¹³C‐detected IPAP‐INADEQUATE for simultaneous measurement of one‐bond and long‐range scalar or residual dipolar coupling constants

Abstract

The sensitivity of cryoprobes, which are rapidly becoming available, means that the measurement of coupling constants involving 13C, 13C pairs at the natural abundance of 13C can now, in principle, be done by using tens rather then hundreds of milligrams of compounds. However, a robust method that would yield reliable values of small long-range carbon--carbon coupling constants is still missing. In this Communication, we describe a novel 13C-detected incredible natural-abundance double-quantum transfer experiment (INADEQUATE) experiment for simultaneous correlation of one-bond and long-range 13C- 13C pairs and the measurement of both types of coupling constants in 13C natural abundance samples. This method yields accurate values of one-bond and long-range coupling constants by manipulation of pure phase in-phase (IP) and antiphase (AP) doublets, and is referred to as 13C-detected IPAP-INADEQUATE. It is illustrated by the measurement of interglycosidic (3)J(CCOC) coupling constants in a disaccharide molecule providing important information about the conformation of the glycosidic linkage. Owing to the simplicity of INADEQUATE spectra the carbon-carbon coupling constants are particularly suitable for studies of partially oriented molecules through the measurement of carbon-carbon residual dipolar couplings (RDCs). An example of this approach is presented. We expect the method to find a variety of applications in the conformational analysis of small molecules, determination of diastereoisomers and enantiomers, and studies of molecules in aligned media.

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

“…Relaxation times of 1 and 1.3 s were used, respectively. This corresponds to 2.3 times of the longest T 1 relaxation time of 13 C and 1 H attached to 13 C, respectively. The in-and antiphase spectra were acquired in an interleaved mode using 24 scans in each of 875 complex points.…”

“…The 13 C T 1 relaxation times were determined using the inversion recovery method with 1 H decoupling during the recovery delay. The T 1 relaxation times of 13 C-attached protons were determined using the inversion recovery sequence followed by a gradient selected 1D HSQC. The peak intensities were fitted as single exponential decays to determine the decay constants.…”

“…No window function was used in F 1 . 13 C-detected IPAP INADEQUATE spectra of II were acquired using an 800 MHz triple-resonance cryoprobe with z-gradients and a cold carbon preamplifier as detailed in [13].…”

“…Since then, numerous variations of the INADEQUATE have appeared in the literature. The early experiments focusing on the measurement of n J CC coupling constants were performed using 13 C-detection [9][10][11][12][13]; more recently, several 1 H-detected methods have been proposed [14][15][16][17]. The existing methods can be classified as intensity based [15], J-resolved [9,14] and J-modulated correlation [10][11][12][13]16,17] techniques.…”

“…Practically all NMR experiments designed to select carbon pairs in natural abundance 13 C molecules use 13 C-13 C DQ filtration-the principle introduced for the first time in the seminal INADEQUATE experiments [7,8]. Since then, numerous variations of the INADEQUATE have appeared in the literature.…”