CEFOPERAZONE SODIUM IMPURITY A [EP IMPURITY][5aR-[5aa,6ss(R*)]]-4-Ethyl-N-[1-(4-hydroxyphenyl)-2-oxo-2-[(1,4,5a,6-tetrahydro-1-PIPERAZINECARBOXAMIDE, 4-ETHYL-N-(1-(4-HYDROXYPHENYL)-2-OXO-2-((1,4,5A,6-TETRAHYDRO-1,7-DIOXO-3H,7H-AZETO(2,1-B)FURO(3,4-D)(1,3)THIAZIN-6-YL)AMINO)ETHYL)-2,3-DIOXO-, (5AR-(5A.ALPHA.,6.BETA.(R*)))-1-Piperazinecarboxamide, 4-ethyl-N-(1-(4-hydroxyphenyl)-2-oxo-2-((1,4,5a,6-tetrahydro-1,7-dioxo-3H,7H-azeto(2,1-b)furo(3,4-d)(1,3)thiazin-6-yl)amino)ethyl)-2,3-dioxo-, (5ar-(5aalpha,6beta(R*)))-N-((R)-2-(((5aR,6R)-1,7-dioxo-1,4,5a,6-tetrahydro-3H,7H-azeto[2,1-b]furo[3,4-d][1,3]thiazin-6-yl)amino)-1-(4-hydroxyphenyl)-2-oxoethyl)-4-ethyl-2,3-dioxopiperazine-1-carboxamideN-[(1R)-2-{[(5aR,6R)-1,7-Dioxo-1,4,6,7-tetrahydro-3H,5aH-azeto[2,1-b]furo[3,4-d][1,3]thiazin-6-yl]amino}-1-(4-hydroxyphenyl)-2-oxoethyl]-4-ethyl-2,3-dioxopiperazine-1-carboxamide