scholarly journals Oxygenated Theonellastrols: Interpretation of Unusual Chemical Behaviors Using Quantum Mechanical Calculations and Stereochemical Reassignment of 7α-Hydroxytheonellasterol

Marine Drugs ◽  
2020 ◽  
Vol 18 (12) ◽  
pp. 607
Author(s):  
A-Young Shin ◽  
Hyi-Seung Lee ◽  
Yeon-Ju Lee ◽  
Jong Seok Lee ◽  
Arang Son ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Atomic Orbital ◽  
2D Nmr ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Epoxy Alcohol ◽  
Theonella Swinhoei ◽  
Nmr Data ◽  
Chemical Shift Calculations

A total of eight new oxygenated 4-exo-methylene sterols, 1–8, together with one artifact 9 and six known sterols 11–16, were isolated from the marine sponge Theonella swinhoei collected from the Bohol province in Philippines. Structures of sterols 1–8 were determined from 1D and 2D NMR data. Among the sterols, 8α-hydroxytheonellasterol (4) spontaneously underwent an allylic 1,3-hydroxyl shift to produce 15α-hydroxytheonellasterol (9) as an artifact; this was rationalized by quantum mechanical calculations of the transition state. In addition, the 1,2-epoxy alcohol subunit of 8α-hydroxy-14,15-β-epoxytheonellasterol (5) was assigned using the Gauge-Independent Atomic Orbital (GIAO) NMR chemical shift calculations and subsequent DP4+ analysis. Finally, comparison of the 13C chemical shifts of isolated 7α-hydroxytheonellasterol (6) with the reported values revealed significant discrepancies at C-6, C-7, C-8, and C-14, leading to reassignment of the C-7 stereochemistry in the known structure.

scholarly journals Stereochemistry of Complex Marine Natural Products by Quantum Mechanical Calculations of NMR Chemical Shifts: Solvent and Conformational Effects on Okadaic Acid

Marine Drugs ◽  
2014 ◽  
Vol 12 (1) ◽  
pp. 176-192 ◽  
Author(s):  
Humberto Domínguez ◽  
Guillermo Crespín ◽  
Adrián Santiago-Benítez ◽  
José Gavín ◽  
Manuel Norte ◽  
...  
Keyword(s):  
Natural Products ◽  
Okadaic Acid ◽  
Marine Natural Products ◽  
Chemical Shifts ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Nmr Chemical Shifts ◽  
Conformational Effects

scholarly journals Stabilization of N-, N,N-, N,N′-methylated and unsubstituted simple amidine salts by multifurcated hydrogen bonds

2006 ◽  
Vol 20 (4) ◽  
pp. 169-176 ◽  
Author(s):  
Jarosław Spychała
Keyword(s):  
Chemical Shift ◽  
Hydrogen Bonds ◽  
Chemical Shifts ◽  
2D Nmr ◽  
Biological Properties ◽  
Carbonyl Oxygen ◽  
Relative Strength ◽  
Intramolecular Interactions ◽  
Covalent Bonds ◽  
Natural Isotopic Abundance

In the light of the usefulness of amidines in medicinal chemistry, this paper considers the effects on biological properties and chemical reactivities of organic molecules affected by intramolecular interactions. The study of chemical shifts has been an important source of information on the electronic structure of amidine salts and their ability to form non-covalent bonds with nucleic acids. The NMR and IR results demonstrate that hydrogen bonds are a force for promoting chemical reactions. The thymine O2 carbonyl oxygen in a close proximity to the amidinium cation does interact with the appropriately spaced amidinium NH donor moieties. The1H-15N 2D NMR (GHSQC and GHMBC) spectra with natural isotopic abundance of15N fully confirm the intramolecular character of the bonds. A rule able to estimate the relative strength of the new multifurcated hydrogen bonds is given. The appearance of the ΔδNHchemical shift differences near zero is due to the strong intramolecular interactions. The strength of the H-bond donation by acetamidines is reflected in the N–H dissociation/recombination process (positive charge shift has been invoked to explain other effects on benzamidines). The temperature dependence of chemical shift for the amidine NH protons in dimethyl sulfoxide solutions is herein discussed.

