The condensation of pyridoxal 5-phosphate (I) with ethylenediamine (II) in methanol by means of NaOH gives the corresponding diimine (III), which is reduced with hydrogen over Pt/C in methanol/water yielding the expected diamine (IV). The reaction of (IV) with bromoacetic acid (V) by means of NaOH in methanol/water affords the N,N'-diacetic acid derivative (VI), which is finally treated with MnCl2 in water containing NaOH.