13C Chemical Shifts of Quinolizidines. 2. 13C Spectra of Some Nuphar Alkaloids

1975 ◽  
Vol 53 (12) ◽  
pp. 1714-1725 ◽  
Author(s):  
Robert T. LaLonde ◽  
Thomas N. Donvito ◽  
Amy I-M. Tsai
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Methyl Groups ◽  
Hydroxyl Groups ◽  
Chemical Shift Assignments ◽  
Oxide Formation ◽  
Model Compounds ◽  
Methyl Group ◽  
13C Chemical Shifts

The 13C n.m.r. spectra of nine Nuphar alkaloids: deoxynupharidine, 7-epideoxynupharidine, nupharidine, 7-epinupharidine, nupharolutine, 7-epinupharolutine, thiobinupharidine, thionu-phlutine B, and neothiobinupharidine, have been determined. Also examined were the spectra of five model compounds, 2,2,4,4-tetramethylthiolane, 3(a)-methyl-3(e)-methylthiomethylquinolizidine, 3(e)-methyl-3(a)-methylthiomethylquinolizidine, 3(e)-methylthio-3(a)-methylquinolizidine, and 3-methylfuran. This latter group of spectra were used to assist the chemical shift assignments of the Nuphar alkaloids. The most significant findings of this study are: (i) axial methyl and thiomethylene groups are shielded more than their equatorial counterparts in all cases; (ii) axial and equatorial hydroxyl groups substituted at C-7 of deoxynupharidine and 7-epideoxynupharidine give α-, β-, and γ-effects in ring B similar to those in carbocyclic systems but also produce small upfield shifts in ring A especially at the carbons α to nitrogen; (iii) the effect of a 3-furyl group located at C-4 appears to have nearly the same effect on quinolizidine ring carbons as a methyl group in the same position, the effects being shielding and deshielding at the various ring carbons; (iv) N-oxide formation results in α-, β-, γ-, and δ-shielding and deshielding effects consistent with the incorporation of an axial oxygen into a trans-fused system or the formation of a cis-fused quinolizidine N-oxide; and (v) methylene or methyl groups attached to C-2 and C-4 of a thiolane, including that in the skeleton of the C30 thiaspirane alkaloids, experience deshielding δ-effects.

13C chemical shifts in medium ring and macrocyclic ketolactones

1977 ◽  
Vol 55 (18) ◽  
pp. 3261-3267 ◽  
Author(s):  
Jaswant R. Mahajan ◽  
Hugo C. Araújo
Keyword(s):  
Chemical Shift ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Natural Abundance ◽  
Chemical Shift Assignments ◽  
Substituted Benzenes ◽  
13C Chemical Shifts ◽  
Naphthalene Series ◽  
Medium Ring

Natural abundance 13C Ft nmr spectra of four different series of title compounds have been examined. Unambiguous chemical shift assignments could be made for all the carbons of the 11-membered cis-3,3-dimethyl-5-keto-6-alkyl-8-decenolides. In the rest of the 9- to 16-membered ketolactones, unique as well as logical assignments have been made using the standard 13C chemical shift rules. In the case of two benzo- and naphthoketolactone series examined, the available shielding parameters for the substituted benzenes were employed with success to the naphthalene series for the assignment of aromatic carbons.

Determination of chemical shifts in 6-condensed syringylic lignin model compounds

Holzforschung ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Lucas Lagerquist ◽  
Jani Rahkila ◽  
Patrik Eklund
Keyword(s):  
Chemical Shift ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Model Compounds ◽  
Correlation Peak ◽  
Lignin Model Compounds ◽  
Benzylic Alcohols ◽  
Lignin Model ◽  
C Nmr

Abstract A small library of 6-substituted syringyl model compounds with aliphatic, carboxylic, phenylic, benzylic alcohols and brominated substituents were prepared. The influence of the substituents on the chemical shifts of the compounds was analyzed. All of model compounds showed a characteristic increase in the 13C NMR chemical shift of the methoxy group vicinal to the substitution. This 13C NMR peak and its corresponding correlation peak in HSQC could potentially be used to identify 6-condensation in syringylic lignin samples.

