| The synthesis of eight new 5-fluoro- or 5-chloro analogues of 5,8-dideazaisofolic acid and N{dollar}spalpha{dollar}-(5,8-dideazaisopteroyl-L-ornithine is reported. In addition, the previously described 5-chloro-5,8-dideazaisofolic acid, was synthesized by two new procedures. The six analogues of 5,8-dideazaisofolic acid, were designed as specific inhibitors of thymidylate synthase (TS) and as efficient substrates of folylpolyglutamate synthetase (FPGS), in order to allow the evaluation of the effects of 5-halogenation, 2-methylation, and N{dollar}sp9{dollar}-methylation on enzyme activity. Analogues of N{dollar}spalpha{dollar}-(5,8-dideazaisopteroyl)-L-ornithine, were developed as reversed bridge inhibitors of FPGS. These analogues were designed to assess the effect of fluorination or chlorination at position 5 as well as methylation at position 2 on FPGS inhibition. A brief overview of antifolate cancer chemotherapy and a summary of folate metabolism provides the background for the development of these analogues. A review of inhibitors of the target enzymes TS and FPGS leads into the discussion of the design of the new analogues. The chemistry review emphasizes pertinent earlier work and is followed by a discussion of each of the reactions employed. The formation of the quinazoline nucleus, the lability of the fluorine substituent, the selectivity of heteroaromatic nitration, the protection of the 2-amino group, and other relevant chemical aspects are addressed in detail. The structural confirmation of the compounds by {dollar}sp1{dollar}H and {dollar}sp{lcub}19{rcub}{dollar}F nuclear magnetic resonance (NMR) spectroscopy and mass spectroscopy (MS) are covered in depth. From the preliminary biological data of the analogues as substrates or inhibitors of hog liver FPGS, it appears that the substrate activities of 5,8-dideazaisofolates correlate with the inhibitory potencies of the corresponding L-ornithine analogues; the introduction of the 5-fluoro group enhances FPGS substrate activity significantly, although not as much as 5-chlorination; replacement of a 2-amino group by 2-methyl increases binding to FPGS; and N{dollar}sp9{dollar}-methylation does not enhance FPGS substrate activities for the compounds tested. |
