4-C-Substituted β-D- and β-L-nucleosides of formula (I) or (II), pharmaceutically acceptable salts or compositions thereof, are provided. These compounds and compositions are for use in the treatment of a host infected with human immunodeficiency virus (HIV) and hepatitis B virus (HBV). Related intermediates and processes for their production are also disclosed.Formulas (I) and (II), wherein R 1 is N 3