Studies on the constituents of bocconia cordata. IV. Transformation of sanguinarine into bocconine

Nitration of ethoxysanguinarine with equimolar potassium nitrate and sulfuric acid, followed by treatment with sodium hydroxide and methanol, gives 10-nitromethoxysanguinarine. Successive hydrogenation, diazotization and methanolysis convert 10-nitromethoxysanguinarine into bocconine.     

Synthesis and nuclear magnetic resonance spectroscopic studies of 1‐arylpyrroles

A series of m‐ and p‐substituted 1‐phenyl, 1‐benzyl, 1‐benzoyl, and 1‐(2‐phenylethyl)pyrroles was prepared and their ¹H and ¹³C nmr spectroscopic characteristics were examined. In general, good correlations were observed between the chemical shift values of the β? H and the β? C of pyrroles [except 1‐(2‐phenylethyl)pyrroles] and the Hammettt σ. The observation may be explained in terms of the electronic effects of the substituents which are transmitted through bonds and through space by interaction of the p orbitals between β? Cs of the pyrrole ring and m‐ and p? Cs of the phenyl ring. Substituent constants of 1‐pyrrolyl, 1‐pyrrolylmethyl, and 1‐pyrroloyl groups for the ¹H and ¹³C chemical shifts of phenyl ring are also presented.     

Microstructure elucidation of historic silk (Bombyx mori) by nuclear magnetic resonance

¹H NMR cryoporometry and solid-state ¹³C cross-polarization (CP) magic-angle spinning (MAS) NMR spectroscopy were used to characterize the microstructure of historic and fresh silk samples. Silk is a polymeric bicomponent material composed of fibroin and water located in micropores. According to the ¹H NMR cryoporometry method, the intensity of the water resonance as a function of the temperature was used to obtain the pore size distribution, which was strongly asymmetric with a well-defined maximum at 1.1 nm. Compared with the fresh silk samples, the volume of pores around 1.1 nm decreased distinctly in the historic silk, and more pores larger than 2 nm emerged accordingly. In addition, these results correlated well with solid-state ¹³C CP/MAS NMR spectroscopy as the percentage of random coil in the historic silk sample was much less than that in the fresh silk samples. Therefore, it is suggested that the water-filled microvoids grow larger as the random coil conformation fades away in the degradation process.

Carbon-13 nuclear magnetic resonance studies on high spin iron(III) porphyrins

Carbon-13 NMR studies on a series of high spin iron(III) porphyrins, namely tetraphenylporphyrin iron(III) halides [Fe(TPP) X, X=Cl, Br, I] in CDCl₃ solution are reported. As expected the¹³C shifts are found to be an order of magnitude larger than the corresponding proton shifts. The dipolar contribution, which is quite important for the proton NMR, becomes much less significant for the¹³C shifts. No systematic variation in the¹³C shift across the series is observed, except for the meso-carbon which shows a small but gradual decrease in going from the chloro to the iodo complex. The¹³C shift for the various carbon atoms of the porphyrin ligand shows interesting pattern which is discussed in terms of spin delocalisation mechanisms.     

番红花化学成分研究 III. 番红花花粉中的番红花新苷甲和乙的结构

从番红花(crocus sativus L.)花粉中分到两个新苷, 命名为番红花新苷甲(1)和乙(2)。经理化性质和对它们的IR、UV、^1HNMR和MS数据的分析, 鉴定1为异鼠李素-4'-O-α-L-鼠李吡喃(1→2)β-D-葡萄吡喃糖苷, 2为β-对羟基苯基-乙醇-α-O-α-L-鼠李吡喃糖(1→2)-β-D-葡萄吡喃糖苷。     

Carbon-13 nuclear magnetic resonance studies on dichloropyridoquinolines

Carbon-13 NMR chemical shifts are reported for six angular and one linear dichloropyridoquinolines in CDCl₃. The chemical shift assignments have been made using model compounds, fully coupled spectra, selective proton decoupling and results from lanthanide shift studies. Chlorine substituent effects are compared to those reported for chloroquinolines. The effect of the heteroaromatic nitrogen atoms on ¹³C? ¹H coupling constants in these polycyclic systems are compared to those reported for pyridine systems.     

Dynamic nuclear magnetic resonance spectroscopic studies of (2.2.1)-cryptand incorporating a pinacol unit

The conformational behaviour of the (2.2.1)-cryptand framework has been studied by VT¹H and¹³C NMR spectroscopy, revealing a remarkable rigidity of the skeleton. Low-temperature measurements indicate a slowing down of the torsional motion of the methyl groups about the C–C bond in the pinacol unit with G =46 kJ mol^–1 at 228 K.Presented at the International Seminar on Inclusion Compounds, Jaszowiec, Poland, 24–26 September 1987.     

