Gerhard Laus

Uncaria tomentosa (Willd.) DC.—Ethnomedicinal use and new pharmacological, toxicological and botanical results

The medicinal system of the Asháninka Indians in Perú is portrayed. Three categories of medical disorders and healers are recognized. A human is viewed to consist of a physical and a spiritual being who communicate with each other by means of a regulating element. The significance of Uncaria tomentosa (Willd.) DC. (Rubiaceae), locally known as unã de gato, in traditional medicine is emphasized by its exclusive use by priests to influence this regulation. Pharmacological and toxicological results obtained with extracts or isolated compounds are summarized. Pentacyclic oxindole alkaloids stimulate endothelial cells in vitro to produce a lymphocyte-proliferation-regulating factor. Tetracyclic oxindole alkaloids act as antagonists. A significant normalization of lymphocyte percentage was observed in vivo although total leucocyte numbers did not change.

Alkaloids of Peruvian Uncaria tomentosa

Sixteen plants of Uncaria tomentosa were investigated for their alkaloid content and the alkaloid distribution in various parts of the plant was examined. Two chemical types were identified. Seventeen alkaloids were detected and a seasonal variation in the alkaloid content was observed.

Separation of stereoisomeric oxindole alkaloids from Uncaria tomentosa by high performance liquid chromatography

Abstract Two HPLC methods are presented that allow the rapid separation and determination of the stereoisomeric oxindole alkaloids present in the South American liana Uncaria tomentosa (Willd.) DC (Rubiaceae). Peak purities were established using a dual-wavelength technique. The effect of temperature on resolution was evaluated. The alkaloid pattern of individual plants changes with time. As these alkaloids are readily interconverted, a mild extraction procedure had to be established in order to retain the actual alkaloid composition.

Analysis of the kinetics of isomerization of spiro oxindole alkaloids

The isomerization of the spiro oxindole alkaloids mitraphylline, isomitraphylline, pteropodine, isopteropodine, speciophylline and uncarine F in water has been studied at several temperatures and the rate coefficients have been determined. The effect of pH on the rate of reaction and the equilibrium composition has been investigated. The rate coefficients in water and in organic solvents correlate satisfactorily with the Dimroth–Reichardt solvent polarity parameter. The present results support the existence of a zwitterionic intermediate stabilized by polar solvents and show that protonation of the alkaloids inhibits the isomerization. The crystal structure of pteropodine has been determined.

Ionic liquids as superior solvents for headspace gas chromatography of residual solvents with very low vapor pressure, relevant for pharmaceutical final dosage forms.

1-n-Butyl-3-methylimidazolium dimethyl phosphate (BMIM DMP) was identified as the most suitable ionic liquid as solvent for the headspace gas chromatographic analysis of solvents with very low vapor pressure such as dimethylsulfoxide, N-methylpyrrolidone, sulfolane, tetralin, and ethylene glycol in a realistic matrix of commonly used excipients (carboxymethylcellulose, magnesium stearate, guar flour, and corn starch) in pharmaceutical products. Limits of quantification and limits of detection were in the low microgram per gram range. The detection of traces of sulfolane in a real sample of tablets containing the drug cefpodoxim proxetil demonstrated the applicability of the method.

Packing polymorphism of a conformationally flexible molecule (aprepitant)

This work highlights the structural and thermochemical differences of two modifications of the NK1receptor antagonist aprepitant. Form I° is the stable polymorph and crystallises in the orthorhombic space groupP212121 whereas the metastable form II is monoclinic (space groupP21). The monotropically related polymorphs show only minor differences in melting point and heat of fusion (Tfus,I = 253.6, ΔfusHI = 53.7 kJ mol−1, Tfus,II = 253.0 °C, ΔfusHII = 52.4 kJ mol−1) and often crystallise concomitantly. The forms exhibit a very close structural relationship based on a common 2D packing fragment, which is in fact a stack of 1D N–H⋯O hydrogen bonded ribbon chains. Forms I° and II may therefore be interpreted as two distinct stacking modes of this common 2D unit. The alternative modes are associated with slight differences in weaker intermolecular interactions. Somewhat surprisingly, the aprepitant molecule adopts almost the same conformation in the two crystal structures in spite of its potential conformational flexibility. Hirshfeld surface analysis was successfully deployed to visualise and elaborate the small differences in the molecular environments of the two polymorphs. The study emphasises the benefit of single-crystal structure data for the judgement of the phase purity and of polymorphs exhibiting only weak energetical and structural differences.

Dialkyl Phosphate-Related Ionic Liquids as Selective Solvents for Xylan

Herein we describe a possibility of selective dissolution of xylan, the most important type of hemicellulose, from Eucalyptus globulus kraft pulp using ionic liquids (ILs). On the basis of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is well-known to dissolve pulp, the phosphate anion was modified by substituting one oxygen atom for sulfur and selenium, respectively. This alteration reduces the hydrogen bond basicity of the IL and therefore prevents dissolution of cellulose fibers, whereas the less ordered xylan is still dissolved. (1)H NMR spectra of model solutions and Kamlet-Taft parameters were used to quantify the solvent polarity and hydrogen bond acceptor properties of the ILs. These parameters have been correlated to their ability to dissolve xylan and cellulose, which was monitored by (13)C NMR spectroscopy. It was found that the selectivity for xylan dissolution increases to a certain extent with decreasing hydrogen-bond-accepting ability of anions of the ILs.

Kinetics of isomerization of tetracyclic spiro oxindole alkaloids

The effects of temperature, pH and solvent polarity on the rate of isomerization and the equilibrium composition of the tetracyclic spiro oxindole alkaloids rhynchophylline, isorhynchophylline, corynoxeine and isocorynoxeine have been investigated.

N,N'-Di(alkyloxy)imidazolium Salts: New Patent-free Ionic Liquids and NHC Precatalysts

1-Hydroxyimidazole-3-oxides (2-H, 2-Me) were alkylated with (RO)2SO2 (R =Me, Et) to give the new 1,3-di(alkyloxy)imidazolium cations which were isolated as hexafluorophosphates. Ion metathesis yielded new hydrophobic ionic liquids (bis(trifluoromethanesulfonyl)imides, tris(pentafluoroethyl) trifluorophosphates). Bromination afforded 2-bromo derivatives which were converted to Ni and Pd N-heterocyclic carbene complexes by oxidative insertion. Fifteen crystal structures were determined by X-ray diffraction. The N-alkyloxy groups are twisted out of the imidazole ring plane and adopt either syn or anti conformations in the solid state.

Solvatochromism, halochromism, and preferential solvation of new dipolar guaiazulenyl 1,4-benzoquinone methidesElectronic supplementary information (ESI) available: Absorption maxima of the dyes 6–10 in seven binary solvent mixtures. See http://www.rsc.org/suppdata/ob/b2/b209555f/

The synthesis and the solvatochromic properties of five dyes, obtained by condensation of guaiazulene with 4-hydroxybenzaldehydes, are described. Crystal structures of a quinoid dye and a phenolic dye precursor are presented. The dyes are sensitive to the dipolarity-polarizability of the medium and to the hydrogen-bond donor ability of protic solvents. Their solvatochromism is discussed in terms of Kamlet-Tafts pi* and alpha scales, and their difference in behaviour is interpreted. Alkali and alkaline earth metal salts effect halochromism, with one exception due to extreme steric hindrance. Thus, this dye is capable of measuring solvent polarities without sensing the presence of electrolytes. Preferential solvation of the dyes in a series of binary solvent mixtures is explained quantitatively by solvent-exchange models.