Research and Scholarship
Research in the Du Bois laboratory spans reaction methods development, natural product synthesis, and chemical biology, and draws on expertise in molecular design, molecular recognition, and physical organic chemistry. An outstanding goal of our program has been to develop C–H bond functionalization processes as general methods for organic chemistry, and to demonstrate how such tools can impact the logic of chemical synthesis. A second area of interest focuses on the role of ion channels in electrical conduction and the specific involvement of channel subtypes in the sensation of pain. This work is enabled in part through the advent of small molecule modulators of channel function.
The Du Bois group has described new tactics for the selective conversion of saturated C–H to C–N and C–O bonds. These methods have general utility in synthesis, making possible the single-step incorporation of nitrogen and oxygen functional groups and thus simplifying the process of assembling complex molecules. To date, lab members have employed these versatile oxidation technologies to prepare natural products that include manzacidin A and C, agelastatin, tetrodotoxin, and saxitoxin. Detailed mechanistic studies of metal-catalyzed C–H functionalization reactions are performed in parallel with process development and chemical synthesis. These efforts ultimately give way to advances in catalyst design. A long-standing goal of this program is to identify robust catalyst systems that afford absolute control of reaction selectivity.
In a second program area, the Du Bois group is exploring voltage-gated ion channel structure and function using the tools of chemistry in combination with those of molecular biology, electrophysiology, microscopy and mass spectrometry. Much of this work has focused on studies of eukaryotic Na and Cl ion channels. The Du Bois lab is interested in understanding the biochemical mechanisms that underlie channel subtype regulation and how such processes may be altered following nerve injury. Small molecule toxins serve as lead compounds for the design of isoform-selective channel modulators, affinity reagents, and fluorescence imaging probes. Access to toxins and modified forms thereof (including saxitoxin, gonyautoxin, batrachotoxin, and veratridine) through de novo synthesis drives studies to elucidate toxin-receptor interactions and to develop new pharmacologic tools to study ion channel function in primary cells and murine pain models.
Executive Committee Member, Stanford ChEM-H (2012 - Present)
Founder, Center for Molecular Analysis and Design at Stanford (2009 - Present)
Founding Member, NSF Center for Selective C–H Functionalization (2009 - Present)
Permanent Member, NIH study section, Synthetic & Biological Chemistry A (2009 - 2013)
Honors & Awards
John A. and Cynthia Fry Gunn University Fellow in Undergraduate Education, Stanford University (2011–2020)
Dean’s Award for Distinguished Achievements in Teaching, Stanford University (2008)
Boards, Advisory Committees, Professional Organizations
Founder and Board Member, SiteOne Therapeutics (2010 - Present)
Postdoc, Massachusetts Institute of Technology, Chemistry (1999)
PhD, California Institute of Technology, Chemistry (1997)
BS, University of California, Berkeley, Chemistry (1992)
- The Chemical Principles of Life I
CHEM 141 (Win)
- The Chemical Principles of Life II
CHEM 143 (Spr)
- Independent Studies (4)
Prior Year Courses
- Synthesis Laboratory
CHEM 132 (Win)
- The Chemical Principles of Life I
CHEM 141 (Win)
- The Chemical Principles of Life II
CHEM 143 (Spr)
- Biochemistry I
BIO 188, CHEM 181, CHEMENG 181, CHEMENG 281 (Aut)
- Synthetic and Physical Organic Chemistry
CHEM 35 (Spr)
- Synthesis Laboratory
Postdoctoral Faculty Sponsor
Aaron Bedell, Erin Gray
Doctoral Dissertation Reader (AC)
Johan Both, Cyril Bucher, Alexander Burckle, Spencer Clark, Graham Dick, Matthew Landry, Ross Moretti, Katherine Near, Qunxiang Ong, Andrew Raub, Jacob Tracy
Doctoral Dissertation Advisor (AC)
Kerry Betz, Anna Elleman, Catherine Garrison, Holly Hajare, Anna Koster, Tim MacKenzie, James Mack, Stephen Sarno, Doris Tang
Mutant cycle analysis with modified saxitoxins reveals specific interactions critical to attaining high-affinity inhibition of hNa(V)1.7
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2016; 113 (21): 5856-5861
Improper function of voltage-gated sodium channels (NaVs), obligatory membrane proteins for bioelectrical signaling, has been linked to a number of human pathologies. Small-molecule agents that target NaVs hold considerable promise for treatment of chronic disease. Absent a comprehensive understanding of channel structure, the challenge of designing selective agents to modulate the activity of NaV subtypes is formidable. We have endeavored to gain insight into the 3D architecture of the outer vestibule of NaV through a systematic structure-activity relationship (SAR) study involving the bis-guanidinium toxin saxitoxin (STX), modified saxitoxins, and protein mutagenesis. Mutant cycle analysis has led to the identification of an acetylated variant of STX with unprecedented, low-nanomolar affinity for human NaV1.7 (hNaV1.7), a channel subtype that has been implicated in pain perception. A revised toxin-receptor binding model is presented, which is consistent with the large body of SAR data that we have obtained. This new model is expected to facilitate subsequent efforts to design isoform-selective NaV inhibitors.
