HETCOR Experiments Research Articles

Cytotoxic sesquiterpene lactones from Centaurothamnus maximus and Vicoa pentanema.

The aerial parts of Centaurothamnus maximus yielded three cytotoxic guaianolides, chlorojanerin (1), cynaropicrin (2) and janerin (3). The structure elucidation of 1-3 was based on (1)H and (13)C NMR data, mainly 2D-NMR (1)H-(1)H COSY and (1)H-(13)C HETCOR experiments. Compounds 1-3 showed in vitro cytotoxic activity against human cancer cell lines of malignant melanoma (SK-MEL), epidermoid (KB), ductal (BT-549) and ovarian (SK-OV-3) carcinomas with IC(50) values of 2-6 microgram/mL. In addition, 12 sesquiterpene lactones (4-15), isolated previously from the aerial parts of Vicoa pentanema, were evaluated for cytotoxic and antimicrobial activities. 2alpha- Acetoxy-3beta-hydroxyalantolactone (10) and 8beta-hydroxyparthenolide (14) were found to be the main cytotoxic agents (IC(50) values of 2-6 microgram/mL against SK-MEL, BT-549 and SK-OV-3), while lactones 4, 5, 11 and 15 selectively inhibited the growth of human malignant melanoma (IC(50) value of 3.6-7.3 microgram/mL). Cell aggregation and cell adhesion assays, using HL-60 and HeLa cell lines, evaluated the effect of cytotoxic constituents 1-3, 10 and 14 on immune response and inflammation.

Reaction of 5-halo-1,2,3-thiadiazoles with aliphatic diamines. Synthesis and intramolecular cyclization of bis(1,2,3-triazolyl-1,2,3-thiadiazolyl)sulfides.

Bis[1,2,3]triazolo[1,5-f:5',1'-b][1,3,6]thiadiazepine and [1,5-g:5',1'-b][1,3,7]thiadiazocine ring systems have been synthesized from 5-halo-1,2,3-thiadiazoles and aliphatic diamines. We have found that the last step of the process is the cyclization of initially formed bis(1,2,3-triazolyl-1,2,3-thiadiazolyl)sulfides. The structures of the intermediates and products were supported by different NMR spectroscopic methods (1H coupled 13C NMR, 2D HETCOR, HMBC and 1D INADEQUATE experiments) and mass spectrometry. Differences in the reaction pathway for aliphatic and less nucleophilic aromatic diamines were determined.

Quinoxaline chemistry. Part 15. 4-[2-Quinoxalylmethylenimino]-benzoylglutamates and -benzoates, 4-[2-quinoxalylmethyl- N-methylamino]-benzoylglutamates as analogues of classical antifolate agents. Synthesis, elucidation of structures and in vitro evaluation of antifolate and anticancer activities

We report on an extension of our previous discovery of in vitro anticancer activity of trifluoromethylquinoxalines as analogues of classical and non-classical antifolic methotrexate and trimetrexate. In this case a small number of Schiff bases were obtained from the reaction of 2-bromethyl-3- R-6(7)trifluoromethylquinoxaline and ethyl p-aminobenzoylglutamate, ethyl p-aminobenzoate, p-toluidine instead of the expected 4-[2-quinoxalyl]methyl- N-methylanilino derivatives, which in turn formed with N-methylanilino derivatives. The reaction mechanism has been put forward. Structure elucidation of both Schiff bases and N-methylanilino analogues was achieved by a combination of 1H and 13C NMR spectra and hetcor experiments. Compounds 3a, 3b, 3c, 8, 11, 12, 13, Ie were tested in antifolic enzyme assay [ Lactobacillus casei (LcTS), Leishmania major (LmTs), human Thymidylate synthase (hTs), human TS, human dihydrofolate reductase (hDHFR)] while compounds 3a, 3b, 3c were tested for anticancer activity. These results seem to indicate that the Schiff bases are somewhat active either as anticancer or as folate inhibitors, while compound Ie was selectively active against hDHFR with an inhibition constant (Ki) of 200 nM with a specificity of about 1000-folds with respect to hTS.

