Characterization of Germanium Nanoparticles from Arylgermanium Trihydrides.

Germanium is a promising basis for nanomaterials due to its low toxicity and valuable optical and electronic properties. However, germanium nanomaterials have seen little research compared to other group 14 elements due to unpredictable chemical behavior and high costs. Here, we report the dehydrocoupling of o-tolylgermanium trihydride to amorphous nanoparticles. The reaction is facilitated through reflux at 162 °C and can be accelerated with an amine base catalyst. Through cleavage of both H2 and toluene, new Ge-Ge bonds form. This results in nanoparticles consisting of crosslinked germanium with o-tolyl termination. The particles are 2-6 nm in size and have masses above approximately 3500 Da. The organic substituents are promising for further functionalization. Combined with strong absorption up to 600 nm and moderate solubility and air stability, there are numerous possibilities for future applications.

Structure-Activity Relationships and Antiplasmodial Potencies of Novel 3,4-Disubstituted 1,2,5-Oxadiazoles.

The 4-substituted 3-amino-1,2,5-oxadiazole 1 from the Malaria Box Project of the Medicines for Malaria Venture foundation shows very promising selectivity and in vitro activity against Plasmodium falciparum. Within the first series of new compounds, various 3-acylamino analogs were prepared. This paper now focuses on the investigation of the importance of the aromatic substituent in ring position 4. A number of new structure-activity relationships were elaborated, showing that antiplasmodial activity and selectivity strongly depend on the substitution pattern of the 4-phenyl moiety. In addition, physicochemical parameters relevant for drug development were calculated (logP and ligand efficiency) or determined experimentally (CYP3A4-inhibition and aqueous solubility). N-[4-(3-ethoxy-4-methoxyphenyl)-1,2,5-oxadiazol-3-yl]-3-methylbenzamide 51 showed high in vitro activity against the chloroquine-sensitive strain NF54 of P. falciparum (PfNF54 IC50 = 0.034 µM), resulting in a very promising selectivity index of 1526.

Formation of 5-Aminomethyl-2,3-dihydropyridine-4(1H)-ones from 4-Amino-tetrahydropyridinylidene Salts.

Various 4-aminotetrahydropyridinylidene salts were treated with aldehydes in an alkaline medium. Their conversion to 5-substituted ß-hydroxyketones in a one-step reaction succeeded only with an aliphatic aldehyde. Instead, aromatic aldehydes gave 5-substituted ß-aminoketones or a single δ-diketone. The new compounds were characterized using spectroscopic methods and a single crystal structure analysis. Some of them showed anticancer and antibacterial properties.

Synthesis and Antiprotozoal Activity of Azabicyclo-Nonane Pyrimidine Hybrids.

2,4-Diaminopyrimidines and (dialkylamino)azabicyclo-nonanes possess activity against protozoan parasites. A series of fused hybrids were synthesized and tested in vitro against pathogens of malaria tropica and sleeping sickness. The activities and selectivities of compounds strongly depended on the substitution pattern of both ring systems as well as on the position of the nitrogen atom in the bicycles. The most promising hybrids of 3-azabicyclo-nonane with 2-aminopyrimidine showed activity against P. falciparum NF54 in submicromolar concentration and high selectivity. A hybrid with pyrrolidino substitution of the 2-azabicyclo-nonane as well as of the pyrimidine moiety exhibited promising activity against the multiresistant K1 strain of P. falciparum. A couple of hybrids of 2-azabicyclo-nonanes with 2-(dialkylamino)pyrimidines possessed high activity against Trypanosoma brucei rhodesiense STIB900 and good selectivity.

Antiprotozoal Activity of Azabicyclo-Nonanes Linked to Tetrazole or Sulfonamide Cores.

N-(Aminoalkyl)azabicyclo[3.2.2]nonanes possess antiplasmodial and antitrypanosomal activity. A series with terminal tetrazole or sulfonamido partial structure was prepared. The structures of all new compounds were confirmed by NMR and IR spectroscopy and by mass spectral data. A single crystal structure analysis enabled the distinction between isomers. The antiprotozoal activities were examined in vitro against strains of Plasmodium falciparum and Trypanosoma brucei rhodesiense (STIB 900). The most active sulfonamide and tetrazole derivates showed activities in the submicromolar range.

