The structure of methotrexate, a drug used to treat cancer, resembles that of:

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Methotrexate is a structural analogue of folic acid (also called folate) and thus inhibits the action of the enzyme dihydrofolate reductase, which is necessary for the synthesis of nucleotides and DNA. This interference with nucleotide synthesis results in the inhibition of cell division and DNA repair, which is effective against rapidly dividing cancer cells. Methotrexate is also used for the treatment of autoimmune diseases such as rheumatoid arthritis, psoriasis, and Crohn's disease. Vitamin C, vitamin E, and pyridoxine have different chemical structures than methotrexate and do not function as anticancer drugs.

The Structure of Methotrexate, a Drug Used to Treat Cancer