(2R)-3-{[(7aR,7S)-7-({2-[(cyanomethyl)sulfanyl]acetyl}amino)-7-methoxy-3-methyl-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazin-4-yl]carbonyl}-2-[(3S)-3-carboxy-5-oxo-5-(thioformyl)-4-aza-2-oxapent-3-yl]-5-{[(1-methyl-1,2,3,4-tetraazol-5-yl)sulfanyl]methyl}-3H,2H,6H-1,3-thiazine-4-carboxylic acid