Deamination of an anti-HIV carbocyclic adenine nucleoside, 9-[c-4,t-5-bis(hydroxymethyl)cyclopent-2-en-r-1-yl]-9H-adenine [(+/-)-BCA] and (+/-)-diamino-carbovir by adenosine deaminase under high-pressure (4 kbar) was carried out. Deamination of the former gave the corresponding (-)-hypoxanthine derivative whereas that of the latter produced (-)-carbovir having anti-HIV activity. The enantiomeric excess (e.e.) of both products was nearly 100%.