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Science 27 July 2007:
Vol. 317. no. 5837, pp. 493 - 496
DOI: 10.1126/science.1143272
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Reports

Stabilization of Labile Carbonyl Addition Intermediates by a Synthetic Receptor

Tetsuo Iwasawa, Richard J. Hooley, Julius Rebek, Jr.*

Products of unfavorable chemical equilibria are not readily observed because their high energy and increased reactivity result in low concentrations. Biological macromolecules use binding forces to access unfavorable equilibria and stabilize reactive intermediates by isolating them from the medium. In a similar vein, we describe here a synthetic receptor that allows direct observation of labile tetrahedral intermediates: hemiaminals formed in the reaction of an aldehyde carbonyl group with amines. The receptor encapsulates alkyl-substituted primary amines, then orients them toward a covalently tethered aldehyde function. The hemiaminal intermediates appear at high concentration, confined from the bulk solution and observable at ambient temperature by conventional nuclear magnetic resonance spectroscopy.

Skaggs Institute for Chemical Biology and Department of Chemistry, Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.

* To whom correspondence should be addressed. E-mail: jrebek{at}scripps.edu

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