Sialyl Lewis x and derivatives have been synthesized using £-1,4-galactosyltransferase and recombinant a-2,3sialyltransferase and a-l,3-fucosyltransferase. The enzymatic glycosylations have been achieved on preparative scales with in situ regeneration of UDP-galactose, CMP-7V-acetylneuraminic acid, and GDP-fucose. Additionally, galactosyltransferase and fucosyltransferases have been studied with respect to their substrate specificity and inhibition. The enzymatic procedures have also been used in the synthesis of 2'-deoxy-LacNAc, 2'-amino-2'-deoxy-LacNAc, 2-azido-Lac, Lewis x, the Lewis x analog with GlcNAc replaced with 5-thioglucose, [Gal-l-13C]-LacNAc, [Gal-1 -13C]-sialyl Lewis x, and the corresponding terminal glycal. The synthesized 13C-labeled sialyl Lewis x and intermediates (including Lewis x and sialyl LacNAc) were used for conformational study using NMR techniques combined with calculations based on GESA and MM2 programs. GESA calculation of sialyl Lewis x gave four minimum-energy conformers, and the two (A and B) consistent with NMR results were further refined with MM2 calculation. The one (A') with lower energy was picked as the preferred conformer which had all intemuclear distances and glycosidic torsional angles consistent with the NMR analysis. The glycosidic torsional angle \p of Gal-GlcNAc, for example, was determined to be 18°on the basis of the coupling between Gal-l-13C and GlcNAc, while the predicted value was 15°. The tetrasaccharide appears to form a well-defined hydrophilic surface along NeuAc-Gal-Fuc, and a hydrophobic face underneath NeuAc-Gal-GlcNAc. Comparing the conformation of sialyl Lewis x to sialyl Lewis a indicates that the recognition domain of sialyl Lewis x mainly comes from the sialic acid-galactose-fucose residues.

Facile deprotonation of a number of cationic ruthenium vinylidene complexes, followed by cyclopropenation, is accomplished in acetone. The deprotonation of [Ru]dCd(Ph)CH 2 R + , ([Ru] ) (η 5 -C 5 H 5 )(PPh 3 ) 2 Ru) by n-Bu 4 -NOH induces a novel cyclization reaction and yields the neutral cyclopropenyl complexes [Ru]-CdC(Ph)CHR (3b, R ) CN; 3c, R ) Ph; 3d, R ) CHdCH 2 ; 3e, R ) CHdCMe 2 ). Complex [Ru]-CdC(C 6 H 9 )CHCN + (3k) is similarly prepared. Protonation of 3b-3e regenerates the corresponding vinylidene complexes. Deprotonation of [Ru]dCdC(Ph)CH 2 COOMe + (2h) by n-Bu 4 NOH induces a different type of cyclization and yields the neutral furan complex [Ru]-CdC(Ph)CHdC(O)OMe (4h). The cyclopropenyl complex containing a methoxy substituent cannot be prepared from [Ru]dCdC(Ph)CH 2 OCH 3 + (2i), but Fof n-Bu 4 NF attacks the CR of 2i to produce the unstable vinyl complex [Ru]C(F)dC(Ph)CH 2 OCH 3 (5). Complex [Ru]-CdC(Ph)C(CN)OCH 3 (9b) was indirectly prepared from the addition of TCNQ to 3b, giving [Ru]dCdC(Ph)CH(CN)TCNQ (6b) followed by methanolysis. Unlike 3, complex 9b is not converted to vinylidene complex, instead, removal of the methoxy substituent by acid gives theis similarly prepared from 4h via a TCNQ complex 6h followed by a methoxy-substituted complex 9h. In the presence of allyl iodide, opening of the three-membered ring of 3b, followed by a subsequent oxidative coupling reaction, gives a dimeric dicationic product {[Ru]dCdC(Ph)-CHCN} 2 2+ (11). Proton abstraction of 11 by n-Bu 4 -NF gives the biscyclopropenyl complex {[Ru]-CdC(Ph)CCN} 2 (12). Molecular structures of complexes 3b, 3f, 4h, 6b, 9b, and 11 have been confirmed by X-ray diffraction analysis.

