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  1. Abstract

    Configurational and conformational analysis of the biologically relevant natural product artemisinin was conducted using carbon–carbon residual dipolar couplings (1DCCRDCs) at natural abundance. These RDCs were measured through the 2D‐INADEQUATE NMR experiment using a sample aligned in a compressed poly (methyl methacrylate) (PMMA) gel swollen in CDCl3. Singular value decomposition (SVD) fitting analysis of all carbon–carbon bonds,1DCCRDCs, in relation to the full configuration/conformational space (32 diastereoisomers) of artemisinin, unambiguously identified the correct configuration of artemisinin.

     
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  2. Abstract

    We present a method to use long‐range CH coupling constants to derive the correct diastereoisomer from the molecular constitution of small molecules. A set of 792JCHand3JCHvalues collected from a single HSQMBC experiment on a sample of strychnine were used in the CASE‐3D (computer‐assisted 3D structure elucidation) protocol. In addition to the most commonly used3JCHcoupling constants, the subset of 322JCHvalues alone showed an excellent degree of configuration selection. The study is mainly based on comparison of DFT‐calculated2,3JCHvalues with experimental ones, critical for the case of2JCH. But the configuration selection also works well using3JCHvalues predicted from a semi‐empirical Karplus‐based equation limited to H−C−C−C fragments. The robustness, shown using strychnine as a proof of concept, makes theJ‐based CASE‐3D analysis a viable option for the application in fields such as peptide and carbohydrate research, organic synthesis, natural‐product identification and analysis, as well as medicinal chemistry.

     
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  3. Abstract

    We present a method to use long‐range CH coupling constants to derive the correct diastereoisomer from the molecular constitution of small molecules. A set of 792JCHand3JCHvalues collected from a single HSQMBC experiment on a sample of strychnine were used in the CASE‐3D (computer‐assisted 3D structure elucidation) protocol. In addition to the most commonly used3JCHcoupling constants, the subset of 322JCHvalues alone showed an excellent degree of configuration selection. The study is mainly based on comparison of DFT‐calculated2,3JCHvalues with experimental ones, critical for the case of2JCH. But the configuration selection also works well using3JCHvalues predicted from a semi‐empirical Karplus‐based equation limited to H−C−C−C fragments. The robustness, shown using strychnine as a proof of concept, makes theJ‐based CASE‐3D analysis a viable option for the application in fields such as peptide and carbohydrate research, organic synthesis, natural‐product identification and analysis, as well as medicinal chemistry.

     
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  4. Abstract

    An enhanced computer‐assisted procedure for the determination of the relative configuration of natural products, which starts from the molecular formula and uses a combination of conventional 1D and 2D NMR spectra, and residual dipolar couplings (RDCs), is reported. Having already the data acquired (1D/2D NMR and RDCs), the procedure begins with the determination of the molecular constitution using standard computer‐assisted structure elucidation (CASE) and is followed by fully automated determination of relative configuration through RDC analysis. In the case of moderately flexible molecules the simplest data‐explaining conformational model is selected by the use of the Akaike information criterion.

     
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