Application of the TORO technique of 1H NMR to the structural analysis of cyclic peptide isomers having a slightly distorted symmetry from C2.

The extended TORO technique was applied to the structural analysis of endo-D-Tyr-gramicidin S, cyclo(-Val-Orn-Leu-D-Phe-D-Tyr-Pro-Val-Orn-Leu-D-Phe-Pro-), which has a slightly distorted symmetry from C2, by the insertion of D-Tyr and equivalent α-proton chemical shifts in the 1H NMR spectrum. All NMR signals of the two dominant isomers of this antibiotic with trans–trans prolines were determined by using the extended TORO technique with TOCSY and ROESY spectra. This technique is generally applicable for distinguishing overlapped signals of α- and amide protons from the main chains of peptides. Copyright © 2003 John Wiley & Sons, Ltd.