Homogeneous gold catalysis has been developed explosively during the past decades. Despite the remarkable electrophilic activation of
alkynes by cationic Au(I) catalysts, such as PPh3Au+, one challenge is to overcome their poor stability at high temperature. However, in order to activate some less
reactive substrates, such as internal alkynes, harsher reaction conditions are usually required.
As a good σ-donor and π-receptor, triazole has been applied as a ligand to improve the stability of cationic Au(I) catalysts. Taking
advantage of the good stability of triazole-Au(I) complexes (TA-Au), we successfully achieved good reactivity of intermolecular hydroamination for both terminal and
internal alkynes. Unlike previous reported gold catalysts, the TA-Au catalysts activate alkynes selectively over allenes. With this excellent chemoselectivity, TA-Au
catalysts showed interesting reactivity in propargyl ester and vinyl ether rearrangement. This facilitates the development of otherwise challenging transformations, for
instance, asymmetric synthesis of substituted allenes, Schmittel cyclization, dienal synthesis, and so on.
Gold-catalyzed intermolecular propargyl alcohol addition to alkyne was also achieved using TA-Au catalyst, giving the vinyl ether
followed by a 3,3-rearrangement to generate synthetically useful allenes with high efficiency, substrate tolerability, chemoselectivity and chirality transfer. Other gold
catalysts gave the hydration product almost exclusively. While gold-catalyzed homopropargyl alcohol intramolecular cyclization is a known process, an intermolecular
addition to terminal alkynes was achieved with TA-Au catalyst. A sequential 1,6-enyne cycloisomerization gave an unusual 2,3-dihydrooxepine, which revealed a new reaction
pathway. Diels−Alder reaction of oxepine followed by a 1,3-alkoxyl shift gave hydrobenzofuran derivatives in high yields. Diastereoselective reaction of homopropargyl
alcohol to final product enabled a one-step formation of five stereogenic centers with excellent enantiomeric selectivity.
Complex surface structures with molecular-scale organization and chemical functionalities have garnered tremendous attention in recent
years for applications including biochemical sensors and lithographic resists. Multicomponent alkanethiol-based chemical films assembled onto noble metal surfaces
are commonly utilized due to their rich and well-characterized structures and chemistries. However, the patterning of these films is generally limited to
two-dimensional features due to the reliance on the assembly of monomolecular films and the limited library of molecules available for patterning. The enhancement of
two scanning probe lithographic strategies (nanoshaving and nanografting) by exploiting molecular assembly, topology, and intermolecular interactions will be described
and discussed. The combination of scanning probe lithography and molecular assembly illustrates a general hybrid approach to enhance and to extend the precision,
capabilities, and versatility of lithographic strategies.
The guanidinium modifying enzymes are a large class of enzymes that have been identified to play a significant role in a number of diseases,
such as atherosclerosis, cancer, and multiple sclerosis. The guanidinium modifying enzyme family includes the protein arginine methyltransferases (PRMTs) and the agmatine
deiminases (AgDs), which have only recently become more attractive as drug targets. However, the development of novel pharmaceuticals has been hindered by the lack of tools
and methodologies that are currently available to study these enzymes. To this end, we have successfully developed a novel screening methodology for evaluating the
substrate specificity of the PRMT family of enzymes. This screen has resulted in the identification of PRMT-specific substrates, development of a new inhibitor, and a
chemical probe to further study this enzyme family. Furthermore, we have elucidated the catalytic mechanism of an agmatine deiminase found in Listeria monocytogenes, which is a major contributing factor to Listeriosis infection. Listeriosis is an infection that can lead to miscarriages in pregnant women,
meningitis in newborns, and death in immunocompromised individuals caused by consuming food contaminated with the bacteria, Listeria
monocytogenes. Also, these mechanistic studies have provided valuable information to designing chemical probes that target this family of enzymes.
Dr. Christos Lampropoulos has won an NSF-MRI grant as co-PI with Dr. Tom Pekarek (Physics). This is
for an AC magnetic susceptibility measurement system for the SQUID magnetometer, and it is from the Division for Materials Research.
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