Volume 58, Issue 12

The volume changes of cesium under pressure are discussed with respect to the packing density of the atoms and valence. The element is univalent in densely packed Cs I and Cs II. Valence increases in Cs III (packing density q = 0.973), in Cs IV (q = 0.943), in Cs V (q ≈ 0.99), and in close packed Cs VI. The diminuition of volume beyond ≈15 GPa is caused by this increase only which implies that electrons of the fifth shell act as valence electrons.

Dinuclear nickel(II) and palladium(II) complexes with Schiff-base ligands (derived form salicylaldehyde condensed with 2-amino-1-alcohols or from 2-hydroxy-5-methylisophthaldialdehyde and pyridine-2-carboxaldehyde condensed with semicarbazide, thiosemicarbazide, carbonodihydrazide, or thiocarbonodihydrazide) can be activated with the co-catalysts methylalumoxane (MAO) or tris(pentafluorophenyl)borane/triethylaluminium, B(C 6 F 5 ) 3 /AlEt 3 for the vinyl/addition polymerization of norbornene to reach activities of up to 2.4 · 107 g polymer /mol(metal)·h (molar ratios metal:Al MAO = 1:100, metal:borane:AlEt 3 = 1:9:10). Polymer characterization by GPC gave molar mass distributions of Mw/Mn ≈ 2, thereby indicating a coordination polymerization with a single-site character of the active species.

The reaction of GeHal 4 with MeN(CH 2 CH 2 OSiMe 3 ) 2 affords dihalogermocanes MeN(CH 2 CH 2 O) 2 GeHal 2 (1, Hal = Br; 2, Hal = Cl). Treatment of Me 2 Ge(NMe 2 ) 2 with MeN(CH 2 CH 2 OH) 2 leads to dimethylgermocane MeN(CH 2 CH 2 O) 2 GeMe 2 (3). The composition and structure of 1-3 were established by elemental analyses, 1 H, 13 C NMR spectroscopy, and mass spectrometry. The crystal structure of 1 is reported; structural data obtained from geometry DFT optimization on 1 are in good agreement with experimental results. Values of the electron density in the N→Ge bond critical point and the Laplacian of charge density for 1-3 indicate a closed-shell interaction between the Ge and N atoms.

Single crystals of potassium hydrogenphthalate monohydrate, KHPhth(H 2 O), were grown from aqueous solution using a slow cooling method and the structure was determined by X-ray diffraction analysis. The crystals belong to the monoclinic space group P2 1 /c. Its unit cell parameters are as follows: a = 1.1235(1), b = 0.6689(1), c = 1.1998(2) nm, β = 98.85°, V = 0.8909(1) nm 3 , Dc = 1.657 g/cm 3 , Z = 4, F(000) = 456. The thermal decomposition of the complex was studied using differential scanning calorimetry (DSC), thermogravimetry-derivative thermogravimetry (TGGTG) and FT-IR techniques. With a linear heat rate, the diagrams show three endothermic processes. RCOOK and K 2 CO 3 are produced at 330 and 467°C, respectively, according to FT-IR analysis.

A novel class of difluorinated cyclopropanoic nucleoside analogues containing a hydroxypropyl group and a methylene spacer between the difluorocyclopropane ring and the heterocycle has been prepared.

The electrochemical reduction of chlorinated arenes with electron-donating substituents, i. e. chlorotoluenes, -anisoles and -phenols, is studied. Preparative electrolyses are run in various solventsupporting electrolytes under potentiostatic and galvanostatic conditions at lead or carbon cathodes. A partial and mostly regioselective hydrodechlorination of compounds with two or more chloro substituents is possible under suitable conditions. The replacement of one single chloro substituent, in particular in a para-position, is difficult. Highly toxic and persistent oligochloro derivatives are thus transformed into less problematic compounds with a low degree of chlorination. The chlorine content of real-life materials such as extracts of soil contaminated with chlorinated phenols and Nitrofen ® can also be significantly decreased by electroreduction.

Quinolinium dichromate (QDC) in sulfuric acid oxidizes benzaldehydes to the corresponding acids in a 50% (v/v) acetic acid-water medium. The reaction is first order each in [QDC], [substrate] and [H + ]. The reaction rates have been determined at different temperatures and the activation parameters calculated. The rate decreases with an increase in the water content of the medium. The effects of substituents have been studied. A suitable mechanism is proposed.

