Brian M. Stoltz - US grants

Diazonamides A is an unusual novel halogenated cyclic peptide isolated form the marine ascidian Diazona chinensis possessing potent in vitro activity against HCT-116 human colon carcinoma and B-16 murine melanoma cancer cell lines (IC/50 <15ng/mL). Many biologically active cyclopeptides display encouraging therapeutic potential in vitro and are promising lead structures wherein the absence of ionized C- and N-termini leads to improved bioavailability, more facile membrane permeability, and greater resistance to in vivo enzymatic degradation. However, as with many marine natural products, the amount of material available from natural sources is usually scare making broad spectrum biological screening an advanced testing impossible. Therefore, total synthesis plays an essential role in understanding the effect thee compounds have on cancer cells by proving quantities of material otherwise not available. An original approach to the synthesis of diazonamide A will be described herein. Key features presented in the approach include the rapid functionalization of the tyrosine core by Claisen Rearrangement and a subsequent catalytic asymmetric cyclopropanation to produce the critical quaternary carbon center (C10). Finally, a novel macrocyclic ring-contractive oxazole formation protocol and its potential application to other oxazole containing macrocycles will be described. The striking array of complex structural features present in diazonamide A creates a formidable challenge for synthesis; however, the proposed strategy delivers the natural material in a concise enantioselective fashion (19 steps, best case).

The objective of this research program is the discovery and development of new reaction methodology en route to the synthesis of complex bioactive molecules. Our proposed studies will focus on the advancement of enantioselective palladium- catalyzed oxidation reactions that do not involve oxygen atom transfer. These reactions include the oxidative kinetic resolution of secondary alcohols and new cyclizations that deliver enantiopure heterocycles and carbocycles. The processes that we develop will find utility in the synthesis of a variety of complex biologically active molecules for which there is currently no efficient synthetic roadmap. As a consequence of this approach, we will have a) access to novel, medicinally relevant structures, b) a general method for their synthesis, and c) new synthetic methods that will be beneficial for a host of general applications. Specifically, we plan to target two classes of highly biologically relevant complex alkaloids, the Dragmacidins (1-3) and the Cephalotaxines (e.g., 4). The former have been shown to selectively inhibit brain Nitric Oxide Synthase (bNOS), and may have therapeutic importance for the treatment of Alzheimer's and other neurodegenerative disorders. The latter are potent antitumor agents, and have been used to overcome the Multiple Drug Resistance problems associated with many chemotherapeutic agents. The ultimate impact of our research will resonate across numerous disciplines including synthetic and organometallic chemistry, chemical biology, and human medicine.

Proposal Title: PECASE: The Utilization of Complex Molecule Synthesis to Drive the Development of New Reaction Methods that Promote New Directions in Synthesis. A 'Teufelskreis' of Opportunity.
Institution: California Institute of Technology

The focus of this research is to develop new synthetic methodology in the context of complex molecule synthesis. Projects involving palladium-catalyzed oxidative [4+2] cycloaddition reactions and tandem Bamford-Stevens/Claisen rearrangements will be carried out and a concise, stereoselective route to the hypoglycemogenic diterpenoid, saudin will be developed. In the educational realm, courses on synthesis and pharmaceutical chemistry are being developed and outreach activities enabling students to interact with the broader local community are in place.
With this PECASE award, the Organic and Macromolecular Chemistry Program is supporting the research and educational efforts of Dr. Brian Stoltz of the Department of Chemistry and Chemical Engineering at the California Institute of Technology. Professor Stoltz will focus his research on the development of new synthetic methodology within the framework of natural product total synthesis. The illustrative target molecule, saudin, has interesting biological properties of interest to the pharmaceutical industry. The education activities will stress outreach to local middle schools and high schools and will also focus on course development at the undergraduate and graduate level.

This project was originally funded as a CAREER award, and was converted to a Presidential Early Career Award for Engineers and Scientists (PECASE) award in May 2004.

