Studies of the Stability of Some Amino Acid Carbamates in Neutral Aqueous Solution

The formation of carbamates by the amino acids L-cysteine, DL-α,τ-diaminobutyric acid, DL-α,β-diaminopropionic acid, L-histidine, DL-α-amino-β-methylaminopropionic acid and the dipeptide glycylglycine has been studied by 1H NMR spectroscopy in D2O and, in some cases, in H2O. Values of the binding constants for CO2 to the free amine function (pKc) have been determined. For the diamino acids NMR spectroscopy allows the determination of the stability of the α- and ω-isomers. The results are used to comment on the likely extent of formation of carbamates from these amino acids in vivo.