Reductive Electron Transfer in Phenothiazine-Modified DNA Is Dependent on the Base Sequence

摘要

A new DNA assay has been designed,prepared and applied for the chemical investigation of reductive electron transfer through the DNA.It consists of 5-(10-methyl-phenothiazin-3-yl)-2'-deoxyuridine (Ptz-dU,1) as the photoexcitable electron injector and 5-bromo-2'-deoxyuridine (Br-dU) as the electron trap.The Ptz-dU-modified oli-gonucleotides were synthesised by means of a Suzuki-Miyaura cross-coupling protocol and subsequent automated phosphoramidite chemistry.Br-dU represents a kinetic electron trap,since it undergoes a chemical modification after its one-electron reduction that can be analysed by piperidine-in-duced strand cleavage.The quantification of the strand cleavage yields from irradiation experiments reveals important information about the electron-transfer efficiency.The performed DNA studies focused on the base sequence dependence of the electron-transfer efficiency with respect to the proposal that C~(centre dot -) and T~(centre dot-) act as intermediate electron carriers during electron hopping.From our observations it became evident that excess-electron transfer is highly sequence dependent and occurs more efficiently over T-A base pairs than over C-G base pairs.