COSY NMR Spectra Research Articles

9,10-Dimethoxy-4-oxo-1-phenyl-1,3,4,6,7,11b-hexahydro-[1,4]thiazino[3,4-a]isoquinoline-1-carboxylic Acid

The synthesis of the compound 9,10-dimethoxy-4-oxo-1-phenyl-1,3,4,6,7,11b-hexahydro-[1,4]thiazino[3,4-a]isoquinoline-1-carboxylic acid (4) was described for the first time using a reaction between 6,7-dimethoxy-3,4-dihydroisoquinoline and phenyl-substituted thiodiacetic anhydride 3. The reaction proceeded in excellent yield and furnished the compound 4 as a single diastereomer. The structure and relative configuration of 4 was elucidated using a combination of spectroscopic techniques–1H, 13C, COSY, HSQC, HMBC, and NOESY NMR spectra, as well as elemental analysis.

Intramolecular Hydrogen Bonding in N6-Substituted 2-Chloroadenosines: Evidence from NMR Spectroscopy.

Two forms were found in the NMR spectra of N6-substituted 2-chloroadenosines. The proportion of the mini-form was 11-32% of the main form. It was characterized by a separate set of signals in COSY, 15N-HMBC and other NMR spectra. We assumed that the mini-form arises due to the formation of an intramolecular hydrogen bond between the N7 atom of purine and the N6-CH proton of the substituent. The 1H,15N-HMBC spectrum confirmed the presence of a hydrogen bond in the mini-form of the nucleoside and its absence in the main form. Compounds incapable of forming such a hydrogen bond were synthesized. In these compounds, either the N7 atom of the purine or the N6-CH proton of the substituent was absent. The mini-form was not found in the NMR spectra of these nucleosides, confirming the importance of the intramolecular hydrogen bond in its formation.

Determination of the quantitative and qualitative composition of unsaturated polyester resins by NMR spectroscopy

Qualitative and quantitative composition of unsaturated polyester resin derived from known monomers mixture was investigated by means of NMR spectroscopy. To obtain the most comprehensive data of polyester microstructure 1H, 13C и {1H;1H} COSY NMR spectra were registered. NMR spectroscopy has been proven to be accurate and highly reliable method for composition analysis of unsaturated polyester resins.

ISOLATION AND CHARACTERIZATION OF A SECONDARY METABOLITE FROM THE AERIAL PARTS OF Launaea (Lactuca) taraxacifolia

Launaea (Lactuca) taraxacifolia also known as wild lettuce is a medicinally important plant of the Asteraceae family. The plant was selected for this study due to its widespread use in traditional medicine and on the basis that the plant is almost going into extinct in Nigeria. The extraction was carried out by subjecting the air dried pulverized plant materials into trichloromethane solvent for a period of some days, followed by filtration and concentration. Separation and purification of the various constituents of the crude were done using thin layer and column chromatography. The mobile phases and solvent blends employed were: normal hexane, trichloromethane, ethyl ethanoate and methanol. The extraction, purification, concentration and chromatographic separations of the extracts were carried out at Post-graduates, chemistry laboratory, Michael Okpara University of Agriculture, Umudike, Nigeria. The NMR spectra analysis was investigated at Monash University Malaysia while the FTIR and GC-MS were carried out at Nanotechnology and Research Institute Malaysia. The NMR analysis was done using a Bruker VSP 500MHZ model machine. The GC-MS was performed using an Agilent 7000 model while the FTIR analysis was carried out on an Agilent 4500 series FTIR system. The structural elucidation of the proposed compound was deduced using GC-MS, FTIR, NMR (13C and 1H) and 2D COSY NMR spectra. This chemical investigation resulted in the isolation of a novel compound SB3 (Octadecahydro-10-(1,2,3,4-tetrahydronaphtalen-3-yl)-4,4-dimethoxy-6b,12b,14b-trimethyl Picen-3-(4H,6bH,14bH)-one. Compound SB3 was isolated using 50% hexane and 50% trichloromethane at an Rf value of 0.692. The MS spectrum of compound SB3 gave a molecular ion peak at m/z 545.81, which corresponded to a molecular formula of C37H53O3.

