Interactions between oligonucleotides having a left-handed helical structure and ethidium bromide

Area of Science:

• Nucleic acid chemistry
• Oligonucleotide synthesis
• Structural biology

Background:

• Cyclic nucleosides offer unique structural and functional properties.
• Understanding modified oligonucleotides is crucial for developing novel therapeutic and diagnostic tools.

Purpose of the Study:

• To synthesize novel oligonucleotides incorporating specific cyclic nucleoside residues.
• To investigate the structural characteristics and complex formation of these modified oligomers.

Main Methods:

• Chemical synthesis of oligonucleotides containing 8,2'-S-cycloadenosine (As), 8,2'-S-cycloinosine (Is), 6,2'-O-cyclouridine (Uo), and 6,2'-O-cyclocytidine (Co) residues.
• Characterization of the glycosidic torsion angle (chi) of the synthesized residues.
• Complex formation studies with ethidium bromide.

Main Results:

• Successful synthesis of oligonucleotides with cyclic nucleoside residues, exhibiting a glycosidic torsion angle of approximately 120 degrees.
• Oligomers AspUo, AspIs, and a mixture of (pCo)4 + (pIs)4 demonstrated complex formation with ethidium bromide.
• Ethidium bromide intercalation into the base pairs of a left-handed double helix formed by these modified oligonucleotides is proposed.

Conclusions:

• Novel cyclic nucleoside-containing oligonucleotides can be synthesized with defined structural features.
• These modified oligonucleotides can form complexes with intercalating agents like ethidium bromide.
• The findings suggest potential for these modified nucleic acids in structural studies and drug development.