Synthesis and Biological Activity of Folic Acid and Methotrexate Analogues Containing l-threo-(2S,4S)-4-Fluoroglutamic Acid and dl-3,3-Difluoroglutamic Acid

The stereospecific syntheses of L-threo-gamma-fluoromethotrexate (1t) and L-threo-gamma-fluorofolic acid (3t) are reported. Compounds 1t and 3t have no substrate activity with folylpoly-gamma-glutamate synthetase isolated from CCRF-CEM human leukemia cells, and compound 1t inhibits human dihydrofolate reductase at similar levels as methotrexate. The synthesis of DL-3,3-difluoroglutamic acid (6) and its incorporation into DL-beta,beta-difluorofolic acid (4) are also reported. Compound 4 acts as a better substrate for human CCRF-CEM folylpoly-gamma-glutamate synthetase than folic acid (V/K = ca. 7-fold greater). Thus, replacement of the glutamate moiety of methotrexate and folic acid with 4-fluoroglutamic acid and 3,3-difluoroglutamic acid results in folates and antifolates with altered polyglutamylation activity.