Exploring the chemistry and biology of apoptolidin

Apoptolidin is a highly functionalized macrocyclic polyketide natural product that has been shown to potently induce apoptosis in sensitive cancer cell lines with an exceptionally high degree of selectivity. For this reason, apoptolidin represents an exciting new lead compound for the treatment of cancer. It has been proposed that the activity of apoptolidin is a direct consequence of its ability to inhibit mitochondrial ATP synthase.; An abundant supply of apoptolidin from natural sources has fueled ongoing investigations of this compound based on the direct modification of its structure. This strategy has provided valuable information regarding the structure-activity relationship (SAR) and mechanism of action of apoptolidin.; Apoptolidin was shown to equilibrate with its ring-expanded isomer, isoapoptolidin, and the biological significance of this isomerization was evaluated. Numerous derivatives of apoptolidin were synthesized to probe the minimum structural requirements for its desired biological activity. These include alcohol modifications that independently scan seven of the eight hydroxyl groups present in apoptolidin. Several of these modifications were designed to prevent isomerization to isoapoptolidin. A variety of cleavage strategies were investigated that reduce the complexity of apoptolidin and parse its structural features. Apoptolidin was demonstrated to undergo intermolecular Diels-Alder cycloadditions and to photoisomerize to two new compounds. These reactions lead to changes in the macrocyclic core that have significant conformational consequences. Biological evaluation of derivatives of apoptolidin provided data indicating that mitochondrial ATP synthase inhibitory activity alone does not lead to the induction of apoptosis in sensitive cell lines.; The information provided by direct modification of apoptolidin was used in the design and synthesis of novel analogues of apoptolidin that substitute the sensitive macrocyclic core with chemically less reactive scaffolds. These analogues demonstrated some aspects of the biological activity of apoptolidin and are valuable tests of our SAR and mechanistic hypotheses.; Finally, four photo-affinity label derivatives of apoptolidin were prepared and applied toward the discovery of new biological targets. Two new reagents for photoaffinity labeling were designed and synthesized specifically for this purpose. Using this labeling strategy, apoptolidin was shown to have protein interactions in common with the mitochondrial ATP synthase inhibitor oligomycin.