No abstract

4-[(3′-Carbohydroxypropyl)thio]-5-(methylthio)tetrathiafulvalene was synthesized and used as a mediator for the oxidation of glucose oxidase both free in solution and after covalent attachment to the enzyme through carbodiimide coupling to amine residues in the protein. The modified enzyme was characterized by isoelectric focusing gel electrophoresis and found to have a higher pI than the native enzyme. Electrochemical studies show that the singly oxidized tetrathiafulvalene derivative attached to the enzyme can act as a mediator for the direct reoxidation of the enzyme at electrode surfaces, whereas the doubly oxidized dication is not a mediator. Similar results are found for mediation by the tetrathiafulvalene derivative in solution. The application of the modified enzyme in membrane enzyme electrodes was investigated, and the response were analyzed to give kinetic information about the modified enzyme kinetics. Our studies show that the modified enzyme has good stability on storage in the absence of glucose but is less stable during continuous operation in a glucose sensor. This appears to arise from reactions between the tetrathiafulvanene groups attached to the modified enzyme and traces of hydrogen peroxide generated by the enzymatic reaction of glucose with oxygen present in the solution.

No abstract

The oxime ethers 2a-e have been cyclised with Bu,SnH to the alkoxyamino-3-methylidenechromanes 3a-e. Seven-membered ring formation was observed when the oxime ethers 7a. b were converted into the dibenzo[b,e]oxepines 8a. b under similar conditions. 1 -Methoxyaminoindanes 12a. b were produced from the cyclisation of the substrates I l a , b and the cis-fused cyclic products 15a, b and 18 were obtained from compounds 14a. b and 17, respectively.The construction of carbocyclic rings using intramolecular radical cyclisation has become a common strategy in organic synthesis. The first example of the intramolecular trapping of a radical by an oxime ether was reported by Corey and Pyne in 1983.2 The particular advantage of using an oxime ether seems to ! i F in the extra stability of the alkoxy aminyl radicalPaper 410289 1 K

No abstract