Biosynthetic studies using 18O isotope shifts in 13C nuclear magnetic resonance

1982 ◽  
Vol 60 (13) ◽  
pp. 1637-1642 ◽  
Author(s):  
John C. Vederas
Keyword(s):  
Cytochalasin B ◽  
Brefeldin A ◽  
Isotopic Substitution ◽  
Upfield Shift ◽  
13C Nuclear Magnetic Resonance ◽  
18O Isotope ◽  
Microbial Biosynthesis ◽  
Biosynthetic Studies ◽  
Versicolorin A ◽  
C Nmr

Isotopic substitution with oxygen-18 induces an observable upfield shift in the 13C nmr positions of directly-attached carbons, and in some cases, β-carbons. The magnitudes of these shifts range from about 0.05 ppm to 0.01 ppm, and are dependent on structure in an empirically predictable fashion. Incorporation of doubly labeled (13C, 18O) precursors into polyketides followed by 13C nmr analysis can identify carbon–oxygen bonds remaining intact during microbial biosynthesis. This technique has been applied to studies on antibiotics such as brefeldin A, cytochalasin B, granaticin, and lasalocid A, as well as aflatoxin precursors such as averufin, versicolorin A, and sterigmatocystin.

Magnitudes of 18O isotope shifts in 13C nuclear magnetic resonance spectra of ketones and alcohols

1980 ◽  
Vol 58 (13) ◽  
pp. 1311-1315 ◽  
Author(s):  
James Diakur ◽  
Thomas T. Nakashima ◽  
John C. Vederas
Keyword(s):  
Nmr Spectra ◽  
Negative Charge ◽  
Carbonyl Oxygen ◽  
Upfield Shift ◽  
Isotope Shifts ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
18O Isotope ◽  
Negative Charge Density ◽  
C Nmr

The magnitudes of 18O-induced isotope shifts in 13C nmr spectra of ketones and aldehydes are dependent on structure and range from about 0.05 ppm to 0.03 ppm for the carbon attached to 18O. An increase in negative charge density on the carbonyl oxygen or conjugation to an aromatic ring reduces the size of the upfield shift. The shifts in [18O]alcohols are solvent-dependent, range from 0.03 ppm to 0.01 ppm, and tend to decrease in the order tertiary ≥ secondary ≥ primary ≥ phenols.

Medium-sized cyclophanes. XX. 13C nuclear magnetic resonance of cyclophanes: p-orbital compression shift and orbital deformation

1976 ◽  
Vol 54 (21) ◽  
pp. 3412-3418 ◽  
Author(s):  
Tetsuo Takemura ◽  
Takeo Sato
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Molecular Geometry ◽  
Methylene Carbon ◽  
Upfield Shift ◽  
13C Nuclear Magnetic Resonance ◽  
Orbital Axis ◽  
C Nmr

The 13C nmr spectra of [2.2]meta-, metapara-, and paracyclophanes were determined. By comparing the chemical shifts with those of acyclic models two types of anomalies were revealed.(1) Bridging methylene carbon resonances for [2.2]metacyclophanes having an alkyl group ortho to the bridge were shifted upfield as a result of van der Waals' compression. The upfield shift is much larger (5–12 ppm) for cyclophanes than for models (2–4 ppm) reflecting the rigid nature of the molecular geometry of the former.(2) Interestingly, inner aryl carbon resonances in [2.2]metacyclophanes and protonated aryl carbon resonances in [2.2]paracyclophanes were shifted downfield by 6–7 ppm. The complementary upfield shift of uncompressed atoms, hydrogen or carbon, connected to those carbons was also noticed. The downfield shift of compressed sp2 carbon results from interaction between two p-orbitals along the same orbital axis, p-orbital compression, and is attributable to decreased electron density.

