Synthesis and Structure−Activity Relationships of Nonaromatic Taxoids:  Effects of Alkyl and Alkenyl Ester Groups on Cytotoxicity

Several new nonaromatic taxoids are synthesized by means of the beta-lactam synthon method. These include taxoids modified with 3-methylbut-2-enoate, 3-methylbutanoate, and cyclohexanecarboxylate groups in place of the benzoate at the C-2 position. In addition, taxoids with 2-methylprop-1-enyl, 2-methylpropyl, (E)-prop-1-enyl, and cyclohexyl groups at the C-3' position are also prepared in combination with the modifications at C-2. The alkyl and alkenyl ester groups at C-2 displayed pronounced effects on the in vitro cytotoxicity. Two of the fully aliphatic taxoids possess similar or stronger activity than paclitaxel and docetaxel. It is clear that the 2-benzoate does not play a unique role, and replacement with the appropriate alkyl and alkenyl groups provides taxoids with equivalent or superior activity.