Volume 60, Issue 8

The new orthorhombic polymorph β-HgB 4 O 7 has been synthesized under high-pressure and hightemperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 600 °C. β-HgB 4 O 7 is isotypic to the known ambient pressure phases MB 4 O 7 (M = Sr, Pb, Eu) and the high-pressure phase β-CaB 4 O 7 crystallizing with two formula units in the space group Pmn2 1 with lattice parameters a = 1065.6(2), b = 438.10(9), and c = 418.72(8) pm. The relation of the crystal structure of the high-pressure phase β-HgB 4 O 7 to the normal pressure phase α-HgB 4 O 7 as well as the relation to the isotypic phases MB 4 O 7 (M = Sr, Pb, Eu) and β-CaB 4 O 7 are discussed.

The high-pressure (HP) modification of CePtSn was prepared under multianvil high-pressure (9.2 GPa) high-temperature (1325 K) conditions from the normal-pressure (NP) modification. Both modifications were investigated by powder and single crystal X-ray data: TiNiSi type, Pnma, a = 746.89(9), b = 462.88(4), c = 801.93(7) pm, wR2 = 0.0487, 452 F 2 values, 20 variable parameters for NP-CePtSn, and ZrNiAl type, P6̅2m, a = 756.919(5), c = 415.166(4) pm, wR2 = 0.0546, 252 F 2 values, 14 variable parameters for HP-CePtSn. Both modifications are built up from platinumcentered trigonal prisms. Together, the platinum and tin atoms form different three-dimensional [PtSn] networks in which the cerium atoms fill channels. The crystal chemistry and chemical bonding of NP- and HP-CePtSn is discussed. Susceptibility measurements of HP-CePtSn indicate Curie-Weiss behavior above 40 K with an experimental magnetic moment of 2.55(1) μB/Ce atom, indicating trivalent cerium. No magnetic ordering could be detected down to 2 K.

The new compound Ga 2.81 O 3.57 N 0.43 was crystallized under high-pressure / high-temperature conditions in a spinel-type structure from a prestructured gallium oxonitride ceramic, which was obtained from the single-source molecular precursor [Ga(O t Bu) 2 NMe 2 ] 2 by thermal treatment in an ammonia atmosphere. The optimized precursor-derived gallium oxonitride ceramic remains nanocrystalline up to 600 °C and can be transformed at 7 GPa and 1100 °C into the crystalline phase Ga 2.81 O 3.57 N 0.43 . The structure, homogeneity, and nitrogen to oxygen ratio were determined using TEM coupled with an electron energy loss spectrometer (EELS) and an energy dispersive X-ray (EDX) spectrometer. For phase analysis and structure confirmation, X-ray powder diffraction data were measured.

A four-coordinated Rh(I) complex with a new heterocyclic carbene ligand, functionalized by amino donor pendants, 4, was synthesized and characterized by elemental analyses, NMR and IR spectroscopy, and the molecular structure of the title compound has been determined by X-ray crystallography. Crystallographic data: monoclinic, P2 1 /m, a = 7.9307(5), b = 25.0061(12), c = 8.0780(6) Å , β = 101.366(6)°, V = 1570.58(17) Å 3 , ρ calc = 1.3515(1) g cm −3 , Z = 2. The experimentally obtained structural parameters for compound 4 compare reasonably well with those calculated at the semi-empirical ZINDO/1 level of theory carried out to elucidate conformational flexibility and steric hindrances.

The reaction of the 2,3-dianilino-quinoxaline 1 with an equivalent of triethyl orthoformiate results in a cyclic aminalester 2. An excess of triethyl orthoformate results in the carbene dimer 4. With the help of boron trifluoride, 2 can be transformed into the imidazolium salt 3. Reaction of 1 with KO t C 4 H 9 leads to a quinoxaline derivative 5 under anellation of a benzene ring whereas the related pyrazino-quinoxaline 6 (formed from tetraaminobenzene tetrahydrochloride and bis-(3- trifluoromethylphenyl) oxalimidoyl chloride) does not react under similar conditions. However, 6 can be activated towards anellation by employing the complex fragment [(tbbpy) 2 Ru] 2+ , tbbpy: bis(4,4’-di-tert-butyl-2,2’-bipyridine). This generates an unusual ruthenium complex 9 which could be characterised by X-ray diffraction. Complex 9 contains a pentacene derivative and coordinates the ruthenium fragment at the amidinate moiety thus forming a four-membered chelate ring. Isolation of a second ruthenium complex 8 which contains an intact pyrazino-quinoxaline 6 in which the metal is also coordinated to an amidinato group supports the assumption that the anellation reaction occurs only after metal complexation at the amidinate group. In contrast to this, the smaller [(tmeda) 2 Pd] 2+ fragment reacts with the pyrazino-quinoxaline 6 to form the mononuclear Pd complex 10. Its structural motif (X-ray diffraction) shows that the palladium centre coordinates at the 1,4-diamino group of the intact pyrazino-quinoxaline to form a five-membered chelate ring. This suggests that the bulkiness of the complex fragment determines whether or not an anellation reaction can take place.

