The molecular structure of 3(5)-methyl-4,5(3)-trimethylenepyrazole hydrochloride and its13C and15N NMR spectroscopy

The title compound (C₇N₂H₁₀, HC1, 1/2H₂O) crystallizes in the space groupC2/c with cell parameters:a=11.651(9),b=16.309(1),c=9.167(1)Å,=94.95(3)°,Z=8, withd=1.287 g cm^–3. One of the chlorine atoms lies on a twofold axis, the second and the oxygen atom of the water molecule have disordered positions. Intermolecular interactions through hydrogen bonds are established between nitrogen atoms of the pyrazole ring and chlorine atoms or the water molecule. In this way, chains of molecules are built; these chains, through van der Waals interactions, form layers which are stacked in the a direction. The¹H,¹³C, and¹⁵N NMR (this last using the double labelled compound) have been recorded in solution and the¹³C NMR spectrum also in the solid state (CP/MAS technique). The NMR parameters ( andJ's) thus obtained are discussed using the molecular structure.     

Anti-Markovnikov hydroarylation of styrenes catalyzed by an in situ generated ruthenium complex

An efficient and practical catalytic system for the anti-Markovnikov ruthenium-catalyzed hydroarylation of styrenes with acetophenone, allowing a straightforward access to bibenzyl backbones, is described for the first time: this process, involving regioselective C-H bond activation, is complementary to a Friedel-Crafts type reaction giving the branched adduct.     

Recent synthetic approaches toward non-anomeric spiroketals in natural products

Many natural products of biological interest contain [6,5]- and [6,6]-spiroketal moieties that can adopt various configurations, benefiting or not from anomeric conformation stabilizing effects. The spiroketal fragments are often important for the biological activity of the compounds containing them. Most stable spiroketal stereoisomers, including those benefiting from conformational anomeric effects (gauche conformers can be more stable than anti conformers because of a contra-steric stabilizing effect), are obtained easily under acidic conditions that permit acetal heterolysis (formation of tertiary oxycarbenium ion intermediates). The synthesis of less stable stereoisomers requires stereoselective acetal forming reactions that do not permit their equilibration with their most stable stereoisomers or, in the case of suitably substituted derivatives, concomitant reactions generating tricyclic products that quench the less stable spiroketal conformers. Ingenuous approaches have been recently developed for the synthesis of naturally occurring [6,6]- and [5,6]-nonanomeric spiroketals and analogues. The identification of several parameters that can influence the stereochemical outcome of spirocyclization processes has led to seminal improvements in the selective preparation of the non-anomeric isomers that are discussed herein. This review also gives an up-dated view of conformational anomeric effect which represents a small fraction of the enthalpic anomeric effect that makes gem-dioxy substituted compounds much more stable that their 1,n-dioxy substituted isomers (n > 1). Although models assuming sp3-hybridized oxygen atoms have been very popular (rabbit ears for the two non-bonding electron pairs of oxygen atom), sp2-hybridized oxygen atoms are used to describe the conformational anomeric effect.     

Efficient and simple synthesis of 6-aryl-1,4-dimethyl-9H-carbazoles

A synthetic method for the preparation of 6-aryl-1,4-dimethyl-9H-carbazoles involving a palladium catalyzed coupling reaction of 1,4-dimethyl-9H-carbazole-6-boronic acids and (hetero)aryl halides is described.     

Synthesis and testing of chromogenic phenoxazinone substrates for beta-alanyl aminopeptidase

Novel 7-N-(beta-alanyl)aminophenoxazin-3-one salts 27a-d have been synthesized and tested as chromogenic substrates for beta-alanyl aminopeptidase, which is present in Pseudomonas aeruginosa, the most common respiratory pathogen in patients with cystic fibrosis. The biological results show that 7-N-(beta-alanyl)amino-1-pentylphenoxazin-3-one trifluoroacetate salt 27a is a chromogenic substrate for this bacterium, with a low degree of diffusion in nutrient media for growing bacterial cultures and a bright red colour, making it easily distinguishable from the agar background.     

