Asymmetric epoxidation by chiral ketones derived from carbocyclic analogues of fructose.

A number of carbocyclic analogues of the fructose-derived ketone 1 have been prepared and investigated for asymmetric epoxidation. The studies show that the oxygen atom of the pyranose ring of 1 has an impact on the catalyst's activity and selectivity. Conformational, electronic, and steric effects are discussed.

Synthesis, characterization, solution stability, and X-ray crystal structure of the thiolatocobalamin gamma-glutamylcysteinylcobalamin, a dipeptide analogue of glutathionylcobalamin: insights into the enhanced Co-S bond stability of the natural product glutathionylcobalamin.

Glutathionylcobalamin (gamma-glutamylcysteinylglycinylcobalamin; gamma-GluCysGly-Cbl) is a natural product which functions as an intermediate in the biosynthesis of the active B(12) coenzymes adenosylcobalamin and methylcobalamin. Of interest to the present studies is glutathionylcobalamin's unique stability in comparison to other thiolatocobalamins, notably the > or =6 x 10(4) fold less stable cysteinylcobalamin, Cys-Cbl. In order to determine which parts of the glutathione tripeptide contribute to the overall stability of glutathionylcobalamin, two cysteine-containing dipeptides, which are truncated versions of glutathione, were used to synthesize their corresponding cobalamins, specifically gamma-glutamylcysteinylCbl (gamma-GluCys-Cbl) and cysteinylglycinylcobalamin (CysGly-Cbl). As with glutathionylCbl, the dipeptide gamma-GluCys-Cbl forms a stable thiolatocobalamin. However and most interestingly, CysGly-Cbl is observed to be unstable much like Cys-Cbl. The results require that the extra stability of glutathionylcobalamin and its congeners, compared to cysteinylcobalamin and its analogues, must be derived from destabilization by the gamma-NH(3)(+) group in cysteinylcobalamin, or stabilization by the gamma-NHC(=O)- amide linkage in glutathionylcobalamin, or both. To probe any ground-state structural basis for the possible stabilization in gamma-GluCys-containing cobalamins, gamma-GluCys-Cbl was crystallized and yielded the first X-ray structural determination of a true thiolatocobalamin, and only the second structure of a cobalamin containing a Co-S bond, the first example being Randaccio and co-workers' 1999 structure of the thioketone complex, thioureacobalamin, (NH(2))(2)CSCbl. Key features of the structure of gamma-glutamylcysteinylcobalamin include (i) a normal Co-S bond length of 2.267(2) A, (ii) a Co-N(axial) bond length of 2.049(6) A, (iii) two alternate conformations of the gamma-glutamylcysteinyl moiety, and (iv) folding of the corrin ring upward by 24.2 degrees, the highest degree of folding yet observed for a cobalamin. These results do not show any strong stabilization (e.g., no shortened Co-S bond), although it is not clear for certain what the effect is (stabilizing or destabilizing) of the elongated Co-N(axial) bond; instead, the crystallographic results suggest that the metastable Cys-Cbl probably has a Co-S cleavage transition state that is stabilized (along with, possibly, any ground-state destabilization of the Co-S bond). Overall, the results strongly suggest that placing a positive charge on the gamma-NH(3)(+) stabilizes the Co-S bond cleavage transition state, thereby setting the stage for the needed full thermolysis product and kinetic studies-as a function of the axial-base on-off equilibrium-that will be required to understand in even greater detail the unique stability of glutathionyl- (gamma-glutamylcysteinylglycinyl-) and gamma-glutamylcysteinylcobalamins.

Relative Lewis basicities of six AI(ORF)4- superweak anions and the structures of LiA.

The relative Lewis basicities of six Al(ORF)4- ions, Al[OC(CH3)(CF3)2]4-, Al(OC(CF3)3]4-, Al(OCPh(CF3)2]4-, Al[OC[4-C6H4(tBu)](CF3)2]4-, Al(OC(Cy)(CF3)2]4-, and Al(OCPh2(CF3)]4-, have been determined by measuring their relative coordinating abilities towards Li+ in dichloromethane. The relative Li- Lewis basicities of the Al(ORF)4- ions are linearly related to the aqueous pKa values of the corresponding parent HORF fluoroalcohols. The Lewis basicity of Al[OCH(CF3)2]4- could not be measured because two of these anions can coordinate to one Li+ cation. The structures of LiAl[OCH(CF3)2]4 and [1-Et-3-Me-1,3-C3H3N2][Li[Al[OCH(CF3)2)4]2] were determined.

Chemistry and insulin-mimetic properties of bis(acetylacetonate)oxovanadium(IV) and derivatives.