No abstract

No abstract

The acid and transport properties of the anhydrous Keggin-type 12-tungstophosphoric acid (H(3)PW(12)O(40); HPW) have been studied by solid-state (31)P magic-angle spinning NMR of absorbed trimethylphosphine oxide (TMPO) in conjunction with DFT calculations. Accordingly, (31)P NMR resonances arising from various protonated complexes, such as TMPOH(+) and (TMPO)(2)H(+) adducts, could be unambiguously identified. It was found that thermal pretreatment of the sample at elevated temperatures (≥423 K) is a prerequisite for ensuring complete penetration of the TMPO guest probe molecule into HPW particles. Transport of the TMPO absorbate into the matrix of the HPW adsorbent was found to invoke a desorption/absorption process associated with the (TMPO)(2)H(+) adducts. Consequently, three types of protonic acid sites with distinct superacid strengths, which correspond to (31)P chemical shifts of 92.1, 89.4, and 87.7 ppm, were observed for HPW samples loaded with less than three molecules of TMPO per Keggin unit. Together with detailed DFT calculations, these results support the scenario that the TMPOH(+) complexes are associated with protons located at three different terminal oxygen (O(d)) sites of the PW(12)O(40)(3-) polyanions. Upon increasing the TMPO loading to >3.0 molecules per Keggin unit, abrupt decreases in acid strength and the corresponding structural variations were attributed to the change in secondary structure of the pseudoliquid phase of HPW in the presence of excessive guest absorbate.

Facile ligand substitution is observed when the ruthenium azido complex (PPh 3 )[Ru]-N 3 (1; [Ru] ) Tp(PPh 3 )Ru) is treated with CH 3 CN, yielding the nitrile-substituted ruthenium azido complex (CH 3 CN)[Ru]-N 3 (2). Alkylation, [3 + 2] cycloaddition, and catalytic reactions of complex 2 have been investigated. In the case of [3 + 2] cycloaddition reactions, the metal-bound heterocyclic complexes (CH 3 CN)[Ru]-N 3 C 2 (CO 2 Me) 2 (3a), (CH 3 CN)[Ru]-N 3 C 2 HCO 2 Me (5), and (CH 3 CN)[Ru]-N 3 C 2 HCN (6) are obtained from dimethyl acetylenedicarboxylate, methyl propiolate, and fumaronitrile, respectively. The tetrazolato complex 8) is prepared from 2 and TCNE. Alkylation of 3a with organic bromides affords N-alkylated five-membered-ring organic triazoles. The reaction of CS 2 with 2 produces the thermally unstable thiothiatriazolate (CH 3 CN)[Ru]-N 3 CS(S) (10), which decomposes to the isothiocyanate (CH 3 CN)[Ru]-NCS (11). On the other hand, several cationic imine complexes {(CH 3 CN)[Ru]-(NHdCHR)} + (12a, R ) H; 12b, R ) CH 3 ; 12c, R ) HCdCH 2 ) are formed by the reaction of RCH 2 X with the negatively charged nitrogen atom of the azido ligand on Ru II . The reaction proceeds via formation of an alkylimido intermediate followed by N 2 evolution and proton transfer from the alkyl group to the imido nitrogen atom. Preliminary results on the catalytic activity of 2 are also presented. Interestingly, complex 2 catalyzes the dimerization of some terminal alkynes HCtCR in organic and aqueous medium. Whereas with R ) Ph, SiMe 3 , t-Bu isomeric mixtures of head-to-head and head-to-tail coupling products are obtained, in the case of R ) COOMe, E-selective head-to-head dimerization takes place exclusively. The structures of 1, 8, and 12c have been determined by X-ray diffraction analysis.

No abstract

Three homochiral metal-tryptophanate frameworks, {[Zn2(l-trp)2­(bpe)2(H2O)2]­·2H2O·2NO3} n (1a, l-Htrp = l-tryptophan, bpe = 1,2-bis­(4-pyridyl)­ethylene), {[Co(l-trp)­(bpe)(H2O)]­·H2O·NO3} n (1b), and {[Co(l-trp)­(bpa)(H2O)]­·H2O·NO3} n (2, bpa = 1,2-bis­(4-pyridyl)­ethane), were constructed from Zn2+ or Co2+ ions, bipyridyl ligands, and the amino acid l-tryptophan (l-Htrp), respectively. Compounds 1a, 1b, and 2 were characterized by single-crystal X-ray diffraction analysis. All of the compounds crystallize in the monoclinic space group P21 and form homochiral two-dimensional (2D) layers with rectangle-like (4,4) topologies. Anion-controlled dielectric, luminescence, and nonlinear-optic (NLO) properties were measured for these chiral metal–organic frameworks (MOFs) in the solid state. Emission spectra confirmed that compound 1a exhibited a green emission at 546 nm. Dielectric studies of 1a revealed that it had very low dielectric constant (κ = 2.53 at 1 MHz), thus verifying that it is a promising candidate for interlayer dielectrics. The anion-controlled dielectric properties of 1a were observed after treatment with solutions of different anions. The results revealed a significant change in κ value in the case of the phosphate anion. Secondary harmonic generation (SHG) studies revealed that 1a had a good SHG intensity response that was about twice that of SiO2.