Jan M. Coddington

Quaternary naloxone blocks morphine analgesia in spinal but not intact rats

Quaternary derivatives of naloxone and other compounds are assumed not to enter the central nervous system following systemic administration. We report that i.p. naloxone methylbromide (5 mg/kg) completely reversed the antinociceptive effect of systemically administered morphine (6 mg/kg) in acutely spinalised rats, although it had no effect in the same animals prior to the transection. Naloxone hydrochloride was effective both before and after transection. Nuclear resonance spectra confirmed the purity of both compounds. These results suggest that acute spinal transection allows rapid entry of quaternary naloxone into the spinal cord. Quaternary compounds therefore may need to be used with caution in spinalised animals.

Structures of the pectic polysaccharides from the cell walls of kiwifruit

Abstract The structure and distribution of the neutral side chains of three pectic polysaccharide fractions of kiwifruit, possessing widely differing degrees of branching, were studied by chemical methods, gel-permeation chromatography, and 13 C-n.m.r. spectroscopy, following degradation with a purified endo-polygalacturonase. Three categories of side chain were identified: ( a )(1 → 4)-linked β- d -galactosyl residues, which occurred in regions where the galacturonan backbone contained little rhamnose and small proportions of other neutral sugars; ( b ) side chains containing proportionately less galactose and more arabinose, xylose, and fucose, which occurred in regions where the galacturonan backbone contained increased proportions of rhamnose; and ( c ) large (1 → 4)-β- d -galactans, which were attached to the rhamnogalacturonan backbone. The possible contribution of these side chains to cell-wall breakdown during kiwifruit ripening is discussed.

The constitution of aqueous tin(IV) chloride and bromide solutions and solvent extracts studied by 119Sn NMR and vibrational spectroscopy

Abstract 119Sn NMR spectra were used to investigate the aquohalostannate(IV) complexes formed by SnCl4 and SnBr4 in aqueous and halogen acid solutions. Characteristic chemical shifts were assigned to the complex cations [SnX(H2O)5]3+, [SnX2(H2O)4]2+ and [SnX3(H2O)3]+, [SnX4(H2O)2], and the complex anions [SnX5(H2O)]− and [SnX6]2− (where X = Cl or Br); including the pairs of cis/trans or fac/mer isomers. The CPMAS spectra of crystalline solids containing [SnCl6]2− and cis- or trans-[SnCl4(H2O)2] assisted these assignments. The NMR data yielded quantitative estimates of the amounts of the various species in solution as a function of the tin concentration from 0.1 mol dm−3, where the hydrated stannic ion, Sn4+ (aq), is predominant, to near saturation where auto-complexing results in complex anion formation. Soluble hydrolysis products for which OH-bridged structures are proposed were detected in solutions without added HCl or HBr and increase in amount when NaOH is introduced. Solutions containing excess NaOH reveal [Sn(OH)6]2− which has a chemical shift of — 590 ppm and exhibits the Raman frequencies: 552 (v1), 425 (v2), 290 cm−1 (v5), appropriate for octahedral (Oh) symmetry. The 119Sn NMR spectra of tin(IV) mixed halide aqueous solutions consisted of signals ranging from — 600 ppm (H2O and Cl− ligands) to —2000 ppm (Br− ligands), due to the series of species represented by SnClxBry(H2O)z (where x+y+z = 6), and can be interpreted by relating the chemical shift of the tin nucleus to the sum of ligand electronegativities in a given complex. The solvent extraction of tin halides from aqueous acid solution by diethyl ether or isobutyl methyl ketone has been investigated and tin(IV) shown to be extracted in the form of both molecular [SnX4(H2O)2] and ion-pair H+(aq)[SnX5(H2O)]− complexes. These species can also be generated in solution by adding small amounts of water to [SnX6]2− in acetone. Conjoint use of NMR and Raman spectra enables the major species in these systems to be determined and allows the v(SnX) symmetric stretching frequencies to be identified and assigned.

A revised structure for tagetitoxin

Abstract New MS and NMR data for tagetitoxin required the structure to be revised to one consisting of two fused 6-membered heterocyclic rings.

