High-field 1H Research Articles

Selective access and full characterization of mono-acidic permethylated β-cyclodextrin derivatives and their methyl esters

Three acidic derivatives of permethylated β-cyclodextrin, 2 I- O-carboxymethyl-2 II-VII,3 I-VII,6 I-VII-eicosa- O-methyl-cyclomaltoheptaose, 6 I- O-carboxymethyl-2 I-VII,3 I-VII,6 II-VII-eicosa- O-methyl-cyclomaltoheptaose, 6 I-desoxy-6 I-carboxy-2 I-VII,3 I-VII,6 II-VII-eicosa- O-methyl-cyclomaltoheptaose and the corresponding methyl esters have been synthesized with good yields starting from mono-hydroxy permethylated β-CD prepared via tert-butyldimethylsilyl protection in 6-position and p-methoxybenzyl protection at the 2-position. All of these compounds were fully characterized by high field 1H and 13C NMR and HPLC/MS.

Neutral β-diketiminato nickel(II) monoalkyl complexes

Reaction of NiCl 2(2,4-lutidine) 2 ( 1) with Tl[Me 2NN] ( 3) in THF results in the transmetallation of the β-diketiminate ligand from which the tetrahedral {[Me 2NN]NiCl} 2 ( 4) was isolated in poor yield. After filtration of the TlCl formed in the reaction between 1 and 3 in THF, addition of Grignard reagents RMgBr results in the isolation of monoalkyl complexes [Me 2NN]Ni(R)(2,4-lutidine) (R=Me ( 5), Et ( 6), Pr ( 7)) in 40–70% yield. X-ray structures 5– 7 of show these monoalkyls to be somewhat crowded, square planar species. NMR studies of the diamagnetic monoalkyl complexes show that lutidine dissociation/reassociation occurs on the NMR timescale at room temperature. In ethyl and propyl complexes 6 and 7, an equilibrium between the four coordinate [Me 2NN]Ni(R)(2,4-lutidine) and a lutidine-free species [Me 2NN]Ni(R) (R=Et, Pr) is observed. Broad, high-field 1H resonances consistent with the presence of β-H agostic alkyl groups are observed for the base-free species. The observation of two broad upfield 1H NMR signals at δ −2.7 and −7.3 ppm for the base-free Ni–propyl complex suggests a mixture of primary and secondary β-agostic isomers that reversibly interconvert by β-H elimination/reinsertion. Ethylene slowly inserts into monoalkyls 5– 7 demonstrate to give highly branched ethylene oligomers.

Antineoplastic Agents 390. Isolation and Structure of Phakellistatin 12 from a Chuuk Archipelago Marine Sponge

A new cancer cell growth inhibitory (P388 lymphocytic leukemia ED 50 2.8 μg/mL) cyclodecapeptide designated phakellistatin 12 ( 2) has been isolated as a trace (1.7×10 −6% yield) constituent of the Western Pacific Ocean (Federated States of Micronesia-Chuuk) sponge Phakellia sp. Employing principally a combination of high resolution FAB with high field (500 MHz) 1H, 13C and 2-D NMR and chiral GC analyses the structure (all S chirality) cyclo-Ile-Phe-Thr-Leu-Pro-Pro-Tyr-Ile-Pro-Pro was assigned.

Dynamic1H and2H NMR investigations of acetonitrile confined in porous silica

In this work, the molecular dynamics of acetonitrile and acetonitrile-d3 confined in silica pores of nominal diameter 6 and 20 nm are studied by high field 1H and 2H NMR, and the results are discussed with reference to the bulk substances. NMR line-shapes, spin–lattice relaxation times (T1), spin–spin relaxation times (T2) and diffusivities (D) are reported as a function of temperature. The line-shape and relaxation measurements clearly reveal a two-component system in the solid phase, consisting of a narrow line superimposed on a broad complex resonance. The melting process takes place over a certain temperature region, due to an appreciable pore size distribution. Below the melting region, the narrow line originates solely from the surface layer, while the broad line is attributed to the crystalline solid at the interior of the pore. The confining geometry restricts the mobility of the liquid probe molecules and gives rise to significantly shorter T1 and T2 relaxation times and reduced self-diffusion rates, as compared to the bulk substance. This observation is also reflected in increased activation energies of the reorientational and translational motions. True intra-grain diffusivities were obtained for the probe molecules by using the short diffusion time model, and extrapolating to zero observation time.

