NOE Difference Experiments Research Articles

6-Deoxyclitoriacetal from Clitoria macrophylla

A new rotenoid, 6-deoxyclitoriacetal, was isolated from the roots of Clitoria macrophylla and its structural assignment was established unambiguously by a series of HETCOR, COLOC and NOE difference experiments. In vitro tests showed that this compound possessed strong cytotoxic activity against cultured P-388 lymphocytic leukemia cells, but was not active with cultured KB cells. However, marginal activity was observed with vinblastine-resistant KB-V1 cells, and this was enhanced by the addition of vinblastine. This rotenoid may, therefore, interact with P-glycoprotein.

Structure of Manasse's dimer fromendo-2-hydroxyepicamphor by NOE difference spectroscopy

Reduction of (1R)-(+)-camphorquinone by zinc in acetic acid yields a mixture of endo-2-hydroxyepicamphor and 3-hydroxycamphor. The former undergoes reaction in anhydrous methanol with HCl gas to furnish a stable crystalline solid, first reported in 1902. High-resolution electron impact mass spectrometry showed the solid to be a dimer of formula C22H36O4. The 13C{1H} spectrum showed 11 discrete environments, in keeping with a symmetrical dimer. High-field 1H NOE difference experiments were used to determine not only the connectivity but also the stereochemistry of the system. All of the NOE experiments are consistent with only one structure, that of the symmetrical dimer. In addition, 2D carbon-proton correlation experiments (HETCOR) were used to assign unambiguously its 13C{1H} spectrum.

EPC synthesis of gem-difluorocyclopentane derivatives

gem-Difluorocyclopentane derivatives were obtained in optically pure form by thermal or photochemical radical cyclization of the coresponding haloalkenes. Reductive or thermal elimination of the chiral auxiliary and appropriate elaborations afforded some difluoromethyl-cyclopentanols and -cyclopentantriols. The structure of the compounds was elucidated on the basis of 1 H, 13 C and 19 F NMR data and of NOE difference experiments.

Determination of the Stereochemistry of Chemotherapeutics Derived from 5‐Nitrofurfural: NOE Difference Spectroscopy as a Simple and Reliable Method

AbstractHomonuclear NOE difference spectroscopy is shown to be a rapid and reliable tool for the determination of stereochemistry regarding the ‐C=N‐ substructure of 5‐nitrofurfural derivatives of type 1–10, including several known chemotherapeutic agents. The assignments resting on the NOE difference experiments are in full agreement with those based on 13C‐NMR data.

Isolation and structural elucidation of griffithine by 1D and 2D NMR techniques

The isolation and structure elucidation of a novel dimeric alkaloid, griffithine, from the leafy shoots of Sophora griffithii Stock (Papilionaceae) is described. The alkaloid possesses a 12-membered ring system formed by the linking of C-10 and C-10′ of the alkaloid with the N-1 and N-1′ atoms, respectively. The structure was established on the basis of extensive 1D and 2D NMR studies. The relative stereochemistry at the chiral centres was determined by NOE difference experiments. 10-Oxosparteine was isolated for the first time from the leafy shoots of Sophora griffithii.

Structural and dynamic aspects of non-intercalative (1:1) binding of a thiazole-lexitropsin to the decadeoxyribonucleotide d-[CGCAATTGCG]2: An 1H-NMR and molecular modeling study.

The location, orientation and dynamics of a thiazole-containing analogue of distamycin 1 bound to the decadeoxyribonucleotide d-[CGCAATTGCG]2 have been studied by non-exchangable and imino proton NMR resonances of the 1:1 complex. Using NOE difference, COSY and NOESY experiments, lexitropsin (1) was located in the minor groove of DNA at 5'-CAAT sequence. This was concluded by an intermolecular NOE between the ligand and a minor groove A4H2 proton. The NOE cross-correlations in the NOESY map confirmed that the DNA decamer duplex in the 1:1 complex remains in a right-handed B-conformation similar to that in the free decamer. Experiments on non-exchangeable and exchangeable proton NMR resonances placed the N-formylamino terminus of drug 1 on the 5'-C3 nucleotide, while the rest of the molecule extends onto the 5'-AAT sequence. The structural evidence for sequence preferential binding at 5'CAAT rather than 5'AATT suggests this reflects an attempt on the part of the sterically demanding inward directed sulfur of the thiazole to minimize compression by moving part of the molecule to the somewhat wider CG base site. The lack of evidence for a 2:1 drug:DNA complex, in contrast to distamycin, is in accord with this interpretation. The lexitropsin 1 was found to be in an exchange between the equivalent 5'-CAAT sites at a rate of approximately 35S-1 with a delta G degree of 65 +/- 5 kJ mol-1 at 303 K. The experimental data suggests a slide-swing mechanism for this exchange process.