1H and 13C NMR study of tetrahydro-1,4-benzothiazepine conformationsElectronic supplementary information (ESI) available: crystal data, structure refinement and a perspective view of the X-ray crystal structure of 1. See http://www.rsc.org/suppdata/p2/b2/b205768a/

The variable temperature (298–178 K) 1H NMR spectra of tetrahydro-1,4-benzothiazepines 1–10 are described and discussed. Compounds 2–10 exist as two puckered mirror-image (enantiomorphic) conformers, with benzothiazepine ring chair-to-chair interconversion barriers of ca. 10 kcal mol−1 in CD2Cl2 solution. A similar interconversion was detected for compound 1, of lower symmetry. The ground state conformations of 1–10 were assigned on the basis of the magnitudes of 1H–1H vicinal coupling constants. The 1H and 13C NMR spectral assignments were determined by 1H–1H COSY, HETCOR, and NOESY experiments. The stereochemistry and conformation of compound 1 was further confirmed by a single crystal X-ray structure determination.

Solid-State Nuclear Magnetic Resonance Study of Sepiolite and Partially Dehydrated Sepiolite

AbstractThe assignment of the 29Si CP/MAS-NMR spectrum of naturally-occurring sepiolite clay was re-examined using 29Si COSY and 1H-29Si HETCOR pulse sequences. Each of the three main resonances at −92.1, −94.6 and −98.4 ppm has been attributed to one of the three pairs of equivalent Si nuclei in the basal plane, and the resonance at −85 ppm to Q2(Si-OH) Si nuclei. On the basis of the COSY experiment, the resonance at −92.1 ppm is unambiguously assigned to the intermediate, near-edge Si sites. The HETCOR experiment revealed that the resonance at −94.6 ppm cross-polarizes almost entirely from the Mg-OH protons, and therefore is assigned to the central Si position. The remaining resonance at −98.4 ppm correlates strongly to the protons of the structural water molecules and therefore is assigned to the edge Si sites. Nearly complete rehydration was achieved at room temperature by exposing sepiolite samples that had been partially dehydrated at 120°C to water vapor or to D2O vapor. The rehydration results support the 29Si NMR peak assignments that were made on the basis of the COSY and HETCOR experiments.The 29Si CP/MAS-NMR spectrum corresponding to the folded sepiolite structure in which approximately one half of the structural water has been removed by heating to 350°C is reported for the first time. The chemical shift values and relative intensities are significantly different compared to the resonances that are observed in the corresponding spectrum of the true sepiolite anhydride. These observations support the earlier claim that sepiolite heated to ∼350°C exists as a distinct phase to be differentiated from that of the completely dehydrated state.

Structural Investigations of Solid Proteins at Natural Abundance Using 2D Multiple-Pulse NMR

Results from multiple-pulse 2D 1H−13C correlation experiments are described for natural proteins in the solid state. Detailed HETCOR experiments on the complex silk fibroin proteins Samia cynthia ricini (S. c. ricini) and Bombyx mori (B. mori) demonstrate that while the expected dipolar-mediated 13C and 1H correlations are observed, additional chemical shift and coupling information involving amide linkages and dilute peptides are also detected indirectly. This is an important result since we show that the 1H chemical shifts for −NH groups in S. c. ricini are not resolved in the CRAMPS experiments, thereby preventing their direct measurement. Chemical shifts via dipolar couplings (two-spin and multiple-spin interactions) are also detected for dilute peptides in the silk fibroins, again providing key structure information for these functional residues that is completely absent in the CRAMPS data. Relative dynamics of bulky side groups from dilute amino acid residues are apparent from the 2D multiple-pulse ...

Solid-State NMR Studies of the As-Synthesized AlPO4-5/TPAF Microporous Aluminophosphate

As-synthesized AlPO4-5 aluminophosphate molecular sieve prepared in a fluoride medium, using the quaternary tetrapropylammonium (TPA+) cation template, is characterized by a variety of solid-state NMR techniques. 19F MAS spectra show two distinct populations, with the same isotropic chemical shift. While 31P MAS experiments distinguish four different crystalline environments, both 19F−31P CP-MAS and HETCOR experiments reveal that only two signals belong to the AlPO4-5 framework, whereas the remaining two are attributed to crystalline byproducts. 27Al MAS and 3Q-MAS spectra indicate, in addition to the tetrahedral environment, the presence of pentacoordinated Al species in close proximity to fluorine atoms, as is additionally shown by the 19F−27Al HETCOR experiment. An 27Al−{19F} REDOR experiment strongly supports the existence of an Al−F bond (rAl-F < 2 A which forms the fifth coordination position of one of the twelve aluminum sites of the unit cell.

An 1H and 13C NMR conformational study of 2-(benzotriazol-1-yl)-substituted tetrahydropyrans

Proton and carbon NMR signals for 2-(benzotriazol-1-yl)tetrahydropyrans are assigned on the basis of spin decoupling, H,H-COSY, HETCOR, and nuclear Overhauser enhancement experiments. Conformational preferences are deduced. It was found that 2-(benzotriazol-1-yl) substituents: (i) prefer the equatorial orientation; and (ii) display a rotameric preference to minimize the electronic repulsion and (or) steric interaction.Key words: anomeric, NMR, tetrahydropyrans.

