Part one describes the synthesis and bioactivity of syrbactin derivatives. The syrbactins are a class of structurally similar natural products that were discovered to effectively induce apoptosis in various cancer cell lines through irreversible binding and inhibition of the constitutive proteasome. The success of proteasome inhibitors bortezomib and carfilzomib as cancer therapeutics has promoted further interest in the syrbactins. Previous work conducted by the Pirrung laboratory exploring the structure-activity relationship of syrbactin analogs has inspired the investigation into the synthesis of a unique set of syrbactin derivatives in efforts to create next-generation proteasome inhibitors with improved potency and enhanced overall efficacy. In this work, a novel set of syrbactin based derivatives have been proposed, synthesized, and the biological activities have been evaluated. Additionally, thiasyrbactin derivatives have been discovered to have unique properties resulting in rare and selective inhibition of the immunoproteasome. The immunoproteasome has been linked to a variety of diseases including various cancers, autoimmune, and neurodegenerative diseases, and is therefore, a novel therapeutic target.

Part two describes the development of peptide assembly by ligation of hydroxyl amino acids threonine and homoserine with mildly activated esters. Many advances in the field of peptide chemistry have occurred allowing for the synthesis and bioevaluation of complex peptides and proteins. The development of native chemical ligation (NCL), a chemoselective cysteine-based peptide-coupling technique, provided a breakthrough in the chemical synthesis of peptides. Cysteine is one of the least abundant amino acids in natural peptides; thus, additional ligation methods based on other amino acids are essential. Recently, the Pirrung laboratory has developed a method of peptide assembly reacting β-hydroxylamines including serine, with activated esters to form amide bonds. This strategy mimics the mechanism of NCL via transesterification and subsequent acyl transfer to form a native peptide bond at the ligation site. In this work, peptide assembly with mildly activated esters has been successfully extended to the hydroxyl amino acids threonine and homoserine, expanding the scope of this ligation method. The utility of this method was further demonstrated by the synthesis of the opossum peptide, antivenom lethal toxin neutralizing factor-10 (LTNF-10).

Cannabichromene (CBC) is a cannabinoid of special interest because it has been reported as both scalemic and racemic from Cannabis plants with an unknown absolute stereochemistry. This observation can be explained by the (partial) racemization of the natural, or original, single CBC enantiomer produced through biosynthesis. CBC was resolved chromatographically, and the enantiomer matching the major enantiomer of scalemic CBC isolated from commercially available, naturally derived cannabinoid products was identified. It was determined that CBC racemized rather slowly under laboratory conditions. However, irradiation of CBC with sunlight can lead to facile racemization. Due to unsuccessful attempts of resolving CBC as well as to prevent its potential racemization, CBC was converted to its [2 + 2] cycloaddition product, cannabicyclol (CBL). Natural CBC was determined as the R absolute stereochemistry based on chiroptical data for related natural products and the absolute configuration of a CBL analog determined by X-ray crystallography.

The derivatization of indoles is an important transformation because of the numerous biologically relevant indole-containing compounds. Due to their electron-rich nature, indoles typically behave as nucleophiles in a reaction. However, indoles containing a leaving group on the nitrogen and an electron-withdrawing group on the ring can undergo a cine substitution reaction allowing for C2-functionalization. Pioneering work of Somei showed the cine substitution of N-methoxy 3-formylindole with a variety of oxygen-, nitrogen-, and carbon-centered nucleophiles. However, due to the lack of availability of N-methoxy indoles and challenge of making them, N-sulfonyl indoles were chosen as ideal substrates for cine substitution. The cine substitution of N-phenylsulfonyl 3-substituted indoles with primary alkyl alcohol nucleophiles afforded the desired products in 67 to 88% yield. Formation of side products, for example, 3-substituted indole and sulfonylated nucleophile, can be greatly dependent on the reaction conditions.

The aim of this dissertation is the discovery of novel small molecule insulin mimics. Natural product demethylasterriquinone B1 (DAQ B1) is an orally active insulin mimic, but this small molecule contains a quinone moiety that hindered further development of this drug class. The Pirrung lab has successfully replaced the offensive quinone with a pyrone ring derived from the natural product kojic acid, while maintaining the promising biological activity of DAQ B1.

