Di(ethylene glycol) methyl ether methacrylate (DEGMEMA)‐derived gels align small organic molecules in methanol

García, Manuela E.; Woodruff, Shannon R.; Hellemann, Erich; Tsarevsky, Nicolay V.; Gil, Roberto R.

doi:10.1002/mrc.4400

Cited by 23 publications

(11 citation statements)

References 31 publications

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“…3a, b ). Using only 1 D CH RDCs it was not possible to assign the correct configuration of retrorsine 41 mainly due to lack of information about the quaternary chiral center at C11. However, the configuration analysis of retrorsine was accomplished using 13 C RCSAs 20 .…”

Section: Resultsmentioning

confidence: 99%

Relative configuration of micrograms of natural compounds using proton residual chemical shift anisotropy

et al. 2020

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3D molecular structure determination is a challenge for organic compounds or natural products available in minute amounts. Proton/proton and proton/carbon correlations yield the constitution. J couplings and NOEs oftentimes supported by one-bond 1H,13C residual dipolar couplings (RDCs) or by 13C residual chemical shift anisotropies (RCSAs) provide the relative configuration. However, these RDCs or carbon RCSAs rely on 1% natural abundance of 13C preventing their use for compounds available only in quantities of a few 10’s of µgs. By contrast, 1H RCSAs provide similar information on spatial orientation of structural moieties within a molecule, while using the abundant 1H spin. Herein, 1H RCSAs are accurately measured using constrained aligning gels or liquid crystals and applied to the 3D structural determination of molecules with varying complexities. Even more, deuterated alignment media allow the elucidation of the relative configuration of around 35 µg of a briarane compound isolated from Briareum asbestinum.

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Section: Resultsmentioning

confidence: 99%

Relative configuration of micrograms of natural compounds using proton residual chemical shift anisotropy

et al. 2020

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“…As a fourth example, we chose the alkaloid retrorsine, a compound examined in a number of earlier NMR studies, Figure 6. 48 It is noteworthy that a previous attempt at RDC-based configuration assignment was unsuccessful. 48 Using the stretching device, we collected 16 ΔRCSAs to test whether ΔRCSAs could assign the correct configuration in contrast to the RDC results.…”

Section: ■ Methods Sectionmentioning

confidence: 99%

“…48 It is noteworthy that a previous attempt of RDC-based configuration 19 assignment was unsuccessful. 48 Using the stretching device, we collected sixteen RCSAs to test whether RCSAs could assign the correct configuration in contrast to the RDC results.…”

Section: (D) Retrorsinementioning

confidence: 99%

Determination of Relative Configuration from Residual Chemical Shift Anisotropy

et al. 2016

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Determination of relative configuration is frequently a rate-limiting step in the characterization of small organic molecules. Solution NMR-based nuclear Overhauser effect and scalar J-coupling constants can provide useful spatial information but often fail when stereocenters are separated by more than 4-5 Å. Residual dipolar couplings (RDCs) can provide a means of assigning relative configuration without limits of distance between stereocenters. However, sensitivity limits their application. Chemical shift is the most readily measured NMR parameter, and partial molecular alignment can reveal the anisotropic component of the chemical shift tensor, manifested as residual chemical shift anisotropy (RCSA). Hence, (13)C RCSAs provide information on the relative orientations of specific structural moieties including nonprotonated carbons and can be used for stereochemical assignment. Herein, we present two robust and sensitive methods to accurately measure and apply (13)C RCSAs for stereochemical assignment. The complementary techniques are demonstrated with five molecules representing differing structural classes.

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“…If this is not the case, either by the presence of paramagnetic metal ions [24] or anisotropic susceptibility of diamagnetic macromolecules [25] or, more general, the presence of an anisotropic medium, the molecules will be partially oriented with respect to the external magnetic field, and residual dipolar couplings (RDCs) can be measured (detailed reviews can be found at [26][27][28][29][30][31]). An anisotropic environment is generated by an alignment medium (AM), examples for AMs are stretched gels [32][33][34][35][36][37][38][39][40] or lyotropic liquid crystalline (LLC) phases [41][42][43][44][45][46][47][48][49].…”

Section: Rdcs In Structure Elucidationmentioning

confidence: 99%

The Advanced Floating Chirality Distance Geometry Approach―How Anisotropic NMR Parameters Can Support the Determination of the Relative Configuration of Natural Products

2020

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The configurational analysis of complex natural products by NMR spectroscopy is still a challenging task. The assignment of the relative configuration is usually carried out by analysis of interproton distances from NOESY or ROESY spectra (qualitative or quantitative) and scalar (J) couplings. About 15 years ago, residual dipolar couplings (RDCs) were introduced as a tool for the configurational determination of small organic molecules. In contrast to NOEs/ROEs which are local parameters (distances up to 400 pm can be detected for small organic molecules), RDCs are global parameters which allow to obtain structural information also from long-range relationships. RDCs have the disadvantage that the sample needs a setup in an alignment medium in order to obtain the required anisotropic environment. Here, we will discuss the configurational analysis of five complex natural products: axinellamine A (1), tetrabromostyloguanidine (2), 3,7-epi-massadine chloride (3), tubocurarine (4), and vincristine (5). Compounds 1–3 are marine natural products whereas 4 and 5 are from terrestrial sources. The chosen examples will carefully work out the limitations of NOEs/ROEs in the configurational analysis of natural products and will also provide an outlook on the information obtained from RDCs.

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Di(ethylene glycol) methyl ether methacrylate (DEGMEMA)‐derived gels align small organic molecules in methanol

Cited by 23 publications

References 31 publications

Relative configuration of micrograms of natural compounds using proton residual chemical shift anisotropy

Relative configuration of micrograms of natural compounds using proton residual chemical shift anisotropy

Determination of Relative Configuration from Residual Chemical Shift Anisotropy

The Advanced Floating Chirality Distance Geometry Approach―How Anisotropic NMR Parameters Can Support the Determination of the Relative Configuration of Natural Products

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