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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 79²J_CHand³J_CHvalues 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 used³J_CHcoupling constants, the subset of 32²J_CHvalues alone showed an excellent degree of configuration selection. The study is mainly based on comparison of DFT‐calculated^2,3J_CHvalues with experimental ones, critical for the case of²J_CH. But the configuration selection also works well using³J_CHvalues 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. 

Abstract The conformation in solution of monocrotaline, a pyrrolizidine alkaloid presenting an eleven‐membered macrocyclic diester ring, has been investigated using a combination of isotropic and anisotropic nuclear magnetic resonance parameters measured in four solvents of different polarity (D₂O, DMSO‐d₆, CDCl₃, and C₆D₆). Anisotropic nuclear magnetic resonance parameters were measured in different alignment media, based on their compatibility with the solvent of interest: cromoglycate liquid crystal solution was used for D₂O, whereas a poly (methyl methacrylate) polymer gel was chosen for CDCl₃and C₆D₆, and a poly (hydroxyethyl methacrylate) gel for DMSO‐d₆. Whereas the pyrrolizidine ring shows anE₆exo‐puckered conformation in all of the solvents, the macrocyclic eleven‐membered ring adopts different populations ofsyn‐parallel andanti‐parallel relative orientation of the carbonyl groups according to the polarity of the solvent.