An improved method of preparing a sugar modified nucleoside analog
includes a protocol in which a hydroxy group of a sugar is selectively
deprotected and oxidized prior to nucleophilic modification of the
corresponding carbonyl group. The modified sugar is then coupled to a
heterocyclic base that is modified with a dual nucleophilic reagent in a
further step that provides N6-modified adenosine analogs with high
stereoselectivity.