One‐ and two‐dimensional gradient‐selected HSQMBC NMR experiments for the efficient analysis of long‐range heteronuclear coupling constants

Abstract

Three new gradient‐selected NMR experiments for the analysis of long‐range heteronuclear coupling constants are presented. They are demonstrated on a series of compounds including sucrose, strychnine and a complex macrolide, phormidolide, isolated from a marine cyanobacterium. These 1D and 2D heteronuclear single quantum multiple bond correlation (HSQMBC) experiments provide pure absorption, antiphase lineshapes for precise, direct measurement of nJ(C,H) coupling constants. The example compounds were chosen to demonstrate the high sensitivity and ease of spectral interpretation provided by these HSQMBC experiments. In addition, suppression of one‐bond CH correlations has been introduced into the HSQMBC pulse sequence. Copyright © 2000 John Wiley & Sons, Ltd.

Accurate measurement of long-range heteronuclear coupling constants from undistorted multiplets of an enhanced CPMG-HSQMBC experiment

“…The proposed CPMG-HSQMBC experiment which is a straightforward amendment of the original HSQMBC sequence [6] starts with a composite pulse based CPMG-INEPT element as shown in Fig. 1.…”

“…These are summarized in detail by Marquez et al [5]. The HSQMBC experiment [6] in particular has found widespread application since it allows extraction of heteronuclear coupling constants for both protonated and quaternary carbons via heteroatoms (e.g., O and N) in the coupling pathway. It also offers good sensitivity and straightforward implementation on most spectrometers.…”

Spin-edited 2D HSQC–TOCSY experiments for the measurement of homonuclear and heteronuclear coupling constants: Application to carbohydrates and peptides

“…In particular, the gradient-enhanced version of the HSQC-TOCSY experiment allows (i) a careful analysis and straightforward interpretation from clean spectra, (ii) can take profit of the sensitivity-enhanced features traditionally associated to the regular HSQC pulse scheme, and (iii) offers excellent dispersion/resolution properties associated to the much better resolved F1 X dimension [2]. In addition to the classical structure elucidation strategy based on 1 H and X chemical shift assignments, typically applied for 13 C and 15 N in molecules such as carbohydrates and peptides, the regular HSQC-TOCSY pulse scheme has also been largely modified in many different ways with the aim to measure heteronuclear long-range coupling constants, n J (XH) n > 1, in both natural abundance and labelled molecules [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”

“…The resulting in-phase 1 H magnetization obtained at the end of this initial step is suitable for further propagation via a homonuclear 1 H-1 H TOCSY transfer to other relayed protons. Since the initial heteronuclear coherence transfer is based on the large and rather uniform 1 J (HX) values, this approach is very useful to determine even small, several-bond away n J (XH) coupling constants which are difficult to obtain using other NMR methods, such as HMBC [4] or long-range optimized HSQC experiments [5], in where the inter-pulse delays are directly optimized on small n J (XH) values and where the final measurements are often performed on highly complicated anti-phase or mixed-mode multiplet patterns. On the contrary, the main drawbacks of HSQC-TOCSY-type experiments rely in the fact that only couplings on protonated heteronucleus can be measured and the overall sensitivity largely depends of the transfer efficiency during the TOCSY step [3].…”

Anomeric spirocycles by solvent incorporation: reactions of O-peracylated (glyculopyranose and glyculopyranosyl bromide)onamide derivatives with ketones

“…A resonance in the range of 92.4-100.1 ppm could be attributed to an aminal type carbon and this corroborated that the nitrogen was in an endocyclic position in 8. To confirm the difference in the constitution of the heterocyclic parts of the spirocycles, CMPG-HSQMBC experiments [26][27][28] were carried out with 6a and 8e. In these spectra cross peaks (indicated by asterisks in the formulae of the respective compounds in Fig.…”