Pteridines, XC Syntheses, Oxidations, Properties, and Reactions of 2-Thiopteridine-4,6, 7- trione Derivatives

A new efficient synthesis for 2-thiopteridine-4,6,7-triones (6-10, 15) has been found in the condendation of the appropriate 5,6-diaminopyrimidine (1-5, 14) with oxalic acid in DMF. Analogous condensations with dimethyl oxalate led to S-alkylation probably via an intermediate O-methylation of the DMF. 8-Methyl-2- thiopteridine-4,6,7-trione (10) shows a ring contraction to 9-methyl-2-thioxanthine (13) on base treatment. Oxidations by H20 2 and KMn04 respectively lead to the corresponding 2-sulfinate 22 and the 2-sulfonates 17 -19. Oxidative desulfurization takes place in formic acid with H 20 2 forming first the sulfinate 22, which then eliminates S02 to give pteridine-4,6,7-trione (23). Nucleophilic displacements of the 2-sulfonate group by ammonia and amines form the corresponding leucopterin derivatives 20, 21 and 24. The newly synthesized compounds have been characterized by elemental analyses, UV-spectra and pKa-determinations. The ionization sequences of the acidic hydrogens have been assigned based on these physical data