4-Amino-1-[(2R,3RS,5S)-2-(hydroxymethyl)-3-oxido-1,3-oxathiolan-5-yl]-2(1H)-pyrimidinone; [2R-(2α,3αβ,5α)]-4-Amino-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]-2(1H)-pyrimidinone S-Oxide; [2R-(2α,3αβ,5α)]-4-Amino-1-[2-(hydroxymethyl)-3-oxido-1,3-oxathiolan-5-yl]-2(1H)-pyrimidinone