Purines pyrimido pyrimidines

The pKz values of pyrimido[4,5-rf]pyrimidin-4-one and pyrimido[4,5-rf]pyrimidine-4-thione have been determined to be 7.20 and 6.23, respectively. When compared with the pjKa values of the corresponding purine and pteridine analogs, it can be seen that the pyrimido[4,5-d]pyrimidines are more acidic. The greater acidity of these compounds can probably be attributed to their lack of ability to form strong internal hydrogen bonds (58JOC1451). 

Nucleoside Pyrophosphates. - The synthesis of 8-aryl-3-P-o-ribofuranosylimiazo[2,l-i]purine 5 -phosphates (122) from AMP or ATP has been described. To access these fluorescent nucleotide derivatives, a combination of Kornblum oxidation reaction and imidazole formation was employed. For this conversion, the appropriate adenosine phosphate, present in its free acid form, was treated with p-nitro-acetophenone in DMSO in the presence of DBU. Treatment of a 5-(chloroethyl)-4-(triazole-l-yl)pyrimidine-nucleoside with benzylhydrazine offered the 6,6-bicyclic pyrimido-pyradazin-7-one, the precursor to (123). This triphosphate was used as a substrate for DNA polymerases. ... 

Nucleophilic Displacement. Sulfones can be displaced by a variety of nucleophiles, the most common of which are the amines. Using this cleavage technique, a range of libraries, including pyrimidines, pyrimido[4,5-iflpyrimidines, purines, and triazines, each possessing a diverse variety of amine functionalities, have been prepared. 

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