The isoflavonol 7,8,3’-trihydroxy-6,4’-dimethoxy-isoflavone (1) was isolated from the methanol extract of the bark of the trunk of Dipterix odorata. The structure was determined from spectral data and with aid of his acetylation to obtain 1a as a strategy to help the assignments of the 2D NMR experiments.

A compound (née frankiamide) isolated from Frankia was initially structurally elucidated on the basis of NMR and MS. However, X-ray analysis provided a structure that is in discord with this structure and in light of this the structure has now been revised and the compound renamed as demethyl (C-11) cezomycin.

Two new mexicanolide-type B, D-seco limonoids named xyloccensin M(1) and N (2) were isolated from the stem bark of Xylocarpus granatum. Their structures were elucidated with the help of modern spectroscopic techniques.

Titanyl acetylacetonate, TiO(acac) 2 , is used as an efficient catalyst for the reduction of carbonyl compounds with sodium borohydride under aprotic condition. Reduction reactions are performed in CH 3 CN and THF. The corresponding alcohols are obtained in high to excellent yields and the chemoselective reduction of aldehydes over ketones is achieved successfully.

Reaction of N-{3-cyano-6-[4(5-oxo-2-phenylhydrazono-4,5-dihydroimidazol-1-yl)phenyl]-4-phenylpyridin- 2-yl}formimidic ethyl ester (3) and 3-[4-(3-amino-4-imino-5-phenyl-3,4-dihydropyrido[ 2,3-d]pyrimidin-7-yl)phenyl]-2-phenyl-5-phenylhydrazono-3,5-dihydroimidazol-4-one (4) with different reagents has been investigated and discussed. Some of the obtained compounds were tested for their antimicrobial activity.

The alkaloids evolitrine, acronycidine, melicopine, melicopidine, normelicopine, normelicopidine, acronycine, noracronycine, 12-desmethylacronycine, (+)-cis-1,2-dihydroxy-1,2-dihydroacronycine, and (-)-trans-1,2-dihydroxy-1,2-dihydroacronycine were isolated from Medicosma subsessilis bark, together with the new 1-oxo-2-hydroxy-1,2-dihydro-12-desmethylnoracronycine. The structure of the latter compound was elucidated on the basis of spectral data and partial synthesis.

1,5-Benzodiazepin-2-ones (3a - d) were obtained fromω-carbethoxy visnaginone or ω-carbethoxy khellinone and substituted 1,2-phenylenediamines. Reactions of active nitriles such as malononitrile and ethyl cyanoacetate with substituted 6-dimethylaminomethylene furocoumarins (4a,b) are described. Additionally, reaction of substituted 6-dimethylaminomethylene furocoumarins with different amino acids gave furochromen-6-ylidenemethyl amino acids (7 - 9). Compound 7 was coupled with glycine ethyl ester to form amino acetic acid ethyl ester (10).

The red coloured ethyl acetate extract of the Streptomyces sp. isolate GW37/3236 delivered the two new antibiotics 13-O-acetyl-bisanhydro-13-dihydrodaunomycinone (3c) and 4,13-O-diacetylbisanhydro- 4-O-demethyl-13-dihydrodaunomycinone (3d) and additionally several known compounds. The quinones 3c and 3d are the first naturally occurring quinone acetates. Their structures were derived by comparison of the NMR data with those of bisanhydro-13-dihydrodaunomycinone (3b) and by interpretation of the 2D NMR data accompanied by the molecular weight and formula. 2-Acetamido-3-hydroxybenzamide (5) was also isolated from the extract and was identified by comparison of the NMR data with those of 2-acetamidobenzamide and by 2D NMR correlations. 6,9,11- Trihydroxy-4-methoxy-5,12-naphthacenedione (4) is isolated for the first time as a natural product.

A novel class of cyclopropanoic muramyldipeptide analogues containing an additional methylene spacer between the cyclopropane ring and the lactyl residue has been prepared by a straightforward synthesis starting from isopropyl (R)-lactate.