Applications of ammonium formate-catalytic transfer hydrogenation. Part V (1). Transfer hydrogenolysis of peptides containing p-chlorophenylalanine as a convenient method for preparation of deuterium labeled peptides.
Dehalogenation of chlorine bound to aromatic nuclei has been achieved using ammonium formate-catalytic transfer hydrogenation (AF-CTH) techniques. The use of deuterated ammonium formate as the transfer agent in the CTH process when performed in a deuterated solvent medium results in the predominant formation of the labeled product. Thus, ND+4 DCOO(-)-CTH of [D-Ala2, p-ClPhe4]-Leu-enkephalin in 80% CD3COOD/D2O yielded [D-Ala2, Phe (4D)4]-Leu-enkephalin. Levels of D-incorporation were measured by fast atom bombardment-mass spectrometry (FAB-MS) and/or by 13C n.m.r. spectroscopy. Using D-labeled and unlabeled ammonium formate in stoichiometrically similar reactions, it was concluded that the hydrogenation exhibited a primary kinetic isotope effect. Reactant and product concentrations were determined by amino acid analysis and reversed phase HPLC.