Novel post DNA synthesis chemistry for preparing oligonucleotides containing O6-modified purines.

O6-alkylguanine DNA alkyltransferase (AGT) is a key target for inhibition during cancer chemotherapy. A large number of O6-modified-guanine analogues have been developed as AGT inhibitors, of which benzyl and (4-bromothenyl) have been used clinically. Since the normal AGT substrate is the alkylated guanine in DNA, the inhibition of AGT by oligonucleotides containing these compounds offers a promising therapeutic approach in terms of efficacy. In order to prepare such oligonucleotides, we have synthesised the novel phosphoramidite analogue of the 2'-deoxyriboside of 2-amino-6-methylsulfonylpurine. Following the incorporation of the analogue into DNA, the subsequent nucleophilic displacement of the methylsulfanyl group by alkoxide provides a convenient route to a variety of oligonucleotides containing O6-modified guanines.