Evaluation of the Tubulin-Bound Paclitaxel Conformation:  Synthesis, Biology, and SAR Studies of C-4 to C-3‘ Bridged Paclitaxel Analogues

The important anticancer drug paclitaxel binds to the β-subunit of the αβ-tubulin dimer in the microtubule in a stoichiometric ratio, promoting microtubule polymerization and stability. The conformation of microtubule-bound drug has been the subject of intense study, and various suggestions have been proposed. In previous work we presented experimental and theoretical evidence that paclitaxel adopts a T-shaped conformation when it is bound to tubulin. In this study we report additional experimental data and calculations that delineate the allowable parameters for effective paclitaxel−tubulin interactions.