Regular ArticleThe anti-cancer drug, fluorouracil (5-FU), has been used to treat stomach cancer and breast cancer, but strong side effects are a serious problem.1) Therefore, the chemical modification of 5-FU has been attempted to improve absorption and reduce side effects.2,3) 5Ј-Deoxy-5-fluorouridine (doxifluridine, 5Ј-DFUR), which is a prodrug of 5-FU, has been applied to malignant tumors.The synthetic methods for nucleotides were reported using mixture of diphosphorus pentaoxide and phosphoric acid, 4) and polyphosphoric acid. 5,6) The phosphorylation reaction by these agents required high temperature such as 85-100°C. Since then, Yoshikawa et al. demonstrated the synthesis of adenosine 5Ј-phosphate by the reaction of adenosine with phosphoryl chloride in triethyl phosphate at Ϫ10-0°C.
7)Furthermore, the synthetic method for guanosine derivatives with phosphorus trichloride 8) were demonstrated. Because of the phosphorylation with these agents was accompanied by various side reactions, the protection of the other functional groups was required before phosphorylation. In addition, the experimental operation of phosphorylation with these agents was extremely complicated.We succeeded in the phosphorylation of nucleosides and nucleotides using inorganic phosphorylating agents such as cyclo-triphosphate 9,10) and monoimido-cyclo-triphosphate.
11)Phosphorylation with these agents can be achieved by a onepot reaction in aqueous solution at 25-40°C without side reactions. Sodium cyclo-triphosphate, Na 3 P 3 O 9 (P 3m ), and sodium monoimido-cyclo-triphosphate, Na 3 P 3 O 8 NH (MCTP) are simple and efficient inorganic phosphorylating agents. As shown Fig. 1, P 3m and MCTP have six-membered rings composed of three and two P-O-P linkages, respectively. In the phosphorylation of nucleosides 9) and nucleotides 10) by P 3m , the 2Ј-and 3Ј-OH groups of the b-D-ribofuranosyl unit on the nucleosides and nucleotides were selectively phosphorylated with the yield of 80-97% without protection of the other hydroxyl groups. In the reaction of nucleoside or nucleotides and P 3m , the main products were 3Ј-monophosphate or 3Ј,5Ј-diphosphate derivatives. In the case of MCTP, the 2Ј-and 3Ј-OH groups of the b-D-ribofuranosyl unit on the nucleosides and nucleotides were phosphorylated to give 2Ј-and 3Ј-diphosphoramidophosphate esters with the yield of 14-60%.11) And 2Ј-diphosphoramidophosphate esters were dominant.In the present work, we studied the reaction of 5Ј-DFUR with P 3m or MCTP in aqueous solution in order to synthesize phosphate derivatives of 5Ј-DFUR, and then investigated the reactivity of the 2Ј-and 3Ј-OH groups of the b-D-ribofuranosyl unit.
Results and DiscussionPhosphorylation of 5 -DFUR with P 3m Phosphorylation was carried out according to the previously described method. [12][13][14] HPLC analysis served as a tool for evaluating the yields of products by their peak areas. HPLC condition was as follow; TSKgel SAX column, column temperature of 40°C, 0.33 M potassium chloride solution as eluent, flow rate of 1.0 ml/min,...