[en] The known methods for the synthesis of pteridines fused to other heterocycles, including natural compounds, are reviewed. The data are systematized according to the type of the fused ring.

[en] The formation of singlet oxygen by photodynamic agents is shown to be notably amplified by the combination of UV-B radiations plus tryptophan in aqueous medium because of the formation of N-formylkynurenine, a tryptophan photoproduct which is also a good photosensitizer. The biological implication of these effects is discussed. (author)

No abstract available

[en] The value of serum neopterin as tumor marker was verified in 104 breast cancer patients. Based on the results the evaluation of neopterin cannot be recommended, neither for the decision of treatment after primary therapy nor for monitoring of the breast cancer. (author)

No abstract available

[en] Short communication

No abstract available

[en] Spectrophotometric titration of tetrahydropterins with incremental amounts of N₃ showed that 6,7-dimethyl-7,8-dihydropterin was an intermediate in the oxidation of 6,7-dimethyltetrahydropterin at the two electron-equivalent oxidation point. The eventual end product at four electron equivalents was 6,7-dimethylpterin. In the case of unsubstituted tetrahydropterin, the dihydro form was clearly not an exclusive product at the two electron equivalent point, and this was attributed to the disproportionation of different forms of dihydropterin to tetrahydropterin and pterin. The azide radical oxidized tetrahydropterins to trihydropterin radicals, PnH₃, with overall second-order rate constants at pH 7 of 4.1, 3.8, and 2.9 X 10⁹ M^-1 s^-1 for tetrahydropterin, 6,7-dimethyltetrahydropterin, and 6-carboxylated tetrahydropterin, respectively. At pH 10 the rate constants are slightly larger due to the presence of the deprotonated enolate forms of tetrahydropterins. Spectra vary somewhat with substitution in the pterin molecule, but all species have a strong peak (ε ∼ 9000 M^-1 cm^-1) near 320 nm and lower absorption above this, with a tail extending to 580 nm

[en] The hydration of pteridine was investigated over the pH range 1 to 10 at 25.0⁰, utilizing a spectrophotometric method. Above pH 7.5, the hydration of this heterocyclic Schiff base is catalyzed by hydroxide ions and by the basic component of a number of buffers (imidazole, 1,2-dimethylimidazole, borate, carbonate, triethylamine). The general base catalysis conforms to a Bronsted plot with an exponent β = 0.64 +- 0.03. Below pH 7.5, the reaction is catalyzed predominantly by hydronium ions. The value of 0.50 +- 0.02 for the ratio k/sub H₃O⁺//k/sub D₃O⁺/ indicates a preequilibrium protonation of pteridine. However, in a few instances the acidic component of buffers capable of bifunctional catalysis (H₂PO₄^-, H₂AsO₄^-, and HCO₃^- also exhibited an enhancement in the rate of hydration. The solvent isotope effect for water catalysis, k/sub H₂O//k/sub D₂O/, has a value of 3.4 +- 0.4 which is similar to those of a number of other reactions involving water in a cyclic mechanism. (auth)

[en] The synthesis of biopterin, D(and L)-erythro-neopterins, and their derivatives having a substituent at the 2-amino group via the 2-methylthio analogues is described. The 2-(methylthio)pteridines were synthesized by condensation of 4,5-diamino-6-hydroxy-2-(methylthio)pyrimidine with 5-deoxy-L-arabinose and D(and L)-arabinose phenylhydrazones, followed by oxidation with K₃[Fe(CN)₆] and O₂ in the presence of KI in an acidic solution, respectively. Aminolysis of these thioethers with ammonia and other amines in the presence of acetic acid gave the title compounds. (author)