CHEMICAL SYNTHESIS AND BIOLOGICAL CHARACTERIZATION OF PHOSPHOROTHIOATE ANALOGS OF 2',5'-3'-DEOXYADENYLATE TRIMER

In continued studies to elucidate the requirements for binding to and activation of the 2',5'-oligoadenylate (2-5A) dependent endoribonuclea se (RNase L), four 2-SA trimer analogs were examined to evaluate the e ffect of chirality of phosphorothioate substitution on biological acti vity. The chemical syntheses and purification of the four isomers of P -thio-3'-deoxyadenylyl-(2'-5')-3'-deoxyadenosine, by the phosphoramidi te approach, is described. The isolated intermediates were characteriz ed by elemental and spectral analyses. The fully deblocked compounds w ere characterized by H-1 and P-31 NMR and HPLC analyses. The 2',5'-(3' dA)3 cores with either Rp or Sp chirality in the 2',5'-internucleotide linkages will bind to but will not activate RNase L. This is in contr ast to 2',5'-A3 core analogs with either RpRp or SpRp phosphorothioate substitution in the 2',5'-internucleotide linkages which can bind to and activate RNase L. There are also marked differences in the ability of the 2',5'-A3 analogs to activate RNase L following introduction of the 5'-monophosphate. For example, the 5'-monophosphates of 2',5'-(3' dA)3-RpRp and 2',5'-(3'dA)3-SpRp can bind to and activate RNase L, whe reas the 5'-monophosphates of 2',5'-(3'dA)3-RpSp and 2',5'-(3'dA)3-SpS p can bind to but can not activate RNase L.