Structure determination of two oligomannoside-type glycopeptides obtained from bovine lactotransferrin,by 500 MHz 1H-NMR spectroscopy

The elucidation of the structures of two carbohydrates units, N-glycosidically linked to an asparagine residue of bovine lactotransferrin, is described. These carbohydrate structures are of the oligomannoside type and contain eight or nine mannose residues, respectively. The potency of 500 MHz ¹H-NMR spectroscopy in primary structure determination of two closely related carbohydrate chains present in a mixture is demonstrated. This implies that 500 MHz ¹H-NMR spectroscopy can disclose microheterogeneity which is almost untraceable using other approaches.     

Furanoheliangolides and other compounds from Calea hymenolepis

Calea hymenolepis afforded in addition to known compounds two new furanoheliangolides, one being a Diels-Alder adduct with myrcene, a p-hydroxyacetophenone derivative and two dimeric ones, again being formal Diels-Alder adducts. The structures were elucidated by highfield ¹H NMR spectroscopy.     

Sesquiterpene lactones from helogyne hutchisonii

The aerial parts of Helogyne hutchisonii afforded, in addition to known sesquiterpene lactones, two new heliangolides and two germacranolides. The structures were elucidated by high-field ¹H NMR spectroscopy.     

Proton relaxation rate and fluorometric studies of manganese and rare earth binding to concanavalin A

The binding of Mn²⁺, Ca²⁺, and rare earth ions to apoconcanavalin A has been studied by water proton relaxation enhancement, electron paramagnetic resonance spectroscopy, and fluorescence spectroscopy. An electron paramagnetic resonance and water proton relaxation rate study of the titration of apoconcanavalin A with Mn²⁺ gives evidence of two equivalent binding sites per monomer with K_D = 50 μm ± 4 μm. When a similar Mn²⁺ titration of apoconcanavalin A is performed in the presence of Ca²⁺ ion, very little free Mn²⁺ is detected by electron paramagnetic resonance until the two Mn²⁺ binding sites per monomer are filled. The substitution of a rare earth ion for Ca²⁺ ion in the above experiment often resulted in a slight displacement of Mn²⁺ from the transition metal site as detected by electron paramagnetic resonance. A water proton relaxation rate study of the titration of apoconcanavalin A with Gd³⁺ reflects two binding sites with a K_D = 40 μm ± 4 μm and two with a K_D = 200 μm ± 50 μm. The fluorescence emission spectrum of concanavalin A (λ_em = 340 nm) is slightly quenched by the addition of Tb³⁺ while Tb³⁺ fluorescence is greatly enhanced. A fluorometric titration of apoconcanavalin A with Tb³⁺ also reflects two sites with a K_D = 40 μm ± 15 μm and two with a K_D = 270 μm ± 50 μm.     

2-Oxo-labda-8(17),13-dien-15-OL from Ophryosporus chilca

The aerial parts of Ophryosporus chilca afforded several prenylated p-hydroxyacetophenones, two labdane derivatives and a cinnamyl ester. Ophryosporus peruvianus also contains prenylated p-hydroxyacetophenones. Three compounds were isolated for the first time; their structures were established by ¹H NMR spectroscopy.     

Dimeric chromenes and mixed dimers of a chromene with euparin from Encelia canescens

The investigation of Encelia canescens afforded, in addition to several known compounds, four new dimeric p-hydroxyacetophenone derivatives, two epimeric chromene dimers and two epimeric mixed dimers of euparin and encecalin. Furthermore, derivatives of tremetone and of encecalin were present. The structures were elucidated hy high field ¹H NMR spectroscopy.     

Homoleptic platinum(II) and palladium(II) complexes of 1,5,9-trithiacyclododecane: the crystal structures of [Pt(12S3)2](PF6)2 · 2CH3NO2 and [Pd(12S3)2](BF4)2 · 0.5H2O

The synthesis, spectroscopy, electrochemistry, and crystal structures of two new mononuclear homoleptic Pt(II) and Pd(II) complexes with the crown trithioether 1,5,9-trithiacyclododecane (12S3) are reported. In contrast to behavior with analogous smaller ring trithiacrowns, both metal complexes exhibit exodentate axial sulfur donors, a consequence of the preferred conformation of the 12S3 ligand. The lack of two axial metal-sulfur interactions correlates with the observed electronic spectroscopy and oxidative electrochemistry displayed by the complexes and contrasts with properties exhibited by complexes containing smaller polythioether macrocycles. The two complexes have electronic spectra dominated by charge transfer, not d-d bands and show no M²⁺/M³⁺ couples. Both complexes show a fluxional 12S3 ligand in solution due to a 1,5-metallotropic shift, an uncommon observation of this particular type of intramolecular ligand exchange. The ¹⁹⁵Pt NMR chemical shift of −4201 ppm for [Pt(12S3)₂]²⁺ is consistent with an alternating positioning of the four sulfur lone pairs on the coordinated thioethers. Although 12S3 is poorly pre-organized for facial complexation, its flexibility to position a sulfur in an exodentate fashion enables it to form stable complexes with d⁸ metal ions such as Pt(II) and Pd(II).     

