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2,4-Disubstituted pteridine derivatives  (1-3)  react with acyl radicals very selectively in position 7 by a nucleophilic Substitution mechanism  (4-10).  Oxidation of the 2-methylthio group proceeds with m-chloroperbenzoic acid in good yields to the corresponding 7-acyl-2-methylsulfonyl-4-aminopteridines  (11-16).  The methylsulfonyl group can easily been displaced by nucleophiles such as aliphatic amines  (27, 29, 32-42, 45),  cyclic amines  (56-  61),  aromatic amines  (30, 31)  and amino acids  (43-54).  Oxygen nucleophiles lead to 7-acyl-isopterin derivatives  (62-66).  The acyl side-chain is also prone to structural modifications leading to the corresponding secondary alcohols on NaBH 4  reduction  (74-77)  or to imino derivatives on reactions with amines  (67-73)  which can analogously been reduced to 2,4-disubstituted 7-( l-aminoalkyl)pteridines  (80-85).  An interesting H-shift was observed during heating of  32, 78  and  79  with benzylamine leading not to the benzylimines but the isomeric benzylideneamino derivatives  86-88.  Various acetylations by acetic anhydride (AC2O) gave  89-93  and reduction of the pyrazine moiety to the 5,6,7,8-tetrahydro-pteridine derivatives  94-96  proceeded in the expected manner. The characterization of ther newly synthesized pteridine derivatives was performed by  1 H-NMR spectra, UV-spectra and elemental analyses. Measurements of the basic pK a  values of a selection of 2,4,7-trisubstituted pteridines were pteridines to characterize the dication, monocation and the neutral species by their UV-spectra.

Synthesis of 7-Acyl-2,4-disubstituted Pteridines by Radical Nucleophilic Substitution and Displacement Reactions