Resolution enhancement in spectra of natural products dissolved in weakly orienting media with the help of H homonuclear dipolar decoupling during acquisition: Application to H–C dipolar couplings measurements

In weakly orienting media such as poly-c-benzyl-L-glutamate (PBLG) a polymer that forms a chiral liquid crystal in organic solvents, the spectral resolution for embedded molecules is usually poor because of numerous H, H dipolar couplings that generally broaden proton spectra. Therefore H, C dipolar couplings are difficult or impossible to measure. Here, we incorporate Flip-Flop decoupling during detection into an HSQC experiment. Flip-Flop removes the H, H dipolar couplings and scales the chemical shifts of the protons as well as the H, C dipolar couplings during detection. A resolution gain by a factor 1.5–4.2 and improved signal intensity by an average factor of 1.6–1.7 have been obtained. This technique is demonstrated on (+)-menthol dissolved in a PBLG/CDCl3 phase. 2006 Elsevier Inc. All rights reserved.