Argyrotoxins A-C, a trisubstituted dihydroisobenzofuranone, a tetrasubstituted 2-hydroxyethylbenzamide and a tetrasubstitutedphenyl trisubstitutedbutyl ether produced by Alternaria argyroxiphii, the causal agent of leaf spot on African mahogany trees (Khaya senegalensis)

Three previously undescribed metabolites named argyrotoxins A-C, were isolated, together with the well known porritoxinol, its closely related phthalide, a phthalide derivative, zinniol, alternariol and its 4-methyl ether from Alternaria argyroxiphii E.G. Simmons & Aragaki, the causal agent of leaf spot on African mahogany trees, Khaya senegalensis A. Juss. (Meliaceae). The known compounds were identified comparing their physical and spectroscopic properties to those previously reported in literature. Argyrotoxins A-C were characterized essentially by NMR (1H, 13C, COSY, HSQC, HMBC and NOESY NMR spectra) and HRESIMS spectra as 4-(7-methoxy-6-methyl-3-oxo-1,3-dihydro-isobenzofuran-5-yloxy)-2-methyl-butyric acid, 5-but-2-enyloxy-N-(2-hydroxyethyl)-2-hydroxymethyl-3-methoxy-4-methyl-benzamide and 1-(5-(hydroxymethyl)-3-methoxy-4-(methoxymethyl)-2-methylphenoxy)-3-methylbutane-2,3-diol, respectively. The absolute configuration of argyrotoxin A was determined through electronic circular dichroism, by applying the biphenyl chiroptical probe approach. The phytoxicity of all metabolites isolated was evaluated by leaf puncture assay at concentration of 1 mg/mL. Zinniol proved to be the most active compound causing necrotic lesions on young leaves of Hedera elix L., Phaseolus vulgaris L. and Quercus ilex L. Argirotoxins A and B were found active, to a minor extent, on Phaseolus vulgaris L. leaves, while porritoxinol exhibited activity on holm oak leaves. The other secondary metabolites herein reported for A. argyroxiphii were inactive.

Preparation of 6-amino-6-deoxy cellulose and its derivatives used as chiral separation materials

In order to find a facile and practical method to synthesize amino cellulose in bulk with high regional selectivity and high degree of substitution, the reaction conditions to brominate cellulose and to reduce azido group were carefully studied and some interesting phenomena were observed. With the optimized method, 6-amino-6-deoxy cellulose could be easily prepared with very simple separation techniques. The degree of substitution of the amino group amounted to 0.97 which was determined by 1H NMR spectrum of 6-benzamido-6-deoxy cellulose. Moreover, the amino group was evidenced to be at the C6 of glucose unit by 1H-1H COSY NMR and 1H-13C HSQC NMR spectra. In addition, three cellulose 6-acetamido-6-deoxy-2,3-bis(phenylcarbamate)s were prepared from the 6-amino-6-deoxy cellulose prepared with the techniques optimized in the present study. The developed cellulose derivatives were used as chiral selectors with which chiral stationary phases (CSPs) were prepared. The CSPs exhibited enantioseparation power to some chiral compounds.

Characterization of four unknown impurities in azithromycin and erythromycin imino ether using two-dimensional liquid chromatography coupled to high-resolution quadrupole time-of-flight mass spectrometry and nuclear magnetic resonance.

