SYNTHESIS OF ANTICANCER AGENTS

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This grant application describes the proposed total syntheses of a number of potent antitumor agents of natural origin, namely lomaiviticins A and B, cytoskyrin A, amphidinolide N and caribenolide I, as well as a number of related molecules for biological screening. The proposed total synthesis of the lomaiviticins would involve the dimerization of an advanced a-halo enone intermediate to generate the C2-symmetric polycyclic framework. Further elaboration of the sterically crowded central core would then be facilitated by the temporary incorporation of a bridging cyclic tether. Two alternative such tethers have been devised, namely a tetrahydrothiophene and a carbocycle bearing a pendant ester group, increasing the flexibility of the overall strategy. Once the required structural motifs are installed, either of these bridges could be oxidatively cleaved to reveal the necessary functionalities for completion of the target molecules. For cytoskyrin A, a biomimetic cascade process to furnish the cage-like framework of the target molecule has been experimentally demonstrated. Involving the acid-catalyzed dimerization of an anthraquinone derivative followed by a bis-enolization/ double intramolecular Michael addition sequence, careful monitoring of this cascade allows for the selective generation of the central core of not only cytoskyrin A, but also that of a number of other structurally related biologically active natural products. This cascade process would be amenable to the production of not only these natural products themselves, but also to that of specifically targeted analogs, which would be screened for antitumor activity. The proposed syntheses of amphidinolide N and caribenolide I feature a unified, highly convergent strategy involving the sequential asymmetric alkylation of a chiral 1,3-dihydroxyacetone equivalent to establish the complete carbon framework of the target molecules, followed by a highly selective macrolactonization to generate the 26-membered ring in each case. The significance of the proposed work will lie specifically in the area of cancer chemotherapy research, and in the development of new synthetic strategies and technologies for general use in the drug discovery and development process.