Leucovorin (Calcium Folinate) Imp B (EP):(2S)-2-[[4-[[[(6RS)-2-amino-5-formyl-4-oxo-1,4,5,6,7,8-hexahydropteridin-6-yl]methyl]formylamino]benzoyl]amino]pentanedioic acid (5,10-diformyltetrahydrofolic acid).