Medium- and Long-Distance 1H–13C Heteronuclear Correlation NMR in Solids

A simple method for obtaining 1H–13C HETCOR solid-state NMR spectra reflecting only medium- and long-range 1H–13C correlation peaks is presented. By dephasing the magnetization of protons directly bonded to a 13C nucleus, the short-range correlation peaks, which contain limited structural information, can be cleanly suppressed without reducing the long-range cross peaks significantly. The resulting reduction of resonance overlap simplifies spectral assignment. The dephasing of the intensity of a given peak in the HETCOR spectrum traces out a 1H–13C distance-dependent REDOR curve. This medium- and long-distance (MELODI) HETCOR experiment is demonstrated on a mixture of amino acids with 13C in natural abundance. It is useful for resonance assignment of proteins and other organic solids with partial or no 13C labeling.

N-{2-(4-methoxyphenyltelluro)ethyl}morpholine ( L1) and its platinum(II) and ruthenium(II) complexes. Synthesis and crystal structure of L1 and trans-[PtCl 2( L1) 2

The first tellurated derivative of morpholine, N-{2-(4-methoxyphenyltelluro)ethyl}morpholine ( L 1 ) has been synthesized by reacting in situ generated ArTe − with 4-(2-chloroethyl)morpholine hydrochloride under N 2 atmosphere. The compound L 1 gives molecular ion peak at m/ z 351 and is characterized structurally. The donor atoms N and Te in compound L 1 are rightly oriented for its ligation in bidentate mode. The TeC(alkyl) is 0.02 Å longer than TeC(aryl). The complexes of ligand L 1 having composition [PtCl 2( L 1 ) 2] ( 1) and [RuCl 2( p-cymene) L 1 ] ( 2) have been synthesized. The compound 1 has been characterized structurally. The Pt has a square planar geometry in complex 1 and two molecules of ligand L 1 bonded through Te alone are trans to each other (PtTe=2.583(2) Å). The 13C{ 1H} NMR spectrum of complex 1 is as expected. The 1H NMR spectrum of single crystals of complex 1 shows multiplication of signals, which is supported by HETCOR experiments. The complex 2 also has ligand L 1 in a monodentate coordination mode, bonded through Te alone. This is supported by deshielded CH 2Te and ArCTe signals in 1H and 13C{ 1H} NMR spectra of complex 2 with respect to those of free ligand L 1 . The HETCOR spectrum of complex 2 has been used to authenticate the assignments of CH 2Te group, as its two protons appear to be magnetically non-equivalent.

The synthesis and characterization of N-(diphenylthiophosphinyl)- P-phenyl-thiophosphonamidic acid phenyl ester and related compounds chiral at phosphorus

The synthesis and spectroscopic characterization of three novel phosphorus(V) compounds, chiral at phosphorus, are reported. All three compounds were characterized by X-ray crystallography, and for one compound a 1H– 31P HETCOR experiment was performed.

Characteristic 1H Chemical Shifts of Silk Fibroins Determined by 1H CRAMPS NMR

CRAMPS NMR of 1H was used for the structural analysis of some natural silk fibroins such as Tussah Antheraea pernyi and Bombyx mori in the solid state. We were able to resolve all expected 1H NMR resonances. When tied to the resolution of 13C NMR via 2D 1H−13C HETCOR experiments, overlapping proton resonance under CRAMPS are able to be further resolved. The simplified 1H signals of these natural proteins could be successfully assigned on the basis of the conformation-dependent 1H chemical shifts of model polypeptides. The 1H chemical shift of the Hα signals of Tussah A. pernyi fibroin adopting an α-helix conformation (4.0 ppm) agrees with that of α-helical poly(l-alanine) (3.9 ppm) to within ±0.1 ppm. A well-defined poly(l-alanylglycine), [Ala-Gly]12, was used as a model polypeptide of B. mori silk fibroin. The 1H CRAMPS spectra of B. mori fibroins adopting the silk I or silk II form were similar to those of [Ala-Gly]12 adopting a corresponding conformation. The Hα chemical shifts of the silk I fibroin we...

