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