On-column isomerization of sugars during high-performance liquid chromatography: analysis of the elution profile

Four monosaccharides (glucose, galactose, mannose and fructose) and one disaccharide (maltose) were subjected to high-performance liquid chromatography with UV or refractive index detection. Various profiles such as broad, tailed and splitted peaks were produced, depending on column temperature and eluent flow-rate because these saccharides underwent isomerization. In contrast, -methylglucoside, a non-converting derivative, always produced a sharp peak. By analyzing these profiles kinetic constants of the isomerization were obtained and compared with the literature data.     

Interplay of Theory and Experiment: Reversal of the Torquoselectivity of the Electrocyclic Ring Opening of 3-Acetylcyclobutene by a Lewis Acid

Theoretical predictions, accompanied by firm experimental verification, are presented on the "torquoselectivity" of the thermal ring opening of 3-acetylcyclobutene (1). 3-Acetylcyclobutene was synthesized from commercially available 1,1-cyclobutanedicarboxylic acid. Thermolysis of 3-acetylcyclobutene resulted in a mixture of E- and Z-dienes with a slight preference for the E-diene. This preference was reversed by the Lewis acid, ZnI(2), as predicted from theoretical calculations.     

Synthesis of carbon-14 labeled 1-[bis(4-fluorophenyl)methyl]-4-(2,3,4-trimethoxybenzyl)piperazine dihydrochloride (14C-KB-2796)

Benzyl-14C-1-[bis(4-fluorophenyl)methyl]-4-(2,3,4-trimethoxybenzyl) piperazine dihydrochloride (14C-KB-2796), a new cerebral vasodilator, was synthesized in order to investigate the metabolic fate. The synthesis of carboxy-14C-2,3,4-trimethoxybenzoic acid (IV) was accomplished by the reaction of 2,3,4-trimethoxybromobenzene (II) with ter-butyllithium followed by carboxylation with 14C-carbon dioxide generated from 14C-barium carbonate. Formyl-14C-2,3,4-trimethoxybenzaldehyde (VI) was prepared by the reduction of the methyl ester of IV. The free base of 14C-KB-2796 was obtained by the condensation of VI with bis(4-fluorophenyl)methyl-piperazine, and converted to I. An overall radiochemical yield from 14C-barium carbonate was 39%, the specific activity was 1,816.7 MBq/mmol (49.1 mCi/mmol) and its radiochemical purity was 99% in reverse isotope dilution analysis and thin layer chromatographic method.     

Influence of co-solvents in the highly efficient selective monohydrolysis of a symmetric diester

The influence of the co-solvents in the selective monohydrolysis of a symmetric diester, in an aqueous NaOH medium at 0 °C, has been examined. The reactions were found to proceed through reaction media consisting of water with a small amount of a co-solvent and the starting symmetric diester. Slightly polar aprotic solvents that are slightly miscible with water, such as THF and acetonitrile, were found to be effective co-solvents.     

Differentiating alpha- and beta-aspartic acids by electrospray ionization and low-energy tandem mass spectrometry

Spectra obtained by low-energy electrospray ionization tandem mass spectrometry (ESI-MS/MS) of 34 peptides containing aspartic acids at position n were studied and unambiguously differentiated. beta-Aspartic acid yields an internal rearrangement similar to that of the C-terminal rearrangements of protonated and cationized peptides. As a result of this rearrangement, two different ions containing the N- and the C-terminal ends of the original peptide are formed, namely, the bn-1 + H2O and y"l - n + 1 - 46 ions, respectively, where e is the number of amino acid residues in the peptide. The structure suggested for the y"l - n + 1 - 46 ion is identical to that proposed for the vn ions observed upon high-energy collision-induced dissociation (CID) experiments. The intensity of these ions in the low-energy MS/MS spectra is greatly influenced by the presence and position of basic amino acids within the sequences. Peptides with a basic amino acid residue at position n - 1 with respect to the beta-aspartic acid yield very intense bn-1 + H2O ions, while the y"l - n + 1 - 46 ion was observed mostly in tryptic peptides. Comparison between the high- and low-energy MS/MS spectra of several isopeptides suggests that a metastable fragmentation process is the main contributor to this rearrangement, whereas for long peptides (40 AA) CID plays a more important role. We also found that alpha-aspartic acid containing peptides yield the normal immonium ion at 88 Da, while peptides containing beta-aspartic acid yield an ion at m/z 70, and a mechanism to explain this phenomenon is proposed. Derivatizing isopeptides to form quaternary amines, and performing MS/MS on the sodium adducts of isopeptides, both improve the relative intensity of the bn + 1 + H2O ions. Based on the above findings, it was possible to determine the isomerization sites of two aged recombinant growth proteins.     

