Folate analogs. 35. Synthesis and biological evaluation of 1-deaza, 3-deaza, and bridge-elongated analogs of N10-propargyl-5,8-dideazafolic acid

Structural modifications at the pyrimidine ring and at the C-9,N-10-bridge region of the thymidylate synthase (TS) inhibitors N-10-propargyl-5,8-dideazafolate (1; PDDF; CB 3717), 2-desamino-N10-propargyl-5,8-dideazafolate (2, DPDDF), and 2-desamino-2-methyl-N-10-propargyl-5,8-dideazafolate (3, DMPDDF) have been carried out. Methods for the synthesis of 2-desamino-N-10-propargyl-1,5,8-trideazafolate (4), 2-desamino-2-methyl-N-10-propargyl-3,5,8-trideazafolate (5a), and 2-desamino-2-methyl-N10-propargyl-5,8-dideaza-1,2-dihydrofolate (6) have been developed. The bridge-extended analogues isohomo-PDDF (7) and isohomo-DMPDDF (8) contain an additional methylene group interposed between N-10 and the phenyl ring of 1 and 3, respectively. All new compounds were evaluated as inhibitors of TS and the growth of tumor cells in culture. Selected analogues were tested as substrates of folylpolyglutamate synthetase (FPGS) and striking differences in substrate activity were observed among these compounds, indicating that structural modifications at the pyrimidine ring of classical antifolates profoundly influence their polyglutamylation. Enzyme inhibition data established that both N1 and N3-H of the pyrimidine ring are essential for efficient binding of quinazoline-type antifolates to human TS.