Labdane derivatives from Planaltoa lychnophoroides

The investigation of a representative of the small Brazilian genus Planaltoa afforded, in addition to known compounds, a new toxol derivative and two ent-labdane derivatives, closely related to austrofolin. The structures were elucidated by high field ¹H NMR spectroscopy. The chemotaxonomic situation is discussed briefly.     

Further glaucolides from south african Vernonia species

The investigation of three South African Vernonia species afforded minute amounts of five new glaucolides, two monoepoxides and three diepoxides. The structures were elucidated by ¹H NMR spectroscopy. The roots of Vernonia sutherlandii contain, in addition to vernonataloide, bergamotene and santalene, minute amounts of the corresponding acetoxy derivatives.     

Flavone di-C-glycosides from Scutellaria baicalensis

From the roots of Scutellaria baicalensis two new di-C-glycosylflavones have been isolated. Their structures have been established on the basis of mass, ¹H and ¹³C NMR spectroscopy as chrysin 6-C-glucoside-8-C-arabinoside and chrysin 6-C-arabinoside-8-C-glucoside.     

Seven germacranolides and four eudesmanolides from Tithonia rotundifolia

The aerial parts of Tithionia rotundifolia afforded, in addition to two known sesquiterpene lactones, eleven new ones, seven germacranolides and four eudesmanolides. The structures were determined by ¹H NMR spectroscopy.     

Myrianthic acid: a triterpene acid from the rootwood of Myrianthus arboreus

Arjunolic acid and a new triterpene acid, myrianthic acid, were isolated from the rootwood of Myrianthus arboreus. The structures of the two compounds were elucidated by IR, ¹H NMR and mass spectroscopy.     

Mid-infrared spectroscopy and short wave infrared hyperspectral imaging—A novel approach in the qualitative assessment of Harpagophytum procumbens and H. zeyheri (Devil's Claw)

Harpagophytum procumbens (Burch.) DC. ex Meisn. subsp. procumbens (Pedaliaceae) is an important African medicinal plant growing in the Kalahari region of southern Africa. This species, together with its close taxonomic ally Harpagophytum zeyheri are collectively referred to as Devil's Claw and are used interchangeably for the treatment of inflammation-related disorders. Although the two taxa are botanically and chemically similar, H. zeyheri contains lower levels of harpagoside and these two species have not been proven to exhibit equipotent pharmacological activity. Due to these taxonomic similarities, effective quality control methods are required to distinguish between the two species. Differentiation between the two species was achieved using single point mid-infrared spectroscopy in combination with chemometric data analysis. The orthogonal projections to latent structures discriminant analysis (OPLS-DA) model had good predictive ability, as illustrated by the model statistics: R²X (cum predictive + orthogonal) = 0.86 and Q² (cum) = 0.63. Short wave infrared (SWIR) hyperspectral imaging could distinguish between the two species with acceptable model statistics: R²X and R²Y of 0.99 and 0.78, respectively. This study demonstrated that both MIR single point spectroscopy and SWIR hyperspectral imaging coupled with chemometric modelling are reliable and rapid methods to determine the authenticity of Harpagophytum spp.     

Types of sesquiterpene-coumarin ethers from Achillea ochroleuca and Artemisia tripartita

In addition to known derivatives, four new sesquiterpene-coumarin ethers were isolated from the roots of Achillea ochroleuca and Artemisia tripartita and identified by ¹H and ¹³C NMR spectroscopy, including lanthanide induced shifts. The new compounds are isofraxidin derived ethers which differ from the previously described derivatives by ring cleavage and methyl migration within the terpenoid unit. The chemosystematic importance of sesquiterpene-coumarin ether accumulation within the two genera is briefly discussed.     

Synthesis and NMR characterization of the novel mixed-ligand Pt(II) complexes cis- and trans-Pt(Ypy)(pyrimidine)Cl2 and trans,trans-Cl2(Ypy)Pt(μ-pyrimidine)Pt(Ypy)Cl2 (Ypy = pyridine derivative)

