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The preparation of four new lipophilic analogues of the natural pyrone pironetin is described. The nine-carbon side chain of the latter has been replaced in one analogue by a 4-phenylbutyl chain and in the other three analogues by long aliphatic chains of thirteen and sixteen carbons, all of them bearing two stereogenic centers. Their cytotoxic activity and their interactions with tubulin have been investigated. It has been found that all four are cytotoxic towards two either sensitive or resistant tumoral cell lines with similar IC 50 values in each case, thus indicating that, like the parent natural compound, they also display a covalent mechanism of action. However, one of them operates in all likelihood through a mechanism very similar to pironetin whereas the other three seem to be cytotoxic via a different mechanism.

Abstract:The stereoselective preparation of several molecules containing structural fragments of the tetrahydrofuran and spiroacetal type is described. Their degree of cytotoxicity and their interactions with tubulin have been investigated. It has been confirmed that the tetrahydrofuran derivatives are cytotoxic but, in contrast to previous reports, it has been found that the cytoxicity is not due to interactions with the microtubule network. Furthermore, and also in contrast to a previous report on closely related compounds, the spiroacetal derivatives do show interactions with tubulin, even though the precise mechanism and the binding site still remain to be established.