期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 134, 期 44, 页码 18345-18353出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja3069648
关键词
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资金
- Defense Threat Reduction Agency (DOD-DTRA) [HDTRA1-09-1-0009]
- National Institute of General Medical Sciences, National Institutes of Health [GM36700, GM067866]
- National Science Foundation [TG-CHE100059]
Transesterification catalysts based. on stereochemically defined, modular, functionalized ladder-molecules (named spiroligozymes) were designed, using the inside-out design strategy, and mutated synthetically to improve catalysis. A series of stereochemically and regiochemically diverse bifunctional spiroligozymes were first synthesized to identify the best arrangement of a pyridine as a general base catalyst and an alcohol nucleophile to accelerate attack on vinyl trifluoroacetate as an electrophile. The best bifunctional spiroligozyme reacted with vinyl trifluoroacetate to form an acyl-spiroligozyme conjugate 2.7 X 10(3)-fold faster than the background reaction with a benzyl alcohol. Two trifunctional spiroligozymes were then synthesized that combined a urea with the pyridine and alcohol to act as an oxyanion hole and activate the bound acyl-spiroligozyme intermediate to enable acyl-transfer to methanol. The best trifunctional spiroligozyme carries out multiple turnovers and acts as a transesterification catalyst with k(1)/k(uncat) of 2.2 X 10(3) and k(2)/k(uncat) of 1.3 X 10(2). Quantum mechanical calculations identified the four transition states of the catalytic cycle and provided a detailed view of every stage of the transesterification reaction.
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