Stereochemistry in solution of spiro-2,2′-dioxybiphenyl-cyclotriphosphazenes: an NMR spectroscopic study combined with molecular dynamics simulations

The stereochemistry in solution of spirocyclophosphazenes 1–3 containing 2,2′-dioxybiphenyl groups, tris(2,2′-dioxybiphenyl)cyclotriphosphazene [N3P3(O2C12H8)3] (1) and the chloro derivatives [N3P3Cl2(O2C12H8)2] (2) and [N3P3Cl4(O2C12H8)] (3), was studied using high field 1H, 13C and 31P NMR spectroscopy (variable temperature experiments) combined with molecular dynamics (MD) simulations. The ambient temperature spectra, after full assignments, showed a unique set of signals (four and six for hydrogens and carbons, respectively) for the corresponding nuclei of all the biphenoxy systems. This isochrony was compatible with symmetry equivalence as well as with fast interconversions on the NMR time scale between the stereoisomers RRR, SSS, RRS, SSR (1), RR, SS, RS, SR (2) and R, S (3). Dynamic NMR studies evidenced that atropoisomers of 1–3 are populated at low temperature (≤ 183 K) bearing out fast racemization of the NP(O2C12H8) units in solution at ambient temperature. The MD trajectories, which were long enough (50 ns) to monitor time-averaged processes on the NMR scale, were selectively compatible with DNMR results, and provided insights into the motional properties of 1–3. They significantly complemented the experimental information on the exchange process of 3, due to the inherent limitation of the single use of the NMR technique when NMR active diastereotopic nuclei are absent in the investigated system.

Crown ether substituted cobalta bis(dicarbollide) ions as selective extraction agents for removal of Cs+ and Sr2+ from nuclear waste

A series of crown ether derivatives of the cobalta bis(dicarbollide) closo-[(1,2-C2B9H11)2-3,3′-Co]− (1) anion was prepared using two synthetic strategies. The first method employs dioxane ring cleavage of the closo-[{8-(C4H8O2)-1,2-C2B9H10}-3,3′-Co-(1′,2′-C2B9H11)]0 zwitterionic species with sodium oxymethyl crowns, producing a series of anions with spacer bonded crown ether moieties varying in crown ether ring size. Three compounds of this group; closo-[{8-(15-crown-5-CH2O)-(CH2CH2O)2-1,2-C2B9H10}-3,3′-Co-(1′,2′-C2B9H11)]− (2), closo-[{8-(18-crown-6-CH2O)-(CH2CH2O)2-1,2-C2B9H10}-3,3′-Co-(1′,2′-C2B9H11)]− (3) and [{8-(21-crown-7-CH2O)-(CH2CH2O)2-1,2-C2B9H10}-3,3′-Co-(1′,2′-C2B9H11)]− (4) were prepared in high yields. The second approach involved reaction of deprotonated closo-[8,8′-(OH-1,2-C2B9H12)2-3,3′-Co]− with p-toluenesulfonyl esters derived from hydroxymethyl crown ethers. Only compounds bearing one crown ether ring resulted in preparative amount from this reaction, the [(8-{(15-crown-5-CH2O)-1,2-C2B9H10}-3,3′-Co-{8′-(HO)-1′,2′-C2B9H10}]− (5) and [{8-(21-crown-7-CH2O)-1,2-C2B9H10}-3,3′-Co-(8′-HO-1′,2′-C2B9H10)]− (6). All compounds were characterized by high field 1H and 11B NMR methods, HPLC and MS, with electrospray ionization, and the molecular structure of the Cs+ complex of species 5 was determined by single crystal X-ray diffraction analysis. These compounds represent the first examples where oxygen crown ethers were successfully bonded to the cage of anion 1. The scope and limitations of the use of these compounds in the liquid–liquid extraction of Cs+ and Sr2+ from nuclear waste were studied, including comparison of extraction efficiency and selectivity of the covalently bonded species under study with synergistic mixtures of hexabrominated anion 1 with crown ethers. As a rule, crown ethers linked to the cobalta bis(dicarbollide) cage display distribution coefficients for Cs+ and Sr2+ comparable to the crown ethers mixed with the hexabromoderivative of 1, however, they were found to exhibit better selectivity with respect to Na+ cation.

