2H exchange into the indole ring in gramicidin peptides

by Gu, Hong; Koeppe II, R. Erdman

The indole ring of Fmoc-Trp can be selectively deuterated at positions 2 and 5 and incorporated into peptides by solid-phase synthesis (J.Am.Chem.Soc. 2003, 125, 12268-76). In cold trifluoroacetic acid-d1, Fmoc-1-Me Trp exchanges more rapidly than Fmoc-Trp (Biophys. J. 2004, 86, 73a). A new focus is to try the method for introducing deuterium on indole or 1-Me-indole rings in existing peptides (post synthesis), for use in 2H-NMR expts. The new method will help to answer an important exptl. question whether the substitution of one Trp in a subunit of a gramicidin channel by Phe or by 1-Me-Trp will alter the av. orientations of the remaining tryptophans. 2H-incorpration and peptide integrity were measured by mass spectrometry. In prototype expts. involving a synthetic analog of gramicidin A with 3 Trp and one Phe, the av. mass of the peptide increased by 6 daltons. The time periods for max. exchange before peptide damage, the 2H-NMR spectra and the deduced indole ring orientations of the exchanged peptides will be presented.