Jennifer M. Schomaker, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): Several of the twenty most important Pharmaceuticals that are currently in use and many natural products with interesting biological activities contain C-N bonds. The development of methods to construct these bonds in a stereocontrolled manner will allow chemists to continue to efficiently prepare molecules of medicinal interest. Group (IV) transition metal imido complexes have been demonstrated to react with unsaturated substrates to form new C-N bonds. The proposed study builds on this chemistry to access aziridines, vicinal amino alcohols, enamides, ynamides and pyrrolidines that are important compounds in their own right, but also serve as intermediates for many useful synthetic transformations. The goal is to eventually develop enantioselective, catalytic syntheses of these molecules. The proposed research will examine the addition of group (IV) imido complexes to alkenes and strained cyclopropanes to form azametallacyclobutanes and pentanes. The steric and electronic properties of the substrates and the metal imido complexes necessary for facile reaction will be determined. The resulting azametallacycles will be treated with a variety of reagents to generate new nitrogen-containing compounds. The appropriate labeling experiments will be performed to determine the stereochemical outcome of these reactions. Group (IV) metal imido complexes bearing chiral metal-bound ligands or chiral auxiliaries on the imido nitrogen will be studied to develop enantioselective C-N bond-forming reactions. Particularly useful would be the development of a method to install C-N bonds via meso desymmetrization of alkenes. Protonation of the metal-carbon bond of an azametallacyclobutene has been shown to release the amine product and regenerate the active imido complex. This same approach will be utilized with azametallacyclobutanes in attempts to render the reactions catalytic in the group (IV) imido complex. Ultimately, the development of the proposed methodology is expected to allow rapid and stereocontrolled access to a number of useful nitrogen-containing compounds. [unreadable] [unreadable] [unreadable]

With this CAREER Award, the Chemistry Division's Synthesis and Catalysis programs are supporting the research of Professor Jennifer M. Schomaker of the University of Wisconsin-Madison. Professor Schomaker will develop new allene oxidation methodologies to permit the rapid and flexible syntheses of complex, enantioenriched and densely functionalized amine motifs that are important components of natural products, ligands for catalysis and probes of biological processes. The first goal of this project is to develop reliable methods for regio- and stereocontrolled allene aziridination to reactive bicyclic methylene aziridine scaffolds. Second, methods to transform these key intermediates into aminated stereotriads (compounds containing three consecutive heteroatom-bearing chiral carbons) will be developed, providing access to a diverse array of nitrogen-containing building blocks for synthesis. Finally, the third goal of this project is to apply allene aziridination to the synthesis of jogyamycin, a complex aminocyclopentitol exhibiting potent antibiotic, antitumor, antiprotozoal and antimalarial activities.

The need for increasingly chemo- and stereoselective catalysis presents exciting challenges for the development of new synthetic organic methodologies. Schomaker's work will identify new paradigms in catalysis for the chemoselective construction of carbon-nitrogen bonds. These new modes of catalysis will enable powerful approaches to the synthesis of biologically relevant molecules. The broader impacts of her work will be realized through collaboration with the PEOPLE program (Pre-College Enrichment Opportunity Program for Learning Excellence) at UW-Madison. She will identify economically disadvantaged local students early in their high school careers and provide mentored opportunities for research experiences focusing on the development of new synthetic methodologies. Students will have ample time to develop valuable laboratory skills, learn to communicate scientifically in both oral and written forms and participate in seminars to broaden their understanding of the role research plays in addressing important societal concerns. Students will also employ social media to track their progress and share their experiences with family, friends and classmates.

