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Treatment of 1-CH 3 B 5 H 8 or 2-CH 3 B 5 H 8 with P(CH 3 ) 3 resulted in the cleavage of the pentaborane framework to give CH 3 B 2 -H 3 •2P(CH 3 ) 3 , and B 3 H 5 •3P(CH 3 ) 3 . The methylated diborane(4) adduct CH 3 B 2 H 3 •2P(CH 3 ) 3 was characterized by mass and NMR spectroscopy, and its reaction chemistry was studied. Hydrogen chloride reacted with CH 3 B 2 H 3 •2P(CH 3 ) 3 to give BH 3 •P(CH 3 ) 3 and CH 3 BHCl•P(CH 3 ) 3

Manno- and galacto-validamines, which are epimers of validamine, were semi-synthesized by the configurational inversion of validamine, a pseudo-sugar analogue of alpha-D-gluco-pyranose that has inhibitory activity for alpha-glucosidases. The inhibitory activities of these analogues were determined against several mannosidases and galactosidase. Manno-validamine shows potent inhibition for the alpha-mannosidases (competitive. K(i) = 4.6 x 10(-5) M for jack beans, and competitive, Ki = 2.8 x 10(-5) M for almonds), and galacto-validamine shows weak inhibition for the alpha-galactosidases (coffee bean and E. coli). The inhibitory effect of the epimers on the N-linked oligosaccharide-processing mannosidases involved in glycoprotein biosynthesis and lysosomal mannosidase from rat liver were also examined. Mannovalidamine shows potent inhibition on the endoplasmic reticulumal alpha-mannosidase (competitive, K(i) = 1.2 x 10(-6) M), Golgi mannosidases IA, II (competitive, K(i) = 2.8 x 10(-5) M), and lysosomal alpha-mannosidase (competitive, Ki = 1.7 x 10(-5) M).

The stereselective oxidation of acyclic allylic silyl ethers with dioxiranes generated in situ from Oxone® and ketones provided erythro epoxides.

Measurements of the electrical conductivity, magnetic susceptibility and thermoelectric power have been carried out on liquid Ag-As 2 Te 3 and Ag-As 2 Se 3 systems. The liquid Ag-As 2 Te 3 system exhibits a deep minimum of the electrical conductivity, diamagnetic peak of the magnetic susceptibility and rapid drop of the positive thermoelectric power at the stoichiometric composition of Ag 6 As 2 Te 3 . reflecting the occurrence of the metal-semiconductor transition. The liquid Ag-As 2 Se 3 system also has the diamagnetic peak of magnetic susceptibility and sign reversion of thermoelectric power near the composition of Ag 6 As 2 Se 3 . However, the electrical conductivity in the selenide system indicates a negative temperature dependence like metals and takes a maximum value at this composition. The observed results have been discussed with the help of the pseudogap model developed by Enderby and Bames. In this result, the unusual behavior of electrical conductivity in the selenide system has been deduced to be associated with the conduction and valence hand edge-parameters rather than the pseudogap width.

It is reviewed that through the observation of solid-state 13 C NMR chemical shift, the main-chain conformation and hydrogen-bonded structure of peptides, polypeptides and proteins in the solid state have been successfully elucidated, and the combination of solid state 13 C NMR and chemical shift calculation by quantum chemistry is a powerful means for the structural characterization. Furthermore, it is briefly introduced that solid state NMR of 15 N and 17 O nuclei is very useful for obtaining information about hydrogen-bonded structure. This review article is communicated on the basis of our recent works on structural characterization of peptides and polypeptides including proteins in the solid state by high-resolution solid-state NMR spectroscopy and its combination with quantum chemical calculation.

As a new type of zincate, we designed various new organozinc derivatives, Me3Zn(R)Li2 (R = Me, CN, SCN), which could be prepared in situ from lithium trimethylzincate and anion species such as methyllithium, lithium cyanide, and lithium thiocyanate. We investigated the reactivities of these zincates toward the halogen (or tellurium)−zinc exchange, Michael addition, carbozincation, and epoxide ring opening reactions. On the basis of their excellent chemical yields and chemoselectivities, these species were considered to be differentiated from ordinary triorganozincates, R3ZnLi. We also discuss the structure of the newly designed zincates using 1H NMR/Raman/in situ FTIR/extended X-ray absorption fine structure (EXAFS) spectroscopic and the density-functional theory (DFT) theoretical studies. All results strongly support the fact that these newly designed zincates are a new category of zincate species. This observation is also identical with the fact that newly designed zincates have a higher and unique reac...

