CAREER: Towards Space- and Time- resolved Generation of p-Benzyne Diradical: Development of Photoswitchable Analogs of Natural Enediyne Antibiotics

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With the support of the Organic Dynamics Program in the Chemistry Division, Professor Vladimir Popik of Bowling Green State University will develop methods for the efficient photochemical generation of reactive ten- and nine-membered ring cyclic enediyne compounds. Several types of precursors that are stable in the dark but produce a high yield of reactive enediynes upon irradiation with light have been designed. The resulting enediyne then undergoes a rapid thermal cycloaromatization producing p-benzyne diradical. The photochemical generation of highly strained cyclic enediyne compounds, which cyclize very rapidly, will be employed to study the p-benzyne diradical using flash photolytic techniques. The two-photon activation of enediyne photoprecursors will be explored. Several structurally different cyclic enediyne precursors, which incorporate one of three photoreactive groups: a-diazodicarbonyl, cyclopropenone, or a-diketone, will be prepared. These compounds will be studied to determine thermal and hydrolytic stability, as well as quantum and chemical yield of the enediyne generation. The kinetics and mechanism of the Bergman cyclization of enediyne photoproducts will be investigated using conventional and time-resolved techniques. Three of the photoswitchable enediynes have been already synthesized and their photochemistry is currently under investigation. The Organic and Macromolecular Chemistry Program supports Professor Vladimir Popik of Bowling Green State University whose research will provide methods for the time- and spatially-resolved generation of reactive enediynes. These methods will supply new tools for exploring the mechanism of Bergman cyclization and for the direct observation of p-benzyne diradicals. Photoswitchable enediynes could also serve as a basis for the development of new photoactivatable enediyne antibiotics and 3-D selective photonucleases. Spatial control of the enediyne cycloaromatization reaction might lead to the development of new approaches to photolithography and information recording. This project provides undergraduate and graduate students with an interdisciplinary training at the interface of synthetic and physical organic chemistry, as well as training in photochemistry and biochemistry. The interdisciplinary nature of the project will require and result in extensive collaboration with other research groups both locally and internationally.