Reaction of 5,6,7,8‐Tetrahydropterin with Iron(III) Acetylacetonate. Detection of Radical Cations by Electrospray Ionization Mass Spectrometry

The experimental conditions developed for the detection of rather stable radical cations in solution by electrospray‐ionization mass spectrometry (ESI‐MS) of a Fe II complex of 2‐amino‐5,6,7,8‐tetrahydro‐5‐methylpteridin‐4 (3 H )‐one ( 1c ) are used to observe the formation of the more unstable radical cations formed from 2‐amino‐5,6,7,8‐tetrahydropteridin‐4(3 H )‐one ( 1a ) and tris(pentane‐2,4‐dionato)iron(III) ([Fe III (acac) 3 ]; 4 ) and to monitor their oxidation to the corresponding p ‐quinonoid dihydropterin complexes. These results contribute to the understanding of the important role played by 6β‐5,6,7,8‐tetrahydro‐ L ‐biopterin ( 1b ; a homologue of 1a ) together with iron as constituent of some cofactors. The complexes obtained from 1a and iron may be considered, e.g. as a model of the cofactor of the phenylalanine hydroxylase. Moreover, we describe an improved synthesis of 1c .