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Herein, we present the solution‐state NMR studies on dextromethorphan (1) under both isotropic and anisotropic conditions. From the measurement of 22 residual dipolar couplings using a stretched polystyrene gel (PS), we show that accurate and detailed structural information is readily determined including the relative stereochemical assignments of chiral centers, validation of diastereomer configuration,...
In‐depth conformational analyses of 10 known eremophilane (= (1S,4aR,7R,8aR)‐decahydro‐1,8a‐dimethyl‐7‐(1‐methylethyl)napththalene) sesquiterpenes, 1–10, from Petasites hybridus were performed with molecular mechanics as well as density functional theory methods. Electronic transition energies and rotational strengths of these eight eremophilane lactones and two petasins were calculated by time‐dependent...
2,7‐Bis(4‐t‐butylphenyl)fluoren‐9‐ylmethyl methacrylate (BBPFMMA) was synthesized as a new candidate of a bulky monomer suitable for asymmetric anionic polymerization (IUPAC nomenclature: asymmetric helix‐chirogenic polymerization) leading to a preferred‐handed helical, optically active polymer. The new monomer was polymerized using the complex of 9‐fluorenyllithium and (S)‐(+)‐1‐(2‐pyrrolidinylmethyl)pyrrolidine...
A chiral cyclotetrapeptide (1) was synthesized from 2‐nitrobenzoic acid and leucine. A single‐crystal X‐ray of the compound revealed a C2‐symmetric bowl‐shaped structure. The cyclic compound had a unique hydrogen‐bonding network composed of three‐centered hydrogen bonds and bifurcated hydrogen bonds between NH and CO of anthranilic residue. The NMR spectra and molecular modeling of 1 also suggested...
The enantioselective organocatalytic methanolysis of cis‐1,2,3,6‐tetrahydrophthalic anhydride mediated by quinidine derivatives with pyridazine or anthraquinone core was investigated, carrying out a detailed nuclear magnetic resonance study of the conformational preferences of the alkaloid catalysts in the pure solvent and in the presence of the reaction substrates and products. No significant interaction...
The effect of the secondary structural feature, that is, nonplanarity of carbon–carbon double bonds, on the rotatory strength of the long‐wavelength π–π* electronic transition has been investigated for the series of monocyclic cis‐dihydrodiol arene metabolites and model compounds. The contribution from nonplanar CC bonds to the overall rotatory strength of the π–π* electronic transition is more significant...
The present work is devoted to the synthesis, conformational analysis, and stereodynamic study of aza‐β3‐cyclodipeptides. This pseudopeptidic ring shows E/Z hydrazide bond isomerism, eight‐membered ring conformation, and chirotopic nitrogen atoms, all of which are elements that are prone to modulate the ring shape. The (E,E) twist boat conformation observed in the solid state by X‐ray diffraction...
The origin of P‐ or M‐chirality of methyl substituted 1,3‐cyclohexadienes are elucidated by time‐dependent density functional theory (TD‐DFT) calculation of 1,3‐cyclohexadiene derivatives and acyclic 1,3‐dienes. The sign‐inversion of the rotatory strength of the lowest excited state between 1,3‐cyclohexadiene and (5R)‐axial‐methyl‐1,3‐cyclohexadiene is caused by the conformation around the (C=)C‐C(‐Me)...
The production and distribution of counterfeit pharmaceuticals present a serious problem worldwide. This is true especially in case of phosphodiesterase type 5 inhibitors for treating erectile dysfunction, where consumers often prefer buying them anonymously from unverified sources. In this study, genuine and counterfeit Cialis® 20 mg tablets were analyzed by electronic circular dichroism, vibrational...
Based on a CSD search, a meta‐analysis of 1179 structures of 19 natural amino acids H3NCαH(R)C′(O)O and their derivatives H3NCαH(R)C′(O)O(H/R/M), protonated, esterified, or coordinated at the carboxylic group, shows that the chirality chain with its two steps, established in the preceding paper for alanine, can be extended to natural amino acids. High diastereoselectivities are observed in the induction...
Based on a Cambridge Structural Database (CSD) search, a meta‐analysis of 116 structures of alanine H3NCαH(CH3)C′(O)O and its derivatives H3NCαH(CH3)C′(O)O(H/R/M), protonated, esterified, or coordinated at the carboxylic group, shows that in the first step of a chirality chain, the L configuration at Cα induces (M) and (P) conformations with respect to rotation around the central C′─Cα bond. In the...
Bridged bicyclic amino acids have high potential applicability as self‐organized, conformationally constrained synthetic building blocks that do not require assistance from hydrogen bond formation. We systematically investigated the intrinsic conformational propensities of dipeptides of bridged bicyclic β‐amino acids by means of accelerated molecular dynamics simulation and density functional theory...
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