Carbon-13 magnetic resonance.  IX.  Methylcyclohexanes

Dalling, Don K.; Grant, David M.

doi:10.1021/ja01001a039

Cited by 458 publications

(111 citation statements)

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“…This was deduced, as for PPAPs in general, 1 from the upfield shift of the axial methyl group at C-11 in the 13 C NMR spectrum (δ C 16.0), due to the γ-gauche interaction shielding of this methyl group by the C-10 allyl group. 20 The value of the chemical shift of C-10 (δ C 39.7) is also in agreement with an equatorial substituent bound to this carbon.…”

supporting

confidence: 58%

“…The values for δ C are attributed to the γ-gauche effect (one equatorial substituent on each side of the gem-dimethyl). 20 With two equivalents of malonyl dichloride, stoichiometry described by Stoltz in the case of the reaction with a TBS enol ether, 19 and a longer reaction time at room temperature, Effenberger annulation 14 could be achieved, but with concomitant O-cyclization. These conditions afforded 10 again (17%) but compound 12 also was isolated as one isomer, with 24% yield (46% corrected yield, based on 48% of recovered ketones).…”

Section: Resultsmentioning

confidence: 99%

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A rapid access to the core skeleton of atypic tricyclic polyprenylated acylphloroglucinols

Delpech¹,

Tolón²,

Marazano³

2010

Arkivoc

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A synthesis of (4S*,6S*)-2,4,6-triallyl-3,3-dimethylcyclohexanones, and the treatment of their TMS enol ethers with malonyl dichloride in the presence of BF 3 •Et 2 O, are reported. Formation of a ketoacid, resulting from acylation without cyclization, and of a tricyclic phloroglucinol derivative, involving Effenberger annulation with concomitant O-cyclization, were obtained. The tricyclic compound has the core skeleton of the hyperibones H and I, atypical natural polycyclic polyprenylated acylphloroglucinols. Mechanistic and stereochemical aspects are discussed.

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supporting

confidence: 58%

Section: Resultsmentioning

confidence: 99%

A rapid access to the core skeleton of atypic tricyclic polyprenylated acylphloroglucinols

Delpech¹,

Tolón²,

Marazano³

2010

Arkivoc

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“…The peaks assigned to C14 (27.3 and 25.9 ppm) have intensity ratios of about 2:1. The chemical shift of the isomeric methyl carbon (C14) is expected to be upfield when it occupies an axial instead of an equatorial position (8). That the major component (27.3 ppm) is the more downfield peak of this pair, indicates therefore that the methyl carbon is equatorial in the predominant isomer.…”

Section: Resultsmentioning

confidence: 99%

Carbon-13 Nuclear Magnetic Resonance Spectroscopy. Structure of the Anticoagulant Warfarin and Related Compounds in Solution

Giannini

Chan

Roberts

1974

Proc. Natl. Acad. Sci. U.S.A.

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Carbon-13 nuclear magnetic resonance spectra have been obtained for the coumarin-related compounds warfarin and phenprocoumon. The spectral assignments indicate that warfarin exists as a mixture of cyclic hemiketal diastereomers in dimethyl sulfoxide solution. The sodium salt of warfarin exists as the ringopen form in water solution.Warfarin has been used as a rodenticide and anticoagulant since the late 1940's, while the sodium salt of warfarin (Coumadin®) has become the most widely used anticoagulant in many hematological diseases and surgical procedures. The rationale for structures 1 and 2 assigned to warfarin and its sodium salt, respectively, has come from chemical synthesis (1) and spectroscopic methods (2). These structures have been assumed to be correct for many years, although no rigorous structural proof has as yet been presented in the literature. Recently, it has been suggested that crystalline warfarin exists as the hemiketal, 3. (Diffraction data indicates a cyclic hemiketal structure in the solid state; E. Valente, W. Clearly, structural information for the dissolved substance is of great interest and importance to those concerned with the mode of action of warfarin. Solution studies of warfarin utilizing infrared and proton nuclear magnetic resonance (NMR) spectra, are difficult to interpret and are ambiguous due to the complexity of the spectra, although the proton NMR spectrum of warfarin is similar to that of the cyclocoumarol, 4 (K. K. Chan, unpublished data). This fact suggests that the keto structure 1 for warfarin in solution may also be incorrect. Much more definitive information seemed possible through use of carbon-13 NMR to differentiate between structures 1 and 3 because the hemiketal carbon (3, position 13) would have a grossly difAbbreviations: NMR, nuclear magnetic resonance; TMS, tetramethylsilane; Me2SO, dimethyl sulfoxdde. Chemical-shift measurements were made using a Brukarian, pulsed FT spectrometer (3) operating at 15.09 MHz for carbon-13. The temperature was maintained at 37.0 i 1°with a Bruker B-ST temperature control unit. Off-resonance and a gated-decoupling (4) technique which turns off the proton noise decoupler during acquisition of data were used in facilitating spectral assignments. A typical spectrum was run with an acquisition time of 0.8 sec, pulse delay of 1.0 sec, sweep width of 5000 Hz and 8K data points. RESULTS AND DISCUSSIONThe assignment of spectral peaks is based on several wellestablished methods which are now common in 18C spectroscopy (for discussion see refs. 5 and 6). For example, the alkyl carbons, Cli, C12, and C14, are known to have characteristic chemical shifts (4) based upon model studies with hydrocarbons. The peaks can be further differentiated by the multiplicity patterns obtained from off-resonance experiments. However, ambiguities were encountered for warfarin and, for example, the C2 and C4 peaks were not assignable by analogy with the resonances of coumarin or 4-hydroxycoumarin. Also, off-resonance did not provide sufficient inf...

