(7aR,7S)-7-({2-[(2-{[(7aR,7S)-4-carboxy-7-methoxy-3-{[(1-methyl-1,2,3,4-tetraazol-5-yl)sulfanyl]methyl}-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazin-7-yl]amino}-2-oxoethyl)disulfanyl]acetyl}amino)-7-methoxy-3-{[(1-methyl-1,2,3,4-tetraazol-5-yl)sulfanyl]methyl}-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazine-4-carboxylic acid