Biosynthetic pathway to rhizobitoxine in Pseudomonas andropogonis

When dl-[4-13C]aspartic acid was provided at regular intervals to Pseudomonas andropogonis cultures between two and three days growth, hydroxythreonine was specifically labelled at C-4 (4-fold enrichment), and rhizobitoxine was specifically labelled at C-4 and C-1 (4-fold and 2-fold enrichments, respectively). The result shows that aspartic acid is converted directly to the 2-amino-4-oxy-but-3-enoic acid moiety of rhizobitoxine. Various l-[U-14C]amino acids were added to P. andropogonis cultures after two days growth. [14C]Aspartic acid was rapidly (<30min) incorporated into rhizobitoxine (ca 1.5%) and hydroxythreonine (ca 0.5%). Incorporation from [14C]homoserine into rhizobitoxine and hydroxythreonine was 5.7 and 3.2% respectively, whereas from [14C]threonine it was 0.05 and 0%. These results suggest that homoserine lies on the pathway to rhizobitoxine and that the biosynthetic pathway to rhizobitoxine branches from the usual aspartic acid→threonine pathway prior to the formation of threonine. Whereas exogenous lysine and methionine had little effect on the biosynthesis of rhizobitoxine, both threonine and homoserine substantially reduced (2.8-fold and 11-fold respectively) the incorporation of 14C from aspartic acid into rhizobitoxine, by P. andropogonis. In the former case this was probably due to feedback inhibition of the aspartic→threonine pathway, and in the latter as a result of competition/dilution. The collective results suggest that the biosynthesis of rhizobitoxine follows the route aspartic acid→homoserine→hydroxythreonine→rhizobitoxine. On the basis of the present results and recent publications, speculation is made concerning the final stages of the biosynthesis of rhizobitoxine, and of the biosynthesis of dihydrorhizobitoxine, a compound that is frequently produced by Bradyrhizobium japonicum.

The variation of xenon-129 n.m.r. chemical shifts with aluminum content in ZSM-5 and ZSM-11 zeolites

The technique of 129 Xe n.m.r. has been applied to the study of electric field effects in ZSM zeolites. For ZSM zeolites in the acid form, the chemical shift at zero coverage varies with aluminum content. This variation is explained by changes in the effective electric field experienced by xenon within the zeolite pores as the aluminium content and, hence, the proton concentration vary

An NMR assay for quantitating lipase activity in biphasic macroemulsions

A novel nuclear magnetic resonance (NMR) assay has been developed to monitor lipase-catalyzed esterification reactions without the need to extract and purify the individual components. The technique measures ratios of ester:alcohol signals and has been shown to be both efficient and reproducible. The assay has proven useful as a quick screen for the effect of varying conditions on the extent of esterification in various biphasic solvent systems and can be applied to both saturated and unsaturated long-chain fatty acid and alcohol substrates. The NMR ratio technique has been used to quantitate the extent of reaction in theCandida cylindracea lipase-catalyzed synthesis of oleyl palmitate, stearyl palmitate, oleyl oleate, oleylgamma-linolenate and oleyl linoleate. The identity of these products was confirmed by high-resolution mass spectrometry.

Conformational isomerism in a series of alkylpiperazonium derivatives investigated by high field 1H and 13C NMR spectroscopy

Abstract Changes in the 1 H and 13 C NMR spectra over the temperature range −30 to +60°C are used to investigate conformational isomerism in N,N′-dimethylpiperazine, the N,N,N′,N′-tetramethylpiperazonium dication and trialkylpiperazonium monocations of the type MeN(CH 2 CH 2 ) 2 N(Me)R + , where R = Me, Et, n -Pr, i -Pr or CH 2 X (X = Cl, Br or I). Measurements of the rate of ring inverson of the heterocyclic cations ( 1–4 ) from line width data yield values of the enthalpy and entropy of activation; Δ H ≠ = 64 to 75 ± 2 kJ mol −1 and Δ S ≠ = 30 to 80 ± 10 J K −1 mol −1 . These are compared with the values derived from the activation energy (Δ G ≠ = 47 to 56 ± 1 kJ mol −1 ) obtained from the coalescence temperatures of NMR signals from appropriate sets of indicating nuclei. The related seven-membered heterocycle N,N,N′,N′-tetramethylhomopiperazonium dication ( 2 ) exhibits a higher barrier to ring inversion than those of the alkylpiperazonium derivatives. For the N,N,N′-trialkylpiperazonium ions ( 4–7 ) with unlike substituents on the quaternary nitrogen, the NMR spectra show that 70–75% of the ground state molecules have the bulkier group in the equatorial situation. Also reported are some 14 N coupling constants, 1 J ( 14 N, 13 C) of 2.5–4.0 Hz, and 3 J ( 14 N, 1 H) of 1.5–2.0 Hz, involving nitrogen atoms of the quaternary centres.

Extended X-ray absorption fine structure and 129Xe nuclear magnetic resonance evidence for highly dispersed molybdenum clusters in zeolite Y

EXAFS and 129Xe NMR data are presented which show that adsorption of Mo(CO)6 in zeolite NaY followed by decomposition at 200 °C produces uniformly dispersed Mo2 clusters in the zeolite supercages; heating to 400 °C causes sintering to an average cluster size of three or four Mo atoms.

Diterpenoids of the wood of Agathis vitiensis

Abstract 3α-Hydroxy-(13 S )-16- nor -pimar-7-en-15-oic acid and (13 S )-pimar-7-en-3α,15,16-triol, two new tricyclic diterpenoids, and kaur-16-en-3α,13-diol and kauran-3α,13,16α-triol, two new tetracyclic diterpenoids, have been isolated from the heartwood of the Fijian species Agathis vitiensis . The structures of the new compounds have been assigned from high field NMR measurements. Other constituents include agatharesinol, sitosterol, abietic acid and agathic acid.