Nonclassical dynamics of the methyl group in 1,1,1-triphenylethane. Evidence from powder 1H NMR spectra.

According to the damped quantum rotation (DQR) theory, hindered rotation of methyl groups, evidenced in nuclear magnetic resonance (NMR) line shapes, is a nonclassical process. It comprises a number of quantum-rate processes measured by two different quantum-rate constants. The classical jump model employing only one rate constant is reproduced if these quantum constants happen to be equal. The values of their ratio, or the nonclassicallity coefficient, determined hitherto from NMR spectra of single crystals and solutions range from about 1.20 to 1.30 in the latter case to above 5.0 in the former, with the value of 1 corresponding to the jump model. Presently, first systematic investigations of the DQR effects in wide-line NMR spectra of a powder sample are reported. For 1,1,1-triphenylethane deuterated in the aromatic positions, the relevant line-shape effects were monitored in the range 99-121 K. The values of the nonclassicality coefficient dropping from 2.7 to 1.7 were evaluated in line shape fits to the experimental powder spectra from the range 99-108 K. At these temperatures, the fits with the conventional line-shape model are visibly inferior to the DQR fits. Using a theoretical model reported earlier, a semiquantitative interpretation of the DQR parameters evaluated from the spectra is given. It is shown that the DQR effects as such can be detected in wide-line NMR spectra of powdered samples, which are relatively facile to measure. However, a fully quantitative picture of these effects can only be obtained from the much more demanding experiments on single crystals.

Synthetic approaches for sulfur derivatives containing 1,2,4-triazine moiety: their activity for in vitro screening towards two human cancer cell lines.

A series of sulfur 1,2,4-triazine derivatives were prepared and evaluated as anticancer compounds for two human breast cancer cell lines (MCF-7, MDA-MB-231) with some of them acting as low micromolar inhibitors. Evaluation of the cytotoxicity using a 3-(4,5-dimethylthiazol-2-yl)-3,5-diphenyltetrazolium bromide (MTT) assay, the inhibition of [(3)H]thymidine incorporation into DNA, and collagen synthesis inhibition demonstrated that these products exhibit cytotoxic effects on these breast cancer cell lines in vitro. The most effective were disulfide and sulfenamide compounds with two valence sulfur atoms. A structure-activity relationship study was performed using X-ray analysis and theoretical calculations at an ab initio density functional theory (DFT) level.

New approaches to the synthesis of sildenafil analogues and their enzyme inhibitory activity.

In the search for new biologically active chemotypes, several sildenafil analogs were prepared and characterized. The presence of the pyrazolo[4,3-e][1,2,4]triazine core is thought to be of interest for the enzyme inhibitory activity of these compounds. The designed derivatives incorporating the sildenafil scaffold were assayed as carbonic anhydrase inhibitors, and for their cytotoxic activity against MCF-7 and K562 cell lines. The X-ray analysis of one of these model compounds was performed and its crystal structure is described/compared to that of sildenafil.

Novel antimicrobial peptide dendrimers with amphiphilic surface and their interactions with phospholipids--insights from mass spectrometry.

