Calcium Folinate Impurity 1

(4- (((2-amino-5- ((S) -4- (4- (((2-amino-4-oxo-1,4-dihydropteridin-6-yl) methyl) amino) benzamido) -4-carboxybutanoyl) -4-oxo-1,4,5,6,7,8-hexahydropteridin-6-yl) methyl) amino) benzoyl) -L-glutamic acid