8-Amino-6-Methoxyquinoline-Tetrazole Hybrids: Impact of Linkers on Antiplasmodial Activity.

A new series of compounds was prepared from 6-methoxyquinolin-8-amine or its N-(2-aminoethyl) analogue via Ugi-azide reaction. Their linkers between the quinoline and the tert-butyltetrazole moieties differ in chain length, basicity and substitution. Compounds were tested for their antiplasmodial activity against Plasmodium falciparum NF54 as well as their cytotoxicity against L-6-cells. The activity and the cytotoxicity were strongly influenced by the linker and its substitution. The most active compounds showed good activity and promising selectivity.

Synthesis and structure-activity relationships for new 6-fluoroquinoline derivatives with antiplasmodial activity.

The substitution of 6-fluoroquinolines was modified in ring positions 2 and 4. The new compounds were tested in vitro for their activities against a sensitive and a multidrug resistant strain of Plasmodium falciparum. Some physicochemical parametres were calculated (log P, log D, ligand efficiency) or determined experimentally (permeability). The most promising compounds were tested for their in vivo activity against Plasmodium berghei in a mouse model. The 6-fluoro-2-{4-[(4-methylpiperazin-1-yl)methyl]phenyl}-N-[2-(pyrrolidin-1-yl)ethyl]quinoline-4-carboxamide possessed proper physicochemical properties and showed high antiplasmodial activity in vitro (IC50 ≤ 0.0029 µM) and in vivo (99.6% activity).

Synthesis of Jacaranone-Derived Nitrogenous Cyclohexadienones and Their Antiproliferative and Antiprotozoal Activities.

The cytotoxic and antiprotozoal activities of the phytoquinoide, jacaranone, and related compounds have been an ongoing topic in recent drug discovery. Starting from the natural product-derived cyclohexadienone scaffold, a series of nitrogen-containing derivatives were synthesized and subsequently evaluated for their antiproliferative and antiprotozoal activity. Anticancer potency was analyzed using different types of cancer cell lines: MDA-MB-231 breast cancer, CCRF-CEM leukemia, HCT-116 colon cancer, U251 glioblastoma, and, in addition, non-tumorigenic MRC-5 lung fibroblasts. Antiproliferative activities at micromolar concentrations could be shown. Antiprotozoal activity was assessed against Plasmodium falciparum NF54 and Trypanosoma brucei rhodesiense STIB900. For all compounds, selectivity indices (SI) were calculated based on assessed cytotoxicity towards L6 cells. In addition, the structure-activity-relationships and physicochemical parameters of these compounds are discussed.

New derivatives of 7-chloroquinolin-4-amine with antiprotozoal activity.

Novel ω-aminoacyl and -alkyl derivatives of 7-chloroquinolin-4-amine were prepared and their structures confirmed by NMR spectroscopy. Their antiprotozoal activities were examined in vitro against the sensitive NF54 strain as well as against the multiresistant K1 strain of Plasmodium falciparum and against Trypanosoma brucei rhodesiense (STIB 900). The results were compared with the activities of clinically used drugs. Their antitrypanosomal activities were only moderate whereas their antiplasmodial activities looked very promising. Some were equal or slightly more active than chloroquine against the sensitive strain. However, in comparison to chloroquine, the activity of the new compounds was decreased much less in the resistant strain. Several possessed activity against both strains in low nanomolar concentration.

New derivatives of quinoline-4-carboxylic acid with antiplasmodial activity.

New analogues of the recently published compound DDD107498 were prepared. Their activities were examined in vitro against the chloroquine-sensitive NF54 strain. The most active were also tested against the multiresistant K1 strain of Plasmodium falciparum. A couple of the newly synthesized compounds showed promising antiplasmodial activity and selectivity. A single compound showed adequate reduction of parasitaemia (98.1%) in mice infected with Plasmodium berghei. Survival time was doubled compared to control. The results of the biological tests of the novel compounds were compared with the activities of drugs in use. Structure-activity relationships were discussed.

A trifunctional linker suitable for conducting three orthogonal click chemistries in one pot.

The feasibility of a one pot approach for conducting mutually orthogonal thiol-Michael addition, copper catalyzed azide-alkyne and inverse electron demand Diels-Alder click chemistry on a tri-functional substrate was demonstrated.

Antiprotozoal activity of bicycles featuring a dimethylamino group at their bridgehead.

