An addition to the oxoacid family: H2B12(OH)12

The acid H(2)B(12)(OH)(12) can be isolated as a crystalline solid by protonation of the hydroxylated borane anion, B(12)(OH)(12)(2)(-). This acidic compound has low solubility in water, conducts protons in the solid state, and has thermal stability to a temperature of 400 degrees C. The conductivity mechanism is a Grotthuss mechanism with a low activation enthalpy (9-13 kcal/mol). This new acid represents an addition to the class of oxoacids, of which sulfuric and phosphoric acid are the most prominent examples.     

Electronic effects steer the mechanism of asymmetric hydrogenations of unfunctionalized aryl-substituted alkenes

Density functional theory (PBE and B3LYP) was used to study asymmetric hydrogenations of alkenes catalyzed by an iridium imidazolylidine oxazoline complex. The calculation predicts that the alkene preferentially coordinates to the site trans to the carbene. The coordinated alkene then reacts first with the H2 ligand, then with the hydride to form alkane. Finally, the alkane is released by equilibrating with extrinsic H2 and alkene. Enantioface selectivities for hydrogenations of trisubstituted alkenes seem to be driven primarily by steric interactions with the adamantyl part of the ligand; only the smallest substituents can adopt a site close to it. Application of this theoretical model leads to correct predictions regarding the experimentally observed sense and magnitude of the enantioselectivities.     

Synthesis of an isomer of the germacranolide isoaristolactone

Photocycloadditlon of (+)-isoplperltenone and cyclobutene-1-carboxylic acid gives an adduct which upon reduction with NaCNBH₃ followed by thermolysis yields an isomer of isoaristolactone in an overall yield of 26%.     

Self-selection in olefin cross-metathesis: the effect of remote functionality

Olefin cross-metathesis (CM) is potentially an attractive method for generating dynamic combinatorial libraries (DCLs). In order for the CM reaction to be useful for DCL production, the course of the reaction and product distribution must be relatively insensitive to functionality remote from the reacting centers. We report on the CM of a series of allyl- and homoallylamides that are strongly dependent on remote functionality. This includes an unusual example of a cis-selective CM. [Reaction: see text]     

A chemical inhibitor reveals the role of Raf kinase inhibitor protein in cell migration

Raf kinase inhibitor protein (RKIP) is a modulator of cell signaling that functions as an endogenous inhibitor of multiple kinases. We demonstrate here a positive role for RKIP in the regulation of cell locomotion. We discovered that RKIP is the relevant cellular target of locostatin, a cell migration inhibitor. Locostatin abrogates RKIP's ability to bind and inhibit Raf-1 kinase, and it acts by disrupting a protein-protein interaction, an uncommon mode of action for a small molecule. Small interfering RNA-mediated silencing of RKIP expression also reduces cell migration rate. Overexpression of RKIP converts epithelial cells to a highly migratory fibroblast-like phenotype, with dramatic reduction in the sensitivity of cells to locostatin. RKIP is therefore the compound's valid target and a key regulator of cell motility.     

Toluene dioxygenase-mediated oxidation of dibromobenzenes. Absolute stereochemistry of new metabolites and synthesis of (−)-conduritol E

Dibromobenzenes (o-, m-, and p-isomers) were converted to the corresponding cis-cyclohexadiene diols by whole-cell fermentation with Escherichia coli JM 109 (pDTG601A), an organism over-expressing the enzyme toluene dioxygenase (TDO). Absolute stereochemistry of new metabolites was determined, and (−)-conduritol was synthesized.     

The synthesis and spectroscopic properties of some but-2-yne tungsten complexes of the type [WIX(CO){Ph2P(CH2)PPh2}(η-MeC2Me)] (X = Cl, Br, I, NO2, NO3, NCS or OH)

Reaction of the cationic complex [WI(CO)(NCMe){Ph₂P(CH₂)PPh₂}(η²-MeC₂ME)][BF₄] with an equimolar amount of MX (MX = NaCl, NaBr, NaI, KNO₂, KNO₃, NaNCS or KOH) in acetone at room temperature gave the neutral complex [WIX(CO){Ph₂P(CH₂)PPh₂}(η²-MeC₂Me)] (1–7) in good yield. Complexes 1–7 have been characterized by elemental analysis (C, H and N), IR and ¹H NMR spectroscopy.     

Synthesis of the branched-chain sugar aceric acid: a unique component of the pectic polysaccharide rhamnogalacturonan-II

Described herein is the synthesis of 3-C-carboxy-5-deoxy-L-xylose (aceric acid), a rare branched-chain sugar found in the complex pectic polysaccharide rhamnogalacturonan-II. The key synthetic step in the construction of aceric acid was the stereoselective addition of 2-trimethylsilyl thiazole to 5-deoxy-1,2-O-isopropylidene-alpha-L-erythro-pentofuran-3-ulose (2), which was prepared from L-xylose. The thiazole group was efficiently converted into the required carboxyl group via conventional transformations. Aceric acid was also synthesized by dihydroxylation of a 3-C-methylene derivative of 2 followed by oxidation of the resulting hydroxylmethyl group. The C-2 epimer of aceric acid was also synthesized using thiazole addition chemistry, starting from L-arabinose.     

Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXXVI Structural Studies in the Copper(I) Halide : Norbornadiene System

The structural characterizations of some copper(I) halide (CuX) adducts with norbornadiene (nbd) are recorded. CuCl : nbd (1:1)₄ (a redetermination), (2:1)_2(|), are systems both based around Cu₄Cl₄ cubane-type cluster arrays. CuBr : nbd (7:3)_(|)( 0.5 MeOH), a complex polymer with 3-symmetry, is believed to be the complex previously described as an adduct of 2:1 stoichiometry. Attempts to obtain an iodide counterpart have resulted in the definition of an ephemeral adduct CuI : MeCN (3:2)_(|). 0.5 C₇H₈ in which, remarkably, the nbd is uncoordinated; the complex is a polymer, related to the [AgX(quinoline)]_(|) (X = Cl, Br) saddle polymer.