Cascade‐ and Orthoamide‐Type Overman Rearrangements of Allylic Vicinal Diols

This article describes the details of two new types of Overman rearrangement from allylic vicinal diols. Starting from identical diols, both bis(imidate)s and cyclic orthoamides were selectively synthesized by simply changing the reaction conditions. Whilst exposure of the bis(imidate)s to thermal conditions initiated the double Overman rearrangement to introduce two identical nitrogen groups in a single operation (the cascade‐type Overman rearrangement), the reaction of cyclic orthoamides resulted in a single rearrangement (the orthoamide‐type Overman rearrangement). The newly generated allylic alcohols from the orthoamide‐type reaction can potentially undergo a variety of further transformations. For instance, we demonstrated an Overman/Claisen sequence in one pot. The most conspicuous feature of this method is that it offers precise control over the number of Overman rearrangements from the same allylic vicinal diols. This method also excludes the tedious protecting‐group manipulations of the homoallylic alcohols, which are necessary in conventional Overman rearrangements. All of the performed rearrangements proceeded in a completely diastereoselective fashion through a chair‐like transition state.     

Selective and Nonselective Cleavages in Positive and Negative CID of the Fragments Generated from In-Source Decay of Intact Proteins in MALDI-MS

Selective and nonselective cleavages in ion trap low-energy collision-induced dissociation (CID) experiments of the fragments generated from in-source decay (ISD) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) of intact proteins are described in both positive and negative ion modes. The MALDI-ISD spectra of the proteins demonstrate common, discontinuous, abundant c- and z′-ions originating from cleavage at the N–Cα bond of Xxx-Asp/Asn and Gly-Xxx residues in both positive- and negative-ion modes. The positive ion CID of the c- and z′-ions resulted in product ions originating from selective cleavage at Asp-Xxx, Glu-Xxx and Cys-Xxx residues. Nonselective cleavage product ions rationalized by the mechanism of a “mobile proton” are also observed in positive ion CID spectra. Negative ion CID of the ISD fragments results in complex product ions accompanied by the loss of neutrals from b-, c-, and y-ions. The most characteristic feature of negative ion CID is selective cleavage of the peptide bonds of acidic residues, Xxx-Asp/Glu/Cys. A definite influence of α-helix on the CID product ions was not obtained. However, the results from positive ion and negative ion CID of the MALDI-ISD fragments that may have long α-helical domains suggest that acidic residues in helix-free regions tend to degrade more than those in helical regions.

Electrochemical enzyme immunoassay using immobilized antibody on gold film with monitoring of surface plasmon resonance signal

Sandwich immunoassay was conducted on a thin gold film set in a surface plasmon resonance (SPR) cell. Monochronal antibody (anti-IgG) was immobilized onto the gold film via 4,4′-dithiodibutyric acid (DDA) and avidin-biotin bonding. Next, IgG sample and alkaline phosphatase-conjugated anti-IgG (ALP anti-IgG) were introduced into the cell successively. Finally, p-aminophenyl phosphate (PAPP) was injected as an enzyme substrate, and the produced p-aminophenol (PAP) was electrochemically measured. Flow did not need to be stopped for incubation for the enzyme reaction, because of the thinness of the cell. In these processes, all the antigen-antibody reactions took place on the gold film. Therefore, the immobilization was performed quickly, and each process could be confirmed by SPR signal. This system had the advantage that the middle of the complicated process could be monitored. For example, the amount of antibody immobilized, which affected on the final electrochemical signal, could be confirmed in the course of immobilization. It was also convenient to investigate process conditions, such as removal of used antigens and labeled antibodies. Good correlation was obtained between the electrochemical current and the SPR signals due to the adsorption of IgG and ALP anti-IgG, and the sensitivity of the electrochemical measurement was much higher than the SPR’s.     

Reaction of carbonyl compounds with xenon difluoride in the presence of silicon tetrafluoride

Reaction of various carbonyl compounds with xenon difluoride in the presence of silicon tetrafluoride was investigated. Aromatic aldehyde, ketones, and α-ketoester react with xenon difluoride to give α,α-difluoroalkyl phenyl ethers. However, acid fluoride, ester, acid cyanide, α-ketocarboxylic acid, or thioester do not afford the corresponding products. In the case of cinnamaldehyde, fluorination was accompanied by intramolecular cyclization to afford fluorinated epoxide.     

Defluorination of homologous chlorofluoroethers to chlorofluoroacetates

The research was focused on the defluorination of chlorofluoroethers to corresponding esters using porous aluminum fluoride (PAF) or MF_n/PAF. In the work up process, the product was easily separated from the reagent. Thus, the reaction would be a practical preparation method for polyfluorinated esters. Trifluoromethyl chlorodifluoroacetate was obtained by the reaction of 1,2-dichlorotrifluoroethyltrifluoromethyl ether with fuming sulfuric acid in 49% yield.     