A simple and sensitive method was developed for the separation and characterization of four unknown impurities in azithromycin and erythromycin imino ether using two-dimensional liquid chromatography coupled to high-resolution quadrupole time-of-flight mass spectrometry (2D LC/QTOFMS) with positive and negative electrospray ionization. The chromatographic separation in the first dimension was performed with a Waters Xbridge RP18 column in gradient mode using binary mobile phase: (A) phosphate buffer (pH 8.2)-acetonitrile (47:53, v/v) and (B) water-acetonitrile (90:10, v/v). In the second dimension, the chromatographic separation was performed using a Shimadzu Shim-pack GISS C18 column with volatile mobile phases: (A) ammonium formate solution (10 mM) and (B) methanol. The molecular formulae and structures of the four impurities were deduced based on the LC/MS/MS data, and further confirmed using 1 H NMR, 13 C NMR, 1 H-1 H COSY, HSQC and HMBC NMR spectra after semi-preparative isolation of impurities. In addition, the mechanism for the formation of the impurities was also proposed. The contradiction between the non-volatile salt mobile phase and mass spectrometry was solved by means of a multiple heart-cutting 2D LC approach and on-line desalination technology. Four impurities were separated and characterized. These results could further improve the method of official monographs in pharmacopoeias and guides to improve the process of reducing impurity content.

Triterpenoid Saponins from Tu Jia Ethnomedicine Bai San Qi and Their Cytotoxicity on Hep G2 and BGC-823 Cell Lines

ObjectiveTu Jia ethnomedicine is a unique medical system inherited and adhibited by Tu Jia minority living in central-south China. Panax japonicus C. A. Mey. (Bai San Qi, 白三七) is recognized as an effective and rare medicinal plant to treat weakness, fatigue and rheumatism in Tu Jia ethnomedicine. This paper is to discover more substance evidence for the application of Tu Jia ethnomedicine. MethodsColumn chromatography and preparative high performance liquid chromatography (HPLC) was applied for isolation and purification; 1H-NMR, 13C-NMR, 1H-1H COSY, HSQC and HMBC NMR spectra were applied for structure identification; Methyl thiazolyl tetrazolim (MTT) assays were applied for cytotoxicity evaluation. ResultsTotally 12 known compounds were isolated by column chromatography and preparative HPLC from rhizomes of Panax japonicus C. A. Mey. (Bai San Qi, 白三七). Structures of these compounds were identified by their NMR spectra. All the 12 compounds were triterpenoid saponins. Five of them were oleanolic acid type, and the remaining 7 were dammarane type. Eleven compounds were assayed for their cytotoxic activity against Hep G2 human liver cancer cell lines and BGC-823 human gastric cancer cell lines. Three of the 11 showed relatively dominant cytotoxicity against these cell lines. ConclusionsA total of 12 known compounds have been identified from Panax japonicus C. A. Mey. (Bai San Qi, 白三七); NMR spectra of compounds with similar skeletons showed regular characteristics; 3 compounds showed relatively dominant cytotoxicity against Hep G2 and BGC-823 cancer cell lines, and the result can be valued as weak while setting the taxol as a positive control.

Synthesis and NMR Characterization of the Prenylated Peptide, a-Factor.

Protein and peptide prenylation is an essential biological process involved in many signal transduction pathways. Hence, it plays a critical role in establishing many major human ailments, including Alzheimer's disease, amyotrophic lateral sclerosis (ALS), malaria, and Ras-related cancers. Yeast mating pheromone a-factor is a small dodecameric peptide that undergoes prenylation and subsequent processing in a manner identical to larger proteins. Due to its small size in addition to its well-characterized behavior in yeast, a-factor is an attractive model system to study the prenylation pathway. Traditionally, chemical synthesis and characterization of a-factor have been challenging, which has limited its use in prenylation studies. In this chapter, a robust method for the synthesis of a-factor is presented along with a description of the characterization of the peptide using MALDI and NMR. Finally, complete assignments of resonances from the isoprenoid moiety and a-factor from COSY, TOCSY, HSQC, and long-range HMBC NMR spectra are presented. This methodology should be useful for the synthesis and characterization of other mature prenylated peptides and proteins.