Mixed-ligand complexes of the type cis- and trans-Pt(Ypy)(pm)Cl₂ where Ypy = pyridine derivative and pm = pyrimidine were synthesized and characterized by IR spectroscopy and by multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopy. The cis compounds were prepared from the reaction of K[Pt(Ypy)Cl₃] with pyrimidine (1:1 proportion) in water, while most of the trans isomers were synthesized from the isomerization of the cis compounds. The cis isomers could not be isolated with the Ypy ligands containing two -CH₃ groups in ortho positions. When the aqueous reaction of K[Pt(Ypy)Cl₃] with pyrimidine was performed in a Pt:pm ratio = 2:1, the pyrimidine-bridged dinuclear species were formed. Only the most stable trans-trans isomers could be isolated pure. In IR spectroscopy, the cis monomers showed two ν(Pt-Cl) bands, while the trans monomers and dimers showed only one ν(Pt-Cl) band. The ¹⁹⁵Pt NMR signals of the cis monomers were found at slightly higher fields than those of the corresponding trans isomers. The δ(¹⁹⁵Pt) of the dimers were found close to those of the trans monomers. The NMR results were interpreted in relation to the solvent effect, which seems important in these complexes. The coupling constants J(¹⁹⁵Pt-¹H) and J(¹⁹⁵Pt-¹³C) are larger in the cis geometry. The crystal structures of the compounds cis-Pt(2,4-lut)(pm)Cl₂, trans-Pt(2,6-lut)(pm)Cl₂ and trans,trans-Cl₂(2,6-lut)Pt(μ-pm)Pt(Ypy)Cl₂ were studied by X-ray diffraction methods and the results have confirmed the configurations suggested by IR and NMR spectroscopies.     

(25R)-Isonuatigenin,an unusual steroidal sapogenin from Vestia lycioides

(25R)-Isonuatigenin, a ⁵-spirosten-3β,25-diol, was isolated from aerial parts of Vestia lycioides. Its structure was elucidated mainly by ¹H NMR and ¹³C NMR spectroscopy. A mixture of (25R)-nuatigenin and (25S)-isonuatigenin was also characterized. This is the first report on the natural occurrence of the two (25R)-isomers.     

Germacranolides from anvillea garcini

The aerial parts of Anvillea garcini afforded three germacranolides, two of which had not being isolated previously. The structures were elucidated by ¹H NMR spectroscopy. The configuration of 9-acetoxy parthenolide at C-9 has been revised.     

In vivo enzymology: 13C NMR measurement of a kinetic isotope effect for methanol oxidation in Methylosinus trichosporium OB3b

The competitive oxidation of ¹³CH₃OH and ¹³CD₃OH has been observed using in vivo ¹³C NMR spectroscopy. Simultaneous ¹H and ²H decoupling gave isotopically shifted ¹³C singlets for the two methanol isotopomers. The measured enzymic isotope effect, kH/kD is approx. 1.8, indicating that CH bond cleavage is not rate-determining.     

Structure and binding properties of hen lysozyme modified at tryptophan 62

The structure of a derivative of hen egg-white lysozyme (EC 3.2.1.17) modified by N-bromosuccinimide at Trp62 has been studied by both ¹H nuclear magnetic resonance spectroscopy and X-ray crystallography. It was shown that this modification, changing the tryptophan residue to an oxindolealanine² residue, only causes minor structural changes at the site of the modification, and that the overall structure of the native enzyme is maintained in the derivative. Both diastereomers of the oxindolealanine-62 lysozyme were observed by the two methods employed, in accordance with previous observations (Norton & Allerhand, 1976). The pK values of the catalytically important carboxyl groups of Glu35 and Asp52 were identical in the native enzyme and its derivative. However, the modified enzyme is virtually inactive in the hydrolysis of the cell-wall mucopolysaccharide of Micrococcus lysodeikticus. The binding of N-acetylglucosamine oligosaccharides to both native lysozyme and Ox-62 lysozyme was studied by nuclear magnetic resonance spectroscopy, observing the perturbations on the lysozyme ¹H n.m.r. resonances, and differences in the perturbations of the two systems demonstrated that binding of (GlcNAc)₃ in particular was not identical in the two systems. The structure of Ox-62 lysozyme-(GlcNAc)₃ was studied by X-ray crystallography and it was shown that only two GlcNAc residues make contact with the enzyme, binding the reducing end residue in a similar mode as the α-anomeric form of GlcNAc binds to the native enzyme (Blake et al., 1967a). On the basis of the results obtained by X-ray crystallography and ¹H n.m.r. spectroscopy, the lack of enzymatic activity of the Ox-62 lysozyme arises from the obstruction by the oxindolealanine residue of sub-site B of the active site, preventing productive binding of the substrate.     

Labdane derivatives,a bisnorditerpene and sesquiterpenes from Rutidosis murchisonii

The aerial parts of Rutidosis murchisonii afforded several new ent-labdanes, a bisnorditerpene and two α-curcumene derivatives. The structures were elucidated by high field ¹H NMR spectroscopy and a few chemical transformations. The absolute configuration of the diterpenes was established by CD and by the Horeau method. The chemotaxonomic aspects are discussed briefly.