FACULTY & STAFF
Rajesh Viswanathan
Assistant Professor
Office: Millis Hall, room 214
E-mail: rajesh.viswanathan [at] case [dot] edu
Chemical Synthesis and Chemical Biology
B. Sc., Madras University, India, 1997
M. Sc., Indian Institute of Technology, Kanpur, India, 1999
Ph. D. Indiana University, Bloomington, 2005
NIH Post-Doctoral Research Fellow, University of Utah, [2005-2008]
Research Interests
Biosynthetic pathway engineering in cyanobacterial alkaloids leading to welwistatin
Welwitindolinone C isothiocyanate (welwistatin) belongs to a family of structurally unique indole alkaloids isolated from the blue-green alga Hapalosiphon welwitschii. Several other cyanobacterial sources have been reported to produce these alkaloids: Hapalosiphon delicatulus, Hapalosiphon hibernicus, Fischerella ambigua, Fischerella muscicola to name a few. This set of terpenoid-indole alkaloids provides an inspiring and challenging area for research. The biosynthetic pathway leading to this family of alkaloids has not been studied in detail. The terpenoid core of fischerindole and welwistatin are presumably arising from the hapalindole core. This proposal aims to dissect this hypothesis by first identifying the gene cluster and thereby the corresponding enzymes and intermediates involved in the biosynthesis of welwistatin. The biosynthetic enzymes will then be re-engineered for the production of welwitindolinones and its analogs. Extensive gene mining experiments will be carried out to track down the specific set that encodes the biosynthetic enzymes. A biomimetic synthetic approach towards the six membered monoterpenoid ring system will also be pursued. Success in this direction will not only aid the preparation of precursors for biosynthesis studies but also yield a concise synthetic approach toward halogenated terpenoid natural products.
Site specific Native Chemical Ligation for protein and small molecule microarrays
Microarrays have become a standard technique to probe protein-protein, protein-antibody and protein-small molecule interactions. Uniform spatial immobilization of a protein or an enzyme in its native fold through site specific tethering will result in a robust and reliable microarray that out-performs randomly oriented counterparts. This proposal is aimed at the development of a unique strategy for the site specific labeling of proteins and other biomolecules utilizing the specific conjugation catalyzed by glutathione S-transferase (GST). It is well known that there is a considerable rate difference between enzyme catalyzed arylation (SNAr) and background thiol conjugation. Given that site specific conjugation of the Cys-SH of glutathione is reliably catalyzed by GST, it is envisioned that this powerful reaction is ideally suited for protein/biomolecule immobilization to derivatized surfaces. Glutathione will be incorporated into the biomolecule of interest using recombinant DNA technology or via post-translational glutathionylation. An appropriately derivatized PEG linker will then be layered on a glass slide containing amino groups on the surface using standard urea forming technology. This surface is now appropriate for spotting of the glutathionlylated bio-molecule. In the presence of GST, incubation of the biomolecule of interest will covalently conjugate to the glass slide. Washing with appropriate buffer (PBST) to remove non-specific adducts followed by incubation with fluorescently labeled protein/antibody will in turn result in a straightforward method of detection. As an application of this strategy, small molecule-protein and antibody-protein interactions will be assayed over glass/gold slides with appropriate analytical detection techniques. As a result, a reliable covalent bond forming reaction will assist in analyzing biological samples for studying interesting regulatory processes in cellular metabolism.
Enantioselective total synthesis of briarellin diterpene pachyclavulariaenones
In recent years, several diterpenoid natural products (bioactive metabolites) have been isolated from the gorgonian soft corals. Among these, the pachyclavulariaenones A-G have been isolated and structurally characterized by Sheu and coworkers. Particularly pachyclavulariaenone G has been shown to exhibit significant levels of cytotoxicity toward P-388 and HT-29 cancer cells. Presumably, pachyclavulariaenones are biogenetically derived from those in the briarellin and eunicellin (cladiellin) family of diterpenoids. This proposal describes an enantioselective synthetic approach toward the family of briarellin diterpenoid Pachyclavulariaenones A and B. Considerable attention is given to the choice of disconnections in order to allow for a flexible synthetic plan. The densely functionalized ring system of pachyclavulariaenones is a challenge to any concise synthetic design. The structurally unique 9-membered ether ring consisting of a tri-substituted olefin at C7 is envisioned via a late stage Claisen rearrangement. A tandem allylation-conjugate-addition-alkylation sequence is envisioned for the construction of the furan ring system along with 3 key stereocenters. An early stage enantioselective Diels-Alder strategy is envisioned for the ring A of pachyclavulariaenones. Unambiguous assignment of absolute stereochemistry will be possible through the completion of the synthesis of the natural product.
In Vivo incorporation of GGPP analogues for proteome wide profiling and imaging
Protein geranylgeranylation followed by membrane localization is one of the key mechanisms involved in the post-translational modifications through which mutant Ras proteins trigger abnormal cell division that results in cancer. Therefore, study of the cell signaling events that are regulated by Ras protein modifications is an important approach towards discovering the molecular targets for therapeutic intervention. This proposal aims at incorporation of chemically viable substrate analogs that will enable profiling of modified Ras proteins at the cellular level. Further advancements in incorporation of organic functionality into Ras proteins will be directed towards in vivo imaging of these biologically relevant tumor causing proteins. This project will involve extensive collaboration with faculty at Case school of Medicine/Radiology.
- Labadie G. R.; Viswanathan R.; Poulter C. D. “Farnesyl Diphosphate Analogues with ω-Bioorthogonal Azide and Alkyne Functional Groups for PFTase-Catalyzed Ligation Reactions”, J. Org. Chem. 2007, 72, 9291-9297.
- Viswanathan R.; Smith C. R.; Prabhakaran E. N.; Johnston J. N. “Free Radical-Mediated Aryl Amination: Convergent Two- and Three-Component Couplings to Chiral 2, 3-Disubstituted Indolines”, J. Org. Chem. [in press].
- Srinivasan, J. M.; Burks, H. E.; Smith, C. R.; Viswanathan, R.; Johnston, J. N. “Free Radical-Mediated Aryl Amination: A Practical Synthesis of (R)- and (S)-7-Azaindoline α-Amino Acid”, Synthesis (Practical Synthetic Procedures) 2005, 2, 330-333.
- Viswanathan, R.; Mutnick, D.; Johnston J. N. “The First Azacyclopentenyl Carbinyl Radical Isomerizations (ACCRI): Independent Use of Steric and Electronic (Polarization) Effects as Gating Elements”, J. Am. Chem. Soc. 2003, 125, 7266-7271.
- Viswanathan, R.; Prabhakaran, E. N.; Plotkin, M. A.; Johnston, J. N. “Free Radical-Mediated Aryl Amination and its Use in a Convergent [3+2] Strategy for Enantioselective Indoline α-Amino Acid Synthesis”, J. Am. Chem. Soc. 2003, 125, 163-168.
- Johnston, J. N.; Plotkin, M. A.; Viswanathan, R.; Prabhakaran, E. N. “Nonconventional Carbon Additions to Azomethines. Aryl Amination/Indoline Synthesis by Direct Aryl Radical Addition to Azomethine Nitrogen”, Org. Lett. 2001, 3, 1009–1011.
- Mullins R. J.; Vedernikov A.; Viswanathan R. “Competition Experiments as a Means of Evaluating Linear Free Energy Relationships”, J. Chem. Ed. 2004, 81, 1357-1361.