Friday May 4th – Presentations

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Resolution of the chiral octanuclear Iron-Oxo-Pyrazolate to its P and M enantiomers

Konstantinos Lazarou[a], Karilys Gonzales[b] and Raphael R. Raptis[a]

[a] Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199.
[b] University of Puerto Rico-Carolina, Carolina, PR 00984.

05:45 PM
Inorganic Chemistry

Enantioselective transition-metal-based catalysis is a well-developed field with numerous applications. However, efficient chiral catalysts based on cheap and abundant first-row metals like Fe are, so far, scarce. In our group we have characterized a family of octanuclear Fe3+-complexes of the general formula [Fe84-O)4(μ-4-R-pz)12X4], [Fe8], where pz = pyrazolato anion, for a variety of terminal X-ligands and 4-R-substituents on the bridging pyrazolates. These complexes contain a central Fe44-O)4-cubane surrounded by four more Fe-centers, the X-ligands coordinated to the latter, forming all together a Fe84-O)4X4-core with tetrahedral geometry. However, the twelve bridging pyrazolato ligands (each bridging one cubane-Fe to one outer-Fe) adopt a propeller-like rotation in order to adjust to the steric requirements of the iron oxide core, and in so doing violate the mirror symmetry of the Td  point group. This reduces the symmetry of the complex to that of the chiral T point group resulting in its crystallization as a racemic mixture of M and P enantiomers. Here we demonstrate that substitution of the terminal Cl, in the case of [Fe84-O)4(μ-4-Cl-pz)12Cl4, by rac-4-sec-Bu-C6H4O, results in spontaneous resolution upon crystallization of the P/S and M/R enantiomers, as shown by single-crystal X-ray crystallography. Further proof of the selectivity of each complex enantiomer towards the R or S enantiomer of the phenol, is given by single-crystal Circular Dichroism experiments.

Serine and Metallo carbapenemases: deciphering broad-spectrum activity and engineering cross-class inhibitors

Orville Pemberton, Nick Torelli, Afroza Akhtar, Priyadarshini Jaishankar, Kyle DeFrees, Adam Renslo, Yu Chen

University of South Florida, University of California San Francisco

05:45 PM
Biochemistry / Chem Bio.

Gram-negative bacterial pathogens expressing the serine carbapenemase KPC-2 and the metallo carbapenemases NDM-1 and VIM-2 threaten the clinical utility of all β-lactam antibiotics. These enzymes have a broad-substrate profile, most likely due to the hydrophobicity and flexibility of their active sites, particularly for the metalloenzymes. Here we demonstrate that this versatility in ligand recognition may expose a potential weakness that can be exploited through rational drug design. Using a fragment-based approach, we report the identification of a series of phosphonate compounds that represent the first cross-class non-covalent inhibitors of KPC-2, NDM-1, and VIM-2. Although our lead optimization specifically targeted KPC-2, the increase in KPC-2 inhibition was mirrored by improvement in activity against NDM-1 and particularly VIM-2. The best of these compounds showed high nM affinity against both KPC-2 and VIM-2, and cell-based activity in MIC testing in combination with imipenem. These findings provide novel chemical scaffolds for antibiotic development against bacteria co-producing serine and metallo carbapenemases, and suggest that the shared ligand binding features and the increased druggability of carbapenemase active sites can be leveraged in developing high affinity cross-class inhibitors.

Development of a practical synthesis of THC and CBD enabling access to novel analogs

Zachary Shultz, James Leahy

University of South Florida, Department of Chemistry

04:50 PM
Organic Chemistry

Medicinal use of the cannabis plant dates back to 2700 BC in ancient China. We now have an understanding of the chemical profile of these plants and what molecules are responsible for their observed therapeutic effects. Δ9 Tetrahydrocannabinol (THC) and cannabidiol (CBD) have been identified as the main cannabinoids that contribute to the myriad of effects such as anti-parasitic, antibacterial, analgesic and anti-anxiety effects. It has been recently discovered that these natural derived cannabinoids may play a role in Alzheimer’s disease by disrupting the formation of β-amyloid plaques. Our interest is to probe the therapeutic potential of this class of compounds and to this end we developed a practical modular synthesis of the cannabinoids. A chemoenzymatic approach to access a chiral building block used to control the stereochemistry found in the cannabinoids was successfully employed. This route allows for a scalable and efficient platform for analog development of both natural and unnatural cannabinoid isomers.

Oncogenic protein kinase Cι drives melanoma cell epithelial-mesenchymal transition by activating vimentin through Par6/RhoA signaling

Wishrawana Sarathi Ratnayake, Christopher Apostolatos, Sloan Breedy and Mildred Acevedo-Duncan

University of South Florida

06:05 PM
Biochemistry / Chem Bio.

