'9 of the 3'-hydroxyl group in one (compounds 28 and 31) or all of the ribose residues (compounds 29 and 32) by 0-methyl functions. The introduction of 0-methyl groups allowed a study of the effect of this small ribose modification on the nucleolytic degradation of 2-5A. It has been shown19~ 20 that besides pppA2/p5'A2'p5'A (Le., compound 27c in Scheme V), di- and monophosphorylated as well as nonphosphorylated derivatives (ie, compounds 27b, ...