The title compound is prepared by two methods. Chlorination of 2',3'-O-isopropylideneinosine-5'-uronic acid (I) with SOCl2 in the presence of DMF produces the chloropurine acid chloride (II), which is further converted into the amide (III) upon treatment with ethylamine. Subsequent displacement of the purine 6-chloro group of (III) with cyclopentylamine (IV) furnishes the cyclopentylamino purine (V). Finally, acidic ketal hydrolysis in (IV) gives rise to the target compound.

Alternatively, the inosine uronic acid (I) is converted to ethyl ester (II) by sequential treatment with thionyl chloride and then ethanol. Subsequent reaction with acetic anhydride in pyridine gives rise to diacetate (III). Chlorination of the inosine ring of (III) to produce (IV) is accomplished by treatment with phosphoryl chloride in the presence of tetraethylammonium chloride. Displacement of the 6-chloro group of (IV) with cyclopentylamine (V) yields amino purine (VI). Finally, aminolysis of the ester groups of (VI) with ethanolic ethylamine leads to the title compound.