Melanoma is one of the fastest growing cancers in the United States, predicting a 14% increase in 2017 compared to 2016. The five year survival rate drops to 4% when melanoma is metastasized and responsible for ˃90% melanoma related deaths. Most available drugs target BRAF (V600E) mutation which occurs in ~60% melanoma cases, yet there is a poor prognosis and tumors acquire resistance to BRAF mutation inhibition. PKC-ι (iota) is an oncogene involved in cell cycle progression, tumorigenesis and cell survival in many cancers. We believe PKC-ι is an effective therapeutic target for invasive melanoma. We reported that PKC-ι is overexpressed in melanoma cells [Int. J. Oncol. 51(5), 1370-1382, (2017)]. In the current study, we have investigated the effects of knockdown of expression of PKC-ι and specific inhibitors on cellular properties of two malignant melanoma cell lines (SK-MEL-2 and MeWo) compared to a normal melanocyte cell line (MEL-NEO-F). Cell viability and WST-1 assay showed that both inhibitors show lesser cytotoxicity to MEL-F-NEO cell line at higher concentrations (˃7.5 μM) compare to significant toxicity on melanoma (˃1 μM).  PKC-ι knockdown/ inhibition decreased the levels of total and phosphorylated levels of PKC-ι. Furthermore, levels of E-cadherin and RhoA were increased while decreasing the levels of Vimentin; a mesenchymal marker associated with EMT. Treatments with inhibitors significantly decreased the phosphorylated Vimentin (S39) while increasing phosphorylation at S33 and S56, thereby preventing the Vimentin intermediate assembly. Immunoprecipitation and reversed immunoprecipitation showed a strong interaction of PKC-ι and Vimentin and immunofluorescence staining proved the observation. mRNA expression levels of PKC-ι, Vimentin decreased upon PKC-ι knockdown. PKC-ι knockdown downregulates Par6 thereby stabilize RhoA even upon TGFβ1 stimulation. We have also showed that PKC-ι inhibition limits the translocation of activated NF-κB p65/p52 complex and β-catenin thereby regulates NF-κB and WNT/β-catenin signaling. Overall, results show that PKC-ι is essential for melanoma progression and metastasis through activation of Vimentin via TGFβ/Par6/RhoA pathway. Therefore PKC-ι could be used as effective therapeutic targets for malignant melanoma.

Standardizing Complex Terpenoid Synthesis

Alexander J. Grenning

University of Florida

05:45 PM
Organic Chemistry

Complex terpenoid natural product synthesis is challenged by scalability, reproducibility, and efficiency (time and yield). My lab aims to develop a chemical strategy to standardize complex cycloheptane synthesis from malonic acid derivatives, ketones/aldehydes, and two different allylic electrophiles. The strategy to be developed is comprised of an operationally simple sequence (2 – 5 steps) to couple the starting materials together yielding the key advanced scaffolds for target (and target-analog) synthesis.1-3

Much like how cross-coupling standardized how biaryl-targets are prepared, we hope to revolutionize how cycloheptane-targets are accessed via standardization. Our route allows for facile recognition of starting materials (retrosynthesis) and efficient synthesis of complex targets. This overall goal also requires significant methodological advancement in the realms of allylic alkylation, [3,3] sigmatropic rearrangements, and malonic acid functional group interconversion.

At the FAME 2018 meeting, I will present an overview of this approach and key recent findings related to new metholodgy and our progress towards various terpenoid natural products.

Representative published work:

(1) Lahtigui, O.; Emmetiere, F.; Zhang, W.; Toledo-Roy, S.; Jirmo, L.; Hershberger, J.; Macho, J.; and Grenning, A. J. “Assembly of Terpenoid Cores by a Simple, Tunable Strategy.” Angew. Chem. Int. Ed. 2016, 55, 15792 –15796.

(2) Fereyduni, E.; Grenning, A. J.; “Factors Governing and Application of the Cope Rearrangement of 3,3-Dicyano-1,5-dienes and Related Studies.” Org. Lett. 2017, 19, 4130.

(3) Scott, S.; Grenning, A. J.; “An Enyne Cope Rearrangement Enables Polycycloalkane Synthesis from Abundant Starting Materials by a Simple Strategy.” Angew. Chem. Int. Ed. 2017, 56, 8125

Photochemistry of (η3-allyl)Ru halide precursors for photo assisted chemical vapor deposition

Christopher R. Brewer,1 Olivia M. Hawkins,1 Bryan Salazar,2 Amy V. Walker2 and Lisa McElwee-White1

1 - Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA
2 - Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, USA

06:05 PM
Inorganic Chemistry

Chemical vapor deposition (CVD) is a potentially attractive technique for the metallization of organic thin films.  However, thermal CVD processes often require high temperatures which are incompatible with organic substrates.  Photochemistry provides an alternative means of initiating precursor decomposition without heating the substrate.  Readily available Ru precursors, such as (η3-allyl)Ru(CO)3X (X = Cl, Br, I), have been used to deposit Ru on functionalized self-assembled monolayers by means of photochemical CVD as a model system for deposition of metal on a thermally sensitive substrate.  Recent work has been conducted to investigate the influence of the halogen of the decomposition of the precursor during the deposition process.  Quantum yields for  carbonyl loss and luminescence results are discussed in the context of precursor design for photochemical deposition techniques.

Phosphorylation induced cochaperone unfolding promotes kinase recruitment and client class-specific Hsp90 phosphorylation

Ashleigh Bachman, Dimitra Keramisanou1 and Ioannis Gelis

Department of Chemistry, University of South Florida, Tampa, FL, 33620, USA

06:25 PM
Biochemistry / Chem Bio.

