Absolute Configurational Assignment of Acyclic Hydroxy Carboxylic Acids:  A New Strategy in Exciton-Coupled Circular Dichroism

A new strategy in exciton-coupled circular dichroism (ECCD) is described for the configurational assignment of α-hydroxy carboxylic acids. Using 9-anthryldiazomethane ( 4), carboxyl groups can be selectively derivatized with a chromophore suitable for exciton coupling. In combination with the 2-naphthoate chromophore linked to the α-hydroxy group, the absolute stereochemistry of α-hydroxy carboxylic acids can be easily deduced from a single CD measurement. The usefulness of the new method is demonstrated with a series of α-hydroxy acids with different side chains. The developed microscale method is also useful for chiral amino acids and natural products containing carboxyl groups or similar structural units.