Enhancement of the optical rotation of α-amino-acids by formation of carbamate (N-carboxy-) salts

Abstract

The optical rotations of fourteen L-α-amino acids dissolved in aqueous potassium carbonate became more positive with time, eventually reaching limiting, values, with optical activity enhancements ranging from <1 to >50 fold. The ¹H n.m.r. signals from the α-protons showed a concomitant down-field shift. These changes are explained by the formation of carbamate (N-carboxy-) salts. The ¹³C n.m.r. spectra also altered with time, showing the gradual appearance of a signal assigned to the carbamate carbon atom.