Improved 2D inverse proton detected C,H correlation NMR techniques for the total assignment of carbon resonances of a highly delta opioid receptor agonist peptide

Assignment of the ¹³C resonances of the highly delta opioid receptor selective cyclic peptide (Formula Presented.) enkephalin (DPDPE) was accomplished by using single‐quantum inverse proton detected 2D heteronuclear correlation spectroscopy. The pulse sequences described provided better sensitivity and resolution than the corresponding, commonly used, multiple‐quantum evolution experiments, since during the SQ‐evolution period there is no line broadening due to scalar and dipolar ¹H‐¹H interactions. The proton detected C,H correlation spectrum, in combination with the H‐TOCSY relay C,H correlation, gave the assignment of all protonated carbons. The C,H correlation optimized for long‐range coupling gave the assignments of all non‐protonated carbons, such as the carbonyl carbons of the peptide bonds. These spectra also allowed the sequential assignment of this molecule.