Synthesis and antitumor activity of an acyclonucleoside derivative of 5-fluorouracil

The pyrimidine acyclonucleoside 5-fluoro-1-[(2-hydroxyethoxy)methyl]uracil (3) was synthesized as part of a program aimed at the development of new 5-fluorouracil derivatives with fewer side effects and a broader margin of safety. Condensation of 5-fluoro-2,4-bis[(trimethylsilyl)oxy]pyrimidine with 2-acetoxyethyl acetoxymethyl ether (6) in the presence of SnCl4 afforded the acetate ester 7, which on deprotection with NaOMe gave 3 in 50-60% overall yield. The 5-bromo and 5-iodo analogues 10 and 11, respectively, were obtained similarly. Reaction of 5-fluoro-4-(methylthio)-2-[(trimethylsilyl)oxy]pyrimidine with 2-acetoxyethyl acetoxymethyl ether and SnCl4, followed by ammonolysis, yielded 5-fluoro-1-[(2-hydroxyethoxy)methyl]cytosine (12). Deamination of 12 with nitrous acid produced 3, thereby confirming that alkylation of 5-fluoro-2,4-bis[(trimethylsilyl)oxy]pyrimidine had occurred at N1. The ID50 of 3 against L1210 mouse leukemia cells in culture was 1.7 x 10(-5) M, as compared with 1 x 10(-6) M for FU. The 5-fluorocytosine analogue 12 was inactive at up to 1 x 10(-4) M, and the other halogenated derivatives 10 and 11 had no effect even at 1 x 10(-3) M. When 3 was given ip in water to P388 leukemic mice at 400 mg/kg (b.i.d. x 4) or 240 mg/kg (q.d. 1-9), a 75% increase in survival was observed relative to untreated controls, and there was no evidence of any host toxicity.