The present invention provides novel anhydrous polymorph forms of [(2R,3S,4R,5R)-5-(6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)]methyl nitrate (compound A), a selective adenosine A1 receptor agonist with a number of therapeutic uses including the treatment of elevated intra-ocular pressure. Also provided are methods for the preparation of the anhydrous polymorphic forms of compound A, pharmaceutical compositions and methods of treatment.