Mupirocin calcium Impurity: [2E,8[2S,3S(1S,2S)]]-5,9-anhydro-2,3,4,8-tetradeoxy-8-[[3-(2-hydroxy-1-methylpropyl)oxiranyl]methyl]-3-methyl-L-talo-Non-2-enonic acid 10-carboxydecyl ester(Pseudomonic Acid E).