Doxorubicin (DOX) is one of the most commonly used and effective chemotherapeutic agents. Despite its clinical benefits, the use of DOX is often limited by serious adverse effects, such as severe cardiotoxicity and myelosuppression. Recent progress in chemical synthesis has enabled the design of modified anthracyclines with a sugar moiety being a desirable subject of research. A series of new analogues of DOX has been synthesised, in which the amino group in the daunosamine moiety was replaced by a formamidine system containing the rest of the cyclic secondary amine with gradually increased ring size. An additional product containing the oxazoline ring in daunosamine moiety was obtained during the synthesis of formamidinodoxorubicin from DOX. Formamidine derivatives demonstrate better anticancer properties when compared with parental DOX, such as lower cardiotoxicity and comparable or higher antiproliferative activity. Also the analogue containing the oxazoline ring in the structure shows promising results. Structural modifications in the sugar moiety, involving oxazoline ring formation, increase the anticancer activity in terms of apoptosis induction and genotoxicity. It can be concluded that chemical modification at the C3′ position is a good method to increase the activity against cancer cells in vitro.