Biopterin chemical structure

Fig. 6.1.3 The chemical structure of the three oxidation stages of biopterin...

The natural cofactor of the AAHs, BH4 (Scheme 2), is a heterocyclic compound chemically classified as a pteridine that includes a fused pyrimidine and pyrazine rings. As many other naturally occurring pteridines BH4 has a pterin structure, which includes an amino substituent in position 2 and an oxo group in position 4 of the pyrimidine ring. The term biopterin is reserved for pterins with a dihydroxypropyl group in position 6. 

The two oxidation states of (17) that are relevant in biopterin-dependent redox reactions are the four-electron and two-electron reduced forms, tetrahydrobiopterin (19) and p-quinonoid dihydrobiopterin (20), respectively. The oxidation state between these two, i.e. a radical, may also be relevant though it has not been detected as an intermediate in enzymatic reactions. Structurally, pteridines and flavins are rather similar and hence show similar chemical behavior in many respects. As a redox coenzyme, (19) is not encountered nearly as frequently as nicotinamides or flavins. It is, however, the cofactor of three very... 

There was no obvious explanation for the side-chain chirality of biopterin or its related aromatic pterin derivatives in the CD spectra. This fact requires that structural determination of all newly found pterins must be carried out by comparison with optically active authentic samples. Indeed, almost all compounds have been obtained as aromatic pterins through the exploration of naturally occurring rare pterins and their structures have been generally determined by chemical syntheses from sugar derivatives, as descried in Sect. 3.2. From the viewpoint of characteristic fluorescence emissions, the application of FDCD to the configurational analyses of aromatic pterin derivatives has been carried out in previous studies [64,65]. Since FDCD analysis of aromatic pterins is approximately 100 times more sensitive than normal... 

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