Use of Replaced Chalcones to Generate a 13C Chemical Shift Staging Factor for Chalcone and Its Derivate

2020 ◽  
Vol 12 (4) ◽  
pp. 464-472
Author(s):  
Thaís F. Giacomello ◽  
Gunar V. da S. Mota ◽  
Antônio M. de J. C. Neto ◽  
Fabio L. P. Costa
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Density Functional ◽  
Chemical Shifts ◽  
Atomic Orbital ◽  
Scaling Factor ◽  
Orbital Method ◽  
Beneficial Effects ◽  
Nuclear Magnetic

Chalcones have attracted the attention of researchers for decades, they are biologically classified as secondary metabolites of low molecular weight. These are considered as the precursors of flavonoids and they are widely distributed in plants such as vegetables, fruits, teas and spices. It has been demonstrating that chalcones possess many important bioactivities including properties of antioxidants and other evidence of its potential beneficial effects on health. Chalcone compounds and its derivatives have been showing a growing interest in the therapeutic properties. Nuclear magnetic resonance (NMR) spectroscopy is one of the most important tools for determining the structures of organic molecules. In the work present a 13C Nuclear magnetic resonance chemical shift protocol of chalcones and derivative based on the application of scaling factor with chalcone molecules. This protocol consists of using density functional theory with gauge-including atomic orbital method to calculating 13C chemical shifts and the application of a parameterized scaling factor in order to ensure accurate structural determination of chalcones and derivative.

scholarly journals Powder Crystallography by Combining NMR and Crystal Structure Predictions

2014 ◽  
Vol 70 (a1) ◽  
pp. C136-C136 ◽  
Author(s):  
Cory Widdifield ◽  
Maria Baias ◽  
Jean-Nicolas Dumez ◽  
Per H. Svensson ◽  
Hugh Thompson ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Chemical Shift ◽  
Structure Determination ◽  
Structure Prediction ◽  
Density Functional ◽  
De Novo ◽  
Chemical Shifts ◽  
2D Nmr ◽  
Other Information ◽  
13C Chemical Shift

State-of-the-art work in the field of NMR crystallography for molecular systems at natural abundance has recently focused on the accurate measurement of 1H chemical shift values. We will show how when coupled with crystal structure prediction (CSP) methods, this protocol is well-suited for solving the crystal structures of small to medium sized organic molecules, including cocaine and the de-novo structure determination of AZD8329.[1,2] As complementary 1D and 2D NMR experiments are needed for the 1H assignment process, other information, such as isotropic 13C chemical shift values (δiso) are measured. Unfortunately, 13C chemical shifts are not generally useful for structure determination. Additional NMR parameters that are sensitive to structure would ensure that the structure determination procedure is robust, and would provide more accurate refinements when studying larger or more challenging systems. Here, we measure 13C chemical shift tensors for a variety of prototypical organic pharmaceuticals and use density functional theory computations under the gauge-including projector augmented-wave (GIPAW) formalism to probe whether these parameters may be discriminatory for unit cell determinations and structure determination (notably when added to the CSP + 1H chemical shifts protocol).

scholarly journals Structure Revision and Protein Tyrosine Phosphatase Inhibitory Activity of Drazepinone

Marine Drugs ◽  
2021 ◽  
Vol 19 (12) ◽  
pp. 714
Author(s):  
Fei Cao ◽  
Li Pan ◽  
Wen-Bin Gao ◽  
Yun-Feng Liu ◽  
Cai-Juan Zheng ◽  
...  
Keyword(s):  
Detailed Analysis ◽  
Protein Tyrosine Phosphatase ◽  
Inhibitory Activity ◽  
Chemical Shifts ◽  
Tyrosine Phosphatase ◽  
2D Nmr ◽  
Nmr Data ◽  
Structure Revision ◽  
Ic50 Values

From the marine-derived fungus Penicillium sumatrense (Trichocomaceae), a pair of enantiomers [(+)-1 and (−)-1] were isolated with identical 1D NMR data to drazepinone, which was originally reported to have a trisubstituted naphthofuroazepinone skeleton. In this study, we confirmed the structures of the two enantiomers as drazepinone and revised their structures by detailed analysis of extensive 2D NMR data and a comparison of the calculated 13C chemical shifts, ECD, VCD, and ORD spectra with those of the experiment ones. (+)-1 and (−)-1 were evaluated for their PTP inhibitory activity in vitro. (−)-1 showed selective PTP inhibitory activity against PTP1B and TCPTP with IC50 values of 1.56 and 12.5 μg/mL, respectively.

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