1-[(5-Benzyl-1,3-thiazol-2-yl)diazenyl]naphthalene-2-ol: X-ray structure, spectroscopic characterization, dissociation studies and application in mercury(II) detection

A new thiazolylazo reagent, 1-[(5-benzyl-1,3-thiazol-2-yl)diazenyl]naphthalene-2-ol, has been synthesized for the first time. Single crystals of the azo dye were grown from a saturated solution by the vapour diffusion technique. The compound was analyzed using the single-crystal X-ray diffraction technique, and the chemical structure was also confirmed by ATR-IR, 1H, 13C, COSY and HSQC NMR spectra. The pKa dissociation constant of the substance was determined in volumes of methanol (MeOH), dioxane and acetonitrile (MeCN)] by means of the potentiometric method. The Yasuda–Shedlovsky extrapolation procedure was employed to obtain the value of pKa in aqueous solution. The chelate complex of the azo dye with mercury(II) was studied spectrophotometrically. A method for Hg(II) ion determination with the new reagent was elaborated and the limit of detection calculated.

Synthesis and characterization of chitosan alkyl urea

Chitosan is a versatile material employed for various purposes in many fields including the development of chiral stationary phases for enantioseparation. Chitosan alkyl urea is a kind of intermediate used to prepare enantioseparation materials. In order to synthesize the intermediates, in the present work, a new way to prepare chitosan alkyl urea has been established: chitosan was first reacted with methyl chloroformate yielding N-methoxyformylated chitosan, which was then converted to chitosan alkyl urea through amine-ester exchange reaction. With a large excess of methyl chloroformate and primary amine of low stereohindrance, the amino group in chitosan could be almost completely converted to ureido group. The as-prepared chitosan alkyl urea derivatives were characterized by IR, 1H NMR, 13C NMR,1H-1H COSY and 1H-13C HSQC NMR spectra. The chemical shifts of hydrogen and carbon atoms of glucose unit were assigned. It was found that the degree of substitution was obviously lower if cyclopropyl amine, aniline, tert-butyl amine and diethyl amine were used as reactants for the amine-ester exchange reaction. The reason was explained with the aid of theoretical calculations.

The density matrix theory of triple‐quantum filtered COSY (TQF‐COSY) NMR experiments applied to an AX system of spins S=1: An example of passive coupling in two‐dimensional NMR spectroscopy

AbstractThe 2D Triple‐Quantum Filtered (TQF) COSY NMR spectrum of an AX spin system of spin‐1 has been calculated by numerical density matrix calculations. The basic phase cycle to achieve triple quantum filtration and phase‐modulation of the signal during t1 consists of 12 steps. If nuclei A and X are not coupled, the calculations predict no peaks at all. If nuclei A and X are coupled and the multiplets are not resolved in the conventional 1D spectrum, two diagonal peaks are detected. If nuclei A and X are coupled and the multiplets are resolved in the conventional 1D spectrum, only diagonal and near‐diagonal peaks are detected. One does not observe cross peaks if nuclei A and X are coupled because the coupling is passive. It is believed that the calculations presented here will be needed to calculate the Exclusive Correlation Spectroscopy (E.COSY) of an AX system of spins S=1.

The DQF-COSY NMR Experiment, a Way to Detect Small J Couplings in the Case of Fast Relaxing Nuclei: Application to <sup>59</sup>Co in the Tetrahedral Mixed-Metal Cluster HRuCo<sub>3</sub>(CO)<sub>11</sub>(PPh<sub>3</sub>)

The first investigation and analysis of 59Co 2D NMR homonuclear chemical shift correlation spectra for a ruthenium-based tetrahedral mixed-metal cluster HRuCo3(CO)11(PPh3) are reported. For this cluster in solution and by contrast to the conventional COSY NMR experiment, the double-quantum filtered (DQF) COSY NMR spectrum proves the existence of a scalar coupling constant between 59Co nuclei. In order to obtain a value of this coupling, the 2D COSY spectrum for a three-spin 7/2 AX2 system has been simulated by numerical density matrix calculations. The comparison between experimental and theoretical 2D NMR COSY spectra gives a spin-coupling constant |1J(59Co-59Co)| ＜ 300 Hz for this cluster.

