7-halogenated 7-deaza-2'-deoxyxanthine 2'-deoxyribonucleosides

Abstract

The synthesis of the 7-halogenated derivatives 1b (7-bromo) and le (7-iodo) of 7-deaza-2'-deoxyxanthosine (1a) is described. A partial Br --> I exchange was observed when the demethylation of 6-methoxy precursor compound 4b was performed with Me3SiCl/NaI. This reaction is circumvented by the nucleophilic displacement of the MeO group under strong alkaline conditions. The halogenated 7-deaza-2'-deoxyxanthosine derivatives We show a decreased S-conformer population of the sugar moiety compared to the nonhalogenated 1a. They are expected to form stronger triplexes when they replace 1a in the 1 (.) dA (.) dT base triplet.