Browsing by Subject "Polyketide"
Results Per Page
Sort Options
Item Embargo Biochemical Characterization of an Atypical Polyketide Synthase (PKS) from the Apicomplexan Parasite Toxoplasma gondii(2023) Keeler, AaronThe phylum Apicomplexa encompasses multiple obligate intracellular parasites that pose significant burdens to human health including the causative agents of malaria, toxoplasmosis, and cryptosporidiosis which infect millions of humans and cause hundreds of thousands of deaths each year. During their complex life cycles, apicomplexan parasites coordinate the function of specific proteins to both evade the host immune system and thrive under stressful conditions. Notably, Toxoplasma gondii has been found to harbour multiple polyketide synthase (PKS) genes by bioinformatic analysis, suggesting they can produce secondary metabolite polyketides. While secondary metabolite biosynthetic gene clusters (BGCs) have been known in Apicomplexa for over two decades, limited studies on these enzymes have been completed to date and there have been no characterized products, leaving a void in our understanding of the role of these enzymes in parasite biology. Therefore, characterization of these proteins may aid in our ability to target these biosynthetic enzymes as sources of potential therapeutic candidates in Apicomplexa.While protists are underexplored for biosynthetic potential, research points to this kingdom as an untapped potential for new chemical space. T. gondii for instance possesses multiple putative PKS biosynthetic gene clusters (BGCs) however there have been no secondary metabolite products elucidated thus far. Therefore, our work explores a T. gondii PKS, TgPKS2, and investigates the architecture, predicted structures, and activity of multiple domains within this synthase. Subsequently, Chapters 2 and 3 describes our initial studies on TgPKS2 including hydrolysis activities of acyltransferase (AT) domains, mutagenesis studies, and a first of its kind self-acylation activity of acyl carrier protein (ACP) domains in a modular type I PKS. Chapter 4 further emphasizes the unique attributes of TgPKS2, delving into a never before characterized chain release mechanism, while Chapter 5 compares TgPKS2 transacylation activity to well-characterized bacterial and fungal systems. Combined, these chapters describe our work to biochemically explore TgPKS2, discover the role it plays within the T. gondii life cycle, and further our work to elucidate the metabolite(s) produced by this synthase. Altogether, this research lays the ground work for exploring other apicomplexan and eukaryotic polyketide synthases and significantly increases our knowledge of the biochemical properties of these unique proteins.
Item Open Access Design and Synthesis of Natural and Unnatural Macrocycles(2019) Lee, HyunjiMacrocycles have received growing appreciation for their potential in probing a broader biological space, and there are a significant number of bioactive macrocycles in nature. In addition, a macrocyclic scaffold provides interesting features, including high binding affinity and target selectivity due to the pre-organized conformation. Despite the therapeutic potential and valuable pharmacological characteristics, this class of scaffolds has been poorly exploited in the field of drug discovery because of synthetic challenges and incompatibility to the conventional Lipinski’s rule of five. Therefore, efficient approaches for the generation of diverse and complex macrocycles are needed to develop novel macrocyclic agents.
In an attempt to construct a diverse set of macrocycles, we designed a natural product-like macrocycle library containing a tetrahydropyran core. Our strategy for the generation of the library is based on the tandem allylic oxidation/oxa-conjugate addition for the stereoselective synthesis of a 2,6-cis-tetrahydropyran ring. The incorporation of various building blocks and the utilization of diverse macrocyclization methods were carried out to rapidly increase skeletal diversity and complexity. Appendage diversification was performed to further modulate the physicochemical properties of the macrocycles. Cheminformatic analyses demonstrated that our macrocycle library covers a distinct chemical space compared to drug-like space, while significantly overlapping
with macrocyclic natural product space.
We also explored a modular strategy for the synthesis of a macrocycle from nature, forazoline A, polyketide natural product. Forazoline A exhibits potent in vivo efficacy against the fungal pathogen Candida albicans displaying a synergistic effect with amphotericin B. Our approach towards the synthesis of forazoline A relied on the construction of three major fragments with the desired stereochemistry and the assembly of those fragments. In the dissertation, the synthetic studies of cyclohexane, thiazolidine, and alkyl chain fragments were introduced. Construction of the highly functionalized cyclohexane moiety was efficiently accomplished utilizing Mukaiyama aldol, Bayer–Villeger reaction, and addition of lithium dimethyl cuprate. Synthesis of the thiazolidine fragment was investigated via oxa-conjugate addition and Pummerer-type rearrangements. Finally, the alkyl chain fragment was synthesized through epoxidation, regioselective ring opening, and β-ketoester formation.