Application of 13C-labeling and 13C–13C COSY NMR experiments in the structure determination of a microbial natural product

The elucidation of the structures of complex natural products bearing many quaternary carbons remains challenging, even in this advanced spectroscopic era. (13)C-(13)C COSY NMR spectroscopy shows direct couplings between (13)C and (13)C, which comprise the backbone of a natural product. Thus, this type of experiment is particularly useful for natural products bearing consecutive quaternary carbons. However, the low sensitivity of (13)C-based NMR experiments, due to the low natural abundance of the (13)C nucleus, is problematic when applying these techniques. Our efforts in the (13)C labeling of a microbial natural product, cyclopiazonic acid (1), by feeding (13)C-labeled glucose to the fungal culture, enabled us to acquire (13)C-(13)C COSY NMR spectra on a milligram scale that clearly show the carbon backbone of the compound. This is the first application of (13)C-(13)C COSY NMR experiments for a natural product. The results suggest that (13)C-(13)C COSY NMR spectroscopy can be routinely used for the structure determination of microbial natural products by (13)C-enrichment of a compound with (13)C-glucose.

Preparation of novel cyclic olefin copolymer with high glass transition temperature

ABSTRACTA series of novel cyclic olefin copolymers (COCs), including ethylene/tricyclo[4.3.0.12,5]deca‐3‐ene (TDE), ethylene/tricyclo[4.4.0.12,5]undec‐3‐ene (TUE), and ethylene/tricyclo[6.4.0.19,12]tridec‐10‐ene (TTE) copolymers, have been synthesized via effective copolymerizations of ethylene with bulk cyclic olefin comonomers using bis(β‐enaminoketonato) titanium catalysts (1a [PhNC(CH3)CHC(CF3)O]2TiCl2; 1b: [PhNC(CF3)CHC(Ph)O]2TiCl2). With modified methylaluminoxane as a cocatalyst, both catalysts exhibit high catalytic activities, producing high molecular weight copolymers with high comonomer incorporations and unimodal molecular weight distributions. The microstructures of obtained ethylene/COCs are established by combination of 1H, 13C NMR, 13C DEPT, HSQC 1H13C, and 1H1H COSY NMR spectra. DSC analyses indicate that the glass transition temperature (Tg) increases with the enhancement of comonomer volume (TDE < TUE < TTE). High Tg value up to 180 °C is easily attained in ethylene/TTE copolymer with the low content of 35.8 mol %. TGA analyses reveal that these copolymers all possess high thermal stability with degradation temperatures (Td) higher than 370 °C in N2 and air. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3144–3152

Luminescence phenomena of biodegradable photoluminescent poly(diol citrates)

The possible origin of luminescent properties of biodegradable photoluminescent polyesters (BPLPs) has been revealed by isolation and identification of luminescent agent from the hydrolyzate of BPLP. Elemental analysis, ESI-MS, (1)H, (13)C, 2D HSQC and COSY NMR spectra confirmed the chemical structure as 5-oxo-2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyridine-3,7-dicarboxylic acid (TPA).

Biosynthesis, isolation, and NMR analysis of leukotriene A epoxides: substrate chirality as a determinant of the cis or trans epoxide configuration

Leukotriene (LT)A₄ and closely related allylic epoxides are pivotal intermediates in lipoxygenase (LOX) pathways to bioactive lipid mediators that include the leukotrienes, lipoxins, eoxins, resolvins, and protectins. Although the structure and stereochemistry of the 5-LOX product LTA₄ is established through comparison to synthetic standards, this is the exception, and none of these highly unstable epoxides has been analyzed in detail from enzymatic synthesis. Understanding of the mechanistic basis of the cis or trans epoxide configuration is also limited. To address these issues, we developed methods involving biphasic reaction conditions for the LOX-catalyzed synthesis of LTA epoxides in quantities sufficient for NMR analysis. As proof of concept, human 15-LOX-1 was shown to convert 15S-hydroperoxy-eicosatetraenoic acid (15S-HPETE) to the LTA analog 14S,15S-trans-epoxy-eicosa-5Z,8Z,10E,12E-tetraenoate, confirming the proposed structure of eoxin A₄. Using this methodology we then showed that recombinant Arabidopsis AtLOX1, an arachidonate 5-LOX, converts 5S-HPETE to the trans epoxide LTA₄ and converts 5R-HPETE to the cis epoxide 5-epi-LTA₄, establishing substrate chirality as a determinant of the cis or trans epoxide configuration. The results are reconciled with a mechanism based on a dual role of the LOX nonheme iron in LTA epoxide biosynthesis, providing a rational basis for understanding the stereochemistry of LTA epoxide intermediates in LOX-catalyzed transformations.