Evidence for a common molecular basis for sequence recognition of N3-guanine and N3-adenine DNA adducts involving the covalent bonding reaction of (+)-CC-1065.

The antitumor antibiotic (+)-CC-1065 can alkylate N3 of guanine in certain sequences. A previous high-field 1H NMR study on the (+)-CC-1065d[GCGCAATTG*CGC]2 adduct (* indicates the drug alkylation site) showed that drug modification on N3 of guanine results in protonation of the cross-strand cytosine [Park, H.-J.; Hurley, L. H. J. Am. Chem. Soc. 1997, 119, 629.]. In this contribution we describe a further analysis of the NMR data sets together with restrained molecular dynamics. This study provides not only a solution structure of the (+)-CC-1065(N3-guanine) DNA duplex adduct but also new insight into the molecular basis for the sequence-specific interaction between (+)-CC-1065 and N3-guanine in the DNA duplex. On the basis of NOESY data, we propose that the narrow minor groove at the 7T8T step and conformational kinks at the junctions of 16C17A and 18A19T are both related to DNA bending in the drugDNA adduct. Analysis of the one-dimensional 1H NMR (in H2O) data and rMD trajectories strongly suggests that hydrogen bonding linkages between the 8-OH group of the (+)-CC-1065 A-subunit and the 9G10C phosphate via a water molecule are present. All the phenomena observed here in the (+)-CC-1065(N3-guanine) adduct at 5'-AATTG* are reminiscent of those obtained from the studies on the (+)-CC-1065(N3-adenine) adduct at 5'-AGTTA*, suggesting that (+)-CC-1065 takes advantage of the conformational flexibility of the 5'-TPu step to entrap the bent structure required for the covalent bonding reaction. This study reveals a common molecular basis for (+)-CC-1065 alkylation at both 5'-TTG* and 5'-TTA*, which involves a trapping out of sequence-dependent DNA conformational flexibility as well as sequence-dependent general acid and general base catalysis by duplex DNA.

NMR spectroscopy for studying structure and intramolecular dynamics of modified analogs of steroid hormones

Special features of the use of homo- and heteronuclear correlation methods of NMR in one and two dimensions for studying the spatial structure and intramolecular dynamics of modified analogues of steroid hormones (MASH) are considered. The application of these methods to the assignment of resonances in the high-field 1H NMR region and to the determination of the most stereospecifically important parameters, such as the vicinal constants of spin-spin coupling (3JH-H) and nuclear Overhauser effects (NOE), are discussed using the example of NMR studies of some estrogens and androgens at 300 MHz and on the basis of literature data. The most efficient combination of the methods and the necessary modification of each of them may be chosen considering the spectral and relaxation parameters of MASH in liquid medium, including the anisotropy of the overall diffusive motion. The characteristics of MASH are the wide use of correlations through long-range couplings (COSY-45 and DQF-COSY), the application of the 4,5JH-H constants for the determination of spatial structure, and the advantage of heteronuclear HSQC methods with and without 13C decoupling over the corresponding HMQC methods in both resolution and sensitivity. In the conformationally rigid MASH molecules, the anisotropy of the MASH diffusive motion in liquid adversely affects the determination of interproton distances by the calibrating processing method for the NOE difference and NOESY spectra: it results in both overestimated and underestimated distance values depending on the polar angle ratios of the reference and the determined distances. Under certain conditions, conformationally mobile MASH demonstrate the additional contribution of the scalar relaxation mechanism between the indirectly (scalarly) bound protons. This mechanism is responsible for the underestimated values of NOE and the corresponding errors in the distance determination.

