[(7aR,7S)-7-({2-[(cyanomethyl)sulfanyl]acetyl}amino)-4-formyl-7-methoxy-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazin-3-yl]methyl (7aR,7S)-7-({2-[(cyanomethyl)sulfanyl]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-carboxylate