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|Title:||Oxyanion hole stabilization by C-H·O Interaction in a transition state -a three-point interaction model for cinchona alkaloid-catalyzed asymmetric methanolysis of meso -cyclic anhydrides|
|Authors:||Yang, H. |
|Citation:||Yang, H., Wong, M.W. (2013-04-17). Oxyanion hole stabilization by C-H·O Interaction in a transition state -a three-point interaction model for cinchona alkaloid-catalyzed asymmetric methanolysis of meso -cyclic anhydrides. Journal of the American Chemical Society 135 (15) : 5808-5818. ScholarBank@NUS Repository.|
|Abstract:||Oxyanion holes are commonly found in many enzyme structures. They are crucial for the stabilization of high-energy oxyanion intermediates or transition states through hydrogen bonding. Typical functionalities found in enzyme oxyanion holes or chemically designed oxyanion-hole mimics are N-H and O-H groups. Through DFT calculations, we show that asymmetric methanolysis of meso-cyclic anhydrides (AMMA) catalyzed by a class of cinchona alkaloid catalysts involves an oxyanion hole consisting of purely C-H functionality. This C-H oxyanion hole is found to play a pivotal role for stabilizing the developing oxyanion, via C-H·O hydrogen bonds, in our newly proposed three-point interaction transition-state model for AMMA reactions, and is the key reason for the catalyst to adopt the gauche-open conformation in the transition state. Predicted enantioselectivities of three cinchona alkaloid catalysts, namely DHQD-PHN, DHQD-MEQ, and DHQD-CLB, based on calculations of our transition-state model, agree well with experimental findings. © 2013 American Chemical Society.|
|Source Title:||Journal of the American Chemical Society|
|Appears in Collections:||Staff Publications|
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