Session V

Tuesday, May 23rd

Session V


Progress towards the total synthesis of nannocystin A

Kyle Delgado and Steven T. Diver

University at Buffalo, Department of Chemistry

Nannocystin A is a macrocyclic natural product containing a polyketide and a tripeptide domain, which has been shown to act as a potent anticancer, antibiotic, and antitumor agent. Our approach involves the synthesis of the polyketide domain by a tandem ene-yne metathesis/dienyl isomerization sequence, a method previously developed in our lab. Additional key reaction includes an asymmetric copper-catalyzed propargylic etherification. The tripeptide domain will be synthesized by a series of amidation reactions. These two domains will then be combined by an amidation step, followed by a final macrolactonization. Our model studies and progress towards the total synthesis of nannocystin A will be presented along with future plans for the completion of the synthesis.


Fluorescent Kinase Inhibitors: Novel Modality for HER2 status of Breast Cancer cells

Heajin Lee, Wenjun Liu, A. S. Brown, Ralf Landgraf, James Wilson

University of Miami

The EGFR/ERBB family of tyrosine kinase receptors are related with intracellular communications such as cell proliferation, metabolism, and numerous biological responses. The dysregulation of their signal pathway contributes to development of cancer malignancies. This receptor family is a conventional chemotherapeutic target as well as a diagnostic modality. Especially, the ERBB2, also known as HER2 is prognostic biomarker implicated in about 20% of invasive breast cancer. The HER2 status is a crucial factor to decide the treatment type for patients. Common assays used to measure the activated ERBB level analyze tyrosine phosphorylated substrates or the receptors themselves. However, these lysate-based assay results cannot show the difference between a significant mechanistic value and actual clinical relevance. Fluorescent probes can overcome this current detection limit as they provide real-time readouts with minimum perturbation of living cells. My research has focused on developing fluorescent probes for ERBB2 to explore the signaling dynamics in a receptor unit at alive single cell. As an effort to develop novel small molecular tools for ERBB2 cancer biology, I have synthesized fluorescent kinase inhibitors targeting ATP binding pocket of ERBB2 by activation states. Our fluorescent kinase inhibitors are capable of identifying the ERBB2(+) cells as well as tracking rapid perturbations of the activation states at the level of individual cells. The significance of our research is that these probes provide fast, cost efficient, and precise detection methodology for breast cancer diagnosis and research. The rational design strategy, synthesis, optical profile, confocal imaging and biochemical evaluations will be presented.


Regulation of Lipids is Central to Replicative Senescence in Fibroblasts

Darleny Lizardo, Yen-Lung Lin, Omer Gokcumen and G. Ekin Atilla-Gokcumen

University at Buffalo, Department of Chemistry

Cellular senescence is a state of permanent cell-cycle arrest that occurs following an extended period of proliferation in culture or in response to stress. Several studies have proposed that the senescence response evolved as a fail-safe mechanism to protect cells from cancer. Additionally, senescent cells have been shown to accumulate with age suggesting that senescence may contribute to organismal aging. Upon entering the senescent state, cells undergo dramatic morphological and metabolic changes as well as changes in gene expression. The protein machinery underlying cellular senescence has been heavily studied yet we still have a poor understanding of the role that lipids play in this phenomenon. In this study, the lipid profiles of proliferating and replicative senescent fibroblast cells were investigated using liquid chromatography–mass spectrometry-based lipidomics. Our results show that there is a specific accumulation of polyunsaturated triacylglycerols in replicative senescent fibroblasts. Comparative transcriptomic analysis indicates that the expression levels of lipid-regulating genes are highly regulated during replicative senescence and suggests that CD36-mediated fatty acid uptake and their diversion to glycerolipid biosynthesis could be responsible for the accumulation of triacylglycerols. Our current efforts are toward elucidation of biochemical mechanisms that are responsible for these changes. Gaining a better understanding of the molecular mechanism that accompany replicative senescence will open new research paths for novel therapeutic and diagnostic approaches for human pathologies that replicative senescence is involved in.


DAHP Hydrazone, a nM Inhibitor of DAHP Synthase That Controls Unbound Subunits‘Conformations

Maren Heimhalt, Jenny Zheng, Jennifer Wild, Funing Lin, Naresh Balachandran and Paul J. Berti

McMaster University

Bacterial 3-deoxy-D-arabinoheptulosonate 7-phosphate synthase (DAHPS) is an antimicrobial target.  We previously reported that DAHP oxime is a potent, transition-state mimic inhibitor with Ki = 1.5 μM.  It displays slow dissociation, with a residence time, tR, of 83 min.   One drawback of this inhibitor is 15% residual enzyme activity even at high inhibitor concentrations.  We now report that DAHP hydrazone is an improved DAHPS inhibitor, with a 125-fold lower Ki value, 12 nM, and complete inhibition at high concentrations, though with a reduced residence time, tR = 3.5 min.  The crystal structure reveals the differences in binding of DAHP oxime and DAHP hydrazone to DAHPS. DAHP oxime binds to only two of the subunits in the DAHPS tetramer, DAHP hydrazone binds to three.  Both inhibitors induce a closed conformation in the bound subunits; however, DAHP hydrazone also induces a closed conformation in the unbound subunit, leading to an overall closed4 conformation.  In contrast, the unbound subunits of DAHPS·(DAHP oxime)2 are in an open conformation, with the protein having an overall closed2:open2 conformation.   Thus, rather than binding to all four subunits, DAHP hydrazone’s ability to completely inhibit DAHPS appears to arise from its ability to control the conformation of the unbound subunits.  This mode of inhibition is being characterized in detail.


Helical Aromatic Oligoamide Foldamers: Synthesis and Characterization

Alan Connor and Dr. Bing Gong

 University at Buffalo, Department of Chemistry

The main goal of the Gong group at the University at Buffalo is to develop greater structural understanding of intramolecular forces that induce folding of unnatural peptides, i.e. foldamers. Past foldamers developed in the Gong lab utilized three center hydrogen bonded linked aromatic peptides that were not observed in the unfolded state even at elevated temperatures in organic solvent. Increased flexibility has been sought in order to overcome this extremely high stability and to observe tunable protein-like folding behavior. By switching three center hydrogen bonds with two center allowed for partial bond rotation next to the amide. These newly developed foldamers have been characterized with circular dichroism and 2D NMR techniques demonstrating increased flexibility.