N-{2-(4-Methoxyphenyltelluro)ethyl}morpholine ( L1) and bis{2-( N-morpholino)ethyl}telluride ( L2): synthesis and complexation with palladium(II) and mercury(II). Crystal structures of trans-[PdCl 2( L1) 2] and trans-[PdCl 2( L2) 2

The reactions of 4-(2-chloroethyl)morpholine hydrochloride with ArTe − and Te 2−, generated in situ (under N 2 atmosphere) have resulted in N-{2-(4-methoxyphenyltelluro)ethyl}morpholine ( L 1 ) and bis{2-( N-morpholino)ethyl}telluride ( L 2 ), respectively, which are first tellurated derivatives of morpholine. 1H- and 13C{ 1H}-NMR spectra of L 1 are as expected but HETCOR experiments are used to assign the overlapping signals of CH 2Te and CH 2N in 1H-NMR spectrum of L 2 . The complexes of stoichiometries [PdCl 2( L 1 / L 2 ) 2] ( 1/ 3) and [HgBr 2( L 1 / L 2 )] 2 ( 2/ 4) are synthesized. The NMR ( 1H and 13C{ 1H}) spectra of all the four complexes have CH 2Te and ArCTe signals deshielded with respect to those of free L 1 / L 2 , indicating that the two ligands coordinate through Te only. The trans Pd-complexes 1 and 3 are characterized structurally and their PdTe bond lengths (average) are 2.596 and 2.600 Å, respectively. The Pd-Cl bonds in 1 are marginally shorter (average 2.312 Å) in comparison to those of 3 (average 2.325 Å). The geometry of palladium is square planar. The TeC(aryl) is shorter than TeC(alkyl). The dimeric mercury complexes 2 and 4 appear to be formed through the formation two bromo bridges between Hg atoms.

Salvimultine, a New Noricetexane Diterpene from the Roots of Salvia multicaulis

A new noricetexane diterpene, salvimultine, has been isolated from the polar fractions of Salvia multicaulis. Its structure was established as 1(10)-seco-2(10)-cyclo-icetexane by using 1D and 2D NMR spectral methods, including COSY, HETCOR, COLOC, and NOESY experiments as well as HRMS.

Analysis of1H and13C NMR spectra ofcis- andtrans-10-substituted decal-2-ones by 2D NMR techniques

The 1H and 13C NMR chemical shift assignments of 10-substituted decal-2-ones, cis (H, CH3 and CO2CH3) and trans (H, CH3, OH and CO2C2H5) were based on 2D COSY and HETCOR experiments, supported by selective spin decoupling experiments. The discrimination between the cis and the trans conformations was ruled out on the basis of the J(1a,9) magnitudes related to dihedral angles (Karplus rule) and also on the 13C shielding values of C-4 of the cis compounds, which are much more shielded than those of the trans counterparts. The best and fastest criterion of differentiation between cis and trans conformers is the constant appearance in the 13C PND spectra of the cis series of some signals of broadened linewidth and low intensity, essentially C-4, C-5 and C-7, a clue to site exchange processes; the trans counterparts showed only sharp signals because of their existence as a single conformation. Copyright © 2000 John Wiley & Sons, Ltd.

Analysis of 1H and 13C NMR spectra of cis‐ and trans‐10‐substituted decal‐2‐ones by 2D NMR techniques

The 1H and 13C NMR chemical shift assignments of 10-substituted decal-2-ones, cis (H, CH3 and CO2CH3) and trans (H, CH3, OH and CO2C2H5) were based on 2D COSY and HETCOR experiments, supported by selective spin decoupling experiments. The discrimination between the cis and the trans conformations was ruled out on the basis of the J(1a,9) magnitudes related to dihedral angles (Karplus rule) and also on the 13C shielding values of C-4 of the cis compounds, which are much more shielded than those of the trans counterparts. The best and fastest criterion of differentiation between cis and trans conformers is the constant appearance in the 13C PND spectra of the cis series of some signals of broadened linewidth and low intensity, essentially C-4, C-5 and C-7, a clue to site exchange processes; the trans counterparts showed only sharp signals because of their existence as a single conformation. Copyright © 2000 John Wiley & Sons, Ltd.

