a purine nucleobase + D-ribose => a purine D-ribonucleoside + H2O
a purine nucleobase + d-ribose => a purine d-ribonucleoside + h2o
a purine nucleobase + D-ribose => a purine D-ribonucleoside + H2O
a purine nucleobase + d-ribose => a purine d-ribonucleoside + h2o