C?H bond dissociation enthalpies of fluorinated formates and estimation of their rate constants for the reactions with OH radicals: A DFT study

Density functional theory was used to estimate the lifetime of fluorinated formates, which are primary products from the oxidation of hydrofluoroethers. First, the C? H bond dissociation enthalpies (BDEs) of 10 fluorinated formates, C_nF_{2n + 1}OC(O)H (n = 1–4) and C_nHF_2nOC(O)H (n = 1–3) have been calculated by using the density functional theory with (RO)B3LYP/6‐311G(d,p). Secondly, from these computed BDEs, the rate constants k_OH of the hydrogen abstraction reaction between the fluorinated formates and OH radicals have been estimated using the formulation proposed by Heicklen (Int. J. Chem. Kinet. 13 , 651, 1981). We modified the formulation proposed by Heicklen in order to relate BDEs to k_OH for formates based on the results of the ab initio studies using standard transition state theory with the G2(MP2) level. Consequently, the k_OH of all the formates considered here are estimated to be around 1.5–4.7 × 10^?14 cm³ molecule^?1 s^?1 at 298 K. Their lifetimes concerning with the decomposition by OH radicals (τ_OH) in atmosphere have been evaluated as 0.4–4.5 years from the estimated k_OH. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 524–530, 2002     

Coordination structures of the silver ion: infrared photodissociation spectroscopy of Ag(+)(NH(3))(n) (n = 3-8)

Infrared (IR) spectra are measured for Ag(+)(NH(3))(n) with n = 3-8 in the NH-stretch region using photodissociation spectroscopy. The spectra of n = 3 and 4 exhibit absorption features only near the frequencies of the isolated NH(3), indicating that every NH(3) molecule is coordinated individually to Ag(+). For n >or= 5, the occupation of the second shell is evidenced by lower-frequency features characteristic of hydrogen bonding between NH(3) molecules. Density functional theory and MP2 calculations are carried out in support of the experiments. A detailed comparison of the experimental and theoretical IR spectra reveals the preference for a tetrahedral coordination in the n = 5 and 6 ions. Likewise, most of the features observed in the spectra of n = 7 and 8 can be assigned to isomers containing a tetrahedrally coordinated inner shell as the basic structural motif. These results signify that the ammonia-solvated Ag(+) ion has a propensity toward a coordination number of four and the resulting tetrahedral Ag(+)(NH(3))(4) complex forms the central core of further solvation process.     

Site-Selective Synthesis and Concurrent Immobilization of Imine-Based Covalent Organic Frameworks on Electrodes Using an Electrogenerated Acid

Imine-based covalent organic frameworks (COFs) are crystalline porous materials with prospective uses in various devices. However, general bulk synthetic methods usually produce COFs as powders that are insoluble in most of the common organic solvents, arising challenges for the subsequent molding and fixing of these materials on substrates. Here, we report a novel synthetic methodology that utilizes an electrogenerated acid (EGA), which is produced at an electrode surface by electrochemical oxidation of a suitable precursor, acting as an effective Brønsted acid catalyst for imine bond formation from the corresponding amine and aldehyde monomers. Simultaneously, it provides the corresponding COF film deposited on the electrode surface. The COF structures obtained with this method exhibited high crystallinities and porosities, and the film thickness could be controlled. Furthermore, such process was applied for the synthesis of various imine-based COFs, including a three-dimensional (3D) COF structure.     

Improved stability of Opalmon tablets under humid conditions IV: effect of polysaccharides and disintegrants on the stability and dissolution property of Opalmon tablets

We studied the effects of dextran, dextrin, and disintegrants on the chemical stability of Opalmon tablets containing Limaprost-alfadex (Limaprost/alpha-cyclodextrin complex) and found that the addition of dextran or dextrin significantly improved the chemical stability of Opalmon tablets under high humidity, compared to lactose. We also examined how dextran stabilizes Limaprost in Opalmon tablets and studied the formulation of Opalmon tablets in order to achieve higher chemical stability, rapid dissolution and reduced stickiness. The results suggested that dextran increases stabilization after moisture adsorption by decreasing the dissociation of Limaprost-alfadex to the free drug and alpha-cyclodextrin in the dextran matrix, when compared with the lactose matrix. The stickiness of Opalmon tablets containing dextran and dextrin was negligible when dextran and dextrin amounted to less than 20% of the formulation. By selecting a proper disintegrant, we obtained Opalmon tablets with higher chemical stability and rapid dissolution properties.