<prompt> Which of the following antitumor agents works by impairing de novo purine synthesis?Acyloguanosine5-FluorouracilMethotrexate antifolateAllopurinol  <response>: Among the given antitumor drugs, methotrexate which is folic acid analog act as a folate antagonist that inhibit the conversion of DHFADihydro folic acid to tetra hydrofolic acid THFA. We know that follic acid is utilized in de novo synthesis. Where as 5-fluorouracil act as pyrimidine antagonist by inhibiting the conversion of deoxyuridine acid to deoxythymidylic acid. And Allopurinol act by inhibiting uric acid synthesis. ESSENTIALS OF MEDICAL PHARMACOLOGY-SEVENTH EDITION -K.D TRIPATHI Page:864,862,216 