A CD exciton chirality method for determination of the absolute configuration of threo-beta-aryl-beta-hydroxy-alpha-amino acid derivatives

The absolute configuration of threo-beta-aryl-beta-hydroxy-alpha-amino acids was studied by CD exciton chirality method using 7-diethylaminocoumarin-3-carboxylate as a red-shifted chromophore. Bischromophoric derivatives for a series of threo-beta-aryl-beta-hydroxy-alpha-amino acids (3a-h) were prepared and their CD spectra measured in CH2Cl2. By combining the data of CD and NMR coupling constants, we are able to correlate their preferred conformer (B) and the positive CD to the corresponding (2S,3R)-absolute configuration. These results are consistent with those obtained from serine and threonine derivatives, which represent the simplest form of beta-hydroxy-alpha-amino acids. This CD method could thus become a general method for determining the absolute configuration of threo-beta-aryl-beta-hydroxy-alpha-amino acids.