The synthesis of new 5-amino-3-methylisothiazolo[5,4-d]pyrimidines ser
ies is reported. The cytotoxic activity of these compounds has been de
termined on the two tumor cell lines (P-388 and KB). Two representativ
e compounds 7 and 8 displayed a significant cytotoxic action. The resu
lts point a possible involvement of structural features in the inhibit
ion effect against tumors.