Solid phase synthesis of oligodeoxyribonucleoside phosphorodithioates from thiophosphoramidites

Area of Science:

• Chemical Synthesis
• Oligonucleotide Chemistry
• Biochemistry

Background:

• Antisense oligonucleotides are modified nucleic acid sequences targeting specific RNA or DNA.
• Phosphorothioate linkages are common modifications to enhance nuclease resistance.
• Developing novel oligonucleotide modifications is crucial for improving therapeutic efficacy.

Purpose of the Study:

• To describe the solid-phase synthesis of oligonucleoside phosphorodithioates up to 20-mers.
• To characterize the synthesized phosphorodithioate-containing DNA analogues.
• To evaluate the stability and hybridization properties of these modified oligonucleotides.

Main Methods:

• Solid-phase synthesis using protected nucleoside thiophosphoramidites.
• High-Performance Liquid Chromatography (HPLC) for purification.
• Polyacrylamide Gel Electrophoresis (PAGE) and 31P Nuclear Magnetic Resonance (NMR) for characterization.
• UV melting point (Tm) measurements for hybridization studies.

Main Results:

• Successful synthesis of oligonucleoside phosphorodithioates up to 20 bases in length.
• HPLC purification yielded homogeneous products, but 31P NMR indicated 8-9% phosphorothioate impurities.
• The compounds exhibit excellent solubility in water and high stability against oxidation, hydrolysis, and nucleases.
• Hybridization studies showed a greater melting point depression per linkage compared to phosphorothioates.

Conclusions:

• Oligonucleoside phosphorodithioates can be synthesized using solid-phase methods.
• These modified oligonucleotides possess favorable stability and solubility profiles.
• The increased Tm depression suggests enhanced binding affinity to complementary DNA, indicating potential as improved antisense agents.