DESCRIPTION (provided by applicant): RNA is an important messenger between DNA and proteins and was long thought to be lacking in structural complexity. However, recent work has shown that small molecules can bind to well-defined RNA-containing structures to provide a strategy for treating diseases ranging from cancer to bacterial infections to malaria. Complex amines, where the nitrogen-bearing carbon is embedded in an array of neighboring chiral centers, readily bind to the ribosome and are found in many therapeutics. However, in addition to their beneficial activities, they often exhibit toxic side effects due to non-selective binding o other biological targets. Tuning reactivity in complex amines is challenging using existing synthetic methodology, hampering efforts to identify molecules that bind only to the ribosome. This proposal focuses on developing a versatile, unified strategy for the stereoselective synthesis of highly functionalized amines. A key feature of allene aziridination is the exquisite control over the type of carbon-heteroatom bond that is installed at each one of the three allene carbons in the synthesis of our complex amines. The axial chirality of the allene substrate is transferred to point chirality in any desired target with excellent fidelity. In addition, selectiv access to any one of eight amine stereotriads can be achieved from a single racemic allene precursor. This unique feature of our chemistry minimizes the use of protecting groups, oxidation state changes and stereochemical inversions that plague current synthetic approaches. The flexibility and versatility of allene aziridination will transform the ways in whic complex amines are synthesized to access novel chemical space for tuning molecular function to address important questions related to human health. To showcase the versatility of allene aziridination as a unified strategy towards the synthesis of diverse bioactive amines, our methodology will first be applied to the synthesis of novel analogues of the aminoglycosides (AGs) to decrease their ototoxicity, a goal having important implications for cystic fibrosis patients. In a second application of our new methods, a systematic study of the hydrogen bonding interactions involved in binding of a potent aminocyclopentitol, jogyamycin, to the 30S subunit of the ribosome, will be carried out. Specific interactions important for the beneficial antimalarial and antitumor activities will be identified. Finally, potent anthraquinone antibiotics that bind to both the major and minor grooves of DNA, in contrast to the minor groove binding exhibited by doxorubicin, will be synthesized. The role of the heteroatom identity and stereochemistry in the unique bicyclic aminosugars present in these compounds will be unraveled through the judicious design and preparation of analogues. This will shed light on how the cardiotoxicity and multi-drug resistance in this class of anthracyclines differs from doxorubicin. The biological testing of our new molecules will carried out in collaboration with the UW Small Molecule Screening and Synthesis Facility, which has resources necessary to undertake the biological assays needed in our work.

Designer Silver Catalysts for Tunable C-H and C=C Bond Amination

One of the major challenges facing chemists in the 21st century is identifying cheap and sustainable ways to transform substances obtained from petroleum and biorenewable sources into useful building blocks for the synthesis of critically needed pharmaceuticals, agrochemicals, polymers, and fuels. The carbon-hydrogen single bond (C-H) and carbon-carbon double bond (C=C) are two of the most common chemical bonds in organic compounds and represent convenient locations to introduce new functionality into those compounds. However, it is difficult to achieve a desired reaction at only one specific C-H or C=C bond of the many that are present in a single molecule. In this project, Dr. Schomaker is developing new silver catalysts that transform these bonds to important and useful carbon-nitrogen bonds with high yields, less waste, and with the ability to selectively make many different useful products from a single starting compound. Studies to understand the unique features of silver that enable such high, predictable levels of control over this reactivity are key to designing improved and durable catalysts that efficiently transform precious hydrocarbon feedstocks into valuable materials, even using water as reaction solvent. Dr. Schomaker is active in outreach programs related to her research interests in catalysis to educate and engage the general public, especially young women, in fields related to science, technology, engineering and mathematics (STEM). Her activities include developing hands-on experimental modules centered on topics related to silver catalysis for "Expanding Your Horizons", a STEM-centered program for girls in 6-8th grades, as well as entertaining and educational demonstrations on silver chemistry for "Science is Fun" public presentations.

With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Jennifer Schomaker of the University of Wisconsin is developing low-cost, modular catalysts for the tunable functionalization of C-H bonds to valuable C-N bonds. Such methods are crucial for streamlined syntheses of pharmaceuticals, agrochemicals, chiral ligands and amine building blocks, but represent a long-standing challenge in the field of catalysis. To address this issue, Dr. Schomaker is pursuing a fundamental understanding of the unique features of silver complexes that enable them to achieve catalyst-controlled transformations of C-H bonds to C-N bonds through metal-catalyzed nitrene transfer processes. A combination of variable temperature (VT) NMR, diffusion spectroscopy, mechanistic and computational studies (density functional theory and higher-level ab initio methods such as CASSCF) are being employed to assess how the features of N-donor ligands influence the electronic structure of the metal nitrene, the dynamic/fluxional behavior of reactive intermediates in solution and promotion of non-covalent interactions between substrate/catalyst to influence the site of the C-H functionalization event. Ultimately, this work is establishing universal design principles for the synthesis of catalysts that facilitate non-directed C-H functionalizations capable of overriding innate reactivity preferences that are extendable to other metals and other C-H oxidation reactions, particularly in an asymmetric context. Dr. Schomaker is also active in a number of STEM outreach programs to engage and educate students in her community about the importance of catalysis in solving challenges that currently face our society. She is particularly interested in increasing the representation of women in STEM disciplines to support the broader impacts of this work.

