Solution-phase synthesis of phosphorothioate oligodeoxynucleosides by the phosphotriester method

Area of Science:

• Organic Chemistry
• Oligonucleotide Synthesis
• Medicinal Chemistry

Background:

• Phosphorothioate oligonucleosides are crucial in nucleic acid therapeutics.
• Current synthesis methods face challenges with efficiency and side reactions.
• Protecting group strategies are vital for successful oligonucleotide assembly.

Purpose of the Study:

• To investigate a phosphorothioate triester method for solution-phase synthesis of phosphorothioate oligonucleosides.
• To evaluate the impact of different S-protecting groups on synthesis fidelity.
• To optimize the assembly of decathymidine nonaphosphorothioate.

Main Methods:

• Utilized a phosphorothioate triester approach for oligonucleotide synthesis.
• Employed fully protected 3 -phosphorothiolate thymidine with O-cyanoethyl and S-2,4-dichlorobenzyl protecting groups.
• Investigated blockwise assembly and deprotection strategies.

Main Results:

• Successfully assembled decathymidine nonaphosphorothioate using the developed method.
• Identified side reactions including internucleoside linkage breakage (1.8%) and phosphate diester formation (0.9%).
• Demonstrated that replacing the S-2,4-dichlorobenzyl group with a 4-nitrobenzyl group halved internucleoside bond breakage.

Conclusions:

• The phosphorothioate triester method is effective for synthesizing phosphorothioate oligonucleosides.
• Protecting group selection significantly influences the yield and purity of the synthesized oligonucleotides.
• Further optimization of protecting groups can enhance the reliability of oligonucleotide synthesis.