| pubmed-article:7420353 | pubmed:abstractText | 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. | lld:pubmed |