View details for DOI 10.1073/pnas.1603486113
View details for Web of Science ID 000376779900044
View details for PubMedID 27162340
Synthesis of the Paralytic Shellfish Poisons (+)-Gonyautoxin 2, (+)-Gonyautoxin 3, and (+)-11,11-Dihydroxysaxitoxin
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2016; 138 (18): 5994-6001
The paralytic shellfish poisons are a collection of guanidine-containing natural products that are biosynthesized by prokaryote and eukaryote marine organisms. These compounds bind and inhibit isoforms of the mammalian voltage-gated Na(+) ion channel at concentrations ranging from 10(-11) to 10(-5) M. Here, we describe the de novo synthesis of three paralytic shellfish poisons, gonyautoxin 2, gonyautoxin 3, and 11,11-dihydroxysaxitoxin. Key steps include a diastereoselective Pictet-Spengler reaction and an intramolecular amination of an N-guanidyl pyrrole by a sulfonyl guanidine. The IC50's of GTX 2, GTX 3, and 11,11-dhSTX have been measured against rat NaV1.4, and are found to be 22 nM, 15 nM, and 2.2 μM, respectively.
View details for DOI 10.1021/jacs.6b02343
View details for Web of Science ID 000375889100041
View details for PubMedID 27138488
Asymmetric synthesis of batrachotoxin: Enantiomeric toxins show functional divergence against NaV
2016; 354: 865-869
View details for DOI 10.1126/science.aag2981
Inhibition of Sodium Ion Channel Function with Truncated Forms of Batrachotoxin
ACS Chem. Neurosci.
2016; 7 (10): 1463-1468
View details for DOI 10.1021/acschemneuro.6b00212
Angewandte Chemie (International ed. in English)
2014; 53 (23): 5760-5784
The paralytic agent (+)-saxitoxin (STX), most commonly associated with oceanic red tides and shellfish poisoning, is a potent inhibitor of electrical conduction in cells. Its nefarious effects result from inhibition of voltage-gated sodium channels (Na(V)s), the obligatory proteins responsible for the initiation and propagation of action potentials. In the annals of ion channel research, the identification and characterization of Na(V)s trace to the availability of STX and an allied guanidinium derivative, tetrodotoxin. The mystique of STX is expressed in both its function and form, as this uniquely compact dication boasts more heteroatoms than carbon centers. This Review highlights both the chemistry and chemical biology of this fascinating natural product, and offers a perspective as to how molecular design and synthesis may be used to explore Na(V) structure and function.
View details for DOI 10.1002/anie.201308235
View details for PubMedID 24771635
- Organocatalytic C-H hydroxylation with Oxone (R) enabled by an aqueous fluoroalcohol solvent system CHEMICAL SCIENCE 2014; 5 (2): 656-659
Selective Intermolecular Amination of C-H Bonds at Tertiary Carbon Centers
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
2013; 52 (43): 11343-11346
C-H insertion: A method for intermolecular amination of tertiary CH bonds is described that uses limiting amounts of substrate and a convenient phenol-derived nitrogen source. Structure-selectivity and mechanistic studies suggest that steric interaction between the substrate and active oxidant is the principal determinant of product selectivity.
View details for DOI 10.1002/anie.201304238
View details for Web of Science ID 000330735800022
View details for PubMedID 24000186
Marked difference in saxitoxin and tetrodotoxin affinity for the human nociceptive voltage-gated sodium channel (Nav1.7) [corrected].
Proceedings of the National Academy of Sciences of the United States of America
2012; 109 (44): 18102-18107
Human nociceptive voltage-gated sodium channel (Na(v)1.7), a target of significant interest for the development of antinociceptive agents, is blocked by low nanomolar concentrations of (-)-tetrodotoxin(TTX) but not (+)-saxitoxin (STX) and (+)-gonyautoxin-III (GTX-III). These findings question the long-accepted view that the 1.7 isoform is both tetrodotoxin- and saxitoxin-sensitive and identify the outer pore region of the channel as a possible target for the design of Na(v)1.7-selective inhibitors. Single- and double-point amino acid mutagenesis studies along with whole-cell electrophysiology recordings establish two domain III residues (T1398 and I1399), which occur as methionine and aspartate in other Na(v) isoforms, as critical determinants of STX and gonyautoxin-III binding affinity. An advanced homology model of the Na(v) pore region is used to provide a structural rationalization for these surprising results.