Project Summary/Abstract: Our work in the previous funding period was inspired by synthetic challenges inherent in molecules that directly bind to the ribosome or indirectly impact its function. Structure-activity relationship studies are difficult in these classes of molecules, due to lack of flexible synthetic methods to enable flexible changes to the positioning, stereochemistry and steric environments of key amine and alcohol groups that engage in H- bonding or electrostatic interactions with the binding site; the same is true for altering alkyl and aryl groups that participate in hydrophobic or ?-? interactions. Our versatile methods streamline syntheses of stereochemically complex amine 'triads' present in natural products that inhibit protein synthesis, including aminocyclitols, anthracyclines, and tetracyclines. This enables us to construct 'unnatural products' inspired by bioactive natural products, where diversity can be achieved in: 1) heteroatoms installed in the amine 'triad' building blocks, 2) stereochemical relationships amongst the three contiguous, heteroatom-bearing sp3 carbon centers of the triad, and 3) densely functionalized carbo- and heterocyclic scaffolds. A library of >1000 unique compounds in novel amine chemical space displaying significant stereochemical complexity has shown promising activities against drug-resistant malaria and tuberculosis, Chaga's disease, hepatocellular carcinoma, and other biological targets. This renewal builds on our expertise in securing complex, densely functionalized amine motifs to investigate structure-activity relationships in molecules that impact protein synthesis, primarily through interactions with the ribosome. Analogs of the potent antimalarial natural product jogyamycin will be prepared to probe how binding to the ribosome is impacted; these studies are key to the design of simpler synthetic amine scaffolds that show similar bioactivity, but better selectivity for parasitic vs. eukaryotic mitochondrial ribosomes, lowered toxicity, and less propensity to develop resistance. In the same manner, our expertise in complex amine synthesis will be applied to the design of 'hybrid' anthracyclines that mitigate the toxicity and multi-drug resistance seen in the widely-used antitumor drug doxorubicin (DOX) and other related drugs of significance to the treatment of cancer. We have secured the aid of several collaborators to assess the biological activities of our compounds and provide insight into the design of 2nd-generation libraries, including the Eli Lilly Open Innovation program, GSK (in progress), Corteva Agrisciences, several academic colleagues (Prof. Taifo Mahmud, Prof. Dev Arya, Prof. Silvia Cavagnero, Dr. Desiree Bates), and the University of Wisconsin Medicinal Chemistry Center.

Project Summary/Abstract Optogenetics encompasses a broad array of tools and techniques that involve the use of light, in conjunction with molecular genetic tools, to drive and monitor activity of specific types of excitable cells in the nervous system and heart. Compared to traditional electrophysiological techniques, these methods are far less invasive and have the potential to monitor and manipulate electrical activity at multiple sites at the same time. The promise of optogenetics is not solely limited to expanding our basic understanding of complex organ systems but will also have a profound impact on the development of new therapeutics. Despite their promise, the current generation of optogenetic actuators are inferior compared to standard electrophysiological methods. While the membrane potential in a typical electrophysiological experiment can be changed by hundreds of millivolts on a sub- millisecond timescale, the current generation of light-activated ion channels are able to drive membrane potential by only a few millivolts in a millisecond. Much of the cutting-edge development in the field has focused on modifying and reengineering naturally-occurring ion channels, but these approaches have some inherent limitations. Herein, we propose to develop a new class of synthetic probes that serve as light-activated actuators for controlling membrane potential and ion concentrations with high temporal and spatial resolution. Employing a chemical synthesis approach towards these probes will allow us much greater flexibility to engineer and design more efficient actuators having the necessary throughput to drive cellular membrane potential. In addition, these chemical ion carriers can be combined with genetically encoded light-activated probes to provide even greater flexibility. The proposed research capitalizes on the expertise of a synthetic chemist (Prof. Schomaker, UW- Chemistry) and an ion channel electrophysiologist (Prof. Chanda, UW-Neuroscience). The two specific aims will focus on: a) the design and synthesis of photoactive ionophores and ion carriers, b) Characterization of the optical and transport properties of these designer ionophores and ion carriers.

