M. Ghosn
2011
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Georgetown University-Graduate School of Arts & Sciences
Abstract
The unique structure of 1,8-diarylnaphthalenes provides an excellent opportunity to design sensors with a chromophoric binding pocket and the ability to transform a binding event with a chiral substrate into a strong and quantifiable signal. Since both arene rings readily rotate about the two chiral axes, 1,8-bis(3’-formyl-4’-hydroxyphenyl)naphthalene exists as a mixture of enantiomeric anti-conformers that rapidly interconvert via a meso syn-isomer. Diimine formation between this stereodynamic probe and chiral substrates disturbs this equilibrium and strongly favors the population of a single diastereomer through intramolecular hydrogen bonding. The cofacial arrangement of the two salicylaldehyde rings favors intramolecular π−π interactions and subsequent generation of intense Cotton effects at high wavelengths. This sensor provides information about the absolute configuration and enantiomeric composition of a wide range of amino alcohols and amino acids based on well-defined and understood central-to-axial chiral amplification processes. The incorporation of moderate bulk in the form of methyl groups into the orthopositions of 1,8-bis(3’-formyl-4’-hydroxyphenyl)naphthalene resulted in the formation of conformational isomers that are stable to interconversion and separable at room temperature. The axially chiral stereoisomers of 1,8-bis(2’-methyl-4’-hydroxy-5’-