Substituent Effects on Rates and Stereoselectivities of Conrotatory Electrocyclic Reactions of Cyclobutenes. A Theoretical Study

Substituent effects on the geometries and conrotatory electrocyclic ring openings of cyclobutenes were studied. This work extends the original investigations to many more substituents and provides a comprehensive theory of substituent effects on geometries and reaction rates. The effects of substitution at the 1 position are minimal; donor substituents raise the activation energy slightly, and powerful acceptor substituents slightly lower the activation energy. Substituents on C(3) cause small distortions of the cyclobutene geometry, in the same direction as the favored stereochemistry of reaction. Donors prefer outward rotation, while strong acceptors prefer inward rotation. The activation energy changes and cyclobutene geometrical perturbations were found to correlate with Taft sigma(R)(0) parameters. Amino, hydroxy, fluoro, chloro, methyl, cyano, formyl, and vinyl substituents were studied in the 1 position. Boryl, dimethylboryl, nitroso, formyl, nitro, carboxyl (neutral, protonated, and deprotonated), cyano, trifluoromethyl, sulfoxyl, sulfonyl, sulfinic acid, imino, N-protonated imino, ammonio, ethynyl, methyl, mercapto, chloro, fluoro, hydroxyl, amino, lithium oxy, vinyl, and acetyl were calculated as substituents in the 3 position. Comparisons with experimental results are given when available, and predictions are made in other cases.     

Dicationic (BINAP)palladium-catalyzed enantioselective aldol reaction of aldehydes with a silyl enol ether: a simplified practical procedure

The dicationic ((R)-BINAP)palladium-catalyzed enantioselective aldol reaction of benzaldehyde with 1-phenyl-1-trimethylsilylethene has been reinvestigated regarding the reaction conditions in the presence of ((R)-BINAP)palladium chloride and AgSbF₆ with 3 Å molecular sieves. The simplified practical procedure with 1 mol % catalyst loading realized the high performance of 98% yield and 76% ee with reliable reproducibility.     

Immunoelectrophoresis of red blood cells performed on microcapillary chips

Immunoanalysis of blood cells on a microcapillary electrophoresis (nuCE) chip has been studied using sheep erythrocytes (ShE) as an example. Two different buffer solutions, the phosphate-buffered saline (PBS) and the gelatin veronal buffer (GVB) were examined in regard to the electrokinetic transport behavior of ShE suspended in these solutions inside the rectangular channel engraved on a quartz chip. This clarified two advantages of the use of GVB for on-chip cell electrophoresis: gelatin coatings prevent (i) nonspecific sticking of ShE on the channel wall, and cause (ii) an appreciable reduction in the zeta potential of the wall suppressing the electroosmotic flow of the buffer solution. As a result ShE suspended in the GVB can smoothly migrate from the cathode to the anode, which is the opposite flow direction of immunoglobulin G (IgG) antibodies under the physiological pH condition of 7.4. Based on these results, on-chip capillary cell immunoelectrophoresis of ShE and rabbit anti ShE antibodies (IgG) have been proposed and successfully accomplished using the GVB. It is demonstrated that the variation of the cell migration velocity originating from the change in the surface charge after binding antibodies is applicable to the fast detection of immune reactions and also to single-cell typing.     

Synthesis of 3,3,3-trifluoroprop-1-enyl compounds from some enolizable aldehydes

2,2,2-Trifluoroethyldiphenylphosphine oxide [Ph₂P(O)CH₂CF₃] (2) is known to give no Horner reaction product with enolizable aldehydes. We found, however, that some enolizable aldehydes such as N-Boc-pyrrolidine-2-aldehyde (9) gave the expected 3,3,3-trifluoroprop-1-enyl compounds by reaction with 2. The products could be further transformed to some 2,2,2-trifluoroethyl-substituted nitrogen-containing heterocycles by using radical cyclization or Heck reaction.