Structure verification through computer-assisted spectral assignment of NMR spectra

The validation of a molecular organic structure on the basis of 1D and 2D HSQC, COSY and HMBC NMR spectra is proposed as an alternative to the methods that are mainly based on chemical shift prediction. The CCASA software was written for this purpose. It provides an updated and improved implementation of the preceding computer-assisted spectral assignment software. CCASA can be downloaded freely from http://www.univ-reims.fr/LSD/JmnSoft/CASA. Two bioactive natural products, a triterpene and a benzophenone, were selected from literature data as examples. The tentative matching between the structure and the NMR data interpretation of the triterpene unexpectedly leads to the hypothesis of an incorrect structure. The LSD software was used to find an alternative structure that improved the 2D NMR data interpretation and the carbon-13 chemical shift matching between experimental values and those produced by the nmrshiftdb2 prediction tool. The benzophenone example showed that signal assignment by means of chemical shift prediction can be replaced by elementary user-supplied chemical shift and multiplicity constraints.

Identification of Grass-specific Enzyme That Acylates Monolignols with p-Coumarate

Lignin is a major component of plant cell walls that is essential to their function. However, the strong bonds that bind the various subunits of lignin, and its cross-linking with other plant cell wall polymers, make it one of the most important factors in the recalcitrance of plant cell walls against polysaccharide utilization. Plants make lignin from a variety of monolignols including p-coumaryl, coniferyl, and sinapyl alcohols to produce the three primary lignin units: p-hydroxyphenyl, guaiacyl, and syringyl, respectively, when incorporated into the lignin polymer. In grasses, these monolignols can be enzymatically preacylated by p-coumarates prior to their incorporation into lignin, and these monolignol conjugates can also be "monomer" precursors of lignin. Although monolignol p-coumarate-derived units may comprise up to 40% of the lignin in some grass tissues, the p-coumarate moiety from such conjugates does not enter into the radical coupling (polymerization) reactions of lignification. With a greater understanding of monolignol p-coumarate conjugates, grass lignins could be engineered to contain fewer pendent p-coumarate groups and more monolignol conjugates that improve lignin cleavage. We have cloned and expressed an enzyme from rice that has p-coumarate monolignol transferase activity and determined its kinetic parameters.

Complexes of (bpy)2Ru(II) and (Ph2bpy)2Ru(II) with a series of thienophenanthroline ligands: synthesis, characterization, and electronic spectra

A series of complexes (bpy)2LRu(II) and (Ph2bpy)2LRu(II), where bpy is 2,2′-bipyridine, Ph2bpy is 4,4′-diphenyl-2,2′-bipyridine and L is 1,10-phenanthroline (phen), [1]benzothieno[2,3-c][1,10]phenanthroline (btp), naphtho[1′,2′ : 5,4]thieno[2,3-c][1,10]phenanthroline [ntpl, l=linear], and naphtho[1′,2′ : 4,5]thieno[2,3-c][1,10]phenanthroline (ntph, h=helical) were synthesized and characterized using 2D COSY NMR spectra. The UV spectra were assigned to study their metal to ligand charge transfer (MLCT) excited states. Complexes of (bpy)2LRu(II) showed identical absorption wavelengths (λ max) for the MLCT of all four members of the series with the only variation being the intensity (log ε ) for each. The MLCT of (Ph2bpy)2LRu(II) showed the similar behavior only with different wavelengths showing that in this heteroleptic series of complexes the MLCT is exclusively to the bpy ligands with none to thienophenanthroline (btp, ntpl, or ntph).