? DESCRIPTION (provided by applicant): The objective of this research program is to discover and develop new reaction methodology en route to the synthesis of complex bioactive molecules. Our proposed studies will focus on the investigation and optimization of technologies that enable the synthesis of core structural and stereochemical subunits prevalent in many bioactive, polycyclic natural products. The processes that we develop will find utility in the synthesis of a variety of structures for which there is currently no efficient synthetic roadmap. Importantly, the methods presented in this application will be useful outside of the contexts described herein and will arm practitioners of synthetic chemistry (in academic, government, and industrial laboratories) with a new set of important tools to access enantioenriched and functionally diverse chemical building blocks for synthesis. The research proposed in this grant application is focused on a) the development of new iridium- and palladium-catalyzed stereoselective alkylation reactions that produce densely substituted building blocks for synthesis, b) the development of palladium- catalyzed conjugate addition processes, c) the utilization of these novel methods for the synthesis of fused, spiro, and bridged ring system arrays, and d) the implementation of these new tactics in the syntheses of multiple natural and non-natural bioactive small molecules. Specifically, we outline approaches to isopalhinine A, the yuccaols A-E, and the abietane diterpenoids. These molecules are not only important from a biological standpoint, they also serve as a testing ground for our new technologies. As a consequence of this approach, we will have access to a) novel, medicinally relevant structures, b) a general platform for their synthesis, and c) new synthetic methodology that will impact a host of diverse applications.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A large number of biological systems will be studied using macromolecular crystallography.

DESCRIPTION (provided by applicant): Escherichia coli K1 is the most common cause of meningitis in neonates. Ineffectiveness of antibiotic therapy over the last few decades and the emergence of antibiotic resistant E. coli strains imply that there is a great unmet need for new methods of treatment and prevention. Incomplete understanding of the mechanisms involved at every step of pathogenesis is attributed to this poor outcome. For example, the mechanisms by which E. coli K1 enters the human brain microvascular endothelial cells (HBMEC) that constitute the BBB and disrupts tight junctions (TJs) are poorly understood. We have established that outer membrane protein A (OmpA) of E. coli interacts with endothelial cell gp96 (Ecgp); a receptor specifically expressed on HBMEC, to invade and disrupt the TJs. The importance of OmpA-Ecgp interaction is further supported by our findings that 1) E. coli strains that either lack OmpA or express non-functional OmpA do not induce meningitis in a newborn mouse or rat model and 2) Mice in which Ecgp expression was suppressed were resistant to E. coli infection. Intriguingly, OmpA interaction with Ecgp triggers the production of nitric oxide (NO) due to iNOS activation and thereby enhances the expression of the receptor to allow the bacteria to invade more efficiently. In agreement, iNOS-/- mice are resistant to E. coli infection and also administration of an iNOS specific inhibitor, aminoguanidine (AG), during high-grade bacteremia prevented the occurrence of meningitis. Novel computer modeling methods were utilized to study the interaction of OmpA and Ecgp and to identify small molecule inhibitors that prevent the E. coli invasion of HBMEC. Three small molecules exhibited more than 80% inhibition of E. coli invasion in HBMEC both in vitro and in vivo. Our studies have also revealed that Ecgp interaction with Robo4 at the HBMEC membrane increases upon infection with E. coli. Further, a GTPase activating protein, IQGAP1, which binds both actin and b-catenin, appears to play a role in the invasion process. IQGAP1 is a client protein for Stat3, which was shown to be associated with Ecgp, indicating that IQGAP1 might be relaying Ecgp mediated signals to induce E. coli invasion. Thus, our hypothesis is that the interaction of OmpA and Ecgp is fundamental to initiate signaling events that induce E. coli invasion and increased permeability of the BBB. In Aim 1, we propose to define the binding domains of Ecgp that orchestrate the interaction of Ecgp/Robo4 with OmpA. Next, to understand whether Ecgp interaction with Robo4 contributes to signaling events to induce NO production and thereby modulating IQGAP1 association with b-CAT to dislodge it from TJs will be tested in Aim 2. Then, in Aim 3 we will modify the antagonists for higher inhibition efficiency and couple them to nanoparticles, which will carry a load of iNOS inhibitors to deliver to brain to prevent E. coli induced meningitis in newborn rats. Translational medicine is the outcome of this application in which studies of basic biology and applied technology to develop new strategies of prevention will be integrated.