Cross-linking of amino acids by formaldehyde. 13C N.M.R. spectra of model compounds

1975 ◽  
Vol 28 (4) ◽  
pp. 917 ◽  
Author(s):  
MK Dewar ◽  
RB Johns ◽  
DP Kelly ◽  
JF Yates
Keyword(s):  
Amino Acids ◽  
Chemical Shifts ◽  
Cross Linking ◽  
Model Compounds ◽  
13C Chemical Shifts

The use of 13C N.M.R. for the identification of the site of cross- linking of amino acids by formaldehyde has been evaluated by use of model compounds, such as 2,4-dimethylphenol for tyrosine. The 13C chemical shifts of the formaldehyde-derived methylene carbons occur within the range 50-60 p.p.m. downfield from Me4Si. Estimated shifts in lysine-lysine and tyrosine-glutamine cross-linked systems fall just outside this region. The 13C spectra of a number of related phenols, amines and protected amino acids are also reported.

CORE LEVEL CHEMICAL SHIFTS AND LINE SHAPES FOR SYSTEMS WITH DIFFERENT VALENCIES AND Cu-O NETWORKS

2000 ◽  
Vol 14 (32) ◽  
pp. 3791-3830 ◽  
Author(s):  
K. KARLSSON ◽  
O. GUNNARSSON ◽  
O. JEPSEN
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Core Level ◽  
Photoemission Spectrum ◽  
Main Peak ◽  
Model Compounds ◽  
Line Shapes ◽  
Impurity Model ◽  
Anderson Impurity Model ◽  
Good Agreement

We have studied the Cu -2p core level photoemission spectrum of a variety of cuprates, mainly focusing on the chemical shift and the shape of the leading peak. The spectra are calculated using the Anderson impurity model and we obtain a very good agreement with the experimental data. We find that the shape of the leading peak depends crucially on the structure of the Cu - O network. The main peak turns out to be quite narrow if the network consists of Cu - O - Cu bond angels of the order of 90°. On the other hand, if the Cu - O atoms are arranged with bond angles of approximately 180°, the main peak becomes substantially broader and contains a rather complicated structure. However, in some cases it is not sufficient only to consider the Cu - O network because interactions with other atoms are also important. In the model compounds Cu 2 O , CuO and NaCuO 2, where Cu is formally monovalent, divalent and trivalent, respectively, we find that the number of 3d electrons is rather similar. Nevertheless, the binding energy increases with the valence as expected from chemical intuition. The spectra exhibit a large variation in the strength of the d9-like satellite and in the width of the main line. We, furthermore, study the chemical shift of three inequivalent Cu atoms in YBa 2 Cu 3 O 6.5, and compare the results with the model compounds, which suggests that the different Cu atoms in YBa 2 Cu 3 O 6.5 have formal valences of approximately one, two and three. These findings are analyzed and related to the formal valence.

scholarly journals Carbon-13 NMR Chemical Shift of Methyl Group: A Useful Parameter for Structural Analysis of C-Methylated Flavonoids

2006 ◽  
Vol 1 (11) ◽  
pp. 1934578X0600101
Author(s):  
Pawan K. Agrawal ◽  
Chandan Agrawal ◽  
Shravan Agrawal
Keyword(s):  
Structural Analysis ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Nmr Chemical Shift ◽  
Methyl Group ◽  
Nmr Chemical Shifts ◽  
Nmr Study ◽  
Pterocarpus Santalinus ◽  
Group A ◽  
C Nmr

The 13C NMR resonances corresponding to the C-Me group of C-6 and/or C-8 C-methylated-flavonoids absorb between 6.7–10.0 ppm and typically between 6.7–8.7 ppm. A comparative 13C NMR study reflects that the 13C NMR chemical shifts reported for 6-hydroxy-5-methyl-3′,4′,5′-trimethoxyaurone-4-O-α-L-rhamnoside from Pterocarpus santalinus and 8-C-methyl-5,7,2′,4′- tetramethoxyflavanone from Terminalia alata are inconsistent with the assigned structures, and therefore need reconsideration.

