3-Amino-2-(4-(((5aR,6S)-6-methoxy-1,7-dioxo-1,3,4,5a,6,7-hexahydroazeto[2,1-b]furo[3,4-d][1,3]thiazin-6-yl)carbamoyl)-1,3-dithietan-2-ylidene)-3-oxopropanoic Acid