(7aR,7S)-3-{1-[(7aR,7S)-4-carboxy-7-methoxy-6-oxo-7-{[2-(thiophen-2-yl)acetyl]amino}-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazin-3-yl]-4-oxo-3-aza-2,5-dioxahex-6-yl}-7-methoxy-6-oxo-7-{[2-(thiophen-2-yl)acetyl]amino}-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazine-4-carboxylic acid