1H-Detected IPAP DEPT-INADEQUATE and IPAP RINEPT-INADEQUATE for the measurement of long-range carbon-carbon coupling constants

The sensitivity of cryoprobes, which are rapidly becoming available, have brought about the possibility of measurement of C-13, C-13 coupling constants at the natural abundance of C-13 using tens rather than hundreds of milligrams of compounds. This relatively recent development lays the foundation for a more routine use of the C-13, C-13 long-range coupling constants in the conformational analysis of molecules. We have designed novel H-1-detected INADEQUATE experiments optimized for long-range C-13, C-13 correlations and the measurement of long-range coupling constants. These experiments incorporate refocusing Of (1)J(CH) coupling constants prior to the formation of DQ coherences and H-1-decoupling during the long carbon-carbon evolution intervals. Such modifications significantly enhance their performance over H-1-detected INADEQUATE experiments currently in use for mapping the one-bond C-13, C-13 correlations. H-1 or C-13 polarization is used a starting point in long-range correlation H-1-detected IPAP DEPT-INADEQUATE or RINEPT-INADEQUATE experiments. These correlation experiments were modified yielding in-phase (IP) or antiphase (AP) C-13, C-13 doublets in F-1. Procedures were developed for their editing yielding accurate values of small C-13, C-13 coupling constants. The methods are illustrated using mono- and disaccharide samples and compared with related 13 C-detected experiments by means of the measurement of interglycosidic C-13, C-13 coupling constants of a disaccharide. (c) 2007 Elsevier Inc. All rights reserved.