The Design, Synthesis, and Biological Evaluation of Conformational Analogues of Dactylolide, Zampanolide and GEX1A

Polyketide natural products have classically captured the attention of the organic and medicinal chemical community owing to their intricate structural architecture and their powerful biological properties. Polyketides are biosynthetically constructed on an enzymatic assembly line through sequential Claisen condensations with malonyl-CoA and methylmalonyl-CoA to build the carbon scaffold. Accessory domains and oxidative tailoring events in the enzymatic machinery install the intricate oxidative and stereochemical elements that are often associated with a compound’s potent biological activities. The intrinsic stereochemical elements decorating the polyketide backbone force the molecule to preferentially adopt specific conformational preferences, in which Hoffmann aptly described as “flexible molecules with a defined shape.”

This thesis aims to describe the relationship between the conformational preferences and biological properties of the polyketide natural products, zampanolide, dactylolide and GEX1A. To do so, our laboratory has employed a combination of chemical and biological synthesis, computational, 1D and 2D solutional NMR studies and biological assays to describe this relationship. The characterization of these relationships represents an innovative approach to rational design to identify novel active analogues of natural products that may be further studied for their therapeutic potential.

The first two chapters of this thesis provide the background and report our studies involving the covalent microtubule stabilizing agents, zampanolide and dactylolide. The compounds represent viable therapeutics for the treatment of multi-drug resistant cancer. Previously, our lab completed a total synthesis of both of the macrolides and described their low energy conformational preferences of the macrolactone ring. With this analysis, our lab identified a degree of rigidity about the southwestern region of the macrolide. This rigidity is associated with the allylic strain about the trisubstituted olefin. To probe the role the C17-methyl plays in determination the conformational preferences and the biological properties of zampanolide and dactylolide, our lab has completed a synthesis of a 13-desmethylene-17-methyl-analogue series of zampanolide and dactylolide. Additionally, the removal of the alkyl groups in the analogues abbreviates the synthesis compared to that of the natural product. Upon completion of the analogue series, our lab performed our conformational analysis and evaluated the cytotoxic effects to discern the relationship between the macrolides’ conformational preferences and antiproliferative effects of the natural products.

This thesis also addresses our efforts to study the relationship between the biological activity and conformational preferences of type-I polyketide GEX1A. GEX1A proves to be an interesting lead for a therapeutic in our acute myeloid leukemia and Niemann-Pick type C disease studies and requires further evaluation of the compound’s potential as a drug candidate. Two chapters in this thesis address the background and our investigation in the characterization of GEX1A’s conformation-activation activity relationship using computational and solutional NMR studies. These studies confirm previously predicted conformational preferences of the polyketide and identifies two previously undiscovered bond rotations that promote the identification of four potential conformational families. This thesis further proposes to complete a synthesis towards a methyl-shifted analogue that is predicted to force the analogue into a specific conformational family about one of the rotatable bond dihedrals.

Together, these projects highlight our lab’s over-arching program to investigate natural products’ therapeutic potential for treatment of disease. This thesis places specific interest in characterizing the conformational preferences of the natural products and relate the derived conformational families to the biological properties of the compounds.