Probing interactions by means of pulsed field gradient nuclear magnetic resonance spectroscopy

Molecular self-diffusion coefficients (D) of species in solution are related to size and shape and can be used for studying association phenomena. Pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy has been revealed to be a powerful analytical tool for D measurement in different research fields. The present work briefly illustrates the use of PFG-NMR for assessing the existence of interactions in very different chemical systems: organic and organometallic compounds, colloidal materials and biological aggregates. The application of PFG-NMR is remarkable for understanding the role of anions in homogenous transition metal catalysis and for assessing the aggregation behaviour of biopolymers in material science.     

The application of two-dimensional nuclear magnetic resonance spectroscopy in computer-assisted structure elucidation

One of the most powerful tools for the determination of an unknown organic structure is two dimensional NMR spectroscopy. In some cases, this information quickly leads to a unique structure, but in many cases there remains a larger number of structural possibilities. A linked system of computer programs has been developed which uses several types of 2-D NMR data and generates all possible topological structures consistent with these data and user-input constraints. When symmetry is present, algorithms based on group theory limit the structures to those consistent with all the different symmetries that are possible. Applications of these programs to problems described in the literature, in which 2-D NMR was used to determine the structures of natural products, are described.     

Molybdenum-95 nuclear magnetic resonance studies. Monosubstituted molybdenum carbonyls

Summary The⁹⁵Mo n.m.r. spectra for a series of molybdenum(0) complexes [Mo(CO)₅L] (L=N,P,As, or Sb donor ligands) have been observed; resonances occur in the –1433 to –1864 ppm range for the twenty-six complexes with the⁹⁵Mo shielding order being: N1J(⁹⁵Mo–³¹P) coupling constants areca. 135 Hz and 220 Hz for phosphines and phosphites, respectively. Factors that influence the trends in coupling constants and chemical shifts are discussed.     

Structure elucidation of deoxylutein II isomers by on-line capillary high performance liquid chromatography-(1)H nuclear magnetic resonance spectroscopy

Thermal and iodine-catalyzed photochemical (Z/E)-isomerization of deoxylutein II [(3R,6'R)-3-hydroxy-3',4'-didehydro-beta,gamma-carotene, anhydrolutein I] (2), the dehydration product of lutein [(3R,3'R,6'R)-beta,varepsilon-carotene-3,3'-diol] (4), yielded multi-component mixtures of (Z)-isomers. By I(2)-catalyzed photoisomerization, (9Z)-2, (9'Z)-2, (13Z)-2, (13'Z)-2 and (15Z)-2 are generated as main products. In addition, this thermodynamic-equilibrium mixture contains traces of (9Z,9'Z)-2 and other (di-Z)-isomers in minor concentrations. Thirteen isomers are chromatographically separated and detected on-line by UV-vis and mass spectrometry. (all-E)-Deoxylutein II (2) and six of its (Z)-configured isomers are separated by capillary HPLC (acetone-d(6)/D(2)O = 85:15) and detected on-line by (1)H NMR spectroscopy in a microprobe. With the microprobe and the active detection volume of 1.5 microl, it is possible to perform structure elucidation with very small amounts available for various (Z)-isomers of deoxylutein II (2) in the isomerization mixture.     

Structural studies of vinylidene fluoride-tetrafluoroethylene copolymers by nuclear magnetic resonance spectorscopy

The application of high-resolution nuclear magnetic resonance (n.m.r.) spectroscopy to structural studies of copolymers is illustrated by an investigation of the vinylidene fluoride (VF₂)-tetrafluoroethylene (F₄E) system. Copolymers of VF₂ with F₄E are of topical interest owing to their ferroelectric behavior, and n.m.r. provides the only method for accurate determination of their composition and chemical microstructure. Many copolymer properties are highly sensitive to these structural variables, which must be characterized prior to the evaluation of physical behavior. A series of copolymers with compositions ranging from 100 to 50 mol% VF₂ is studied by proton, carbon-13, and fluorine-19 n.m.r. Proton and carbon-13 n.m.r. experiments distinguish monomer sequence triads. Fluorine-19 n.m.r. is the method of choice for the most detailed study because this probe resolves all monomer sequence pentads, as well as some longer-range sequences. Assignment of microstructure at this detailed level is aided by an extrapolation of known assignments for PVF₂ homopolymer, and computer simulation of peak probabilities based on a terpolymerization scheme involving both forward and reverse VF₂ addition, as well as F₄E addition. Necessary statistical relationships between observed carbon sequences and monomer sequences are derived to facilitate the study. The VF₂-F₄E system provides a particularly good example of the potential of high-resolution n.m.r. as an analytical tool for copolymer studies.     

13C nuclear magnetic resonance studies on some substituted isoxazoles

¹³C n.m.r. spectra of some substituted isoxazoles have been examined to ascertain the reactive site in the metallation of 4-substituted 3,5-dimethylisoxazoles. The results obtained indicate that metallation occurred exclusively at the C-5 methyl.