Accurate measurement of small heteronuclear coupling constants from pure-phase α/β HSQMBC cross-peaks

Extending long-range heteronuclear NMR connectivities by HSQMBC-COSY and HSQMBC-TOCSY experiments

“…3. For instance, H15b and H13 protons each exhibit four intense cross-peaks in the 8 Hz HSQMBC spectrum, corresponding to correlations arising from coupling constants in the range of 3.1-7.6 Hz, all experimentally measured from selHSQMBC experiments [23,24]. In comparison, the number of correlations is increased in the 8 Hz HSQMBC-TOCSY experiment recorded with an additional 40 ms TOCSY transfer (compare Fig.…”

“…In contrast to the PIP-HSQMBC experiment [29], a PIP-HSQMBC-TOCSY cross-peak can be the cumulative result of several and different coupling pathway contributions. This would preclude the extraction of n J(CH) using the IPAP methodology or the determination of the relative sign as reported for selective HSQMBC versions [23][24][25][26].…”

“…The proposed experiments retain the simplicity of their 1 H frequency-selective versions (selHSQMBC [23,24], selHSQMBC-COSY [25] and selHSQMBC-TOCSY [26]) which have been recently reported for the quantitative measurement of the magnitude and the sign of n J(CH) and allow a general and routine application with a minimum set-up. Fig.…”

Development of a Karplus equation for 3JCOCH in ester-functionalized glucopyranoses and methylglucuronate.

“…35 Methods for the determination of long-range 1 H- 13 C-couplings based on TOCSY-techniques 36, 37 were not suitable because of the lack of attached protons at the ester carbonyl carbon. We chose the pure-shift in-phase/anti-phase (IPAP) HSQMBC experiment, 38,39 and reproduced previously published 37 1 H-13 C-couplings from a menthol standard in CDCl3 to within 0.7 Hz error (Supplemental Material). In addition, we performed NMR-spectral simulations to complement the results from HSQMBC and J-HMBC experiments.…”

Precise Measurement of Long‐Range Heteronuclear Coupling Constants by a Novel Broadband Proton–Proton‐Decoupled CPMG‐HSQMBC Method

“…Therefore, extraction of the desired heteronuclear coupling constants often requires the use of complex fitting procedures; at worst, extraction of the coupling constants of interest may even be prevented if multiplets are severely distorted. To circumvent this limitation of the HSQMBC method, several modifications have been introduced into the long-range coupling-matched INEPT (insensitive nuclei enhanced by polarization transfer) component of the sequence, such as application of CPMG pulse trains, [16][17][18] selective and band-selective 1808 proton pulses, [19,20] and a perfect echo element. [21] However, even in these amended variants, the resulting HSQMBC peaks appear with complex multiplet patterns in which the undesired proton-proton splittings are superimposed on the antiphase doublets originating from the active heteronuclear coupling interactions.…”