Patent ID: 8686140

Claim:
A method of purifying a salt of pemetrexed having a structure of formula (III), by salting-out of the salt of pemetrexed, wherein, if M 3 + is H + , then each of M 1 + and M 2 + is independently H + , Li + , Na + or K + , provided that both of M 1 + and M 2 + are not H + ; and if M 3 + is Li + , Na + or K + , then each of M 1 + and M 2 + is independently Li + , Na + or K + ; wherein the salting-out of the salt of pemetrexed comprises: a) adding an amount of one or more other water-soluble salts and optionally one or more water-miscible organic solvents to supersaturate the salt of pemetrexed in an aqueous solution, wherein the total molarity of the water-soluble salts is between 20% of the saturation concentration thereof and the saturation concentration thereof; b) adjusting the pH of the solution to a value of at least 5 to crystallize the salt of pemetrexed, wherein the adjusting of pH is unnecessary if the pH is already within this range; and c) crystallizing sufficiently and then separating the resultant solid by filtration or centrifugation; to obtain the salt of pemetrexed.