Excerpt From Gertrude Elion's Laboratory Notebook, 1949 In this page from her laboratory notebook circa 1949, Gertrude Elion records the preparation of 6-Mercaptopurine, which became the first effective chemotherapy for childhood leukemia. Courtesy of GlaxoSmithKline Inc. Heritage Center. Print Full Image Date / time 1949 Institution GlaxoSmithKline Inc. Heritage Center