Evidence of different stoichiometries for the limiting carbonate complexes across the lanthanide(III) series: a capillary electrophoresis-mass spectrometry study

The electrophoretic mobilities (mu ep,Ln) of twelve lanthanides (not Ce, Pr and Yb) were measured by CE-ICP-MS in 0.15 and 0.5 mol L(-1) Alk2 CO3 aqueous solutions for Alk+ = Li+, Na+, K+ and Cs+. In 0.5 mol L(-1) solutions, two different mu ep,Ln values were found for the light (La to Nd) and the heavy (Dy to Tm) lanthanides, which suggests two different stoichiometries for the carbonate limiting complexes. These results are consistent with a solubility study that attests the Ln(CO3)3(3-) and Ln(CO3)4(5-) stoichiometries for the heavy (small) and the light (big) lanthanides, respectively. The Alk+ counterions influence the mu ep,Ln Alk2 CO3 values, but not the overall shape of the mu ep,Ln Alk2 CO3 plots as a function of the lanthanide atomic numbers: the counterions do not modify the stoichiometries of the inner sphere complexes. The influence of the Alk+ counterions decreases in the Li+ > Na+ > K+ > Cs+ series. The K3,Ln stepwise formation constants of the Ln(CO3)3(3-) complexes slightly increase with the atomic numbers of the lanthanides while K4,Ln, the stepwise formation constants of Ln(CO3)4(5-) complexes, slightly decrease from La to Tb, and is no longer measurable for heavier lanthanides.     

Sterically hindered benzophenones via rhodium-catalyzed oxidative arylation of aldehydes

Efficient cross-coupling, allowing a straightforward access to congested benzophenones, between aromatic aldehydes and potassium aryltrifluoroborates, is described in the presence of a rhodium/tri-tert-butylphosphane catalyst system and acetone as cosolvent. The use of the stable phosphonium salts of tri-tert-butylphosphane prevented the use of highly oxidizable tri-tert-butylphosphane and allowed a careful control of the stoichiometry with the rhodium.     

Homophymine A, an anti-HIV cyclodepsipeptide from the sponge Homophymia sp

A new anti-HIV cyclodepsipeptide, homophymine A, was isolated from a New Caledonian collection of the marine sponge Homophymia sp. The structure of homophymine A was determined by interpretation of spectroscopic data, acid hydrolysis, and LC-MS analysis. Homophymine A contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6-trimethyloctanoic acid moiety. Along with four D-, two L-, and one N-methyl amino acids, it also contains four unusual amino acid residues: (2S,3S,4R)-3,4-diMe-Gln, (2R,3R,4S)-4-amino-2,3-dihydroxy-1,7-heptandioic acid, L-ThrOMe, and (2R,3R,4R)-2-amino-3-hydroxy-4,5-dimethylhexanoic acid. In a cell-based XTT assay, homophymine A exhibited cytoprotective activity against HIV-1 infection with a IC50 of 75 nM.     

Synthetic Receptors with Micromolar Affinity for Chloride in Water

A water-soluble coordination cage was obtained by reaction of Pd(NO₃)₂ with a 1,3-di(pyridin-3-yl)benzene ligand featuring a short PEG chain. The cavity of the metal-organic cage contains one nitrate anion, which is readily replaced by chloride. The apparent association constant for chloride binding in buffered aqueous solution is K_a=1.8(±0.1)×10⁵ M⁻¹. This value is significantly higher than what has been reported for other macrocyclic chloride receptors. The heavier halides Br⁻ and I⁻ compete with binding or self-assembly, but the receptor displays very good selectivity over common anions such as phosphate, acetate, carbonate, and sulfate. A further increase of the chloride binding affinity by a factor of 3 was achieved using a fluorinated dipyridyl ligand.