RESUMO
Nineteen preschisanartane-type schinortriterpenoids (SNTs), among which eleven ones were previously undescribed, were isolated from two Schisandra species, S. sphaerandra and S. rubriflora. Their structures were determined using 1D and 2D NMR spectroscopic analyses, NMR data comparison, quantum chemical calculation of NMR parameters, electronic circular dichroism (ECD), X-ray single crystal diffraction, and chemical derivation. Furthermore, structural re-examination of a few previously reported preschisanartane-type SNTs led to the structural revision of preschisanartanin J. Besides, it is suggested that the reported structures of arisanlactone D and schilancidilactone W should be re-checked. Finally, a few isolated SNTs were found to possess neurite outgrowth-promoting activities, and protective activities against neural injuries.
RESUMO
Structural identification of natural products is the foundation for biological activity evaluation and further targeting action research. However, exact and prompt solutions to the structures, in particular, for the stereochemical problems derived from inherent variability and complexity of natural products, have been faced with challenges. In recent years, the quantum chemistry calculation methods (ECD, VCD, 0R, NMR and others) on the basis of Gaussian software undoubtedly provide a powerful tool for the structure elucidation of complex natural products. This review summarizes some successful cases of Gaussian calculation on structure elucidation with a purpose of broadening research and applications of this method.
RESUMO
Structure elucidation of natural products is invariably a task of primary importance for natural product chemists. Especially, the assignment of configuration for multichiral-center molecules, being one of the great challenge for natural product researchers, has received progressively increased attention. During the past decade, quantum chemical calculation of1H and13C chemical shifts and1H-1H spin-spin coupling constants (SSCC) has seen a marked increase in accuracy, affordability, and application. With the advances in theories and techniques, theoretical calculation assisting structural elucidation will undoubtedly become one of the standard tools in structure assignment for each of chemical laboratories. This mini review briefly describes their principles,advantages,and enumerates some representative structural-reassignment examples to elaborate the utility of these quantum chemical techniques in structural assignment.
RESUMO
OBJECTIVE: To investigate the supermolecular inclusion properties of beta-cyclodextrin and luteolin by drug-enzyme interaction fluorescence spectra and analyze the similarities and differences between the interaction optical spectroscopy and the classical method. METHODS: The total energy of the stable inclusion of cyclodextrin-luteolin was calculated by Gaussian quantitative method, and the stable inclusions in the process of interaction between Lut/inclusion complex and LZM were studied by molecular modeling. RESULTS: The fluorescence spectroscopy not only represented the property of the inclusion with higher sensitivity, but also showed the conveying mechanism of LZM to inclusion compound. The molecular modeling showed consistent results with Gaussian quantum calculation; both of the two methods obtained the stable configuration of β-CD-Lut inclusion. CONCLUSION: The relevant result provides an experimental consequence for the pharmacology research of beta-cyclodextrin-luteolin inclusion complex and also offers a new reference to the research of supermolecular inclusion compound.
RESUMO
Quantum chemical calculations were carried out to study the electronic structure and stability of adenine–thymine and the rare tautomer of adenine–thymine base pairs along with their Cu2+ complexes and their interactions with AlNmodified fullerene (C58AlN) using Density Functional Theory (B3LYP method). Since, these two forms of base pairs and their Cu2+ complexes have almost similar electronic structures, their chemical differentiation is an extremely difficult task. In this investigation, we have observed that AlN-doped C60 could be used as a potentially viable nanoscale sensor to detect these two base pairs as well as their Cu2+ complexes.