As the 2-substituted adenosine derivatives having formula [I] in which R1, R2 and R3 each independently represent a substituent other than a hydrogen atom, 2',3',5'-tri-O-acyl derivatives, 5'-O-acyl derivatives, 5'-O-aralkyl derivatives, 3'-O-aralkyl derivatives, 5'-phosphoric esters and cyclic 3',5'-phosphoric esters of the compounds enumerated in Tables 1(A) and (B) can be mentioned.