NEW MATERIAL:A compound shown by the formula I (A1 and A2 are H or ester residue; R is 1W5C alkyl; 1W5C alkylthio or OH) or its salt.

EXAMPLE: N-[4[[2,4-Diamino-6-pteridinyl)methyl]methylamine]benzoyl]7-meth ylthioglutamic acid shown by the formula IV.

USE: An antimalignant tumor agent. Suitable for a large amount of administration, having low toxicity.

PREPARATION: A raw material substance shown by the formula II is reacted with a 2,4-diamino-S-halomethylpteridine shown by the formula III in a solvent such as DMF, etc., at 15W120°C, to give an ester derivative shown by the formula Ia. Then, the ester derivative is treated with water and an inorganic base (e.g., NaOH, etc.,) in a solvent such as methanol, etc., preferably at 15W25°C, to give a compound shown by the formula Ib.