(7aR,7R)-7-{[(3Z)-4-(2-furyl)-5-oxo-3-aza-2-oxapent-3-en-5-yl]amino}-3-[({[(7aR,7R)-7-{[(3Z)-4-(2-furyl)-5-oxo-3-aza-2-oxapent-3-en-5-yl]amino}-3-(hydroxymethyl)-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazin-4-yl]carbonyl}oxy)methyl]-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazine-4-carboxylic acid