Spectral and structural assignments with various N-substituted 1,2,4-triazoles: Noe difference spectroscopy as a powerful tool

The unambiguous discrimination between signals due to H-3 and H-5 in various 1-substituted 1 H-1,2,4-triazoles as well as the differentiation between isomeric 1,3-, 1,5- and 3,4-disubstituted 1,2,4-triazoles by means of NOE difference spectroscopy is described. The assignments based on NOE difference experiments are shown to agree with those resting on triazole- 13C, 1H spin-coupling constants.

Studies on inhibitors of skin tumor promotion, IX. Neolignans from Magnolia officinalis.

Three neolignans, known as magnolol [1], honokiol [2] and the new monoterpenylmagnolol [3], were isolated from the bark of Magnolia officinalis as inhibitors of Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). The structure of 3 was determined from 2D nmr spectral data and difference nOe experiments. The MeOH extract of this plant and magnolol exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two stage carcinogenesis test. This investigation indicates that these neolignans and the extract might be valuable antitumor promoters.

Prenyl bibenzyls from the liverworts Radula perrottetii and Radula complanata

A new dihydrobenzofuran and a new chromene derivatives have been isolated from the liverwort Radula perrottetii, together with the known 3,5-dihydroxy-2-(3-methyl-2-butenyl)bibenzyl, 2( R)-2-isopropenyl-6,7-dihydroxy-4-(2-phenylethyl)dihydrobenzofuran, 2,2-dimethyl-7-hydroxy-5-(2-phenylethyl)chromene, 3,5-dihydroxy-6-carbo-methoxy-2-(3-methyl-2-butenyl)bibenzyl, three bis(bibenzyls) and perrottetins E, F and G. The structures of the new compounds have been characterized as 2( R)-2-isopropenyl-6-hydroxy-4-(2-phenylethyl)dihydrobenzofuran and 2,2-dimethyl-7,8-dihydroxy-5-(2-phenylethyl)chromene by 1H and 13C NMR spectral analysis and synthesis. The structures of the previously reported chalcone and three prenyl bibenzyls, perrottetins A, B and C, and the other two bibenzyls, isolated from R. perrottetii are revised by analysis of their 1H and 13C NMR data, difference NOE experiments and synthesis of their derivatives. Radulanin L, a new bibenzyl with a dihydrooxepin skeleton was isolated from R. complanata together with 2- and 4-(3-methyl-2-butenyl)-3,5-dihydroxybibenzyls and its structure elucidated by comparison of 1H and 13C NMR spectral data with those of radulanins A and H. The structures of the previously reported radulanins A and H isolated from R. complanata are confirmed as correct by difference NOE. Some prenyl-containing bibenzyls showed 5-lipoxygenase and calmodulin in hibitory activity and vasopressin antagonist activity. R. perrottetii is a chemically isolated species in the Radulaceae.

1H and 13C NMR studies on the conformation of N-methyl diastereomers of (+)-glaucine hydrotrifluoroacetate, an aporphine alkaloid salt

A 3 : 1 ratio of N-methyl diastereomers of (+)-glaucine hydrotrifluoroacetate was observed at slow exchange by 1H NMR spectroscopy (300 MHz, CD2Cl2), but the spectrum was too complex to be interpreted solely by one-dimensional methods. However, the E.COSY 2D NMR spectrum afforded all proton chemical shift and coupling constant data for both N-methyl diastereomers. Surprisingly, there are few or no cases where the E.COSY data have been analysed manually and have thereby effected a full assignment of the 1H NMR spectrum of a molecule. While X-ray crystallographically determined structures of aporphine alkaloids have B-rings with either M- or P-conformations [as denoted by the sign of the C(3a)–C(4)–C(5)–N torsion angle], measured vicinal coupling constants together with difference-NOE experiments showed both solution-state species of (+)-glaucine to have the M-conformation for the B-ring. The major and minor solution-state species differ by configuration at nitrogen: the 6S,6aS-major species has an equatorial N-methyl group, and the 6R,6aS-minor species has an axial one. The major contributor to the fast exchange limit structure of glaucine free base has an equatorial N-methyl group.

