Keywords: Antitumour agents / Natural products / Taxoids / TerpenoidsThe retro-aldol reductive fragmentation of different structural types of 7-hydroxy-9,10-dioxotaxoids was investigated, showing that the reaction is typical of taxanes and requires cerium(III) promotion with NaBH 4 in protic medium and alkylboron (aluminium) hydrides in aprotic solvents. The re-

The bifunctional taxoid-colchicinoid hybrids 6-8 were synthesized and evaluated in assays of cytotoxicity and tubulin assembly/disassembly. All compounds showed a high degree of cytotoxicity, but, while 6 and 7 behaved as bifunctional tubulin binders not unlike an equimolecular mixture of taxol and thiocolchicine, 8 was surprisingly devoid of tubulin activity, acting on a distinct and yet to identify molecular target.

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The acylative modification of IDN 5390 (3a), a 7,8-secotaxoid under preclinical development, was investigated. A modest decrease of potency was observed upon acylation of the primary and the enolic hydroxyls, suggesting that, just like in paclitaxel, the hydroxyl groups in the upper right-hand sector are not critical for cytotoxicity. The activity of these analogues, and especially of the chemically robust carbonates 3c and 3d, makes it unlikely that the activity of IDN 5390 is due to in vivo oxidation to a fledgling 7-aldehyde and re-aldolization to the corresponding taxane derivative.

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