Chemical Modification Potentiates the Biological Activities of 2 - 5 A and Its

Chemical modification of p5’A2’(p5’A2’),p5’A by a periodate oxidation/Schiff base formation/borohydride reduction cycle gave a series of 2-5A analogues in which the ribose of the 2’-terminal nucleotide was transformed to an N-substituted morpholine (azahexapyranose). 2’,5’-Oligoriboadenylate 5’-monophosphates bearing this modification were 5-10 times more potent as antagonists of the action of 2-5A or poly(I)*poly(C) than was unmodified p5’A2’p5‘A2’p5’A. Application of this modification to the tetramer triphosphate ppp5’AZ’p5’A2’p5’A2’p5’A resulted in an analogue with 10 times the activity of ppp5’A2’p5’A2’p5’A (2-5A trimer triphosphate) as an inhibitor of protein synthesis or activator of the 2-5A-dependent endoribonuclease. This new 2-5A analogue, the most potent 2-5A derivative reported to date, inhibited translation in extracts of mouse L-cells programmed with encephalomyocarditis virus RNA at a concentration of 10”’ M (concentration for half-maximal inhibition). All such N-substituted morpholine modified 2’,5’-oligoriboadenylates were found to be extremely resistant to degradation by Lcell extracts under conditions where unmodified 2-5A or its derivatives were quickly destroyed. These data demonstrate the necessity for an intact terminal ribose ring for the action of the 2-5A phosphodiesterase. Thus, extensive chemical modification of 2’ terminus of 2-5A may be possible without adversely affecting its biological activity while endowing it with other favorable properties such as resistance to degradation.