This paper described synthesis of 2',5'-oligoadenylate (2-5A) analogs containing the purine acyclonucleoside, 9-[(2'S,3'R)-2',3',4'-trihydroxybutyl]adenine (2). The ability of the analogs to activate recombinant human RNase L was evaluated using 5'-32P-r(C11U2C7)-3' as a substrate. The EC50 value (the concentration of the 2-5A required to cleave half of the RNA) of the parent 2-5A tetramer 13 was 1.0 nM, whereas those of the analog 14 incorporating 2 at the second position from the 5'-end and the analog 15 incorporating 2 at the third position from the 5'-end were 9.0 and 1.7 nM, respectively. The analogs 14 and 15 were only 9- and 1.7-fold less potent than the parent 2-5A 13 itself, in RNase L activation ability. Furthermore, the oligodeoxynucleotide containing 2 was more resistant to nucleolytic hydrolysis by snake venom phosphodiesterase (a 3'-exonuclease) than the unmodified oligodeoxynucleotide. Thus, incorporation of an acyclonucleoside into 2-5A may be useful for developing an antiviral agent based on the 2-5A system.