Preparation of Oligodeoxynucleotides Containing 6-Methylthiopurine Residues by Chemical Synthesis or Specific Methylation

References

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• Compound 3 (2.82 g, 8 mmole) was dissolved in 25 ml of 1 N NaOH aqueous solution at RT. After 30 min, TLC (15% CH3OH/CHCl3) showed the deacylation was completed. Methyl iodide (800 μl, 12.8 mmole) was slowly added and the solution was stirred vigorously for another 30 min. TLC showed that the intermediate had been converted into a new spot with a higher Rf. After work-up, a colourless powder was obtained, which was crystallized to give pure compound 4. Data from NMR, UV and elementary analysis confirmed that 4 was a monomethylated thiopurine nucleoside. The view that 4 is an S-methylated derivative rather than an N1-methylated was further supported by the fact that oxidation with 3-chloroperoxybenzoic acid and subsequent substitution with methylamine, aziridine or thiolacetic acid give corresponding 6-substituted purine deoxynucleosides.
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• Compounds 5 and 6 were confirmed by 1H NMR and 31P NMR
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• 1 OD of a fully deprotected and purified oligomer containing 6-thioinosine (or 6-thioguanine) was dissolved in 100 μl of 0.05 M phosphate buffer (pH 8.5). 20 μl of 10% CH3I/CH3CN (v/v) was added and vigorously mixed for 5 min. The solution was left overnight and the desired oligomer was isolated using a Sep-Pac cartridge (Waters)
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