Post translational modifications of the Hsp90 machinery occur as regular signaling events that mark in the timely progression through the chaperone cycle or as a response to environmental or other stimuli. During the kinase chaperone cycle both Hsp90 and the kinase-specific cochaperone, Cdc37, are subject to multiple phosphorylation events. However, the exact molecular details by which these modifications impact the kinase chaperone cycle remain unexplored. We show that Cdc37 promotes tyrosine phosphorylation of Hsp90 in a client class-specific manner, through an unprecedented mechanism. Cdc37 phosphorylation at Y298 results in partial unfolding of its C-terminal domain and the population of folding intermediates. This phosphorylation-stabilized extended conformation unmasks a high affinity SH2-binding phosphopeptide, which exhibits broad specificity over SH2 domains of non-receptor tyrosine kinase (nRTKs). Docking of these nRTKs on Cdc37 promotes efficient phosphorylation of Hsp90 at Y197, which results in Cdc37 dissociation. Thus the presence Cdc37 imprints a specific phosphorylation pattern on Hsp90 that specifically regulates the kinase chaperone cycle. Overall, we show that by providing client class specificity, Hsp90 cochaperones such as Cdc37 do not merely assist in client recruitment but also shape the post-translational modification landscape of Hsp90 in a client class-specific manner.


Bachman AB, Keramisanou D, Xu W, Beebe K, Moses MA, Vasantha Kumar MV, Gray G, Noor RE, van der Vaart A, Neckers L, Gelis I, Nature Communications, 9 (2018)

Effects of Cl- and NO3- Ions on Cerium Dioxide Nanocluster Structures

Bradley Russell-Webster, Khalil A. Abboud & George Christou.

Department of Chemistry, University of Florida, Gainesville FL 32611-7200, USA

06:25 PM
Inorganic Chemistry

Metal oxide nanoparticles provide exciting prospects for various applications as they exhibit much greater catalytic activities than their bulk counterparts. Of tremendous importance are cerium dioxide nanoparticles (CNPs) owing to their widespread use as catalysts in many industrial and medical processes. Their activity is found to vary according to the surface facets present. It has been determined, both experimentally and theoretically, that the activity of the facets increases in the order (111) < (110) < (100), making synthesis of CNPs with many (100) facets highly desirable. The standard ‘top-down’ synthetic approach provides CNPs with mixtures of sizes and shapes, making it extremely difficult to obtain structural information to atomic resolution, especially of the exact identity of the high-activity (100) facets. Recently the Christou group has worked to shed light into the mysteries of CNPs using a bottom-up synthetic procedure to synthesize molecular analogues of CNPs, so-called ‘Ce/O nanoclusters’. Synthesis of these molecular clusters enables structural characterization to atomic resolution using X-ray crystallography, allowing identification of Ce3+ ions and location of H+ binding sites. In the Ce/O nanoclusters that have synthesized to date, the most thermodynamically stable facets have all been observed, (111), (110) and (100). In CNP synthesis, the use of Cl- or NO3- ions has been reported to control the growth of selected facets by altering of surface free energy by adsorption. This use of these ions has therefore been explored in the synthesis of our Ce/O nanoclusters to compare the effects of Cl- and NO3- ions on facet formation. One important result of this work is that Cl- ions produce an unprecedented amount of surface Ce3+ ions in the resulting Ce/O nanocluster.

Ring Distortion of Vincamine Leads to Intriguing Biological Discoveries

Verrill M. Norwood IV and Robert W. Huigens III

Department of Medicinal Chemistry; Center for Natural Products, Drug Discovery and Development (CNPD3); College of Pharmacy, University of Florida

06:15 PM
Organic Chemistry

Despite the rich history of natural products as sources of bioactive molecules, the 1990s saw a paradigm shift away from natural products and toward the screening of collections of synthetic compounds (i.e. High-Throughput Screening (HTS)). This shift is due to many factors, including the increasing difficulty of identifying new natural products, the ease of sp2-sp2 coupling reactions, and the rise of combinatorial and parallel synthesis methodology used to rapidly generate large compound libraries. Consequently, current drug screening libraries are highly populated with flat (e.g. sp2 hybridized) molecules. These screening libraries have been effective at targeting protein targets with flat binding pockets (e.g. protein kinases), but ineffective against more complex biological targets (e.g. protein-protein interactions). An indole-based ring distortion approach was used to address this current lack of complexity. Commercially available indole containing natural products (NPs) are used to create diverse screening libraries. Herein we report this indole-based method executed on the NP vincamine to yield a library of >100 highly complex small molecules, which are being screened for biological activities. Progress related to both the chemistry and biology of vincamine ring distorted compounds will be presented at this talk.

Photoassisted synthesis of complex molecular motifs

James H. Frederich

Florida State University

06:35 PM
Organic Chemistry

The strategic use of photochemical reactions in chemical synthesis offers a powerful avenue to build complexity. Herein, we report our recent efforts to harness photoinduced ring-opening reactions of pyridazine N-oxides to access natural product frameworks.