Methotrexate α-Methyl Ester Methotrexate EP Impurity I（Amethopterin EP Impurity I） (4S)-4-[[4-[(2,4-diaminopteridin-6-yl)methyl-methylamino]benzoyl]amino]-5-methoxy-5-oxopentanoic acid Methotrexate EP Impurity I/Methotrexate 1-Methyl Ester/Methotrexate α-Methyl Ester/(4S)-4-[[4-[[(2,4-Diaminopteridin-6-yl)methyl]methylamino]benzoyl]amino]-5-methoxy-5-oxopentanoic acid Methotrexate EP Impurity I (Methotrexate-1-Monomethyl Ester) Methotrexate-1-monomethyl ester Methotrexate Impurity I L-Glutamic acid, N-[4-[[(2,4-diamino-6-pteridinyl)methyl]methylamino]benzoyl]-, 1-methyl ester