amethopterin

Vincristine, amethopterin, 6-mercaptopurine, and prednisone for leukemia.

Other analogues of folic acid were in development, and by 1950, methotrexate (then known as amethopterin) was being proposed as a treatment for leukemia.

These analogues - first aminopterin and then amethopterin (now methotrexate) were antagonistic to folic acid, and blocked the function of folate-requiring enzymes.

Aminopterin had disadvantages, and the normal process of making and testing a series of closely related compounds led to a better drug, amethopterin, which differed by a single additional substituent but proved to be one of the most effective drugs for the treatment of blood cancers.