(7aR,7R)-7-{[(2R)-2-({[(7aR,7R)-7-{[(2R)-2-amino-2-phenylacetyl]amino}-3-chloro-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazin-4-yl]carbonyl}amino)-2-phenylacetyl]amino}-3-chloro-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazine-4-carboxylic acid