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.

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.

ChemInform Abstract: CROSS-LINKING OF AMINO ACIDS BY FORMALDEHYDE, (13)C NMR SPECTRA OF MODEL COMPOUNDS

1975 ◽  
Vol 6 (30) ◽  
pp. no-no
Author(s):  
MICHAEL K. DEWAR ◽  
R. B. JOHNS ◽  
DAVID P. KELLY ◽  
JOHN F. YATES
Keyword(s):  
Amino Acids ◽  
Nmr Spectra ◽  
Cross Linking ◽  
Model Compounds ◽  
C Nmr

scholarly journals Real-time prediction of 1H and 13C chemical shifts with DFT accuracy using a 3D graph neural network

2021 ◽  
Author(s):  
Yanfei Guan ◽  
S. V. Shree Sowndarya ◽  
Liliana C. Gallegos ◽  
Peter C. St. John ◽  
Robert S. Paton
Keyword(s):  
Neural Network ◽  
Real Time ◽  
Quantum Chemical ◽  
Organic Molecules ◽  
Chemical Shifts ◽  
13C Chemical Shifts ◽  
Time Prediction ◽  
Nmr Data ◽  
Proton Chemical Shifts

From quantum chemical and experimental NMR data, a 3D graph neural network, CASCADE, has been developed to predict carbon and proton chemical shifts. Stereoisomers and conformers of organic molecules can be correctly distinguished.

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