13C Nuclear Magnetic Resonance of Oximes. I. Solvent and Isotope Effects on the 13C Chemical Shifts of Acetoxime

1972 ◽  
Vol 50 (12) ◽  
pp. 1956-1958 ◽  
Author(s):  
N. Gurudata
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Solvent Effects ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Solvent Interactions ◽  
13C Chemical Shifts ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

The 13C n.m.r. spectrum of acetoxime has been obtained in five representative solvents and the chemical shifts of the three carbon atoms measured. The solvent effects on the chemical shifts are found to reflect specific solute–solvent interactions. The effect of deuteration of the α-protons on the chemical shift of the oximino carbon is also discussed.

1H and 13C NMR Spectral Studies on N-(Aryl)-Substituted Acetamides, C6H5NHCOCH3-iXi and 2/4-XC6H4NHCOCH3-iXi (where X = Cl or CH3 and i = 0, 1, 2 or 3)

2003 ◽  
Vol 58 (12) ◽  
pp. 801-806 ◽  
Author(s):  
B. Thimme Gowda ◽  
K. M. Usha ◽  
K. L. Jayalakshmi
Keyword(s):  
Chemical Shift ◽  
Benzene Ring ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Spectral Studies ◽  
Side Chain ◽  
1H And 13C Nmr ◽  
Methyl Group ◽  
Solution State

35 N-(Phenyl)-, N-(2/4-chlorophenyl)- and N-(2/4-methylphenyl)-substituted acetamides are prepared, characterised and their NMR spectra studied in solution state. The variation of the chemical shifts of the aromatic protons in these compounds follow more or less the same trend with changes in the side chain. The chemical shifts remain almost the same on introduction of Cl substituent to the benzene ring, while that of methyl group lowers the chemical shifts of the aromatic protons. But only 13C-1 and 13C-4 chemical shifts in these compounds are sensitive to variations of the side chain. The incremental shifts in the chemical shifts of the aromatic protons and carbons due to -COCH3−iXi or NHCOCH3−iXi groups in all the N-(phenyl)-substituted acetamides, C6H5NHCOCH3−iXi (where X = Cl or CH3 and i = 0, 1, 2 or 3) are calculated. These incremental chemical shifts are used to calculate the chemical shifts of the aromatic protons and carbons in all the N-(2/4-chlorophenyl)- and N-(2/4-methylphenyl)-substituted acetamides, in two ways. In the first way, the chemical shifts of aromatic protons or carbons are computed by adding the incremental shifts due to -COCH3−iXi groups and the substituents at the 2nd or 4th position in the benzene ring to the chemical shifts of the corresponding aromatic protons or carbons of the parent aniline. In the second way, the chemical shifts are calculated by adding the incremental shifts due to -NHCOCH3−iXi groups and the substituents at the 2nd or 4th position in the benzene ring to the chemical shift of a benzene proton or carbon, respectively. Comparison of the two sets of calculated chemical shifts of the aromatic protons or carbons of all the compounds revealed that the two procedures of calculation lead to almost the same values in most cases and agree well with the experimental chemical shifts.

scholarly journals Detection of methylation, acetylation and glycosylation of protein residues by monitoring 13C chemical-shift changes

2016 ◽  
Author(s):  
Pablo G. Garay ◽  
Osvaldo A. Martin ◽  
Harold A. Scheraga ◽  
Jorge A. Vila
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Biological Processes ◽  
Proof Of Concept ◽  
Post Translational Modifications ◽  
13C Chemical Shifts ◽  
Protein Residues ◽  
Lysine Residues ◽  
13C Chemical Shift ◽  
Good Agreement

Post-translational modifications of proteins expand the diversity of the proteome by several orders of magnitude and have a profound effect on several biological processes. Their detection by experimental methods is not free of limitations such as the amount of sample needed or the use of destructive procedures to obtain the sample. Certainly, new approaches are needed and, therefore, we explore here, as a proof-of-concept, the feasibility of using 13C chemical shifts of different nuclei to detect methylation, acetylation and glycosylation of protein residues by monitoring the deviation of the 13C chemical shifts from the expected (mean) experimental value of the non-modified residue. As a validation test of this approach, we compare our theoretical computations of the 13Ce chemical-shift values against experimental data, obtained from NMR spectroscopy, for methylated and acetylated lysine residues with good agreement within ~1 ppm. Then, further use of this approach to select the most suitable 13C-nucleus, with which to determine other modifications commonly seen, such as methylation of arginine and glycosylation of serine, asparagine and threonine, shows encouraging results.

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