(2R)-3-{[(7aR,7S)-7-({2-[(cyanomethyl)sulfanyl]acetyl}amino)-3-(hydroxymethyl)-7-methoxy-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazin-4-yl]carbonyl}-2-[(3S)-3-carboxy-8-cyano-5-oxo-4-aza-2-oxa-7-thiaoct-3-yl]-5-(sulfanylmethyl)-3H,6H,2H-1,3-thiazine-4-carboxylic acid