Inhibitory effects of glycyrrhetic acid derivatives on 11 beta- and 3 alpha-hydroxysteroid dehydrogenases of rat liver.

Glycyrrhetic acid (GA), an aglycone of glycyrrhizin (GL), is a potent inhibitor of 11 beta- and 3 alpha-hydroxysteroid dehydrogenases. 11 beta-Hydroxysteroid dehydrogenase activity of rat liver microsomes was potently inhibited by GA, 3-deoxyglycyrrhetic acid (3-deoxyGA), 3-ketoglycyrrhetic acid (3-ketoGA), 3-epiglycyrrhetic acid (3-epiGA) and 11-deoxoglycyrrhetic acid (11-deoxoGA), with I50 values of 2-4 x 10(-7) M. However, 18 alpha-stereoisomers (I50 = 3-7 x 10(-6) M) of GA, 3-deoxyGA and 11-deoxoGA were one tenth less inhibitory on the enzyme activity than the corresponding 18 beta-isomers. On the other hand, 18 alpha-stereoisomers of GA, 3-deoxyGA and 11-deoxoGA inhibited 3 alpha-hydroxysteroid dehydrogenase activity of rat liver cytosol more potently than the corresponding 18 beta-isomers. I50 values of 18 alpha- and 18 beta-isomers were 2 and 7 x 10(-6) M, respectively, in the case of GA, 8 and 20 x 10(-6) M in 3-deoxyGA, 3 and 20 x 10(-6) M in 11-deoxoGA. These results indicate that the 18 beta-conformation of oleanane is important for the inhibition of 11 beta-hydroxysteroid dehydrogenase but on the contrary the 18 alpha-conformation is important for the inhibition of 3 alpha-hydroxysteroid dehydrogenase.     

Azetidinyl ketone chemistry. C-Methylation reactions and stereostructure - spectra relationships

The C-methylation of the potassium salt of 1-t-butyl-2-phenyl-3-(p-phenylbenzoyl)azetidine ( 1a ) with methyl iodide was studied in three solvents, and the stereochemical outcome of the reaction was shown to be dependent upon the solvent used. These results are rationalized in terms of the probable relative rates of the reaction in the various solvents and/or the effect of solvent on the structure of the anionic intermediate. Similar treatment of the potassium salt of 1-t-butyl-2-phenyl-3-benzoylazetidine ( 3a ) in ethyl ether gave a comparable result. The configurations of the epimeric C-methyl products ( 2a and 2b , and 4a ) were assigned on the basis of their spectral properties. With the aid of spectral data for a model compound, l-t-butyl-3-benzoyl-azetidine ( 5 ), several stereostructure-spectra relationships for 3-azetidinyl ketones are presented.     

Chromatographic studies of corrosion sites in metallic materials

Many types of corrosion phenomena are controlled by the ionic composition of a small volume of solution at the surface. Localized corrosion and atmospheric corrosion are two examples in which < 1 μl of solution can cause dramatic damage. Ion chromatographic (IC) techniques have been used to analyze these solutions in order to gain a better understanding of the mechanisms which govern them. Two examples are presented. The presence of minor alloying elements at localized corrosion sites in two aluminum alloys has been demonstrated, indicating non-stoichiometric dissolution of the alloy during localized corrosion. In addition, IC analysis allowed the determination of the species responsible for the atmospheric corrosion failure of electrical connectors, including their likely origin.     

High-performance size-exclusion chromatographic determination of the potency of biosynthetic human growth hormone products

A new high-performance size-exclusion chromatography method has been developed for the determination of potency of human growth hormone products. This method has been extensively validated and shown to correlate well with the hypophysectomized rat bioassay which has been used traditionally. The method is much more precise than the traditional bioassay and thus provides more reliable means of producing consistent biosynthetic human growth hormone batches.     

