S in 4-thiouridine and 2-thiocytidine and the exocyclic substituent in 5-carboxymethylaminomethyluridine, enhance the ambivalent nature of the bases. Some of these modifications change the basicity of primary metal-binding sites. 

Seela F, Xu K, Chittepu P, Ming X (2007) Fluorinated 7-deazapurine 2 -deoxyribonucleosides modification at the nucleobase and the sugar moiety. Nucleosides Nucleotides Nucleic Acids 26 607-610... 

Other base-modifications. Hassan and co-workers reported a novel synthesis of pyrazolone nucleosides and their antimicrobial activities. Mata and his group reported the stereoselective AAglycosylation of 2-deo3ythioribosides. This facile synthesis (shown in Scheme 3) involves N-2-deo3yribosylation of a modified nucleobase with 2-deoiythioriboside in the presence of bis-(trimethylsilyl)acetamide, AT-iodosuccinimide and trimethylsilyl trifluoromethanesulfonate to afford stereoselective nucleosides (19) in excellent yields. 

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