Methotrexate analogues—27: Dual inhibition of dihydrofolate reductase and folylpolyglutamate synthetase by methotrexate and aminopterin analogues with a γ-phosphonate group in the side chain

Abstract

γ-Phosphonate analogues of methotrexate (MTX) and aminopterin (AMT) were synthesized from 4-amino-4-deoxy- N 10-methylpteroic acid and 4-amino-4-deoxy- N 10-formylpteroic acid, respectively, by reaction with methyl d,1-2-amino-4-phosphonobutyrate followed by gentle alkaline hydrolysis. The products were compared with the corresponding d,l-homocysteic acid derivatives as inhibitors of dihydrofolate reductase and folylpolyglutamate synthetase, and as inhibitors of cell growth in culture. The γ-phosphonates were somewhat less active than either the γ-sulfonates or the parent drugs as inhibitors of murine dihydrofolate reductase. The MTX γ-sulfonate and γ-phosphonate analogues were equally inhibitory toward mouse liver folylpolyglutamate synthetase ( K i = 190 μM), but in the AMT series the γ-phosphonate ( K i = 8.4 μM) was more potent than the γ-sulfonate ( K i = 45 μM). The AMT analogues were consistently more inhibitory than the MTX analogues against cultured L1210 murine leukemia cells, but neither the γ-phosphonates nor the γ-sulfonates were as potent as their respective parent drugs. The γ-phosphonate analogue of MTX was three times more potent than MTX against the MTX-resistant mutant line L1210/R81, but the AMT γ-phosphonate was less potent than AMT; however, these differences were small in comparison with the level of resistance to all these compounds in the L1210/R81 line. The results suggest than n 10-methyl and n 10-unsubstituted compounds altered at the γ-position do not necessarily follow identical structure-activity patterns in every test system.