Hirohito Tsue

Cationic diazacrown ether for the separation of positional isomers by capillary electrophoresis

The use of a positively charged diazacrown ether, N,N,N,N-tetramethyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane dichloride (1), in capillary electrophoresis is reported, for the first time. The addition of the cationic diazacrown 1 to the running buffer permitted the successful separation of positional isomers of aromatic anions such as naphthalenedisulfonate, naphthalenedicarboxylate and phthalate. At a concentration of 1 of 2 mM, all the analyte anions were completely separated in less than 5 min. The ion association constants of the solute anions with diazacrown 1 were evaluated and the findings are discussed.

Effect of fluorine substitution of α-and β-hydrogen atoms in ethyl phenylacetate and phenylpropionate on their stereoselective hydrolysis by cultured cancer cells

Abstract ( ±) -Ethyl 2-fluoro-2-phenylacetate was stereoselectively hydrolyzed by cultured cells of several rat cancer cell lines to give the carboxylic acid rich in the R enantiomer. The stereoselectivity increased for ( ±)-ethyl 2-fluoro-2-phenylpropionate ( 2b ) with all present cell lines and for ( ±)-ethyl 2-phenyl-3,3,3-trifluoropropionate (3b) with rat hepatoma McA-RH7777 cell line. The stereoselectivity was different for the different cell lines, as McA-RH7777 cells preferred ( R ) - 2b in contrast with the preference towards ( S ) - 2b by other cells such as ras oncogenetransformed rat liver Anr4 cells. These stereoselectivities were different from those for non-fluorinated ( ±)-ethyl 2-phenylpropionate. Thus fluorine atoms are recognized by ester hydrolases of cancer cells, and fluorine substitution on the acyl group will be useful for making estertype anticancer prodrugs more specific to cancer cells.

Unexpected racemization behavior of 8,8′-dialkyl-1,1′-biisoquinoline

Abstract The racemization behavior of a series of atropisomeric 8,8′-dialkyl-1,1′-biisoquinolines, in which methyl, ethyl, and isopropyl groups are introduced for enhancing the transannular steric hindrance, is reported. Contrary to prior expectations, their configurational stability was inversely proportional to the steric size of the alkyl groups.

ipso-Substitution Reaction in the Convergent Stepwise Synthesis of Calix[8]arene with Regioselectively Functionalized Upper Rim

The acid-catalyzed multi-step synthesis of calix[8]arene 1, which contains a regioselectively functionalized upper rim, has been investigated through the careful separation of the resulting by-products. A total of 11 types of cyclic and acyclic by-products were isolated and identified by spectral and microanalytical data. Semiempirical molecular-orbital calculations demonstrated that the synthetic process involves two types of reaction mechanism, one of which leads to the favorably constructed framework, while the other results in undesirable fragmentation reactions via ipso-substitution. A comparison of the theoretical predictions and the observed by-products revealed that steric hindrance, as well as the regioselectivity of the reaction, is also an important factor for determining the reaction pathway. A possible rationale is presented to explain the overall formation process leading to calix[8]arene 1 along with the by-products.

Cationic diazacrown ethers as selectors for the separation of inorganic anions by capillary electrophoresis

Two types of positively charged diazacrown ether derivatives involving two quaternary ammonium ions in the 12- and 18-membered rings have been investigated as selectors for the separation of inorganic anions by capillary electrophoresis. Both the cationic macrocycles largely affected the electrophoretic mobilities of analyte anions, and a group of seven inorganic anions examined in this study was completely separated in less than 2.2 min by the use of the low concentration of the additives. From the determination of ion association constants, the cationic diazacrowns were found to show greater electrostatic interaction with divalent anions than with monovalent ones.

8,8′-Dialkyl-1,1′-biisoquinolines: preparation, absolute configuration and unexpected racemization behaviour†

A series of 8,8′-dialkyl-1,1′-biisoquinolines, in which methyl, ethyl and isopropyl groups are introduced for enhancing the transannular steric hindrance, are synthesized. The atropisomeric biisoquinolines are separated into both enantiomers, of which the absolute configurations and the optical stabilities are determined. Contrary to prior expectations, the racemization behaviour is inversely proportional to the steric size of the alkyl groups.