NMR study of spirophosphoranes derived from 2-aminophenols

Multinuclear magnetic resonance experiments were performed (1H, 13C, 31P, and 15N) for P-H phosphoranes derived from 2-aminophenol, 4-tert-butyl-2-aminophenol, and 4,6-di-tert-butyl-2-aminophenol. Selective heteronuclear 1H{15N} double resonance experiments and two-dimensional 15N/1H HETCOR experiments enabled us to determine various signs of coupling constants (e.g., 2J(31P, N, 1H) > 0; 1J(31P, 15N) < 0). The 1H-coupled 15N NMR spectrum recorded by the INEPT pulse sequence shows the splitting due to 1J(31P, 15N) and 2J(15N, P, 1H). The latter value is useful for polarization transfer experiments from 1H to 15N, once the hydrogen atoms of the N-H functions are replaced by other groups. Isotope-induced chemical shifts 1Δ14/15N(31P) were measured by using the INEPT-HEED pulse sequence. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:11–15, 2000

Fluorine-19 NMR from retrosynthesis to NMR crystallography

Recently, the need for more accurate structure description that will allow to analyze possible retrosynthesis of microporous compounds has led us to use and develop new structural strategies to access structure determination by solid state NMR techniques. At first, an example, AlPO4-CJ2, between crystallogenesis and crystal structure is explored. AlPO4-CJ2 has been studied by hydrothermal in-situ NMR. A soluble species exists in supersaturated liquid as well as the product of redissolution of AlPO4-CJ2. This species, the prenucleation building units (PNBU) is different from structural buildings units (SBU) the sub-ensembles of the crystal. How this PNBU gets into the structure and becomes therefore a structural building unit (SBU) is our main question. To answer it, an HETCOR experiment between fluorine and aluminum has been performed. This experiment shows that when the PNBU enters the solid, it forms at the same time than growing the solid, a fluorinated bridge. On ULM-18 after structure elucidation positioning hydrogen, a dynamic charge compensation mechanism is proposed for the solid formation. On TMPGaPO, a set of 2D experiments using radio frequency driven dipolar recoupling (RFDR) on 19F, Double Quanta on 31P and HETCOR between 19F and 31P allowed analyzing the topology of the network.

New palladium(II) complexes with bis(pyrazol-1-yl)alkanes

The replacement of chloride ligands in [Pd(NN)Cl 2] (NN=bpzm: bis(pyrazol-1-yl)methane, bpzm*: bis(3,5-dimethylpyrazol-1-yl)methane) by a weak donor ligand such as acetonitrile has been achieved by treating the dichloro complexes with AgClO 4 in this solvent. The reactivity of the new precursors [Pd(NN)(CH 3CN) 2][ClO 4] 2 towards a variety of neutral N- and P-donor ligands L (pyridine, triphenylphosphine, triethylphosphine) or L 2 (1,2-bis(diphenylphosphino) ethane, ethylenediamine, N, N, N′, N′-tetramethylethylenediamine, 2,2′-bipyridine, o-phenylenediamine) has been studied. When chloride abstraction from [Pd(NN)Cl 2] is carried out in Me 2CO/H 2O, the cationic hydroxo-bridged dimeric complexes [(NN)Pd(μ-OH) 2Pd(NN)] 2+ are isolated as their perchlorate salts. The hydroxo complexes react with the protic electrophiles H(LL) (acetylacetone, salicylaldehyde and 2-pyrrol carbaldehyde) in a 1:2 molar ratio to give the corresponding mononuclear complexes [Pd(NN)(LL)][ClO 4]. The 13C and 1H NMR assignments have been made on the basis of NOE studies and 1H– 1H COSY and 1H– 13C HETCOR experiments. The structures of [Pd(bpzm)(tmeda)][ClO 4] 2 and [Pd(bpzm*)(sal)][ClO 4] have been determined by single-crystal X-ray diffraction studies; in both complexes the bis(pirazolyl)alkanes act as chelating ligands with coordination around the palladium atom slightly distorted from the square-planar geometry.

2H−{H} CPMAS NMR of Guest−Host Species in Zeolites: An Experimental Study

The feasibility of 2H−{1H} cross-polarization magic-angle spinning (CPMAS) NMR and its implementation in HETCOR experiments is studied using as-made all-silica zeolites. The results presented show that 2H−{1H} CPMAS can be employed successfully in two-dimensional correlation spectroscopy experiments. The effects of experimental and physical parameters (spin rate, RF field strengths, 1H homonuclear dipole−dipole coupling, and the magnitude of the quadrupole coupling constants) on the NMR spectra are studied in detail. In the limit of small quadrupole coupling constants and weak proton homonuclear dipolar coupling, the cross-polarization behavior of the deuterons is similar to spin I = 1/2 systems and proton spin-diffusion is minimal. Samples with larger quadrupole coupling constants and strong proton dipole−dipole coupling exhibit less efficient spin-locking of the deuterons and proton spin-diffusion is more prevalent. In this case, it is necessary to perform proton spin-diffusion experiments in conjunctio...