Through the Looking Glass

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Science  26 Jan 2007:
Vol. 315, Issue 5811, pp. 438
DOI: 10.1126/science.315.5811.438b

Amino acids exist predominantly as L isomers, although the mirror-image D isomers figure in several biochemical pathways. Pyridoxal phosphate-dependent enzymes racemize amino acids for this purpose by binding them through a hydrogen bond-stabilized imine linkage. Park et al. have prepared a small-molecule receptor that binds amino acids through a similar motif but also incorporates a chiral binaphthyl backbone. When L amino acids are bound in the presence of triethylamine base, they are selectively epimerized by proton exchange to the D isomers in order to relieve steric constraints imposed by the framework. The authors could efficiently invert the configurations of 13 chiral amino acids, including those with acidic or basic side chains. Selectivities ranged from 7:1 (for alanine) to 20:1 (for threonine). Acid hydrolysis liberated the epimerized product from the framework, after which the receptor could be recycled. — JSY

J. Am. Chem. Soc. 129, 10.1021/ja067724g (2007).

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