The syntheses and the solid state structural and spectroscopic solution characterizations of VO(Me-acac)2 and VO(Et-acac)2 (where Me-acac is 3-methyl-2,4-pentanedionato and Et-acac is 3-ethyl-2,4-pentanedionato) have been conducted since both VO(acac)2 and VO(Et-acac)2 have long-term in vivo insulin-mimetic effects in streptozotocin-induced diabetic Wistar rats. X-ray structural characterizations of VO(Me-acac)2 and VO(Et-acac)2 show that both contain five-coordinate vanadium similar to the parent VO(acac)2. The unit cells for VO(Et-acac)2 and VO(Me-acac)2 are both triclinic, P1, with a = 9.29970(10) A, b = 13.6117(2) A, c = 13.6642(2) A, alpha = 94.1770(10) degrees, beta = 106.4770(10) degrees, gamma = 106.6350(10) degrees for VO(Et-acac)2 and a = 7.72969(4) A, b = 8.1856(5) A, c = 11.9029(6) A, alpha = 79.927(2) degrees, beta = 73.988(2)degrees, gamma = 65.1790(10)degrees for VO(Me-acac)2. The total concentration of EPR-observable vanadium(IV) species for VO(acac)2 and derivatives in water solution at 20 degreesC was determined by double integration of the EPR spectra and apportioned between individual species on the basis of computer simulations of the spectra. Three species were observed, and the concentrations were found to be time, pH, temperature, and salt dependent. The three complexes are assigned as the trans-VO(acac)2.H2O adduct, cis-VO(acac)2.H2O adduct, and a hydrolysis product containing one vanadium atom and one R-acac- group. The reaction rate for conversion of species was slower for VO(acac)2 than for VO(malto)2, VO(Et-acac)2, and VO(Me-acac)2; however, in aqueous solution the rates for all of these species are slow compared to those of other vanadium species. The concentration of vanadium(V) species was determined by 51V NMR. The visible spectra were time dependent, consistent with the changes in species concentrations that were observed in the EPR and NMR spectra. EPR and visible spectroscopic studies of solutions prepared as for administration to diabetic rats documented both a salt effect on speciation and formation of a new halogen-containing complex. Compound efficacy with respect to long-term lowering of plasma glucose levels in diabetic rats traces the concentration of the hydrolysis product in the administration solution.

Weakly coordinating anions HA2-generated from oxoanions A- and their conjugate acids. Coordination equilibria, ionic conductivities, and the structures of [Cu2(H(CH3SO3)2)4]n and [Cu(CO)(H(CF3CO2)2)]2.

The coordination or ion pairing of the hydrogen-bonded anions H(CF3CO2)2- and H(CH3SO3)2- to NEt4+, Li+, Cu+, and/or Cu2+ was investigated. The structure of [Cu2(H(CH3SO3)2)4]n consists of centrosymmetric dimeric moieties that contain two homoconjugated (CH3SO2O-H...OSO2CH3)- anions per Cu2+ ion, forming typical Jahn-Teller tetragonally elongated CuO6 coordination spheres. The oxygen atoms involved in the nearly linear O-H...O hydrogen bonds (O...O approximately 2.62 A) are not coordinated to the Cu2+ ions. The structure of Cu2(CO)2(H(CF3-CO2)2)2 consists of pseudo-C2-symmetric dimers that contain one homoconjugated (CF3COO-H...OCOCF3)- anion per Cu+ ion, forming highly distorted tetrahedral Cu(CO)O3 coordination spheres. Three of the four oxygen atoms in each hydrogen-bonded H(CF3CO2)2- anion are coordinated to the Cu+ ions, including one of the oxygen atoms in each O-H...O hydrogen bond (O...O approximately 2.62 A). Infrared spectra (v(CO) values) of Cu(CO)(CF3CO2) or Cu(CO)(CH3SO3) dissolved in acetonitrile or benzene, with and without added CF3COOH or CH3SO3H, respectively, demonstrate that HA2- anions involving carboxylates or sulfonates are more weakly coordinating than the parent anions RCO2- and RSO3-. Direct current conductivities of THF solutions of Li(CF3CO2) containing varying concentrations of added CF3COOH further demonstrate that Li+ and NEt4+ ion pair much more weakly with H(CF3CO2)2- than with CF3CO2-.

Structure of a thiolate-bridged polymeric copper(I) compound, catena-(2,9-dimethyl-1,10-phenanthroline)-mu-(thiophenolato)-copper(I).

[Cu(C6H5S)(C14H12N2)], Mr = 380.97, monoclinic, P2(1), a = 10.047 (1), b = 15.797 (2), c = 10.581 (1) A, beta = 90.78 (1) degrees, V = 1679.2 A3, Z = 4, Dm (CCl4/C5H12) = 1.50, D chi = 1.51 g cm-3, lambda(Mo K alpha) = 0.7107 A, mu = 14.2 cm-1, F(000) = 784, T = 293 (1) K, R = 0.026, wR = 0.026 for 2709 observed reflections. The title compound, [Cu(Me2-phen)(C6H5S)]n, exists as chains of [Cu(Me1phen)]+ units linked by thiophenolate S atoms. Large bridging angles at thiolate S atoms [Cu(1)--S--Cu(2)(av.) = 134 (1) degrees] preclude any Cu--Cu bonding [Cu ... Cu = 4.246 (1), 4.284 (1) A] along the chain. The CuI atoms exhibit highly distorted tetrahedral coordination, with the largest deviations from tetrahedral stereochemistry involving the N--Cu--N and S--Cu--S angles [N--Cu--N(av.) = 78.0(2), S--Cu--S(av.) = 126 (3) degrees].

Structure of bis(imidazole)(5,10,15,20-tetraphenylporphinato)iron(III) bis(cis-1,2-dicyanoethylenedithiolato)cuprate(III) Tetrakis(tetrahydrofuran) solvate.

[Fe(C44H28N4)(C3H4N2)2][Cu(C4N2S2)2].-4C4H8O, Mr = 1437.1, triclinic, P1-, a = 10.012 (4), b = 11.604 (6), c = 15.802 (7) A, alpha = 71.42 (4), beta = 87.12 (3), gamma = 78.45 (4) degrees, V = 1704 (1) A3, Z = 1, Dx = 1.40 g cm-3, lambda(Mo K alpha) = 0.7107 A, mu = 6.9 cm-1, F(000) = 747, T = 143 K, R = 0.063 for 4935 unique observed reflections. Fe is six-coordinate, Fe--N(porphinato) (av.) = 1.99 (2), Fe--N(imidazole) = 1.981 (3) A; Cu--S (av.) = 2.172 (8) A.