Pemetrexed EP Impurity B

(2S,2’S)-2,2′-((4,4′-(((S)-2,2′-diamino-4,4′,6-trioxo-4,4′,5,6,7,7′-hexahydro-3H,3’H-[5,6′-bipyrrolo[2,3-d]pyrimidine]-5,5′-diyl)bis(ethane-2,1-diyl))bis(benzoyl))bis(azanediyl))dipentanedioic acid