The synthesis of potential antagonists of the nucleic acid bases has been under way in these laboratories for a number of With the finding that 6-mercaptopurine and 6-thioguanine are inhibitory to a number of transplantable animal tumors6-'* as well as to human le~ kemia,~~.~~ an extensive program was undertaken to study the relationship of chemical structure to antitumor activity among purines related to 6-mercaptopurine and 6- ...