View details for DOI 10.1073/pnas.1206952109
View details for PubMedID 23077250
Fluorescent Saxitoxins for Live Cell Imaging of Single Voltage-Gated Sodium Ion Channels beyond the Optical Diffraction Limit
CHEMISTRY & BIOLOGY
2012; 19 (7): 902-912
A desire to better understand the role of voltage-gated sodium channels (Na(V)s) in signal conduction and their dysregulation in specific disease states motivates the development of high precision tools for their study. Nature has evolved a collection of small molecule agents, including the shellfish poison (+)-saxitoxin, that bind to the extracellular pore of select Na(V) isoforms. As described in this report, de novo chemical synthesis has enabled the preparation of fluorescently labeled derivatives of (+)-saxitoxin, STX-Cy5, and STX-DCDHF, which display reversible binding to Na(V)s in live cells. Electrophysiology and confocal fluorescence microscopy studies confirm that these STX-based dyes function as potent and selective Na(V) labels. The utility of these probes is underscored in single-molecule and super-resolution imaging experiments, which reveal Na(V) distributions well beyond the optical diffraction limit in subcellular features such as neuritic spines and filopodia.
View details for DOI 10.1016/j.chembiol.2012.05.021
View details for Web of Science ID 000307261100016
View details for PubMedID 22840778
Metal-Catalyzed Nitrogen-Atom Transfer Methods for the Oxidation of Aliphatic C-H Bonds
ACCOUNTS OF CHEMICAL RESEARCH
2012; 45 (6): 911-922
For more than a century, chemists have endeavored to discover and develop reaction processes that enable the selective oxidation of hydrocarbons. In the 1970s, Abramovitch and Yamada described the synthesis and electrophilic reactivity of sulfonyliminoiodinanes (RSO(2)N═IPh), demonstrating the utility of this new class of reagents to function as nitrene equivalents. Subsequent investigations by Breslow, Mansuy, and Müller would show such oxidants to be competent for alkene and saturated hydrocarbon functionalization when combined with transition metal salts or metal complexes, namely those of Mn, Fe, and Rh. Here, we trace our own studies to develop N-atom transfer technologies for C-H and π-bond oxidation. This Account discusses advances in both intra- and intermolecular amination processes mediated by dirhodium and diruthenium complexes, as well as the mechanistic foundations of catalyst reactivity and arrest. Explicit reference is given to questions that remain unanswered and to problem areas that are rich for discovery. A fundamental advance in amination technology has been the recognition that iminoiodinane oxidants can be generated in situ in the presence of a metal catalyst that elicits subsequent N-atom transfer. Under these conditions, both dirhodium and diruthenium lantern complexes function as competent catalysts for C-H bond oxidation with a range of nitrogen sources (e.g., carbamates, sulfamates, sulfamides, etc.), many of which will not form isolable iminoiodinane equivalents. Practical synthetic methods and applications thereof have evolved in parallel with inquiries into the operative reaction mechanism(s). For the intramolecular dirhodium-catalyzed process, the body of experimental and computational data is consistent with a concerted asynchronous C-H insertion pathway, analogous to the consensus mechanism for Rh-carbene transfer. Other studies reveal that the bridging tetracarboxylate ligand groups, which shroud the dirhodium core, are labile to exchange under standard reaction conditions. This information has led to the generation of chelating dicarboxylate dinuclear rhodium complexes, exemplified by Rh(2)(esp)(2). The performance of this catalyst system is unmatched by other dirhodium complexes in both intra- and intermolecular C-H amination reactions. Tetra-bridged, mixed-valent diruthenium complexes function as effective promoters of sulfamate ester oxidative cyclization. These catalysts can be crafted with ligand sets other than carboxylates and are more resistant to oxidation than their dirhodium counterparts. A range of experimental and computational mechanistic data amassed with the tetra-2-oxypyridinate diruthenium chloride complex, [Ru(2)(hp)(4)Cl], has established the insertion event as a stepwise pathway involving a discrete radical intermediate. These data contrast dirhodium-catalyzed C-H amination and offer a cogent model for understanding the divergent chemoselectivity trends observed between the two catalyst types. This work constitutes an important step toward the ultimate goal of achieving predictable, reagent-level control over product selectivity.
View details for DOI 10.1021/ar200318q
View details for Web of Science ID 000305321100013
View details for PubMedID 22546004