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Isotropic/Anisotropic NMR editing by resolution-enhanced NMR spectroscopy
Modern resolution‐enhanced NMR techniques can monitor the in situ discrimination of co‐existing isotropic and anisotropic contributions of small molecules dissolved in weakly aligning PMMA/CDCl3 media. The simultaneous sign‐sensitive determination of accurate Δδiso–aniso(1H), Δδiso–aniso(13C) and/or isotropic 1JCH and anisotropic 1TCH coupling constants (and consequently 1H‐13C residual dipolar couplings and 1H/13C residual chemical shift anisotropies) can be performed from spectral‐aliased heteronuclear single‐quantum correlation spectra.
N. Marcó, R. R. Gil and T. Parella
Magn. Reson. Chem, 55, 525-529 (2017). DOI
Structural discrimination from in-situ measurement of 1DCH and 2DHH residual dipolar coupling constants
A fast RDC-assisted strategy involving the simultaneous determination of scalar and total coupling constants from a single 1JCH/2JHH-resolved NMR spectrum is reported. It is shown that the concerted use of the directly measured 1DCH (for all CHn multiplicities) and 2DHH residual dipolar couplings allows an on-the-fly assignment of diastereotopic CH2 protons, as well as of an efficient discrimination between all eight possible diastereoisomeric structures of strychnine, which contains six stereocenters.
L. Castañar, M. García, E. Hellemann, P. Nolis, R.R. Gil and T. Parella
J. Org. Chem., 81, 11126-11131 (2016). DOI
One-Shot determination of residual dipolar couplings. Application to the structural discrimination of small molecules containing multiple stereocenters
A novel approach for the fast and efficient structural discrimination of molecules containing multiple stereochemical centers is described. A robust J-resolved HSQC experiment affording highly resolved 1JCH/1TCH splittings along the indirect dimension and homodecoupled 1H signals in the detected dimension is proposed. The experiment enables in situ distinction of both isotropic and anisotropic components of molecules dissolved in compressed PMMA gels, allowing a rapid and direct one-shot determination of accurate residual dipolar coupling constants from a single NMR spectrum.
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