The first part of the dissertation describes work toward the synthesis of a diverse library of potential activators of the insulin receptor, indolylkojates. Past work in the Pirrung lab developed a synthetic route to candidate kojate-based insulin mimics that relies on the Claisen rearrangement as a key step. This route employs iodoanilines as a starting point in a Sonogashira reaction with an O-propargylated kojate to make the target indolylkojates, but the use of iodoanilines is limited by the low commercial availability of iodoarenes. In the present study, various functionalized arenes were examined as replacements for iodoaniline, but all failed to be productive coupling partners with our functionalized kojate. Finally, success was achieved through the use of a benzyloxy-substituted iodoaniline.

The second part discloses results from the examination of our indolylkojate target compounds for signs of axial chirality. We hypothesized that a large group in the 4-position of the indole would provide sufficient steric bulk that rotation about the indole-kojate bond would be restricted. The synthesis of a (4-bromo)indolylkojate disproved this theory, as chiral chromatography failed to indicate the presence of discreet atropisomers.

The third part details work done to develop a catalyst that would allow the Claisen rearrangement step to be conducted at lower temperatures than those typically required under thermal conditions (160-190 °C). Literature surrounding the catalyzed Claisen rearrangement of O-allyl kojates is scarce, but, using catalysts known to efficiently mediate the rearrangement of (allyloxy)acrylates and allyl aryl ethers, a catalyst screen was developed. Lewis acid Zn(OTf)2 was determined to be the best catalyst for the rearrangement of O-allyl kojates at low temperatures, with the best yield arising from the use of trans-cinnamyl kojate as the substrate.

Asterriquinones display a wide range of biological activity. From antiretroviral and antitumor activity, to anti-diabetes properties and neuroprotection, asterriquinones and their analogs have quickly become a popular target in pharmaceutical research.

The asterriquinone demethylasterriquinone-B1 (DAQ-B1) exhibits insulin mimetic activity in two mouse models of diabetes. It directly activates the tyrosine kinase domain of the insulin receptor and, as a small molecule, is orally active. A substantial amount of SAR work in our and other laboratories identified the key pharmacophore, which includes the quinone. Despite promising early-stage animal studies with compounds of this class, concern about potential long-term toxicity linked to their quinone portion impeded further development. In order to surmount this obstacle, quinone replacements are sought in the synthesis of DAQ-B1 analogs. These replacements include cyclic ketones such as pyrones, pyridones, and cyclohexadienones containing a quarternary center at the 4-position. Two different methods are used in an attempt to synthesize the analogs: a Stille coupling between the desired indole and the halogenated heterocyclic ketone, and a Claisen rearrangement of an (indole)-methyl-kojic acid ether.

Besides exhibiting insulin mimetic activity, DAQ-B1 demonstrates the ability to activate the nerve growth factor (NGF) receptor, which belongs to a class of neurotrophin proteins that support neuronal growth and survival. A fluorinated analog of DAQ-B1, 5E5, activates the TrkA receptor and demonstrates NGF activator activity with 'approximately 200% the effect of a maximal dose of NGF.' A library of fluorinated monoindolylquinones, similar in structure to 5E5, is synthesized from a two step procedure consisting of the acid-catalyzed coupling of fluorinated indoles to 2,5-dichloro-1,4-benzoquinone, followed by methanolysis.

A formidable challenge in the genomic era is the assignment of structure and function to unknown genes in model organisms. Forward chemical genetics seeks to discover and characterize pathways through the identification of novel phenotypes induced by organic small molecules and subsequent isolation of their target gene(s). Downstream

genetic and biochemical strategies to dissect the action of bioactive molecules are often hampered by weak target-ligand interactions, low target abundance, genetic factors, and synthetic inaccessibility of analogs. We present a synthetic scaffold that simultaneously permits fluorescence detection and photoaffinity labeling (diazirine) in a combinatorial library of thousands of drug-like small molecules synthesized through click chemistry. Using this library, we identified several bioactives that alter seedling growth of the model plant Arabidopsis thaliana and generated candidate ethyl methanesulfonate-induced resistant mutants for downstream simple sequence length polymorphism marker-assisted mapping and single nucleotide polymorphism identification by Illumina next-generation DNA sequencing. Our proof-of-principle study will facilitate target identification of novel bioactives and accelerate chemical genetics discoveries.