Pteridines pyridinium salts

Amino-5-nitrosopyrimidines also condense with benzoylacetonitrile, phenacyl-pyridinium bromide and acetonylpyridinium chloride in the presence of sodium cyanide to produce. 7-amino-6-pteridinyl ketones (63JOC1197). Pteridine syntheses from pyridinium salts are not limited to the preparation of pteridyl ketones since pyridinium acetamide... 

The pyridinium ylide (24) is obtained from the reaction of 8-bromotheophylline with pyridine. Alkylsulphonate salts of caffeine have been synthesized. A new purine-into-pteridine ring transformation has been discovered. For example, the quaternary salt (25) was obtained by direct alkylation of an appropriate xanthine with ethyl bromoacetate. Base-catalysed hydrolysis of (25) gave the pyrimidine (26), which could be cyclized to give the isoxanthopterin derivative (27). 

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