Several dimethylamino-derivatives of the new compound-class 3-azabicyclo[3.2.2]nonanes were prepared. For better comparison of activity also a few analogues of bicyclo[2.2.2]octanes and 2-azabicyclo[3.2.2]nonanes were synthesized. Their activities were examined in vitro against the multiresistant K1 strain of Plasmodium falciparum and against Trypanosoma brucei rhodesiense (STIB 900). A couple of the newly synthesized compounds showed promising antiprotozoal activity and selectivity. The results of the biological tests of the novel compounds were compared with the activities of already synthesized compounds and of drugs in use. Structure-activity relationships were discussed.

Synthesis of 3-azabicyclo[3.2.2]nonanes and their antiprotozoal activities.

Several bicyclic compounds, 3-azabicyclo[3.2.2]nonanes, have been prepared. The new compounds were tested for their activities against one strain of the causative organism of Malaria tropica, Plasmodium falciparum K1, which is resistant against chloroquine and pyrimethamine. In addition, their cytotoxicity and their activity against the pathogen of the East African form of sleeping sickness, Trypanosoma brucei rhodesiense, were investigated. Structure-activity relationships are discussed considering data of readily prepared compounds. For the first time, a distinct in vivo activity was observed against Plasmodium berghei in a mouse model. The active compound was further investigated.

Enhancing photoinduced electron transfer efficiency of fluorescent pH-probes with halogenated phenols.

Photoinduced electron transfer (PET), which causes pH-dependent quenching of fluorescent dyes, is more effectively introduced by phenolic groups than by amino groups which have been much more commonly used so far. That is demonstrated by fluorescence measurements involving several classes of fluorophores. Electrochemical measurements show that PET in several amino-modified dyes is thermodynamically favorable, even though it was not experimentally found, underlining the importance of kinetic aspects to the process. Consequently, the attachment of phenolic groups allows for fast and simple preparation of a wide selection of fluorescent pH-probes with tailor-made spectral properties, sensitive ranges, and individual advantages, so that a large number of applications can be realized. Fluorophores carrying phenolic groups may also be used for sensing analytes other than pH or molecular switching and signaling.

Exceptional Oxygen Sensing Properties of New Blue Light-Excitable Highly Luminescent Europium(III) and Gadolinium(III) Complexes.

New europium(III) and gadolinium(III) complexes bearing 8-hydroxyphenalenone antenna combine efficient absorption in the blue part of the spectrum and strong emission in polymers at room temperature. The Eu(III) complexes show characteristic red luminescence whereas the Gd(III) dyes are strongly phosphorescent. The luminescence quantum yields are about 20% for the Eu(III) complexes and 50% for the Gd(III) dyes. In contrast to most state-of-the-art Eu(III) complexes the new dyes are quenched very efficiently by molecular oxygen. The luminescence decay times of the Gd(III) complexes exceed 1 ms which ensures exceptional sensitivity even in polymers of moderate oxygen permeability. These sensors are particularly suitable for trace oxygen sensing and may be good substitutes for Pd(II) porphyrins. The photophysical and sensing properties can be tuned by varying the nature of the fourth ligand. The narrow-band emission of the Eu(III) allows efficient elimination of the background light and autofluorescence and is also very attractive for use e.g. in multi-analyte sensors. The highly photostable indicators incorporated in nanoparticles are promising for imaging applications. Due to the straightforward preparation and low cost of starting materials the new dyes represent a promising alternative to the state-of-the-art oxygen indicators particularly for such applications as e.g. food packaging.

3ß-Hydroxy-28-norolea-12,17-dien-11-one.

The title compound, C29H44O2, was formed by treatment of 11-oxooleanolic acid under strong alkaline conditions. The absolute structure of the chiral mol-ecules could not be determined reliably from the diffraction data, but is known from other triterpenes. The asymmetric unit consists of two mol-ecules, 1 and 2. In both mol-ecules, rings A and B show chair conformations. The other rings show mixed forms between envelope and half-chair conformations with atoms in positions 8, 15 and 21 forming the flaps in rings C, D and E, respectively. Rings D and E of mol-ecule 2 are disordered over two orientations, with occupancies of 0.557 (4) and 0.443 (4), which differ in the direction of the flap in ring E. In the crystal, mol-ecules 1, as well as the mol-ecules 2, are linked by O-H⋯O hydrogen bonds, forming chains parallel to the b axis.

