Synthesis and biological activity of novel 5-fluoro-2 '-deoxyuridine phosphoramidate prodrugs

A series of novel haloethyl and piperidyl phosphoramidate FdUMP prodrug ana logues has been synthesized, and the growth inhibitory activity of these co mpounds has been evaluated against L1210 mouse leukemia cells. All compound s exhibited potent inhibition of L1210 cell proliferation with IC50 values in the nanomolar range. Growth inhibition was reversed by the addition of 5 muM thymidine, suggesting a mechanism of action involving the intracellula r release of FdUMP. P-31 NMR studies carried out on model haloethyl phospho ramidates confirm the release of nucleotide via cyclization of the phosphor amidate anion to the aziridinium ion intermediate followed by hydrolysis of the P-N bond. The data suggests that <50% of the prodrug is converted to F dUMP intracellularly by this pathway. Piperidyl phosphoramidate analogues a re also converted to nucleotide intracellularly, presumably by the action o f an endogenous phosphoramidase.