ABINITIO STUDY OF THE PROTONATION AND THE TAUTOMERISM OF THE 7-AMINOPYRAZOLOPYRIMIDINE MOLECULE

7-Aminopyrazolo{4,3-d]pyrimidine1 (see compound la in Scheme I) is an aromatic moiety present in several nucleosides of both biological and synthetic origins. Among them, formycin (7-amino-3/3-D-ribofuranosyl pyrazolo[4,3-d]pyrimidine) is of particular nterest (see compound lb in scheme I). Formycin is a C-nucleoside analogue of adenosine, which was first isolated from cultures of Norcardia Interforma.lb This nucleoside has been extensively studied due to its antiviral,2-4 antibiotic,lb immunodepressant,5 antitumor,5,6 and antimetabolic4 properties. Nevertheless, its clinical use is hampered by its ease of deamination by adenosine deaminase (E.C.3.5.4.4),7 the enzyme catalyzing the hydrolytic conversion of adenosine (and analogues) to inosine (and analogues). © 1990, American Chemical Society. All rights reserved.