Concerning carbon-13 n.m.r. spectroscopy of 5β-hydroxylated phytoecdysones

The ¹³C n.m.r. spectra of the 5β-hydroxylated phytoecdysones polypodine B, muristerone A and kaladasterone are presented and briefly discussed together with the spectrum of makisterone A. Comparisons with previously reported spectra of ecdysone, ecdysterone and poststerone are made and allow a correction for the C-20/C-24 assignment for ecdysone.     

Substituent effect of the nitro group on alkanes in carbon-13 n.m.r. spectroscopy

Linear correlation coefficients were obtained for the substituent effect of the nitro group in primary nitroalkanes. The solvent effect of chloroform is also discussed, as well as the influence of the scalar relaxation on the half-width of α-carbons in ¹³C n.m.r. spectroscopy.     

Investigation of substituent effects of chalcones by 13C n.m.r. spectroscopy

¹³C chemical shifts for 23 para- and meta-substituted chalcones of the types 1 and 2 have been determined. The aromatic shieldings are compared with previous results for other aromatic derivatives. Correlations of the ¹³C chemical shifts of vinyl carbons and carbonyl carbons as well as ring carbons with Hammett σ parameters, π electron densities and the reactivity parameters of Swain and Lupton provide a consistent picture of electronic effects transmitted through the carbon framework of the compounds studied.     

Electronic effects in some 3-substituted-2-cyclohexenones: A study by carbon-13 n.m.r. spectroscopy

The carbon-13 n.m.r. spectra of some 3-substituted-2-cyclohexenones show very wide variations in chemical shift at C-3 that correlate with Pauling electronegativity χ, even wider variations at C-2 that correlate with the Taft resonance parameter σ_Rº and almost no variation at C-1. These very different effects are shown to be consistent with the electronic distribution for these and related compounds revealed by other spectroscopic techniques. Reasons for the insensitivity of carbon-13 n.m.r. to configurational and conformational variation in simple enamino-ketones are discussed.     

Analogues of the antibiotic puromycin as potential prodrugs of 3′-amino-3′-deoxythymidine

Condensation of L- and D-3′-amino-2′,3′-dideoxynucleosides 2–5 with N-BOC-protected aminoacids 6 and 13 using dicyclohexylcarbodiimide and N-hydroxysuccinimide in DMF is reported to give the N-BOC-protected acylamino aminonucleosides 7– 9 and 14 in 51–81% yield. After deprotection using trifluoroacetic acid the corresponding unprotected new analogues of puromucin 10–12 and 15 were obtained in 43–56% yield. These compounds did not show any significant antiviral activity using HIV (stain HTLV-III B)-infected MT-4 cells as target system.     

Application of carbon-13 n.m.r. Spectroscopy to the structural investigation of ezomycins

Ezomycins A₁, A₂, B₁, B₂, C₁, C₂, D₁ and D₂, antifungal antibiotics, are anhydrooctose uronic acid nucleosides. Their novel structures were confirmed by studying their natural abundance ¹³C n.m.r. spectra in detail from gated proton-decoupled, long-range selective proton-decoupled and selective proton-decoupled spectra. The J(CH) value of the anomeric carbon signal (C-1″) supports the β-configuration.     

Carbon-13 n.m.r. spectroscopy of some Strychnos alkaloids

¹³C N.m.r. spectra have been determined for strychnine and a series of fourteen derivatives. The assignments are based on previously established data and on off-resonance decoupled spectra. The shifts resulting from the alterations in molecular structure are discussed and explained, in part, as a consequence of conformational changes. This detailed study indicates that changes are required in some previously published assignments.     

N.m.r. studies in the heterocyclic series: XVII—carbon-13 spectra of indazole derivatives

The ¹³C chemical shifts of 17 indazole derivatives are discussed as a function of substituent effects and the N-1—H or N-2—H structure of indazole. The presence in solution of the N-1—H tautomer is confirmed.     

A carbon-13 n.m.r. study of sulfur-donor ligand ortho-metalated iron carbonyl complexes

Carbon-13 n.m.r. data are reported for a series of sulfur-donor ligand ortho-metalated iron carbonyl complexes derived from thiobenzophenones. The chemical shift δ153·5–161·4 for the aromatic carbon σ-bonded to iron is readily identified, and occurs in the same region as the signal for the corresponding carbon in a related nitrogen-donor ligand complex. The benzylic carbon gives a signal at δ62·8–63·3, subject to the nature of the complex.     

The structure of 1,2-dithioles studied by 13C n.m.r. spectroscopy

The charge separation between the dithiole ring and oxygen in 3-(1′,2′-dithiole-3′-ylidene)-6-methyl-2,3-dihydropyran-2,4-diones and 3-(1′,2′-dithiole-3′-ylidene)-2,3-dihydrobenzo[b] pyran-2,4-diones has been determined by ¹³C and ¹⁹F n.m.r. spectroscopy. By both methods it is found that these compounds are relatively polar. A correlation is established between the ¹³C chemical shift of some carbon atoms and the S2p binding energies measured by e.s.c.a. in the 1,2-dithiole derivatives. This correlation shows that these ¹³C shifts depend on the positive charge taken by the 1,2-dithiole ring and can then constitute a convenient evaluation of this charge.     