The absolute configuration of the mushroom metabolites involutin and chamonixin

The absolute configurations of the cyclopentanoid fungal metabolites involutin ( 1) and chamonixin ( 2) have been determined by application of the high-field 1H NMR variant of Mosher's method. The experimental results are supported by quantum chemical calculations.

Sesquiterpene lactones and other constituents of Disynaphia multicrenulata from Argentina.

Flowers and leaves of Disynaphia multicrenulata from Argentina afforded a large number of known germacradienolides and heliangolides, a new germacradienolide, a known melampolide, a new parthenolide derivative, one known and seven new cronquistiolides, a new 4Z-melampolide, three known and five new eudesmanolides, a new elemadienolide, a known grazielolide, an isoguaiagrazielolide, two diepoxygermacran-8,12-olides, three common kauranoic acids, pinoresinol, jaceosidin and the sesquiterpene oplopanone. Structures were elucidated by high-field 1H NMR spectrometry. The relationship to the known chemistry of other members of the Disynaphiinae is discussed.

Synthesis of novel heterocyclic polyimides containing trimellitimide acid moieties

4-Nitrobezoyl chloride (2) was reacted with isoeugenol in chloroform in the presence of triethyl amine and ester (4) was obtained in high yield. Ester (4) was reacted with SnCl2·2H2O to give amine-ester (5), and subsequently was reacted with trimellitic anhydride (6) and novel isoeugenol ester-imide derivative (7), as a new monomer was obtained in quantitative yield. Compound (7) was characterized by high-field 1H–NMR, IR, and elemental analysis and then was used for the preparation of model compound (9) and polymerization reactions. 4-Phenyl-1,2,4-triazoline-3,5-dione (PhTD) (8) was allowed to react with compound (7). The reaction is very fast and gives only one double adduct (9) via Diels–Alder and ene pathways in excellent yield. The polymerization reactions of novel monomer (7) with bistriazolinediones [bis(p-3,5-dioxo-1,2,4-triazolin-4-ylphenyl)methane (10) and 1,6-bis(3,5-dioxo-1,2,4-triazolin-4-yl)hexane (11)] were carried out in N,N-dimethylacetamide (DMAc) at room temperature. The reactions are exothermic, fast, and gave novel heterocyclic polyimides (12) and (13) via repetitive Diels–Alder-ene polyaddition reactions. Some structural characterization and physical properties of these novel heterocyclic polyimides are reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1716–1725, 2001

Synthesis of the three isomeric mono-2-, 3-, or 6-hydroxy permethylated β-cyclodextrins and unambiguous high field NMR characterisation

The three isomeric mono-2-, 3- or 6-hydroxy permethylated β-cyclodextrins are good precursors for a wide variety of mono functionalised ‘permethyl’ β-cyclodextrins. In this work, we describe the selective access to mono-6-hydroxy (via the mono-6-tertbutyldimethylsilyl derivative), mono-2-hydroxy (via the mono-2-benzyl derivative) and mono-3-hydroxypermethylated-β-cyclodextrins (by under-methylation of heptakis (2,6-di- O-methyl)-β-cyclodextrin). These derivatives were characterised by high field 1H and 13C NMR spectroscopy. The position of the free hydroxyl group was confirmed unambiguously by 13C NMR after methylation with 13C-labelled methyl iodide.

Structure of the γ-chain of the human IgE FcɛR1 receptor: NMR and molecular dynamics studies

The solution structure of the 37-residue intracellular γ-chain of the human FceR1 receptor protein has been determined using high field 1H nuclear magnetic resonance (NMR) spectroscopy combined with molecular dynamics simulations. Two closely related groups of α-helical structures were found, with disruptions of the helix between residues 20 to 24; for one group the disruption is a type I β-turn, and in the second this region is less structured and acts as a loose ‘hinge’ between the α-helical regions. All structures exhibited a major and a minor hydrophobic region. The two tyrosines of the ARAM (antigen recognition activation motif) consensus motif lie on a single face of the helix, as do the two hydrophobic ARAM leucine and isoleucine residues. Three of the five threonines define a third face. These data are used to propose a model for the in vivo dimer of the γ-chain which is consistent with the susceptibility of the tyrosines and threonines to phosphorylation as an important feature of signal transduction.