A series of new peptide dendrimers with amphiphilic surface, designed around a dendronized ornithine (Orn) core were synthesized and characterized by ESI-MS, ¹H-, ¹³C- NMR, and CD spectrometry. An improved antimicrobial potency against S. aureus and E. coli was detected as a result of an increased charge, higher branching and variable lipophilicity of the residues located at the C-terminus. Minimal inhibitory concentration (MIC) values indicated that the selected dendrimers were not sensitive to the physiological concentration of Na⁺ and K⁺ ions (100 mM), but expressed reduced potency at 10 mM concentration of Mg²âº and Ca²âº ions. Circular dichroism (CD) curves measured under various conditions revealed structure and solvent-dependent curve evolution. ESI-MS studies of gas-phase interactions between selected dendrimers and both anionic (DMPG) and neutral (DMPC) phospholipids revealed the presence of variously charged dendrimer/phospholipid aggregates with 1:1 to 1:5 stoichiometry. The collision-induced fragmentation (CID) of the most abundant [dendrimer/phospholipid]²âº ions of the 1:1 stoichiometry demonstrated that the studied dendrimers formed stronger complexes with anionic DMPG. Both phospholipids have higher affinity towards dendrimers with a more compact structure. Higher differences in CID energy necessary for dissociation of 50% of the complex formed by dendrimers with DMPG vs. DMPC (ΔCID50) correlate with a lower hemotoxicity. Mass spectrometry results suggest that for a particular group of compounds the ΔCID50 might be one of the important factors explaining selectivity of antimicrobial peptides and their branched analogs targeting the bacterial membrane. Both circular dichroism and mass spectrometry studies demonstrated that dendrimers of N(α)- and N(ε)-series possess a different conformation in solution and different affinity to model phospholipids, what might influence their specific microbicidal mechanism.

Determination of the relative configuration of tropinone and granatanone aldols by using TBDMS ethers.

The relative configurations of tert-butyldimethylsilyl (TBDMS) ethers of all four diastereomers of the aldols of tropinone (8-methyl-8-azabicyclo[3.2.1]octan-3-one), as well as of granatanone (9-methyl-9-azabicyclo[3.3.1]nonan-3-one), were determined from NMR data, and from the observed interconversion of the diastereomers (exo,anti to endo,syn and exo,syn to endo,anti). The exo forms invert to endo isomers in the presence of silica gel. The relative configuration of a new isomer of tropinone aldol accessible synthetically through the direct solventless reaction of tropinone and benzaldehyde in the presence of water was determined as exo,syn by comparison of NMR data of the aldol isomers, in particular vicinal coupling constants and shifts corresponding to the side-chain CH group, with data of related TBDMS derivatives and confirmed by single-crystal X-ray diffraction.

2-(3-Chloro-5,6-diphenyl-2,5-dihydro-1,2,4-triazin-5-yl)-2-methyl-propane-nitrile.

The title compound, C(19)H(17)ClN(4), was obtained from the reaction of 3-chloro-5,6-diphenyl-1,2,4-triazine with isobutyronitrile in the presence of lithium diisopropyl-amide as an unexpected product of covalent addition of isobutyronitrile carbanion to the C-5 atom of the 1,2,4-triazine ring. The 2,5-dihydro-1,2,4-triazine ring is essentially planar (r.m.s. deviation = 0.0059 Å) and the 5- and 6-phenyl substituents are inclined to its mean plane with dihedral angles of 89.97 (4) and 55.52 (5)°, respectively. Intra-molecular C-H⋯N inter-actions occur. In the crystal, mol-ecules related by a c-glide plane are linked into zigzag chains along [001] by N-H⋯N hydrogen bonds.

Derivatives of pyrrolo[3,4-d]pyridazinone, a new class of analgesic agents.

A series of N2-{2-[4-aryl(benzyl)-1-piperazinyl(piperidinyl)]ethyl}pyrrolo[3,4-d]pyridazinones 4 and related derivatives 5 were synthesized as potential analgesic agents. The structures of the new compounds were elucidated by micro, spectral and X-ray analysis. Analgesic activity of the compounds was investigated in the phenylbenzoquinone induced 'writhing' and 'hot plate' test in mice and at radioligand binding assay. At 'writhing' test all compounds, without exception, were more active than acetylsalicylic acid (ASA) with ED(50) values ranging from 0.04 to 11 mg/kg (i.p.) (ED(50) for ASA--39.15 mg/kg). Analgesic effect at the 'hot plate' test was observed for three compounds 4c,e,f at the dose 3-5 times higher then that of morphine (ED(50)-3.39 mg/kg). At radioligand binding assay of 4c,e,f only compound 4f exhibited affinity for the µ-opioid receptors similar to that of Tramadol. The acute toxicity of the pyrrolopyridazinones 4, 5 were also studied and non toxic effect was observed at the 2000 mg/kg (5a 1420 mg/kg) i.p. dose level. On the basis of the available pharmacological data S-A relationship is discussed. The preferred conformational characteristic of 4, taken 4c as an example, was also described.

