Fluorine Nuclear Magnetic Resonance of Peptides and Amino-acids

Abstract

WE report here the development of a rapid new method for the analysis of mixtures of peptides and amino-acids. This technique is based on the measurement of the ¹⁹F nuclear magnetic resonance spectra of trifluoroacetyl or other fluorine containing derivatives of peptides and amino-acids. Earlier we reported that fluorine magnetic resonance can be used for the quantitative analysis of mixtures of metals as chelate derivatives of trifluoracetylacetone (unpublished results of R. E. S.). Although the proton resonance spectra of Zr(IV) trifluoracetylacetonate and Hf(IV) trifluoracetylacetonate in chloroform are essentially the same, the fluorine resonance peaks are well separated (0.23 p.p.m.) and easily integrated to provide quantitative analysis of Zr and Hf. It is well known that the fluorine chemical shift is much more sensitive (between one and two orders of magnitude) to small differences in shielding than the proton resonance. Experience with the fluorine magnetic resonance of extremely similar metal chelates¹ led us to conclude that the same advantage could be realized in detecting small differences in chemically and structurally similar peptides and amino-acids. Accordingly, the N-trifluoracetyl derivatives of the amino-acids and peptides shown in Table 1 were prepared and the fluorine NMR spectra measured. It is readily seen in Table 2 and Figs. 1 and 2 that the fluorine nuclei reflect small differences in structure, acting as what might be termed sensors, with the resonance peak for each trifluoracetyl group appearing at a characteristic field position.