Nuphar thiaspirane sulfoxides. 13C nuclear magnetic resonance determined configuration and utilization in the interconversion of thiaspirane stereochemical types

1978 ◽  
Vol 56 (1) ◽  
pp. 56-61 ◽  
Author(s):  
R. T. LaLonde ◽  
C. F. Wong
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Subsequent Reduction ◽  
13C Nuclear Magnetic Resonance ◽  
Sodium Borodeuteride ◽  
C Nmr ◽  
Nuclear Magnetic

The configuration of the sulfoxide oxygen in syn- and anti-thiobinupharidine sulfoxide was determined by employing the 13C nmr sulfoxidation increments of C-6. Establishment of the 13C nmr line assignments for C-6 included the study of the C-6 and C-6′ deuterated thiobinupharidine and the corresponding sulfoxides. Thermolysis of syn-thiobinupharidine sulfoxide in DMSO and subsequent reduction with sodium borodeuteride in methanol yielded thiobinupharidine, labelled with deuterium only at C-6, and thionuphlutine B, labelled with deuterium at both C-6 and C-6′. Treatment of the anti sulfoxide in xylene or DMSO resulted in no thiobinupharidine or thionuphlutine B. Similarly, syn-neothiobinupharidine sulfoxide gave neothiobinupharidine and a new thiaspirane, thionuphlutine C. These two compounds were not produced from anti-neothiobinupharidine sulfoxide heated in xylene.

13C nuclear magnetic resonance spectra of the spirobenzylisoquinoline alkaloids and related model compounds

1977 ◽  
Vol 55 (18) ◽  
pp. 3304-3311 ◽  
Author(s):  
Donald W. Hughes ◽  
Bala C. Nalliah ◽  
Herbert L. Holland ◽  
David B. MacLean
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Isoquinoline Alkaloids ◽  
Model Compounds ◽  
Related Model ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The natural abundance 13C nuclear magnetic resonance spectra of a number of spirobenzylisoquinoline alkaloids and related model compounds have been recorded. The carbon resonances of the alkaloids were assigned by comparison with the spectra of other isoquinoline alkaloids and with those of the model compounds. It has been shown that 13C nmr spectroscopy may be used to differentiate between diastereomers in this series.

scholarly journals Structural Elucidation of Pimarane and Isopimarane Diterpenoids: The 13C NMR Contribution

2008 ◽  
Vol 3 (3) ◽  
pp. 1934578X0800300 ◽  
Author(s):  
Ana M. L. Seca ◽  
Diana C. G. A. Pinto ◽  
Artur M. S. Silva
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
Nmr Assignments ◽  
Structural Elucidation ◽  
Synthetic Compounds ◽  
Chiral Centers ◽  
Pimarane Diterpenoids ◽  
Biosynthetic Studies ◽  
C Nmr ◽  
Natural And Synthetic

13C NMR spectroscopy is actually one of the first tools used for the structural elucidation of natural and synthetic compounds and it is also used in biosynthetic studies. The aim of this review is to present the 13C NMR assignments of a large number of pimarane diterpenoids, describing the most significant effects caused by different substitution patterns and different stereochemistry at their chiral centers.

A 13C nuclear magnetic resonance study of aliphatic ketone protonation in sulfuric acid solutions

1976 ◽  
Vol 54 (5) ◽  
pp. 718-725 ◽  
Author(s):  
Robert A. McClelland ◽  
William F. Reynolds
Keyword(s):  
Sulfuric Acid ◽  
Molecular Size ◽  
Nuclear Magnetic Resonance Study ◽  
Suitable Alternative ◽  
Acidic Solutions ◽  
H Nmr ◽  
Organic Bases ◽  
13C Nuclear Magnetic Resonance ◽  
Sulfuric Acid Solutions ◽  
C Nmr

A 13C nmr investigation of the protonation in sulfuric acid of the aliphatic ketones MeCOR (R = Me, Et, i-Pr, tert-Bu), 3-pentanone, and the cyclic ketones from cyclobutanone through cyclooctanone is reported. With the exception of cyclobutanone which is considerably less basic, these ketones are all very similar in their basicity, with half-protonation in the region 73–78% H2SO4. The acidity dependence of the protonation is discussed; there appears to be a small dependence on molecular size. 13C nmr is shown to be a suitable alternative to 1H nmr in the study of the protonation of weak organic bases in strongly acidic solutions.

