Synthesis of 5′-functionalized adenosine: suppression of cyclonucleoside formation

A new method of preparation for 5′-amino-2′,3′-isopropylidene adenosine 1, an important precursor to many adenosine derivatives, is described. This procedure suppresses the undesired intramolecular cyclization and does not require chemical protection of the exocyclic amino group of the adenine ring. The use of a 5′-phophate triester activating group is representative of natural biological substitution at this position, which likely contributes to its greater stability and selective reactivity. This sequence is efficient and should allow easy access to compounds of type 1 in high yield.