Phosphinsubstituierte Chelatliganden. XVIII. Penta- und Tetracarbonylmetall-Komplexe des Chroms,Molybdäns und Wolframs mit sekundären und tertiären Phosphinothioformamid-Liganden

Phosphine Substituted Chelate Ligands. XVIII. Penta- and Tetracarbonylmetal Complexes of Chromium, Molybdenum, and Tungsten with Secondary and Tertiary Phosphinothioformamide Ligands Mono- and bidentately coordinated phosphinothioformamide complexes are obtained by photochemical substitution of the metal hexacarbonyls M(CO)₆ (M ? Cr ( a ), Mo ( b ), W ( c )). The M(CO)₅ · THF adducts react with secondary thioamides under exclusion of light to give the P-coordinate pentacarbonyl complexes [(CO)₅MPPh₂C(S)NHR¹] (R¹ ? Ph ( 1a – c ), Me ( 2a )). The photoreaction of M(CO)₅ · THF with secondary and tertiary thioamides at low temperatures leads to the formation of the P, S-chelate complexes . The corresponding N-silylated complexes 6a – c (R¹ ? Me₃Si, R² ? Ph) are obtained by direct photosubstitution of M(CO)₆ in cyclohexane solution. The labile bis(thioformamide) complexes [(CO)₄M(PPh₂C(S)NHMe)₂] ( 7a – c , cis-trans isomers) are synthesized in low yields according to the same procedure. The attempted alkylation of the chelate complexes 3a – c remains unsuccessful, whereas the secondary thioformamides react with n-BuLi/CH₂Br₂ to give the methylene bis(thioformirnidoesters) [Ph₂PC(NR¹)S]₂CH₂ (R¹ ? Ph (8), Me ( 9 )) in quantitative yields.     

Angular distributions of photoelectrons in resonantly enhanced multiphoto ionization via the 7s[1 1/2]0 1 and 8s[1 1/2]0 1 states of Xe

Photoelectron angular distributions have been measured for the three-photon resonant one-photon ionization, (3+1), of Xe via the 7s[1 1/2]⁰ ₁ and 8s[1 1/2]⁰ ₁ states. The results are in good agreement with the theoretical predictions of Tang and Lambropoulos [13] for the 8s[1 1/2]⁰ ₁, but not for the 7s[1 1/2]⁰ ₁ state. Furthermore, the results are compared to those which have been obtained by Blazewicz et al. [1] for the three-photon resonant two-photon ionization, (3+2), of Xe via the 6s[1 1/2]⁰ ₁ state.     

Etude des dimensions moleculaires des polymeres dissous dans des melanges binaires de solvants polaires et non polaires—I. Polyvinyl-2 pyridine

We have studied the molecular dimensions of poly-2-vinylpyridine in solution in binary solvent mixtures consisting of a non polar and a polar component, viz. benzene-ethanol and benzene-chloroform. We have also studied the preferential solvation of the same polymer in the above mixtures using light scattering. We have observed a conformational transition of P2VP taking place in a composition region for each solvent mixture. This transition shows as a discontinuity in the unperturbed dimensions, in the long range interactions parameter and in the parameter of preferential solvation of the polymer. We think that this transition is related to the existence of two ordered structures of the polymer chain, one stable before and the other after the transition region.     

Substituted chromans and tetrahydrofuro[2,3-b]benzofurans (trapped tetrahedral intermediates) from 3-phenyl-2-benzofuranones

The previously discovered neighboring group reaction has been extended to the synthesis of chroman derivatives (i.e., 4, 5, 6) containing geminal methyls in the 2-position, a feature common to certain physiologically active natural chromans. In two instances, cyclic ortho ester by-products (8), not observed in previous work, were formed as a result of the intramolecular trapping of tetrahedral intermediates. Reasons for the incursion of this unexpected side reaction are discussed.     

On the magnetic properties and the phase composition of the Cr2O3?MnOx-system (2 ≥ x ≥ 1.5)

The mixed oxide system Cr₂O₃? MnO_x (2 ≥ x ≥ 1.5) was investigated by X-ray diffraction, by measurements of magnetic susceptibility, and by chemical determination of excess oxygen (BUNSEN'S method). The Presence of the antiferromagnetic oxides Cr₂O₃, β-MnO₂, α-Mn₂O₃ and a ferromagnetic phase Cr_1?yMn_yO₂ was stated. The formation of the latter with fourvalent chromium is explained by a lattice induction effect of the MnO₂ (rutile type).     

Electron-impact studies—LXX. Substituent effects in the negative-ion spectra of nitroaryl esters

The negative-ion mass spectra of a variety of substituted nitroaryl benzoates and aryl nitrobenzoates have been studied. Pronounced proximity effects are observed in the spectra of ortho-substituted compounds. The meta and para pairs fragment in a similar manner. Linear plots are observed for many cleavages using either the McLafferty or Harrison methods. Evidence is provided which suggests that the fragmentations of meta and para isomers may proceed by the same mechanistic pathway. The magnitude of ρ does not appear to provide precise information concerning the nature of the transition state for a particular reaction of a negative ion.