15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. II. Protonation of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine in dimethyl sulfoxide

1990 ◽  
Vol 68 (11) ◽  
pp. 2033-2038 ◽  
Author(s):  
Giovanna Barbarella ◽  
Massimo Luigi Capobianco ◽  
Luisa Tondelli ◽  
Vitaliano Tugnoli
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Dimethyl Sulfoxide ◽  
Phosphate Group ◽  
Nmr Data ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Nuclear Magnetic

The preferential protonation sites of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine were established by nitrogen-15 and carbon-13 NMR in dimethyl sulfoxide, in the presence of varying amounts of CF3COOH. The nitrogen-15 NMR data show that in d(CpC) the capability of the two N3 nitrogens to accept the proton is slightly different. In d(TpT) and d(ApA) the protonation of the phosphate group leads to significant variations of the chemical shift of the carbons adjacent to phosphorus. Keywords: deoxydinucleotides, protonation, 15N and 13C NMR.

scholarly journals 13C nuclear magnetic resonance spectroscopy to check 1,3-random, 2-random pattern of fatty acid distribution in olive oil triacylglycerols

2005 ◽  
Vol 19 (2) ◽  
pp. 109-117 ◽  
Author(s):  
Giovanna Vlahov
Keyword(s):  
Oleic Acid ◽  
Fatty Acid ◽  
Olive Oil ◽  
Random Distribution ◽  
Fatty Acid Distribution ◽  
Computer Method ◽  
Random Pattern ◽  
13C Nuclear Magnetic Resonance ◽  
Oleic And Linoleic Acids ◽  
C Nmr

The fatty acid distribution between the 1,3- and 2-positions of triglycerides was determined in the olive oil set sampled in the Marche region, by using the13C NMR method which applies the DEPT pulse sequence. The results confirmed that the oleic and linoleic acids were not randomly distributed at the 2-position of triacylglycerols but were lower for oleic acid and higher for linoleic acid compared to the theoretical values expected for a random distribution. Moreover, the unsaturated acids deviated from the 2-random distribution at different extents according to the acid concentration of triglyceride.The13C NMR results, they were obtained for three olive oil samples characterized by high, medium and low oleic acid at 2-position (Ofound) corresponding to a low, medium, high deviation rate from the 2-random pattern, were compared to those calculated by the computer program based on the 1,3-random-2-random distribution of fatty acids in the triglycerides.The molar concentrations of the triglyceride species LLL and OLL were calculated from the molar concentrations of oleic and linoleic acids at the 2- and 1,3-positions obtained by using13C NMR and the computer method. The LLL and OLL triglycerides determined by the computer method were found to be markedly higher in the “high Ofound” oil as compared to NMR. No differences were detected between the two methods for both triglyceride species in the “low Ofound” oil.

13C nuclear magnetic resonance and Raman investigations of aqueous carbon dioxide systems

1982 ◽  
Vol 60 (8) ◽  
pp. 1000-1006 ◽  
Author(s):  
Theresa M. Abbott ◽  
Gerald W. Buchanan ◽  
Peeter Kruus ◽  
Keith C. Lee
Keyword(s):  
Carbon Dioxide ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Linear Relationship ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Carbonate Ion ◽  
13C Nuclear Magnetic Resonance ◽  
Wide Range ◽  
C Nmr

13C-nmr spectra of carbon dioxide in water are reported for a wide range in pH. Chemical shifts were determined for the following species: CO2(g), CO2(aq), HCO3−(aq), CO32−(aq). A linear relationship was found between the shift of the 13C line and the fraction of carbonate ion calculated to be present, as well as between the ratio of the area under the 1067 cm−1 (carbonate) Raman peak to the sum of the area under the 1067 cm−1 and 1017 cm−1 (bicarbonate) peaks and the fraction carbonate.

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