Nucleosides. 114. 5'-O-Glucuronides of 5-fluorouridine and 5-fluorocytidine. Masked precursors of anticancer nucleosides.

5'-O-Glucuronides of anticancer nucleosides, 5-fluorouridine and 5-fluorocytidine, were synthesized by three different methods. The best preparative procedure was the one starting from benzyl 5-O-(methyl 2', 3', 4'-tri-O-acetyl-beta-D-glucopyranosyluronate)-2,3-O-isopropylidene-beta-D-ribof uranoside (15) that was obtained almost quantitatively by condensation of benzyl 2,3-O-isopropylidene-beta-D-ribofuranoside (8) with methyl (2,3,4-tri-O-acetyl-alpha-D-glucopyranosyl bromide)uronate (2). After de-O-isopropylidenation of 15, the crystalline product, benzyl 5-O-(methyl 2', 3', 4'-tri-O-acetyl-beta-D-glucopyranosyluronate)-beta-D-ribofuranoside (16), was de-O-benzylated catalytically to 5-O-(methyl 2', 3', 4'-tri-O-acetyl-beta-glucopyranosyluronate)-D-ribofuranose (17). Compound 17 was acetylated to crystalline 5-O-(methyl 2',3',4'-tri-O-acteyl-beta-D-glucopyranosyluronate)-1,2,3-tri-O-acetyl-beta-D-ribofuranose (18) and condensed with trimethylsilylated 5-fluorouracil of 5-fluorocytosine in the presence of SnCl4 to afford the corresponding protected nucleosides 5 and 19 in good yields. Saponification of these compounds gave 5'-O-beta-D-glucuronides of 5-fluorouridine and 5-fluorocytidine (20 and 21) isolated as their crystalline N salts. These glucuronides were substrates of both bacterial and bovine beta-glucuronidase. They were, as expected, much less toxic against several leukemia cell lines in tissue culture.

Nucleosides. 116. 1-(beta-D-Xylofuranosyl)-5-fluorocytosines with a leaving group on the 3' position. Potential double-barreled masked precursors of anticancer nucleosides.

Syntheses of five pairs of cytosine and 5-fluorocytosinexylofuranosyl nucleosides in which the 3'-hydroxyl group is replaced by Cl, Br, OMs, or OTs are described. Those xylosyl nucleosides with a good leaving group at the 3' position exhibit good inhibitory activity against L5178Y and P815 mouse leukemic cells in vitro at rather low concentrations, and like that of ara-C this cytotoxicity is reversed by 2'-deoxycytidine but not by thymidine. Xylosylcytosines are not active against ara-C resistant lines of L5178Y and P815 cells; however, the corresponding 5-fluorocytosine analogues exhibit significant cytotoxicity against these ara-C resistant leukemic cell lines, and this activity is reversed by thmidine but not by deoxycytidine. These data support the "double-barreled" masked precursor hypothesis in that xylosyl-5-fluorocytosines substituted at the 3' position by a good leaving group exhibit activity akin to that of ara-C in the ara-C sensitive lines, while these nucleosides act as 5-fluoropyrimidines in the ara-C resistant lines.

Nucleosides. 102. Synthesis of some 3'-deoxy-3'-substituted arabinofuranosylpyrimidine nucleosides.

The synthesis of some 3'-deoxy-3'-substituted arabinofuranosylcytosine (4a-d) and uracil (7a-d, 8a-d, X =Br, I, N3, SCN) nucleosides was accomplished by treatment of the requisite 2',3'-anhydrolyxofuranosylpyrimidine nucleoside (5,6a,b) with the appropriate ammonium salt in refluxing ethanol. Cleavage of the oxirane ring provided the desired 3'-deoxy-3'-substituted pyrimidine nucleosides (4a-d, 7a-d, and 8a-d). In vitro screening of compounds 4a-d, and 7a-d, with L5178Y cells in culture showed no significant inhibitory properties.

Acyloxy neighboring-group participation in the acid-catalyzed cleavage of methyl 2,3-anhydro-beta-D-ribofuranoside.

The reaction of methyl 2,3-anhydro-beta-D-ribofuranoside with hydrogen bromide in an acetic acid-acetic anhydride solution leads to the formation of methyl 2,3-di-O-acetyl-5-bromo-5-deoxy-alpha,beta-D-xylofuranoside. Similar treatment of methyl 2,3-anhydro-5-O-benzoyl-beta-D-robofuranoside provided methyl 2-O-acetyl-3-O-benzoyl-5-bromo-5-deoxy-alpha,beta-D-xylofuranosides. The position of halogen substitution was ascertained by hydrogenolysis to the resultant 5-deoxy sugars, which were characterized by their n.m.r. spectra. Confirmation of the structural assignment for methyl 2-O-acetyl-3-O-benzoyl-5-deoxy-alpha,beta-D-xylofuranoside was obtained by synthesis from 1,2-O-isopropylidene-alpha-D-xylofuranose. The formation of the 5-bromo derivatives under the reported conditions probably occurred through the intermediacy of the 3,5-acyloxonium ions. Similar conversions were observed when the starting compound was treated with hydrogen chloride, acetyl bromide, or acetyl chloride in acetic acid-acetic anhydride solutions.

Nucleosides LXXXIX. Synthesis of 1-(2-chloro-2-deoxy-alpha- and -beta-D-arabinofuranosyl)cytosines.

1-(2-Chloro-2-deoxy-beta-D-arabinofuranosyl)cytosine (16) and its alpha anomer (18) were synthesized by direct condensation of 3,5-di-O-acetyl-2-chloro-2-deoxy-alpha-D-arabinofuranosyl bromide with trimethylsilylated N-4-acetylcytosine in the absence of catalyst. A new and convenient method for the synthesis of 1,3,5-tri-O-acetyl-2-chloro-2-deoxy-alpha-D-arabinofuranose from methyl 3,5-di-O-benzyl-alpha,beta-D-ribofuranoside is described.