Resolution enhancement in spectra of natural products dissolved in weakly orienting media with the help of 1H homonuclear dipolar decoupling during acquisition:: Application to 1H-13C dipolar couplings measurements

In weakly orienting media such as poly-gamma-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-1, 1H dipolar couplings that generally broaden proton spectra. Therefore H-1, C-13 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-1, H-1 dipolar couplings and scales the chemical shifts of the protons as well as the H-1, C-13 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. (c) 2006 Elsevier Inc. All rights reserved.