Fused pyrimidines. 7 . Nucleosides of pyrimidopyrimidinediones and pteridinediones as potential chemotherapeutic agents

Several nucleoside derivatives of pyrimido[4,5‐ d ]pyrimidine‐2,4(1 H ,3 H )‐dione 1 and 2,4{1 H ,3 H ‐pteridinedione 2 were prepared. Treating the appropriate silylated nucleobase with 1‐ O ‐acetyl‐2,3,5‐tri‐ O ‐benzoyl‐β‐D‐ribofura‐nose 3 in the presence of trimethylsilyl Inflate gave 4 and 8 which, upon debenzoylation, gave 5 and 9 , respectively. Treatment of 4 with phosphorus pentasulfide afforded the sulfur substituted compound 6 . Again, deprotection gave 7 . The arabinose derivatives were obtained by treating 1‐ O ‐acetyl‐2,3,5‐tri‐ O ‐benzoyl‐D‐arabinofuranose 10 with the silylated nucleobases to give 11 and 13 . Debenzoylation gave the free arabinonucleosides 12 and 14 respectively. The deoxy derivative 16 was prepared by the reaction of 1 with 1‐chloro‐3,5‐di‐ O ‐acetyl‐2‐deoxy‐D‐ribofuranose 15 . Deacetylation of 16 with methanolic ammonia gave the α‐anomer 17 .