Rearrangement of 2,3-epoxy alcohol dimethylthiocarbamate derivatives. Synthesis of 2,3-epithio alcohol derivatives under mild conditions.

Transformation of representative 2,3-epoxy alcohols, including 3-trimethylsilyl- and 3-triphenylsilylglycidols, into the corresponding 2,3-epithio alcohol dimethylthiocarbamate derivatives under mild alkaline conditions is reported.

Face-to-face dinuclear scaffolds composed of tetraazamacrocyclic charged and neutral complexes.

A new family of bismacrocyclic homo- and heteronuclear Ni and Cu complexes has been synthesized and characterized. The ligand scaffold is comprised of two 14-membered tetraazamacrocyclic sites held in cofacial orientation. The dinuclear complexes are unique in that one macrocyclic center is neutral while the other one is charged, although the ligand backbones are nearly identical. This leads to a binuclear system of two structurally similar components, differing in their electron-donor abilities. The crystallographically characterized structures in the solid state revealed similarity of the four dinuclear complexes studied. The metal-metal separations are between 4 and 5 A. The strongest electrostatic intramolecular interactions occur in the molecules with neutral and charged components, most differing in donor abilities.

5,6,7,8-Tetra-hydro-quinoline 1-oxide hemihydrate.

In the title compound, C(9)H(11)NO·0.5H(2)O, the asymmetric unit contains two similar mol-ecules of 5,6,7,8-tetra-hydro-quinoline 1-oxide and one water mol-ecule. The water mol-ecule links the two O atoms of both independent N-oxides into dimers via O-H⋯O hydrogen bonds, forming a three-dimensional network along [101], which is additionally stabilized by weak C-H⋯O inter-molecular inter-actions. In each mol-ecule, the saturated six-membered rings exist in a conformation inter-mediate between a half-chair and sofa.

6-(2-Chloro-benz-yl)-1-(4-chloro-phen-yl)-7-hy-droxy-2,3-dihydro-1H-imidazo[1,2-a]pyrimidin-5-one.

The title compound, C(19)H(15)Cl(2)N(3)O(2), was obtained by a one-step cyclo-condensation of 2-amino-1-(4-chloro-phen-yl)imidazoline with diethyl (2-chloro-benz-yl)malonate under basic conditions. In the crystalline state, the mol-ecule exists as the 7-hy-droxy-5-oxo tautomer. The dihedral angles between the fused imidazopyrimidine and aromatic chloro-phenyl and chloro-benzyl rings are 14.2 (1) and 70.7 (1)°, respectively. The conformation of the mol-ecule is influenced by the intra-molecular C-H⋯O and C-H⋯N hydrogen bonds, giving a nearly planar five-ring fused system [maximum deviation from the mean plane = 0.296 (2) Å]. In the crystal structure, strong inter-molecular O-H⋯O hydrogen bonds link the mol-ecules into chains along the c axis. These chains are further stabilized by weak C-H⋯Cl and π-π inter-actions [centroid-centroid distance = 3.6707 (12) Å].

1,2-Bis[1-(3-methyl-sulfanyl-1,2,4-triazin-5-yl)ethyl-idene]diazane.

The mol-ecule of the title compound, C(12)H(14)N(8)S(2), has an N-N gauche conformation. The triazine rings are nearly coplanar with respect to the imide bonds [C-C-C-N torsion angles = -15.3 (3) and -15.8 (3)°] and they are twisted by 77.88 (7)°. The overall conformation of the mol-ecule is stabilized by intra-molecular C-H⋯N hydrogen bonding. The mol-ecular packing is influenced by π-π inter-actions of the triazine systems with a shortest centroid-centroid separation of 3.5242 (12) Å.