Acylgermanes: photoinitiators and sources for Ge-centered radicals. insights into their reactivity.

Acylgermanes have been shown to act as efficient photoinitiators. In this investigation we show how dibenzoyldiethylgermane 1 reacts upon photoexcitation. Our real-time investigation utilizes femto- and nanosecond transient absorption, time-resolved EPR (50 ns), photo-chemically induced dynamic nuclear polarization, DFT calculations, and GC-MS analysis. The benzoyldiethylgermyl radical G• is formed via the triplet state of parent 1. On the nanosecond time scale this radical can recombine or undergo hydrogen-transfer reactions. Radical G• reacts with butyl acrylate at a rate of 1.2 ± 0.1 × 10(8) and 3.2 ± 0.2 × 10(8) M(-1) s(-1), in toluene and acetonitrile, respectively. This is ~1 order of magnitude faster than related phosphorus-based radicals. The initial germyl and benzoyl radicals undergo follow-up reactions leading to oligomers comprising Ge-O bonds. LC-NMR analysis of photocured mixtures containing 1 and the sterically hindered acrylate 3,3-dimethyl-2-methylenebutanoate reveals that the products formed in the course of a polymerization are consistent with the intermediates established at short time scales.

Synthesis and properties of new phosphorescent red light-excitable platinum(II) and palladium(II) complexes with Schiff bases for oxygen sensing and triplet-triplet annihilation-based upconversion.

New Pt(II) and Pd(II) complexes with donor-acceptor Schiff bases are conveniently prepared in only two steps. The complexes efficiently absorb in the red part of the spectrum (ε > 10(5) M(-1) cm(-1)) and show moderate to strong room-temperature phosphorescence in the near-infrared (NIR) region. Particularly, Pt(II) complexes possess phosphorescence quantum yields (Φ) of ~10%, but the emission of the respective Pd(II) complexes is less efficient (Φ ≈ 1%-2%). The complexes exhibit solvatochromic behavior, in which the absorption and emission spectra shift bathochromically in polar solvents. The Pt(II) complexes are embedded in polystyrene to produce oxygen-sensing materials. The Pd(II) and Pt(II) complexes are demonstrated to be efficient sensitizers in triplet-triplet annihilation-based upconversion systems.

Antiprotozoal activity of bicyclic diamines with a N-methylpiperazinyl group at the bridgehead atom.

ω-Aminoacyl and -alkyl derivatives of 4-(4-methylpiperazin-1-yl)bicyclo[2.2.2]octan-2-amines and of 5-(4-methylpiperazin-1-yl)-2-azabicyclo[3.2.2]nonanes were prepared and their activities were examined in vitro against the multiresistant K1 strain of Plasmodium falciparum and against Trypanosoma brucei rhodesiense (STIB 900). Some of the newly synthesized compounds showed very promising antiprotozoal activity and selectivity. A few of the alkylamino-2-azabicyclo[3.2.2]nonanes exhibited high antiplasmodial activity, whereas a single bicyclo[2.2.2]octane derivative was the most potent antitrypanosomal compound. The results of the newly synthesized compounds were compared with the activities of already synthesized compounds and of drugs in use. Structure-activity relationships were discussed.

Induction of caspase-8 and death receptors by a new dammarane skeleton from the dried fruits of Forsythia koreana.

A new naturally occurring compound based on the dammarane skeleton, i.e. cabralealactone 3-acetate-24-methyl ether, was isolated from the aqueous methanolic extract of Forsythia koreana fruits, along with eight known compounds: cabralealactone 3-acetate, ursolic acid, arctigenin, arctiin, phillyrin, rutin, caffeic acid, and rosmarinic acid. The identification of the isolated compounds was based on their spectral analysis including: HREI-MS, 1D and 2D NMR spectroscopy. The selected compounds and the aqueous methanolic extract were evaluated for their cytotoxic activity against human solid tumour cell lines. Cabralealactone 3-acetate-24-methyl ether and ursolic acid were found to be active against human breast cancer cells (MCF-7). The cytotoxicity was associated with the activation of caspase-8, the induction of the death receptors DR4 and DR5, as well as DNA fragmentation, and was thus due to apoptosis rather than necrosis.