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“…6B) structurally similar and were thus assigned to the three non-protonated resonances grouped upfield at about 142-147 ppm (Table 1). Carbon 2 should be deshielded because of a steric interaction (18) with the methyl group attached to C-1. It was assigned to the resonance at about 134 ppm.…”

Section: Resultsmentioning

confidence: 99%

Assignments in the Carbon-13 Nuclear Magnetic Resonance Spectra of Vitamin B ₁₂ , Coenzyme B ₁₂ , and Other Corrinoids: Application of Partially-Relaxed Fourier Transform Spectroscopy

Doddrell

Allerhand

1971

Proc. Natl. Acad. Sci. U.S.A.

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High-resolution Fourier transform NMR at 15.08 MHz was used to observe the proton-decoupled natural-abundance 13C spectra of aqueous solutions of cobinamide dicyanide (0.067 M), cyanocobalamin (0.024 M), dicyanocobalamin (0.14 M), and coenzyme B12 (0.038 M). Assignments were made with the aid of chemical shift comparisons, off-resonance single-frequency proton decoupling, partially-relaxed Fourier transform spectra, and splittings arising from 13C-31P coupling.As expected, the 13C spectra of the corrinoids were appreciably more informative than the corresponding proton spectra. Nearly all the lines in the 13C spectra of the corrinoids were well-resolved single-carbon resonances, in spite of the structural complexity.Partially relaxed 13C Fourier transform NMR spectra, which yield spin-lattice relaxation times of each resolved resonance, were found to be a very useful addition to the arsenal of NMR techniques.Proton nuclear magnetic resonance (NMR) has been useful for investigating the solution properties of vitamin B12 (cyanocobalamin, Fig. 1A) and other corrinoids (1-4). However, even at 220 MHz, proton NMR spectra of corrinoids contain many overlapping lines, as a result of a small range of chemical shifts and complex spin-spin splittings (4). For the study of complex molecules, proton-decoupled spectra of 13C nuclei in natural abundance are, in general, much more resolved and simpler to analyze than the corresponding proton spectra (5). The enhanced sensitivity of the Fourier transform technique (6) relative to continuous-wave N1\IR has expanded the range of accessible 13C spectra (7). We will show that by using the Fourier transform method it is easy to obtain high signal-to-noise ratios on single-carbon resonances in the proton-decoupled natural-abundance 13C spectra of corrinoids, even when the concentration is limited to 0.02 M.There are only two well-known generally applicable aids to the assignment of 13C resonances in complex molecules: comparisons within a series of compounds with similar structures, and the use of splitting patterns arising from incomplete proton-decoupling (5). The former is often complicated by uncertainties in chemical shift changes with structure; the latter is difficult to use when there are many overlapping lines (5). We show below that 13C partially-relaxed Fourier transform (PRFT) spectra (8, 9) provide additional help in making assignments. Intensities in PRFT spectra are given (10) by A = Ao [1 -2 exp(-rT1)],

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Carbon-13 magnetic resonance. IX. Methylcyclohexanes

Cited by 458 publications

References 1 publication

A rapid access to the core skeleton of atypic tricyclic polyprenylated acylphloroglucinols

A rapid access to the core skeleton of atypic tricyclic polyprenylated acylphloroglucinols

Carbon-13 Nuclear Magnetic Resonance Spectroscopy. Structure of the Anticoagulant Warfarin and Related Compounds in Solution

Assignments in the Carbon-13 Nuclear Magnetic Resonance Spectra of Vitamin B ₁₂ , Coenzyme B ₁₂ , and Other Corrinoids: Application of Partially-Relaxed Fourier Transform Spectroscopy

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Carbon-13 magnetic resonance. IX. Methylcyclohexanes

Cited by 458 publications

References 1 publication

A rapid access to the core skeleton of atypic tricyclic polyprenylated acylphloroglucinols

A rapid access to the core skeleton of atypic tricyclic polyprenylated acylphloroglucinols

Carbon-13 Nuclear Magnetic Resonance Spectroscopy. Structure of the Anticoagulant Warfarin and Related Compounds in Solution

Assignments in the Carbon-13 Nuclear Magnetic Resonance Spectra of Vitamin B 12 , Coenzyme B 12 , and Other Corrinoids: Application of Partially-Relaxed Fourier Transform Spectroscopy

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Assignments in the Carbon-13 Nuclear Magnetic Resonance Spectra of Vitamin B ₁₂ , Coenzyme B ₁₂ , and Other Corrinoids: Application of Partially-Relaxed Fourier Transform Spectroscopy