Silicon-29 and carbon-13 n.m.r. studies of organosilicon chemistry. VII—trimethylsilylated silicates

Silicon-29 n.m.r. was used to study the products from trimethylsilylation of minerals. Chemical shifts are reported for four model compounds, viz. the monomer, dimer, linear trimer (from natrolite) and cyclic tetramer (from laumontite). Information is then obtained from the products of trimethylsilylation of the anhydrous calcium silicates wollastonite and pseudo-wollastonite. In the latter case it is shown that the principal products are the four model compounds, and percentage yields are obtained for these.     

Carbon-13 n.m.r. studies. 65—13C spectra of some tricyclo[3.2.1.02,4]octane derivatives

The ¹³C n.m.r. spectra of 18 derivatives of the tricyclo[3.2.1.0^2,4]octanes have been determined. This series includes methyl, hydroxyl and oxo substituted examples to compare the effects of these substituents on the skeletal carbon shieldings with those observed for the corresponding norbornanes and bicyclo[3.2.1]octanes. In general, the trends are similar and the perturbations associated with closely neighboring groups follow a consistent pattern. The shielding data for the exo–exo and exo–endo isomers of tetracyclo[3.3.1.0^2,40^6,8]nonane are also reported.     

Carbon-13 n.m.r. studies of flavanone 5,3′,4′-trihydroxy-7β-glucoside from Juelia subterranea (Balanophoraceae)

The complete structure and stereochemical elucidation of flavanone 5,3′,4′-trihydroxy-7β-glucoside has been achieved by the aid of ¹³C n.m.r.     

13C n.m.r. spectroscopy: Comparison of the spectra of some dimeric Catharanthus alkaloids and their derivatives

The ¹³C n.m.r. spectra of some dimeric Catharanthus alkaloids are reported and assigned. Methods devised to aid in the assignment of resonances in complex molecules are described. The ¹³C n.m.r. spectra of several derivatives of vinblastine are discussed.     

13C n.m.r. studies of some phenanthrene and fluorene derivatives

The ¹H and ¹³C spectra of fluorene, fluorenone, phenanthrene and their 4-methyl and 4,5-dimethyl derivatives have been examined. To complete the analyses for fluorenone and 4-methylfluorenone, ¹H spectra were recorded at 270 MHz. The results from the ¹H spectra permitted unequivocal assignments for the protonated aryl carbons by selective proton decoupling. A consistent set of assignments for the quaternary carbons was obtained through consideration of the dominant relaxation processes operative at these centres. This series of compounds was examined to investigate the shielding effects produced by the close approach of methyl groups separated by five bonds for comparison with the contrasting trends found for methyl carbons separated by three and four bonds. The results indicate that the relative orientation of the methyl groups is an extremely critical factor governing their shieldings and those of neighboring centres.     

Carbon-13 n.m.r. studies of some saturated 1,2-oxazepine derivatives

The influence of incorporating an group, an oxygen atom and the fragment in a saturated 7-membered ring system on carbon-13 n.m.r. chemical shifts is examined, and also, the influence of the dioxolane ring moiety on the ¹³C chemical shifts in these ring systems. Substituent effects are generally additive except in cases where the ring is heavily substituted with methyl groups. A large upfield steric shift (γ effect) of 7–8 ppm is observed in two of the derivatives. An example of long range nonequivalence is also observed. Assignments of the ¹³C n.m.r. spectra have been made by comparison with model compounds, and from proton coupled ¹³C n.m.r. spectra. The synthesis of several new compounds is described.     

13C n.m.r. spectra of lysergic acid derivatives: II—dihydrolysergamides

The conformations of dihydrolysergamides and 10-methoxydihydrolysergamides have been inferred from the study of the chemical shifts of the amide hydrogens and their temperature dependence. The ¹³C chemical shifts have been shown to be sensitive to conformational changes of the piperidine ring. The results indicate that the conformation of the latter depends both on the substituent in position 10 and on the solvent.     

New heterocyclic derivatives of 1′- and 3′-amino-5′,6′,7′,8′-tetrahydro-2′-acetonaphthones

The preparation of 1′-and 3′-amino-5′,6′,7′,8′-tetrahydro-2′-acetonaphthones (IIIa and IIIb) is described, by reduction of the low temperature nitration products of 5′,6′,7′,8′-tetrahydro-2′-acetonaphtone (I). The structures of the nitro isomers (IIa and IIb), and the reduction products, IIIa and IIIb, were elucidated spectroscopically. By known reactions, a series of new heterocyclic compounds prepared from the o-aminoketones, IIIa and IIIb, resulted in two series of new heterocyclic compounds.     

77Se n.m.r. studies of organoselenium compounds: III—substituent effects in 4,4′-disubstituted diphenyl selenides and 4,4′-disubstituted diphenylmethanes studied by 1H, 13C and 77Se spectroscopy

⁷⁷Se N.m.r. spectra of 4,4′-disubstituted diphenyl selenides have been obtained. The chemical shifts could be correlated with substituent constants of the Hammett type or with Swain and Lupton two-parameter equations. No correlations were observed between these ⁷⁷Se shifts and the ¹³C shifts of the CH₂ group of 4,4′-disubstituted diphenylmethanes, the latter shifts showing no correlation with substituent constants. On the other hand linear correlation was observed between the ⁷⁷Se shifts of the 4,4′-disubstituted diphenyl selenides and the ¹H shifts of the CH₂ group of the diphenylmethanes, the ¹³C shifts of their 1-carbons and the ¹⁹F shifts of 4-substituted fluorobenzenes.