(2R)-2-{[(3Z)-4-(2-furyl)-5-oxo-3-aza-2-oxapent-3-en-5-yl]amino}-2-[(2R)-6-[(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]-7-oxo-1,2,4,5,6,7-hexahydropyrrolo[3,4-d][1,3]thiazin-2-yl]acetic acid