1H-nuclear magnetic resonance determination of the enantiomeric purity of aliphatic primary amines, β-aminoalcohols, β-diamines and α-amino-acids with 1 R-(−)-myrtenal: scope and limitations

Abstract

1 R-(−)-myrtenal was tested as a chiral derivatising agent for the determination of the enantiomeric purity of aliphatic primary amines, β-aminoalcohols, β-diamines and α-amino-acids. Derivatisation procedure consists in mixing one equivalent each of the amine and 1 R-(−)-myrtenal directly into the nuclear magnetic resonance (NMR) tube before addition of the appropriate deuterated solvent and, for α-amino-acids, one equivalent of NaOH was added to neutralise the acidic function. Diastereoisomeric imines were completely formed after 12 h and analysed by 1H-NMR except for N-methyl β-diamines for which imidazolidines were obtained. The method gave satisfactory results only for α- and β-arylalkylamines for which CDCl 3 could be advantageously replaced by C 6D 6 or pyridine- d 5 in order to increase the difference between the chemical shifts. The main advantage of the procedure is its simplicity as it does not involve steps such as activation, heating, solvent evaporation and isolation of the product. Its limitations are the limited series of compounds susceptible to be analysed and the small difference between the chemical shifts of the diastereoisomeric imines obtained.