Transesterification characteristics of poly(bisphenol A carbonate) with ethylene terephthalate-Caprolactone copolyester

The transesterification of poly(bisphenol A carbonate) (PC) with ethylene terephthalate (ET)–caprolactone (CL) copolyester (TCL) was investigated with high-field 1H NMR spectroscopy. Under an uncatalyzed condition, ET and CL segments in TCL reacted more easily with PC than the corresponding homopolymers poly(ethylene terephthalate) and poly(ϵ-caprolactone). In a comparison of the transferring rates, aromatic ET segments had higher reaction activity than aliphatic CL segments. Furthermore, the reaction activity appeared to be strongly dependent on the TCL compositions. High and low ET-segment contents were unfavorable to the exchange reaction for both ET and CL segments. These characteristics are discussed on the basis of the TCL structures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 232–238, 2001

Synthesis of novel heterocyclic polyimides containing trimellitimide acid moieties

4-Nitrobezoyl chloride (2) was reacted with isoeugenol in chloroform in the presence of triethyl amine and ester (4) was obtained in high yield. Ester (4) was reacted with SnCl2·2H2O to give amine-ester (5), and subsequently was reacted with trimellitic anhydride (6) and novel isoeugenol ester-imide derivative (7), as a new monomer was obtained in quantitative yield. Compound (7) was characterized by high-field 1H–NMR, IR, and elemental analysis and then was used for the preparation of model compound (9) and polymerization reactions. 4-Phenyl-1,2,4-triazoline-3,5-dione (PhTD) (8) was allowed to react with compound (7). The reaction is very fast and gives only one double adduct (9) via Diels–Alder and ene pathways in excellent yield. The polymerization reactions of novel monomer (7) with bistriazolinediones [bis(p-3,5-dioxo-1,2,4-triazolin-4-ylphenyl)methane (10) and 1,6-bis(3,5-dioxo-1,2,4-triazolin-4-yl)hexane (11)] were carried out in N,N-dimethylacetamide (DMAc) at room temperature. The reactions are exothermic, fast, and gave novel heterocyclic polyimides (12) and (13) via repetitive Diels–Alder-ene polyaddition reactions. Some structural characterization and physical properties of these novel heterocyclic polyimides are reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1716–1725, 2001

New benzodioxepin type strobilurins from basidiomycetes. Structural revision and determination of the absolute configuration of strobilurin D and related β-methoxyacrylate antibiotics

The new antifungal strobilurins I ( 1) and K ( 19) are 3,4-dihydro-2 H-benzo[ b][1,4]dioxepin derivatives. Their structure and stereochemistry was determined by degradation to aldehyde 3. Both enantiomers of 3 were synthesised and the absolute configurations assigned by the high-field 1H NMR variant of Mosher's method. (S)- 3 is identical with the compound derived from the natural products. In the course of these investigations the epoxide structures 15, 16 and 17 previously assigned to strobilurin D, hydroxystrobilurin D and 9-methoxystrobilurin K have to be changed in 18, 21 and 20, respectively. All these compounds possess the same benzodioxepin core structure and ( S)-configuration as strobilurin I ( 1).

A facile synthesis of diastereoisomeric 1,4-diionic organophosphorus compounds

The addition of dialkyl acetylenedicarboxylates to strong CH-acids in the presence of triphenylphosphine leading to highly functionalized 1,4-diionic organophosphorus compounds is reported. These betaines possess two vicinal stereogenic centers and exist as a mixture of two diastereoisomers. Interconversion between the two diastereoisomeric forms of these 1,4-diionic compounds via C-H proton exchange reactions of the (Ph)3P+-CH moieties, preclude their separation. The assignments of the two diastereoisomeric forms of these systems are based on the high-field 1H, 13C and 31P NMR data.