Publisher Summary Nuclear magnetic resonance (NMR) chemical shifts are one of the most important parameters for providing information about molecular structure, and high-resolution NMR spectroscopy has been used as one of the most powerful means for obtaining useful information on the details of the hydrogen bond. This chapter describes recent studies on the hydrogen-bonded structures of peptides and polypeptides in the solid state through the observation of NMR chemical shifts and through theoretical calculations of nuclear shieldings (chemical shifts) to get an understanding of the nature and influence of hydrogen bonds. The chemical shifts in the solid state provide direct information about the hydrogen bond present in peptides and polypeptides with a fixed conformation. The 13 C chemical shift obtained from solid-state NMR is closely related to the electronic structure of a molecule, and therefore, includes information about the three-dimensional structure of the molecule. To reveal the correlation between the structures of peptides and the 13 C chemical shifts, 13 C shielding calculations have been discussed in the chapter using finite perturbation theory with intermediate neglect of differential overlap (FPT-INDO) and by the coupled Hartree–Fock method, using ab initio gauge-invariant atomic orbitals (GIAO-CHF). The chapter concludes that solid-state high-resolution NMR spectroscopy combined with quantum–chemical calculation is a useful methodology for elucidating the hydrogen-bonded structure of peptides and polypeptides—including proteins, in the solid state.

The monodesulfonylation reaction of N, N-bis(methylsulfonyl)-, N, N-bis(phenylsulfonyl)-, and N, N-bis(p-tolysulfonyl)arylamines easily proceeded using tetrabutylammonium fluoride in tetrahydrofuran under mild conditions to give the corresponding N-monosulfonylarylamines in excellent yields.

Four new polyhydroxypyrrolizidines, hyacinthacines A 1 , A 2 , A 3 and B 3 , have been isolated from the bulbs of Muscari armeniacum (Hyacinthaceae) in addition to the known hyacinthacine C 1 , which was isolated from Hyacinthoides non-scripta (Hyacinthaceae). The structures of hyacinthacines A 1 , A 2 , A 3 and B 3 were identified on the basis of extensive NMR studies as (1 S ,2 R ,3 R ,7a R )-1,2-dihydroxy-3-hydroxymethylpyrrolizidine, (1 R ,2 R ,3 R ,7a R )-1,2-dihydroxy-3-hydroxymethylpyrrolizidine, (1 R ,2 R ,3R,5 R ,7a R )-1,2-dihydroxy-3-hydroxymethyl-5-methylpyrrolizidine and (1 S ,2 R ,3 R ,5 R ,7 R ,7a R )-3-hydroxymethyl-5-methyl-1,2,7-trihydroxypyrrolizidine, respectively, or the corresponding enantiomers. The inhibitory activities of these new hyacinthacines against a variety of glycosidases are described.

Four new antibiotics, TMC-171A (2), B (3), C (4) and TMC-154 (5) have been isolated from the fermentation of fungal strains Gliocladium sp. TC 1304 and TC 1282, respectively. Spectroscopic and degradation studies have shown that TMC-171s and TMC-154 were new members of the TMC-151 class of antibiotics, unique polyketides modified with a D-mannose and a D-mannitol or a D-arabitol. These compounds showed moderate cytotoxicity to various tumor cell lines.

The regioselectivity of the cyclization reaction of 2-ethynylbenzyl alcohol and 2-ethynylbenzylamine derivatives promoted by TBAF was investigated. Six-membered ring derivatives were obtained from the compounds, which have a butyl group on the triple bond. Whereas five-membered ring products were afforded from the substrates having hydrogen or aromatic substituents on the acetylene moiety. It was also concluded that both the tetrabutylammonium cation and fluoride anion were essential for the cyclization. Thus, the actual mechanism and catalytic cycle were also suggested.

An all-inorganic complex, [Mn2{(VO3)5}2]6– (1), was synthesized, and the structure determination reveals a dinuclear manganese complex coordinated by two cyclic pentavanadate ligands. The cyclic pentavanadate units sandwich the edge-sharing octahedral dimanganese core through coordination of the oxido group of the pentavanadate. A dinuclear cobalt complex with a cyclic decavanadate, [Co2(OH2)2(VO3)10]6– (2), was also synthesized. The structure analysis reveals a dinuclear cobalt complex with a macrocyclic decavanadate, which is composed of 10 VO4 units joined by the vertex sharings. The CoO6 octahedrons are edge-shared, with each cobalt octahedron coordinated to five oxido groups from the decavanadate. The remaining site is occupied by water. The coordinated water molecules are supported with hydrogen bonds in two directions. Complex 2 in acetonitrile shows no reactivity with dioxygen even at low temperature, and the cyclic voltammogram of 2 shows no redox chemistry in acetonitrile. Complex 2 exhibits chromism by water exposure both in the solid state and in acetonitrile. Complex 2 is green–yellow in color, and the addition of water causes the complex to turn brown. After heating the sample, it returns to its original color in a reversible manner. The EXAFS data in acetonitrile is also reported and is consistent with the solid-state structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

We report herein that the conjugate reduction of α,β-unsaturated esters and amides, such as aryl acrylates, pantolactone esters of acrylic acids, diethyl itaconate and N-crotonylcamphorsultam, with tributyltin hydride proceeded in moderate to high yields in the presence of magnesium bromide diethyl etherate. The effect of metal halide enhancing the yields is also described.

