Application of phenylglycine methyl ester (PGME) to determination of the absolute configuration of carboxylic acids having phenylalkyl group

(R)- and (S)-phenylglycine methyl ester (PGME) was applied to elucidate the absolute configuration of a series of aliphatic carboxylic acids, 2a and 2b (n = 1–6), which possess a phenyl group on the chain, by the process similar to the modified Mosher's method. (S)-PGME was condensed with rac-2a and 2b, and the resulting diastereomeric pair was separated for each of 2a and 2b. Δδ values were calculated from the 1H-NMR chemical shifts of (R)-2a-(or 2b)-(S)-PGME and (R)-2a-(or 2b)-PGME amides. By analyzing the positive and negative distribution patterns for each compound, it was concluded that this new method was successful to predict the absolute configuration of such type of acids, and that no significant interaction between the two phenyl groups, one in the chain and the other in the PGME, was present. Chirality 9:550–555, 1997.