Determination of the major tautomeric form of the covalently modified adenine in the (+)-CC-1065-DNA adduct by proton and nitrogen-15 NMR studies

(+)-CC-1065 is an extremely potent antitumor antibiotic produced by Streptomyces zelensis. The potent cytotoxic effects of the drug are thought to be due to the formation of a covalent adduct with DNA through N3 of adenine. Although the covalent linkage sites between (+)-CC-1065 and DNA have been determined, the tautomeric form of the covalently modified adenine in the (+)-CC-1065-DNA duplex adduct was not defined. A [6-15N]deoxyadenosine-labeled 12 base pair non-self-complementary oligomer, d(GGCGGAGTT*AGG).d(CCTAACTCCGCC) (asterisk indicates 15N-labeled base), containing the (+)-CC-1065 most preferred binding sequence 5'AGTTA, was synthesized and modified with (+)-CC-1065. This [6-15N]deoxyadenosine-labeled 12-mer duplex adduct was then studied by 1H and 15N NMR. One-dimensional NOE difference and two-dimensional NOESY 1H NMR experiments on the nonisotopically labeled 12-mer duplex adduct demonstrate that the 6-amino protons of the covalently modified adenine exhibit two signals at 9.19 and 9.08 ppm. Proton NMR experiments on the [6-15N]deoxyadenosine-labeled 12-mer duplex adduct show that the two resonance signals for adenine H6 observed on the nonisotopically labeled duplex adduct were split into doublets by the 15N nucleus with coupling constants of 91.3 Hz for non-hydrogen-bonded and 86.8 Hz for hydrogen-bonded amino protons. Parallel 15N NMR experiments on the [6-15N]deoxyadenosine-labeled (+)-CC-1065-12-mer duplex adduct show a triplet-like signal around -276.9 ppm and coupling constants of 91.5 and 85.6 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the structure and absolute configuration of the glycerolphosphate-containing capsular polysaccharide of Pasteurellahaemolytica serotype T3 by high-resolution nuclear magnetic resonance spectroscopy

The specific capsular polysaccharide antigen produced by Pasteurellahaemolytica serotype T3 was found to be a high molecular weight teichoic acid composed of equal molar amounts of D-galactose, glycerol, and phosphate and a nonstoichiometric amount of O-acetate. Structural analysis of the polymer employed a combination of one- and two-dimensional 1H and 13C nuclear magnetic resonance methods at high field. Homo- and heteronuclear chemical shift correlation techniques, together with J-resolved and nuclear Overhauser effect (nOe) difference experiments led to the unambiguous assignments of the 1H and 13C resonances corresponding to the D-galactose and glycerol structural units and established that the repeating unit of the polysaccharide antigen was composed of → 4)-α-D-Galp-(1 → 1)-L-glycerol-(3 → units joined by phosphate diester groups. The chirality of the glycerol moiety was established by conformational analysis of a 1-O-α-D-galactopyranosyl-S-glycerol fragment (2) obtained from the teichoic acid by depolymerization with HF, from which the stereochemistry of the glycerol methine carbon centre was related to that of the D-glycose from 1H–1H nOe and 3J values. The chirality was confirmed by gas–liquid chromatographic and mass spectral analysis of the (−)-camphanate ester of 2,3-di-O-methylglycerol derived from permethylated 2. The D-galactosyl residues are partially mono-O-acetylated at C-2 and C-3. Keywords: Pasteurellahaemolytica, capsular polysaccharide, NMR analysis.

A binding site peptide fragment of the nicotinic acetylcholine receptor. Sequence- specific assignment of IH-NMR resonances in the dodecamer α 185–196

The total sequence-specific 1H assignment for the alpha 185-peptide was accomplished by analysis of COSY spectra along with spin-decoupling and confirmatory NOE difference experiments. Some ambiguities in the assignments were successfully addressed utilizing additional peptides with selective amino acid substitutions. The chemical shifts of several of the C alpha H resonances, along with evidence for a slowly exchanging amide at Thr-191 suggest that the alpha 185-peptide may contain a certain amount of non-random coil structure. The role of any such ordered structure in the mechanism of binding to alpha-bungarotoxin remains to be determined. The assignment of the peptide 1H resonances will facilitate the analysis and identification of chemical shift perturbations observed upon formation of the complex between alpha-bungarotoxin and the alpha 185-peptide [7].

Structure of a .beta.-cyclodextrin-vanillin inclusion complex

Vanillin was found to form a stable complex with 0-cyclodextrin. A binding constant value of 1.11 X lo4 M-' was determined for the 1:l complex. 'H NMR chemical shift differences and circular dichroism spectra indicated that both phenolic end and aldehyde end were affected by complexation. 2D nuclear Overhauser enhancement spectroscopy indicated proximity of OCH, in vanillin to the anomeric protons of P-cyclodextrin. 1D difference NOE experiments have revealed that vanillin exists with the phenolic end nearer to the narrower end and the aldehyde end to the wider end of the torusshaped 0-cyclodextrin molecule.

