The Proton NMR Assignment of 1-Aminocyclo-propane-1-carboxylic Acid

The two sets of diastereomeric hydrogen atoms cis and trans to the carboxylate of 1-aminocyclopropane-1-carboxylic acid (ACC) were differentiated by a ¹H-nmr study. The measurement of the ¹H-nmr spectrum of ACC at pH 3.8 during the successive addition of non-chiral lanthanide reagents such as Eu(NO₃)₃, Pr(NO₃)₃ or Gd(NO₃)₃ demonstrated that the hydrogen atoms cis to the carboxylate function of ACC resonate at δ=1.42 and that the hydrogen atoms trans to the carboxylate function of ACC resonate at δ=1.20. The mono-substituted cyclopropanes, cyclo-propanecarboxylic acid (CPC) and cyclopropyl-amine (CPA) were used in complementary lanthanide-reagent shift titrations along with the back titration of an ACC-Eu⁺⁺⁺ complex with DCl to further substantiate the assignment. This assignment allows for the non-destructive, nonisotopic diluting analysis of various biosynthetically derived deuterated ACC's formed from the corresponding deuterated S-adenosyl-L-methionine.