In this project funded by the Chemical Synthesis Program of the Chemistry Division, Professor Brian M. Stoltz of the Division of Chemistry and Chemical Engineering at the California Institute of Technology will investigate the origins of high enantioselectivity in an important asymmetric catalytic alkylation reaction discovered in his laboratory, and apply the knowledge gained toward the development of a broad platform for enantioselective transition metal enolate functionalization chemistry.

The work described could provide unprecedented access to simple chemical building-blocks containing stereogenic centers, and could be widely adopted by synthetic chemists in both academia and industry. This unique collection of tools could enable chemists to push beyond the state-of-the-art in applying such technologies to compounds and substances that are beyond the scope of the current methods. In addition to the on-site, laboratory science described in this grant, the science proposed herein will directly impact the education of scientists at the California Institute of Technology, while the skill set and expertise they gain will broadly impact society-at-large as they too move on to productive careers in academia, industry, and government. Finally, ongoing teaching and outreach efforts with young students (K-6) will impact the lives and decisions of the next generation of students.

With this award, the Environmental Chemical Sciences Program of the Division of Chemistry is funding Professors Paul Wennberg and Brian Stoltz of the California Institute of Technology to investigate the role of autooxidation in environmental processes. Autoxidation of organic compounds is known to be important in combustion, food and wine spoilage, degradation of olefinic liquids, and very broadly in biological systems. The role of autoxidation in the environmental degradation of organic compounds is being explored. A collaborative team of scientists is studying the kinetics and mechanism for autooxidation of a series of model compounds. The goal is to create a model of autoxidation for use in evaluating the rate by which autoxidation converts reduced carbon compounds in the environment to highly oxygenated substances. More broadly, the kinetics of autoxidation described through this study address many gas and condensed phase applications that span science from improved food preservation to reduced aerosol production in open-air combustion.

The role of autoxidation in the environmental degradation of organic compounds remains largely unexplored. Via a collaboration of a team of scientists, including computational, organic, and analytical chemists, the rate of this oxidative chemistry for a diverse set of organic substrates is investigated. Model compounds that characterize many of the reduced organic substrates found in the environment are synthesized to explore the physical chemistry of autoxidation. Using density functional calculations and laboratory observations, a model of autoxidation for use in evaluating the rate by which autoxidation converts reduced carbon compounds in the environment to highly oxygenated constituents is being created. Initial applications include study of the formation and aging of organic aerosols, and the atmospheric oxidation of alkenes by the nitrate radical during the night. Broader impacts of these studies could be far-reaching should it be found that this oxidative chemistry impacts the burden of ozone and aerosol quite generally.

Project Summary/Abstract: The objective of this research program is to discover and develop new reaction methods en route to the synthesis of complex bioactive molecules. Research in our group at Caltech is focused on the general area of chemical synthesis. Specifically, our science has been devoted to the development of new strategies for the preparation of complex molecules that possess significant structural, biological, and physical properties. Concurrent with this program of target-driven synthesis is a dedicated effort directed toward the development of new reaction methods that we anticipate will be useful for a range of applications across numerous disciplines, including synthetic and organometallic chemistry, chemical biology, and human medicine. In this proposal, we outline a multifaceted and integrated program in organic synthesis that encompasses the total synthesis of the highly biologically active natural product jorumycin. Jorumycin, isolated from the sea slug Jorunna funebris, has been shown to possess exceedingly potent antitumor and antibiotic activity (Gram-positive and Gram- negative). The proposed research will provide access to jorumycin and previously unavailable analogs to be used in further biological evaluation. We illustrate a rapid and unusual approach to the construction a pentacyclic core, common to the members of the bis-tetrahydroisoquinoline class of natural product. Upon completion of our target and a host of designed analogs, we will collaborate with Dr. Dennis Slamon of the Translational Oncology Research Laboratory at UCLA who will undertake biological evaluation of our materials. Studies performed at UCLA in conjunction with DMPK studies at WuXi AppTec will then indicate how we can improve upon the architectures already developed by nature to produce efficacious small organic molecules for use as potential chemotherapeutic agents.