Synthesis and biological activity of 5-fluoro-4'-thiouridine and some related nucleosides.

The synthesis of a series of 4'-thio-5-halogenopyrimidine nucleosides, including the 5-fluoro, chloro, bromo and iodo derivatives, has been carried out by condensation of the 2,4-bis-O-trimethylsilyl derivatives of the corresponding pyrimidine bases with the protected 4-thio-D-ribofuranosyl chloride. Among these, the alpha and beta anomers of 4'-thio-5-fluorouridine inhibited the growth of leukemia L1210 cells at concentrations of 4 x 10(-7) and 2 x 10(-7) M, respectively, and that of S. faecium at 4 x 10(-9) and 6 x 10(-10) M, respectively. These compounds retained marked activity against strains of S. faecium resistant to 10(-3) M 5-fluorouracil or 5-fluorouridine. As determined in S. faecium cultures, 4'-thio-5-fluorouridine decreased the total protein content of the cells more markedly than it did their RNA or DNA content. X-Ray crystallography showed that substitution of sulfur for the oxygen in the carbohydrate ring markedly changes the conformation of that moiety.