The title compound, (+)-14,14-difluoro-4-demethoxydaunorubicin hydrochloride (9), was prepared starting from the readily available (−)-hydroxy ester (10). This synthesis featured the efficient synthetic route to (−)-14,14-difluoro-4-demethoxy-7-deoxydaunomycinone (20) employing the Reformatsky reaction of ethyl bromodifluoroacetate with the (−)-siloxy aldehyde (14) and previously developed glycosylation method in which trimethylsilyl trifluoromethanesulfonate was used as an activator. In P388 in vitro test, 9 was found to be fifty times more active than adriamycin (1). Prominent antitumor activity was also observed for 9 in P388 in vivo test.
Reduction of (R) -methyl 2, 5, 12-trihydroxy-6, 11-dioxo-1, 2, 3, 4-tetrahydronaphthacene-2-carboxylate ((R) -5) with lithium tri-tert-butoxyaluminum hydride in dimethyl sulfoxide was found to proceed chemoselectively, giving the corresponding alcohol ((R) -11) in 50-55% yield. The produced (R) -alcohol ((R) -11) could be readily isolated as its acetonide ((R) -12) or tert-butyldimethylsilyl ether ((R) -13). Stereoselective C7α -hydroxylation (the anthracycline numbering) of (R) -13 and urethane formation produced the optically active title compounds, which are the aglycones of unnatural anthracyclines showing excellent anticancer activity.