Project Summary/Abstract: Efficient access to molecules of importance to human health has long driven the development of innovative synthetic methods. In recent years, greater emphasis has been placed on explorations of stereochemically complex molecular space not well-represented in typical compound screening libraries. In this context, N- heterocycles and aminated carbocycles are particularly attractive targets, as they are prevalent in drugs, natural products, biomolecules, and ligands. A unified and modular platform capable of rapid, flexible transformations of a simple set of precursors into azetidines, pyrrolidines, piperidines and amine-bearing carbocycles could speed drug discovery processes in complex amine chemical space. Our premise is that developing general, stereoselective routes to aziridinium ylides and 2-amidoallyl cations, coupled with the ability to divert reactivity of these key intermediates along multiple pathways, will provide a versatile approach to diverse, densely functionalized stereochemically complex N-heterocycles comprising useful bioactive chemical space. In addition to the development of new synthetic methods, biological testing of chemical space unlocked by our proposed work is critical to its long-term significance. Our program centered on new oxidative allene amination methods for the synthesis of densely functionalized and heavily substituted amine motifs has yielded ~500 novel amines that have been submitted to the Eli Lilly Open Innovation Drug Discovery (OIDD) program, as well as other academic and industrial collaborators. Promising results showing a broad range of bioactivities in the amine space covered by this preliminary library. This proposal aims to add even more powerful and versatile methods for the syntheses of complex amines from a set of modular, simple building blocks. All new compounds synthesized in the course of these studies will be submitted for screening through OIDD, the UW- Madison Medicinal Chemistry Center and other academic and industrial programs.

With the support of the Chemistry of Life Processes (CLP) Program in the Division of Chemistry, Professor Jennifer Schomaker in the Department of Chemistry at the University of Wisconsin-Madison aims to develop new biocompatible chemical tools to study diverse and interdependent processes associated with both normal and dysfunctional biology. The ease of synthesis of the proposed tools, coupled with the ability to employ computational studies to tune their complementary (bioorthogonal) reactivity, are attractive features of this new class of compounds. The utility of these tools will be harnessed to develop selective, targeted molecular delivery methods and to tag single-chain antibody fragments capable of permeating the blood-brain barrier. All findings will be made widely available to the broader scientific community to stimulate collaborations that advance and increase the impact of the proposed work. Elements of this research program will be incorporated into multi-course laboratory modules that span analytical, organic and computational chemistry and chemical biology to increase student understanding and appreciation for tackling scientific problems that require multidisciplinary approaches. The Schomaker Lab will partner with UW-Madison Chemistry Opportunities (CHOPs), a program committed to enhancing graduate student diversity. CHOPs participants will tour research facilities, meet with faculty/students and learn about opportunities for interdisciplinary research at UW.

The importance of elucidating details of the function, dynamics, and interdependence of complex biological processes drives the design of innovative new tools to study the behavior of cellular systems. Designed reagents used to probe biological systems must be highly stable, biocompatible, chemoselective, and non-promiscuous, i.e. devoid of the propensity for non-specific labeling. Due to these constraints, studying processes occurring inside cells is challenging, especially when interrogating multiple biomolecules simultaneously in real time. Despite the breadth of current bioorthogonal probes, most are designed to examine a single biological event and often suffer from slow rates, poor chemoselectivity/off-target reactivities, instability or ineffective uptake that limits labeling to a cell surface. This work introduces a new class of heterocyclic alkynes, termed ‘SNO-OCTs’, where the polarizability of the alkyne is predictably tuned for mutually exclusive bioorthogonality with diverse ‘click’ partners. These powerful tools have the potential to allow for the observation of multiple simultaneous or sequential signaling events in vitro and in vivo. Their kinetics, bioorthogonality and physical properties should be molecularly tunable, allowing them to be potentially tailored for specific applications. Moreover, the versatility and modularity of SNO-OCT scaffolds is to be exploited to develop ‘click-and-release’ strategies to deliver small molecules, fluorescent probes and biomolecules to specific sites. Potential applications for these new tools include controlled protein activation, fluorophore activation to detect RNA and other biomolecules via imaging and release of gasotransmitters or drugs to targeted locations. SNO-OCT-based tools for the preparation, bioorthogonal labeling and observation of single-chain antibody fragments (scFv) that are able to cross the blood-brain barrier (BBB) are to be developed. The lack of competing reactivity of SNO-OCTs with sulfur nucleophiles in the biological milieu enables efficient simultaneous functionalization of scFv from yeast surfaces and avoids the traditional need for soluble protein expression and purification. The SNO-OCT ring can be opened with nucleophiles subsequent to the labeling/imaging event to ‘rewrite’ the scFv for further functionalization and analysis. The Wisconsin research team plans to make these probes available to the broader scientific community to broaden their scientific reach and impact.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.