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Tuesday 25 September
Helen and Milton A. Kimmelman Building 11:00
“From “Crowdoxidation” to Organoselenide C-E Bond Cleavage: Enlisting the help of Chalcogens in Analysis of Biological Systems Trough Novel Probe Design” Prof. David G. Churchill [Info]

“From “Crowdoxidation” to Organoselenide C-E Bond Cleavage: Enlisting the help of Chalcogens in Analysis of Biological Systems Trough Novel Probe Design”

Our laboratory is studying small molecule selenium-containing organic and organometallic systems for their potential selective fluorescence imaging properties; our goal is to eventually probing aspects of neurodegenerative disease and disease models in a more precise way based on the present state of the art. Like some transition metals, heavier chalcogens also have capacity for redox with common changes in their valence state from 2 to 4 and from 4 to 6 being possible. Also, reduced heavier chalcogenide centers such as selenium have the ability for metal chelation. The optical characteristics are sometimes profoundly changed by an additional 2+ oxidation state at e.g. a selenium atom when the Se is in an aromatic ring or as a direct aryl substituent to a fluorogenic framework. While the atom which can become chemically oxidized may be contained within an aromatic ring, or present as a substituent, there is also the possibility for C-E bond rupture; C-Se bond c! leavage was studied with selective biothiol detection in mind and therefore, the extent of Se-C rupture possible is a design parameter in these small fluorogenic molecules and its study is ongoing. Sulfur chemistry in biology is dynamic and diverse; therefore, we are hereby exploring the extent of versatility available for selenium in small synthetic molecules in the context of biology, and specifically, towards better understanding and addressing aging and neurodegenerative disease research. Department of Chemistry, KAIST
Sunday 07 October
Helen and Milton A. Kimmelman Building 11:00
“Macrocycle-based Adventures in Self-Assembly” Prof. Jonathan L. Sessler [Info]

“Macrocycle-based Adventures in Self-Assembly”

We are working on new strategies for self-assembly. Systems whose study is relatively advanced are the so-called cyclo[m]pyridine[n]pyrroles. These systems permit self-assembly via anion recognition. They also display substrate-dependent responsive features. This has made them of interest as sensor systems and functional materials whose ground and excited state properties may be “switched” through modulation of solvent, pH, and exposure to ionic and neutral analytes. Complementing work on charged building blocks is the use of electron rich calix[4]pyrroles. Here, anion binding serves to switch the fundamental conformation of the core receptor so as to control self-assembly. This allows the production of monomers, capsules, and oligomers via the judicious choice of calix[4]pyrrole, anion, cation, solvent, and targeted substrate. It also permits control over charge transfer interactions and the construction of multi-state molecular logic devices. One of these has permitted inters-species "chemical communication". Finally, a set of "Texas-size" box-like receptors has been created. These are permitting the chemistry of self-assembly and information storage to be extended into the realm of soft materials. Applications in the realm of water purification are also being explored. This work was made possible by the dedicated efforts of many coworkers and collaborators who will be thanked during the presentation. Support from the U.S. National Science Foundation, US National Institutes of Health, the US Department of Energy, and the Robert A. Welch Foundation is acknowledged. Funding has also come from Shanghai University. The University of Texas at Austin
Tuesday 16 October
Helen and Milton A. Kimmelman Building 11:00
Expeditious Synthesis of Bacterial Glycoconjugates Prof. Suvarn S. Kulkarni [Info]

Expeditious Synthesis of Bacterial Glycoconjugates

Expeditious Synthesis of Bacterial Glycoconjugates Suvarn S. Kulkarni Department of Chemistry, IIT Bombay, Powai, Mumbai-400076 Bacterial glycoconjugates are comprised of rare D and L deoxy amino sugars, which are not present on the human cell surface. This peculiar structural difference allows discrimination between the pathogen and the host cell and offers avenues for target-specific drug discovery and carbohydrate-based vaccine development. However, they cannot be isolated with sufficient purity in acceptable amounts, and therefore chemical synthesis is a crucial step toward the development of these products.1 We recently established short and convenient methodologies for the synthesis of orthogonally protected bacterial D and L-deoxy amino hexopyranoside and glycosamine building blocks starting from cheaply available D-mannose and L-rhamnose.2-4 The one-pot protocols rely on highly regioselective nucleophilic displacements of triflates. These procedures have been applied to the synthesis of various bacterial glycoconjugates2-8 (Figure 1) as well as metabolic oligosaccharide engineering.7 1) Emmadi, M.; Kulkarni, S. S. Nat. Prod. Rep. 2014, 31, 870-879. 2) Emmadi, M.; Kulkarni, S. S. Nature Protocols 2013, 8, 1870-1889. 3) Sanapala, S. R.; Kulkarni S. S. J. Am. Chem. Soc. 2016, 138, 4938−4947. 4) Sanapala, S. R.; Kulkarni S. S. Org. Lett. 2016, 18, 3790–3793. 5) Podilapu, A. R.; Kulkarni, S. S. Org. Lett. 2014, 16, 4336-4339. 6) Sanapala, S. R.; Kulkarni, S. S., Chem. Eur. J. 2014, 20, 3578-3583. 7) Clark, E.; I.; Emmadi, M.; Krupp, K. L.; Podilapu, A. R.; Helble, J. D.; Kulkarni, S. S.; Dube, D. H. ACS Chem Biol 2016, 11, 3365-3373. 8) Podilapu, A. R.; Kulkarni, S. S. Org. Lett. 2017, 19, 5466-5469. Indian Institute of Technology Bombay