This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunomodulators, Subject name: Pharmacology
[{'content': 'Which of the following antitumor agents works by impairing de novo purine synthesis? \nSelect and explain. \nA. Acyloguanosine, B. 5-Fluorouracil, C. Methotrexate (antifolate), D. Allopurinol', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Among the given antitumor drugs, methotrexate which is folic acid analog act as a folate antagonist that inhibit the conversion of (DHFA)Dihydro 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', 'role': 'assistant'}]