5-substituted N-4-hydroxy-2 '-deoxycytidines and their 5 '-monophosphates:Synthesis, conformation, interaction with tumor thymidylate synthase, and in vitro antitumor activity

Convenient procedures are described for the synthesis of 5-substituted N-4- hydroxy-2'-deoxycytidines Ba,lb,d-h via transformation of the respective 5- substituted 3',5'-di-O-acetyl-2'-deoxyuridines la-c,e-h. These procedures i nvolved site-specific triazolation or N-methylimidazolation at position C(4 ), followed by hydroxylamination and deblocking with MeOH-NH3. Nucleosides Ba,b,d-h were selectively converted to the corresponding 5'-monophosphates Ga,b,d-h with the aid of the wheat shoot phosphotransferase system. Conform ation of each nucleoside in D2O solution, deduced from H-1 NMR spectra and confirmed by molecular mechanics calculations, showed the pentose ring to e xist predominantly in the conformation S (C-2'-endo) and the N-4-OH group a s the cis rotamer; Cell growth inhibition was studied with two L5178Y murin e leukemia cell lines, parental and 5-fluoro-2'-deoxyuridine (FdUrd);resist ant, the latter 70-fold less sensitive toward FdUrd than the former, With F dUrd-resistant L5178Y cells, 5-fluoro-N-4-hydroxy-2'-deoxycytidine (5e) cau sed almost 3-fold stronger growth inhibition than FdUrd; 5e was only some 3 -fold weaker growth inhibitor of the resistant cells than of the parental c ells. Thymidylate synthase inhibition was studied with two forms of the enz yme differing in sensitivities toward 5-fluoro-2'-deoxyuridine 5'-monophosp hate (FdUMP), isolated from parental and FdUrd-resistant L1210 cell lines; All N-4-hydroxy-dCMP (6a,b,d-h) and dUMP analogues studied were competitive vs dUMP inhibitors of the enzyme. Analogues 6b,d-h and 5-hydroxymethyl-dUM P, similar to N4-hydroxy-dCMP (6a) and FdUMP, were also N-5,N-10-methylenet etrahydrofolate-dependent mechanism-based, slow-binding inhibitors. 6-Chlol o-dUMP, 5-bromo-dUMP, and 5-iodo-dUMP, similar to dTMP, did not cause a tim e-dependent inactivation of the enzyme. Instead, they behaved as classic in hibitors of tritium release from [5-H-3]dUMP. 5-Bromo-dUMP and 5-iodo-dUMP showed substrate activity independent of N-5,N-10-methylenetetrahydrofolate in the thymidylate synthase-catalyzed dehalogenation reaction. The =N-OH s ubstituent of the pyrimidine C(4) prevented the enzyme-catalyzed release fr om the C(5) of Br- and I- (the same shown previously for H+). While FdUMP a nd 6a showed a higher affinity and greater inactivation power with the pare ntal cell than FdUrd-resistant cell enzyme, an opposite relationship could be seen with 5-hydroxymethyl-dUMP.