Enzyme studies with new analogues of folic acid and homofolic acid.

Many new analogues of dihydrofolate and dihydrohomofolate have been synthesized and tested as substrates of dihydrofolate reductase. Since all of the dihydroderivatives were efficiently reduced by the action of dihydrofolate reductase from L1210 mouse leukemia cells, the tetrahydroderivatives thus formed could be tested directly for cofactor and inhibitor activity with thymidylate synthetase. Although thymidylate synthetase of Escherichia coti showed relatively high sensitivity to changes in the amino acid part of the folate molecule, certain tetrahydro analogues were found to show cofactor activity. These included the aminoadipate, aminopimelate, /I-methylglutamate, and lysine analogues of pteroyhnonoglutamate. All of the tetrahydrohomofolates inhibited thymidylate synthetase to varying degrees, depending on the nature of the amino acid.