Saturday May 5th – Presentations

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The dimerization of benzo[1,2-b:4,5-b']dithiophen-4-ol

Ania Sotuyo and Ronald K. Castellano

Department of Chemistry University of Florida

02:20 PM
Organic Chemistry

BDT (benzo[1,2-b:4,5-b']dithiophen-4-ol) has been a popular building block for optoelectronic materials. Recently, we decided to remake BDT by adding a hydroxyl group for the purpose of accessing a tautomerically capable BDT. As we delved into benzo[1,2-b:4,5-b']dithiophen-4-ol (BDTOH) as a novel π building block, we found some interesting behavior not mentioned in the original literature. Although tautomerization for BDTOH (pKT = 2.75, 99.8% enol) was comparable theoretically with that of anthrone (pKT = -3.10, 99.9% keto), the tautomeric phenomenon was not observed. Instead, the compound undergoes an irreversible chemical oxidation in 10 mM CDCl3, ushering in a new set biaryl dimers. While the dimerization pathway is unknown, NMR studies done in oxygen-free and radical-free environments did not inhibit the process. Further attempts to derivatize BDTOH through synthesis garnered another new set of π-extended dimers.

 

Synthetic Explorations with Unsymmetrical Oxyallyl and 2-Amidoallyl Cations

Rendy Kartika

Louisiana State University

03:00 PM
Organic Chemistry

We have developed a new strategy that enables carbon-carbon bond formation at the α-position of ketone-derived compounds with an exquisite control of regioselectivity via an intermediacy of unsymmetrical silyloxyallyl and 2-amidoallyl cations that are generated under mild catalytic conditions.  This robust chemistry has been applied toward the synthesis of various complex structural motifs, such as all-carbon quaternary centers, 1,4-dicarbonyls, silyldienol ethers, functionalized enamides, heterocyclic compounds, and others.  Our results will be discussed in this presentation.

Catalytic enantio- and regioselective alkynylation of pyridines

Kathryn L. Olsen, Mukesh Pappoppula, Aaron Aponick

University of Florida

03:30 PM
Organic Chemistry

The α-chiral tetrahydroquinoline (THQ) motif is found in a myriad of natural products and biologically active molecules. Alkynylation of pyridines at the α-position would afford chiral 1,2-dihydropyridines containing multiple synthetic handles allowing for functionalization to more complex systems. We have previously reported a highly enantioselective copper catalyzed alkynylation of quinolinium salts using the atropisomeric imidazole-based biaryl P,N-ligand, StackPhos. Encouraged by these results, we envisioned a catalytic enantioselective alkynylation of pyridines using StackPhos. The development of this methodology and its application will be presented.

New Methods for the Synthesis of Molecules Containing All-Carbon Quaternary Centers

Katelyn M. Chandoa, Ryan E. Michaelb and Tarek Sammakiac

a) Avista Pharma Solutions; b) C4 Therapeutics; c) University of Colorado Boulder

03:50 PM
Organic Chemistry

The stereoselectve synthesis of all-carbon quaternary centers has been a long-standing problem in organic synthesis. In this talk, we will describe a new approach to this problem that takes advantage of the reactivity of N-vinyl nitrones and ketenes. When combined, these substrates undergo a cascade reaction that begins with a (3+2) cycloaddition and is followed by a [3,3] sigmatropic rearrangement and a 1,3-shift to produce a 1,4-carbonyl equivalent bearing vicinal stereo centers. Using di-substituted ketenes, products bearing all-carbon quaternary centers are produced with high levels of stereoselectivity. The scope and mechanism of this process will be described in this talk.

Photosensitizers Derived from Chlorophyll

Kevin M. Smith

Louisiana State University

06:15 PM
Organic Chemistry

Chlorin-e6 (1) is a degradation product1-3 from chlorophyll-a that possesses three chemically distinct carboxylate sites (at positions 131-, 152-, and 173-) suitable for conjugation with biomolecules.  An aspartic acid conjugate (Talaporfin, NPe6 or LS-11) originally identified as the 173-conjugate (2),4 but subsequently revised to be the 152-conjugate (3),3,5 is actively undergoing clinical trials as a photodynamic therapy (PDT) sensitizer.

The presentation will summarize the evidence leading to the reassignment of the structure for Talaporfin,3,5 and report syntheses of numerous amino-acid and non-amino acid mono- and bis-conjugates of chlorin e6.3,6-9 The cellular uptake, dark- and photo-toxicity, and in vitro intracellular localization of the new conjugates will also be discussed.

 

Figure 1 – Structures of chlorin-e6 (1) and its 173- (2) and 152- (3) aspartic acid conjugates

 

References

 

K. M. Smith, D. A. Goff and D. J. Simpson, J. Am. Chem. Soc., 107 (1985) 4946. G. W. Kenner, S. W. McCombie and K. M. Smith, J. Chem. Soc., Perkin Trans 1, (1973) 2517. J. A. Hargus, F. R. Fronczek, M. G. H. Vicente and K. M. Smith, Photochem. Photobiol., 83 (2007) 1006. J. C. Bommer and B. F. Ogden, U.S. Patent 4,693,885 (1987). S. Gomi, T. Nishizuka, O. Ushiroda, N. Uchida, H. Takahashi and S. Sumi, Heterocycles, 48 (1998) 2231. R. G. W. Jinadasa, X. Hu, M. G. H. Vicente and K. M. Smith, J. Med. Chem., 54 (2011) 7464. H. Chen, R. G. W. Jinadasa, L. Jiao, F. R. Fronczek, A. L. Nguyen and K. M. Smith, Eur. J. Org. Chem., (2015) 3661. R. G. W. Jinadasa, Z. Zhou, M. G. H. Vicente and K. M. Smith, Org. Biomol. Chem., 14 (2016) 1049. H. Chen, S. W. Humble, Z. Zhou, A. L Nguyen, M. G. H. Vicente and K. M. Smith. J. Porphyrins Phthalocyanines, submitted (2017).

 

Acknowledgements: The author thanks the US National Institutes of Health (grants R01 CA132861 and R01 CA179902) for support of this research.

USF Human Donation Program: Experimental Research in Decomposition

Erin H. Kimmerle, Ph.D.

Florida Institute for Forensic Anthropology and Applied Science, University of South Florida

10:55 AM
Analytical Chemistry

In 2016, USF initiated a human donation program for experimental research in forensic anthropology, outdoor crime scenes, legal medicine, and related forensic sciences.  The 3.5-acre Adam Kennedy Memorial Forensic Field, established for outdoor research utilizes donors for research in forensic anthropology, geochemistry, geophysics, biochemistry, ecology, and forensic art.  Currently, numerous projects investigating human decomposition, the effects of scavenging, geochemical analysis for human identification, and various methods of remote sensing for locating and documenting clandestine graves are underway.  There have been 21 donors and more than 75 pre-donors register.  The establishment of this program and the preliminary areas of research will be discussed.  More specifically, the research on progressive decomposition to establish baseline rates in Florida shows that the effects of vulture and opossum scavenging on remains plays a significant role in the rate of decomposition, more than any other variable.  The scavengers can also cause skeletal fractures and damage that mimics trauma and unexpected alterations to the body and scene.