TRADITIONAL AND FLUOROUS SYNTHESIS APPROACHES TO DICTYOSTATIN ANTICANCER AGENTS

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The overarching aims of this Project are to synthesize the microtubule stabilizing natural product dictyostatin-1 and its analogs, and to evaluate the potential of these compounds as anticancer agents. In addition to the tight collaborative medicinal chemistry aspects of the work, the use of the new technique of fluorous mixture synthesis is also featured. The specific aims are: 1) Assignment of the structure of dictyostatin by total synthesis. Aim 1 is well advanced. We have recently completed the total synthesis of dictyostatin 1, and we now know its full structure, including absolute and relative configurations. It turns out that dictyostatin and discodermolide have the same configurations at all ten shared stereocenters. This structure determination has removed a major roadblock to development of dictyostatin as a potential anti-cancer agent. However, we still would like to learn how similar (spectroscopically, biologically) the isomers are with the same relative configurations at the three main fragments but coupled together in different pairings. This question will be answered by making multiple isomers by fluorous mixture synthesis. We have also nearly completed synthesis of the original Pettit structures, so this work will be finalized. 2) Synthesis of 0.35-1.0 g of dictyostatin for in vivo characterization. To accomplish this goal, the current synthesis must be improved, and a plan to streamline it by increasing convergency is outlined. 3) Synthesis of stereoisomers and analogs of dictyostatin for SAR studies. We will use the recently established synthetic route to make analogs by fluorous mixture synthesis. We plan to make stereoisomers, and to make simplified analogs with the goal of beginning to elucidate the structure/activity relationship. 4) Conformational modeling of dictyostatin and key stereoisomers. Multiconformational searching coupled with MM3 calculations in Macromodel will be used to predict conformational minima of key isomers. Initially, this data will be used to help interpret NMR experiments, and will serve as a basis for analog design as well as for more sophisticated modeling and docking experiments.