2,4(1H,3H)-Pyrimidinedione, 1-(2-deoxy-b-D-erythro-pentofuranosyl)-5-methyl- and 2,4(1H,3H)-Pyrimidinedione, 1-(2-deoxy-b-D-erythro-pentofuranosyl)-5-ethyl- AIDS-212441 AIDS212441