Daunorubicin (DRB) and its two analogues containing a trisubstituted amidino group at the C-3' position of the daunosamine moiety have been compared regarding their cytotoxic activity, cellular uptake, subcellular localization and DNA damaging properties. An analogue containing in the amidino group a morpholine moiety (DRBM) as well as an analogue with a hexamethyleneimine moiety (DRBH), tested against cultured L1210 cells, exhibited lower cytotoxicity then DRB. The decrease of cytotoxic activity was not related to cellular uptake and subcellular localization of drugs. Although all tested drugs were active in the induction of DNA breaks and DNA-protein crosslinks, they differed in the mechanism of induction of DNA lesions. DRB produced DNA breaks mediated solely by topoisomerase II, whereas DRBM and DRBH induced two types of DNA breaks by two separate processes. The first is related to the inhibition of topoisomerase II and the second presumably reflects a covalent binding of drug metabolites to DNA. It is hypothesized that the replacement of the primary amino group (-NH(2)) at the C-3' position of the daunosamine moiety by a trisubstituted amidino group (-N=CH-NRR) may be a route to the synthesis of anthracycline derivatives with enhanced ability to form covalent adducts to DNA.

5-Alkyl- and 5-arylalkyl-3-methylenedihydrofuran-2-ones 13a-e, 3-alkylidenedihydrofuran-2-ones 18a-c, and 3-methylenepyrrolidin-2-ones 16a-e were synthesized utilizing ethyl 2-diethoxyphosphoryl-4-nitroalkanoates 9a-e as common intermediates. All obtained compounds were tested against L-1210, HL-60, and NALM-6 leukemia cells. The highest cytotoxic activity was observed for 3-methylenefuranones 13d,e bearing benzyl or 3,4-dimethoxyphenylmethyl substituents at position 5, with IC(50) values of 5.4 and 6.0 microM, respectively. Contrary to the literature reports, no enhancement in activity due to the presence of a hydroxy group was found when the cytotoxicity of furanones 13a,b,d and 5-(1'-hydroxyalkyl)-3-methylenedihydrofuran-2-ones 6a,b,d was compared. The anticancer activity of pyrrolidinones 16a-e and 3-alkylidenefuranones 18a-c was much weaker than that of furanones 13a-e.

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