The invention relates to a compound of formula (I) ##STR1## Wherein: B is adenine, guanine or hypoxanthine Z is hydrogen or a negative charge R is --[CH.sub.2 CH(R.sup.1)--O].sub.n -R.sup.2, --CH.sub.2 CH.sub.2 X, in which R.sup.1 is hydrogen or (C.sub.1 -.sub.6) alkyl R.sup.2 is hydrogen or (C.sub.1 -.sub.6) alkyl n is a number from 1 to 6 X is OH, F, NR.sup.3 R.sup.4 R.sup.3 and R.sup.4 are independently from each other hydrogen or (C.sub.1 -.sub.6) alkyl and to methods of enzymatically treating these compounds with biocatalysts having cyclic phosphodiesterase activity.