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 (3H)-one (Ic) are used to observe the formation of the more unstable radical cations formed from 2-amino-5,6,7,8-tetrahydropteridin-4(3H) (la) 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 6 beta-5,6,7,8-tetrahydro-L-biopterin (Ib; a homologue of la) together with iron as constituent of some cofactors. The complexes obtained from la 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.