In this study we compare spectroscopic properties of pemoline (2-amino-5-phenyl-2-oxazolin- 4-one) and its acid hydrolysis product 5-phenyl-oxazolidine-2,4-dione. Crystallization of pemoline from aqueous acetic acid gave single crystals of compound 2, the structure of which was determined by X-ray studies. All four crystallographically independent molecules form dimers linked by N-H···O = C hydrogen bonds.

TlTaSe 3 was prepared from a fused mixture of Tl 4 Ta 2 Se 11 , Ta and Se in the molar ratio 1:2:1. The compound shows dimorphism with H-TlTaSe 3 , hexagonal, space group P6 3 /mmc, a = 7.2436(6), c = 5.9736(6) Å , c/a = 1.213 and O-TlTaSe 3 , orthorhombic, space group Pnma, a = 9.554(13), b = 3.6244(6), c=14.7271(17) Å . The crystal structure of H-TlTaSe 3 is isotypic to BaVSe 3 whereas that of O-TlTaSe 3 is closely related to the NH 4 CdCl 3 -type. Characteristic features of the structures are: 1 ∞ [TaSe 3 2− ] chains of regular octahedra sharing faces along [001] for the hexagonal form and columns of double edge-sharing octahedra 1 ∞ [Ta 2 Se 6 2− ] running along [010] for O-TlTaSe 3 . The columns are each separated by Tl + ions with the coordination number CN = 12 and CN = 8 respectively. The structures are compared and discussed in context with other isotypic structures of chalcogenides. The orthorhombic modification O-TlTaSe 3 is a semiconductor while H-TlTaSe 3 shows conventional metallic behaviour. The electronic structures of both modifications are discussed on the base of band structure calculations performed within the framework of density functional theory.

Two new spiranoid withanolides, (20R,22R,23R)-12β ,17β ,22-trihydroxy-1-oxo-12,23-cycloergosta- 2,24-dien-26,23-olide (3) and (23R)-5α,6β ,12β ,21-tetrahydroxy-1,22-dioxo-12,23-cycloergosta- 2,17,24-trien-26,23-olide (4) were isolated from plants of Jaborosa odonelliana and Jaborosa runcinata, respectively. Compounds 3 and 4 were characterized by a combination of spectroscopic methods (1D and 2D NMR, MS) and molecular modelling.

Extensive NMR studies on the novel vinca alkaloid alioline (1) have been carried out. These studies include 1D NMR experiments, i.e. 1 H- 1 H decoupling, NOED, 13 C NMR (broad-band and DEPT) as well as 2D homonuclear (COSY, NOESY and J-resolved) and 2D-hetero COSY experiments.

Ten terpenes, three steroids and one flavone have been isolated from the leaves of Mikania aff. jeffreyi, Asteraceae. Among them there are two new kaurane and one new bis-norlabdane diterpene derivatives. The kaur-16-en-18-oic acid, 4-epi-kaurenoic acid, is predominant in the plant leaves. The structures were elucidated by spectroscopic analysis.

Three new sesquiterpenoids, fascicularones E, F, and G, were isolated from the liquid culture extract of the fungus Hypholoma fasciculare. Their structures were established based on spectroscopic data.

Two new eremophilane sesquiterpenes, eremoxylarins A and B, were isolated from the xylariaceous endophytic fungus YUA-026. Their structures were determined by spectroscopic methods. Eremoxylarins A and B showed antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa.

A series of novel oxathiadibenzo- and oxathiadinaphthalenocrown ethers 1 - 18 have been successfully synthesized in good yield and in a simple way. They were characterized by NMR, mass spectroscopy and elemental analysis.

Some different approaches have been developed in order to determine the most efficient preparation of bis-benzimidazoles 1a - f under solvent-free conditions. All of the selected methods are simple, avoiding heating with corrosive mineral acids. Heating of the reactants on a sand bath method appears to have higher efficiency.

A collection of the marine sponge Pseudoceratina purpurea from the Gulf of Thailand furnished aplysamine-2, two new bromotyrosine derivatives purpuroceratic acids A and B, two known bromotyrosine derivatives, 3-maleimide-5-oxime and common sponge constituents. Aplysamine-2, purpuroceratic acid A and 3-maleimide oxime were evaluated for their in vitro anticancer activity against three cancer cell lines, but only aplysamine-2 exhibited moderate dose dependent growth inhibitory effects.

Stabilized and semi-stabilized phosphoranes can be subjected to solventless Wittig reactions with carbaldehydes. Simple heating of a mixture of added components at 100 °C in an electric oven gives the corresponding olefins in good yield. Alternatively, the Wittig reactions can be carried out in a biphasic medium under ultrasonication. In this case, the Wittig products can be isolated by simple evaporation of the organic phase without additional work-up.