Synthesis of Antimitotic Paxilline Indole Diterpenes

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PROJECT SUMMARY Paxilline indole diterpenes (IDTs) are natural products that exhibit a variety of promising biological activities, but lack of efficient access to the derivatives and analogs of IDTs hinders investigation of their biomedical potential. The long-term goal is to develop new chemical methods and approaches that allow short, general and scalable assembly of natural products with promising biological activities. The objective of this proposal is to develop new chemical methods and approaches for efficient synthesis of IDTs and their otherwise inaccessible analogs and to determine the molecular mechanism of action and a pharmacophore model for inhibition of Eg5. The central hypothesis is that a controlled polycyclization will allow an efficient assembly of the common pentacyclic core of IDTs and will provide a general entry to a broad range of congeners. This hypothesis has been formulated on the basis of the extensive preliminary data produced in the applicant's laboratory. These data demonstrate that a new radical-polar crossover cascade en route to the terpenoid core provides the shortest entry to date into the IDT family. The rationale for the proposed research is that new chemical methods and approaches are necessary to achieve efficient synthesis of IDTs and to develop new and potent inhibitors of Eg5, which can be used as biochemical tools and potential antimitotic leads. The hypothesis will be tested by pursuing three specific aims: 1) development of an intermolecular alkenylation of ketones; 2) development of a general approach to IDTs; and 3) synthesis of antimitotic IDTs and development of potent inhibitors of Eg5. Under the first aim, a new process for intermolecular alkenylation of ketones will be developed. This unique transformation is expected to allow efficient assembly of quaternary centers and to provide a direct access to polycyclization precursors en route to IDTs. The preliminary data produced in the applicant's laboratory demonstrate a proof-of-principle for this approach. Under the second aim, a general and efficient approach to IDTs will be developed. A radical-polar crossover polycyclization is projected to allow short and efficient assembly of the terpenoid core of IDTs. The preliminary findings from the applicant's laboratory indicate that the key vicinal quaternary stereocenters are set in a direct and stereoselective manner using this approach. Under the third aim, a diverse set of antimitotic IDTs and their analogs will be synthesized and used for elucidation of structure activity relationships (SARs). These SAR data will be used to develop chemical probes for determination of the molecular mechanism of action and to establish a pharmacophore model for Eg5 inhibition by IDTs. The proposed research is significant because it will make IDTs readily available for widespread biological studies and will allow the evaluation of these terpenoids as new leads in the treatment of cancer. The approach is innovative, in our opinion, because it relies on new chemical methods to achieve efficient construction of IDTs and represents a new and substantive departure from the previous work in the field.