Amalgam (Na.Hg) reduction of some 4-Substituted-2-amino-3,5-dicyano-6-methoxypyridines. New evidence regarding the oxidation step in their synthesis

The amalgam (Na.Hg) reduction of some 4-substituted-2-amino-3,5-dicyano-6-methoxypyridines 3 results in the formation, in high yields of 3,4-dihydropyridines 2. Highfield 1H and 13C nmr studies provide unambiguous support for the structures proposed. The synthesis of C-4 deuterium labeled dihydropyridine 2c-D, by this procedure, let us understand the role played by this dihydropyridines as intermediates in the necessary oxidation path into the synthesis of pyridines 3 from malononitrile and benzylidenemalononitriles 1 in methanol/sodium methoxide.

The role of N-acetylcysteine in protecting synovial fluid biomolecules against radiolytically-mediated oxidative damage: A high field proton NMR study

High field proton (1H) NMR spectroscopy has been employed to evaluate the abilities of the antioxidant thiol drug N-acetylcysteine and exogenous cysteine to protect metabolites present in intact inflammatory synovial fluid samples against oxidative damage arising from gamma-radiolysis (5.00 kGy) in the presence of atmospheric O2. Although oxidation of urate to allantoin by radiolytically-generated *OH radical was readily circumventable by pre-treatment of synovial fluids with N-acetylcystine (1.00 or 3.00 × 10-3 mol · dm-3) or cysteine (1.00, 2.00 or 5.00 × 10-3 mol · dm-3), both thiols offered only a limited protective capacity with respect to hyaluronate depolymerisation and the production of formate from carbohydrates in general. Radiolytic products generated from the added thiols (predominantly their corresponding disulphides) were simultaneously detectable in 1H Hahn spin-echo spectra of gamma-irradiated synovial fluids, permitting a quantitative evaluation of the radioprotective capacity of these agents. It is concluded that the multicomponent analytical ability of high field 1H NMR spectroscopy provides much useful molecular information regarding mechanisms associated with the radioprotectant actions of thiols in intact biofluids.

All pyruvylated galactose in Schizosaccharomyces pombe N-glycans is present in the terminal disaccharide, 4, 6-O-[(R)-(1-carboxyethylidine)]-Galbeta1,3Galalpha1-.

The large N-linked oligosaccharides released from Schizosaccharomyces pombe by endo-beta-N-acetylglucosaminidase H were examined to determine how the negatively chargedpyruvylated galactoses present (Gemmill,T.R., and Trimble,R.B., 1996, J. Biol. Chem ., 271, 25945-25949) were attached to the oligosaccharide chains. Binding of biotinylated human serum amyloid P and peanut agglutinin to native and depyruvylated S.pombe glycoproteins, respectively, indicated that the pyruvylated epitope was likely to be in the beta configuration. Examination by high-field 1H NMR of whole glycans and a disaccharide fragment released from them on partial acid hydrolysis showed that the pyruvylated galactose species was in fact beta1,3-linked to a second galactose, and this occurred an average of five to six times on nominal Gal57Man64GlcNAc N-glycans. The pyruvate-2,(4,6)Gal-beta1,3Gal epitope is chemically similar to acetaldehyde-Galbeta1,3Gal groups found on the glycoproteins from Paramyxovirus-infected bovine kidney cells (Prehm, P., Scheid,A. and Choppin,P.W. ,1979, J. Biol. Chem ., 254, 9669-9677). The 1:1 stoichiometry between pyruvate and beta-linked galactose in these S.pombe glycans indicates that either pyruvate addition to terminal beta1,3Gal is highly efficient or that pyruvylated Gal is transferred en bloc to alpha1,2-linked Gal residues in theN-linked chains. In contradiction to many galactomannan-producing fungi, which add substantial amounts of Gal in the furanose form to their glycoproteins, all detectable Gal in the large S.pombe galactomannans is in the pyranose form, as found in higher eukaryotes. The current work shows that the S.pombe outer chain structure is a poly-alpha1,6Man backbone 2-O-substituted with either Gal or the pyruvylated galactobiose and contains little alpha1,2-linked or 2-O-substituted Man. This is in contrast to the S. cerevisiae outer chain, which is poly-alpha1,6Man substituted with alpha1,2-linked Man sidechains (Ballou,C.E. ,1990, Methods Enzymol , 185, 440-470).