Synthesis of Aristotelia‐type alkaloids. Part V. Biomimetic synthesis of (±)‐aristomakine and (±)‐aristomakinine

AbstractBiomimetic syntheses of racemic aristomakinine ((±)‐3) and aristomakine ((±)‐4), an unusual indole alkaloid bearing an N‐isopropyl group, are described. The key step is a Grob‐type fragmentation of anti‐15‐aristotelinyl methanesulfonate ((±)‐2) to the intermediate iminium ion I which, upon subsequent hydrolysis, furnished aristomakinine ((±)‐3). On the other hand, the same intermediate could be reduced in situ to aristomakine ((±)‐4). The controversial relative configurations of the two alkaloids have been firmly established by means of NOE difference experiments.

Structural studies of digitoxin and related cardenolides by two-dimensional NMR

The 1H and 13C NMR spectra of the cardenolides digitoxigenin, digoxigenin, digitoxin, and mono- and bis-digitoxigenin digitoxosides have been completely assigned by two-dimensional NMR spectroscopy. The techniques used include phase-sensitive COSY, multiple relay COSY, and carbon–proton correlation (HETCOR and HMQC) spectra. Various aspects of the solution conformation of the steroid moiety of digitoxin and digoxigenin could be determined from coupling constants and NOE difference experiments and they are indicative of an all-chair conformation. The carbohydrate rings in digitoxin and the mono- and bis-digitoxigenin digitoxosides are also in the chair conformation. Keywords: cardenolides, digitoxigenin, digitoxin, 2-dimensional NMR, conformational analysis.

High Field 1H- and 13C-nmr Assignments of Grayanotoxins I, IV, and XIV Isolated from Kalmia angustifolia

Grayanotoxins I [2], IV [3], and XIV [4] were isolated from Kalmia angustifolia var. caroliniana, a North American member of the Ericaceae. Their structures were established from physical and spectral data (mp, ir, [alpha]D, uv, cd, ms, 1H and 13C nmr). High field 1H- and 13C-nmr assignments were made for each compound using 1D and 2D nmr techniques including extensive 1H single-frequency spin-decoupling and nOe difference experiments, one-bond and long-range (COLOC) carbon-hydrogen correlations, and the INADEQUATE carbon-carbon correlation experiment. This is the first report of the presence of grayanotoxins IV and XIV in this source, of complete high field (500 MHz) 1H-nmr assignments for any grayanoid, and of 13C-nmr assignments for grayanotoxins IV and XIV. For grayanotoxin I, ambiguities in the literature 13C-nmr assignments have been removed by definitive assignments made through the use of the INADEQUATE experiment.

Automated phase correction of FT NMR spectra by baseline optimization

A method for fully automated phasing of Fourier transform NMR spectra based on a baseline optimization technique is described. The optimal zero- and first-order phase corrections and a baseline offset for a NMR spectrum can be determined by maximizing the number of data points, or a related value, within a region defined by the baseline offset plus and minus a multiple of the standard deviation of the first and last few data points. A novel optimization technique has been incorporated into the phasing algorithm after Simplex, Powell's steepest descent, and quasi-Newton methods were found to be unreliable in some instances. It is difficult to determine why these optimizers occasionally fail, but the step function nature of the objective function may be responsible. In addition, analysis of contour plots of the objective function versus zero- and first-order phase correction values for some spectra reveals that global maxima corresponding to the best phased spectra exist in every case, but some features of the topography may impair the effectiveness of the various optimization methods. This autophasing method has proven to be very robust for phasing routine spectra, and even for phasing spectra that contain negative peaks such as those from NOE difference and DEPT experiments.

Isolation and characterization of an antimalarial agent of the neem tree Azadirachta indica.

The isolation and structure elucidation of gedunin [1], the antimalarial agent of Azadirachta indica, are reported. Its 1H- and 13C-nmr spectra were assigned by using one- and two-dimensional nmr spectroscopy, especially homonuclear and heteronuclear COSY, nOe difference, and COLOC experiments.

Synthesis of the carbocyclic analogue of oxetanocin A.

2, 3-Bis(benzoyloxymethyl)cyclobutanone (3__∼) was prepared in three steps from diethyl 3, 3-diethoxy-1, 2-cyclobutanedicarboxylate (1__∼). Hydrogenation of the oxime (4__∼) of 3__∼ provided the two amino compounds ((5a)___∼ and (5b)___∼), from which 9-[2, 3-bis(hydroxymethyl)cyclobuthyl]adenines ((9a)___∼ and (9b)___∼) were synthesized in four steps. The steric configurations of 3__∼, (5a)___∼, (5b)___∼, (9a)___∼ and (9b)___∼ were established by 1H-NMR spectroscopies including the NOE difference experiments.