The objectives of this proposal are to prepare and test certain representative members of three families of nucleosides. Each family incorporates a C3-branched tetrose as the glycon component of the nucleoside. Specifically, 9-(3-C-2- hydroxymethyl)-beta-D-erythrofuranosyl)adenine, 1-(3-C- hydroxymethyl-beta-D-threofuranosyl)cytosine, 9-(3-C- hydroxymethyl-beta-D-threofuranosyl)adenine and 9-(3-C- hydroxymethyl-beta-D-erythrofuranosyl)guanine will be prepared and tested as antiviral agents and immune system modulators.