Asymmetric bolaamphiphilic sugar-based hydrogelators ( 1 – 3 ) were synthesized and their gelation ability with and without alkylammonium ions was investigated by CD, TEM, FTIR and NMR. These compounds acted as versatile gelators for organic solvents and water. The xerogels 1 – 3 obtained from water showed well-developed structures of fibrils with diameters of 10–38 nm and length of several hundred micrometers. Particularly, the gelation ability of crown-appended gelator 1 was drastically enhanced by addition of alkylammonium ions 4 and 5 , suggesting that the bridging effect of alkyldiammonium ions could be the primary driving-force for the stabilization due to the intermolecular hydrogen bonding and electrostatic interactions. The present result is a rare case of a hydrogel being stabilized by a host–guest interaction. In addition, the hydrogel 1 with AgNO 3 and KClO 4 induced the formation of nanotubular and vesicular structures of silica by sol–gel polymerization of TEOS, respectively. These results indicate that hydrogel 1 acted as a template to produce inorganic nanomaterials.

Inspired by the considerable difference of catalytic activity and stereocontrolling ability between the conformationally rigid, homo- and heterochiral quaternary ammonium bromides 1, conformationally flexible, N-spiro chiral quaternary ammonium bromides of type 4 have been designed and synthesized. Reliable procedures for the preparation of the appropriately substituted biphenyl subunits have been established by the repeated use of ortho magnesiation–halogenation as a key synthetic tool. The relationship between the structure of achiral biphenyl moiety and the reactivity and selectivity of 4 has been evaluated in the asymmetric alkylation of glycinate Schiff base 2 under typical phase-transfer conditions, leading to the identification of 4l as an optimal catalyst structure to exhibit an excellent enantiocontrol in the reactions with various alkyl halides. The molecular structure of 4l was determined by X-ray crystallographic analysis and its unique behavior in solution was examined by a variable-temperature 1H NMR study. These investigations uncovered that the observed high chiral efficiency originated from the efficient asymmetric phase-transfer catalysis of homochiral-4l, which rapidly equilibrated with heterochiral-4l of low catalytic activity and stereoselectivity.

N‐Hydroxyphthalimide derivatives are readily obtained in good yields by the reaction of phthalic anhydrides with hydroxylamine hydrochloride in the presence of pyridine under microwave irradiation.

A highly efficient direct asymmetric aldol reaction of a glycinate Schiff base with aldehydes has been achieved under mild organic/aqueous biphasic conditions with excellent stereochemical control, using chiral quaternary ammonium salt 1b as a phase-transfer catalyst. The initially developed reaction conditions, using 2 equiv of aqueous base (1% NaOH (aq)), exhibited inexplicably limited general applicability in terms of aldehyde acceptors. The mechanistic investigation revealed the intervention of an unfavorable yet inevitable retro aldol process involving the chiral catalyst. On the basis of this information, a reliable procedure has been established by use of a catalytic amount of 1% NaOH (aq) and ammonium chloride, which tolerates a wide range of aldehydes to afford the corresponding anti-beta-hydroxy-alpha-amino esters almost exclusively in an essentially optically pure form.

The conjugate reduction of aryl acrylates performed with tributyltin hydride in the presence of magnesium bromide diethyl etherate in dichloromethane gave the corresponding saturated esters in moderate to high yields. The reduction of α-methylene-γ-benzyloxycarboxylic acid esters proceeded syn -selectively, but α-methylene-β-oxycarboxylic acid esters afforded reductive elimination products under the reaction conditions.

A series of C2-symmetric chiral quaternary ammonium bromides 10 and 11 have been designed as a new, purely synthetic chiral phase-transfer catalyst, and readily prepared from commercially available optically pure 1,1‘-bi-2-naphthol as a basic chiral unit. The details of the synthetic procedures of each requisite chiral binaphthyl subunit have been disclosed, and the structures of the assembled N-spiro chiral quaternary ammonium bromides 11a and 11f were unequivocally determined by single-crystal X-ray diffraction analysis. The reactivity and selectivity of these chiral ammonium bromides as chiral phase-transfer catalysts have been evaluated in the asymmetric alkylation of the benzophenone Schiff base of glycine ester 7 under mild liquid−liquid phase-transfer conditions, and the optimization of the reaction variables (solvent, base, and temperature) has also been conducted. Further, the scope and limitations of this asymmetric alkylation have been thoroughly investigated with a variety of alkyl halides, in...

Remarkable contrast between chemospecificities in acid-mediated arylation of δ- and γ-ketocarboxylic acids was revealed: in the presence of P2O5–MsOH, TfOH, PPA, and MsOH, arylation of δ-ketocarboxylic acid 1A with arenes takes place at the carboxycarbonyl carbon, while that of γ-ketocarboxylic acid 1B takes place at the ketone carbonyl carbon, specifically.

Facile asymmetric synthesis of l -Dopa and related amino acid esters has been achieved by phase-transfer catalysis of the rationally designed C2-symmetric chiral quaternary ammonium salts 1. The ‘scale-up’ experiment performed with 5.00 g of tert-butyl glycinate-benzophenone Schiff base (2) represents the practical aspect of our approach.