Reaction mechanism in the photochemistry of the antileukaemic agents 2-chloro-and 2-bromo-2 min-deoxyadenosine, studied by nanosecond laser flash photolysis

摘要

The reaction mechanism in the UV photochemistry of 2-chloro-2 min-deoxyadenosine (Cladibrine) and 2-bromo-2 min-deoxyadenosine in aqueous solution has been studied by laser photolysis at nanosecond time resolution. It is found that excitation at 266 nm wavelength produces heterolytic cleavage of the halogen-carbon bond by one-photon absorption and formation of the unstable 2-hydroxy tautomer of 2 min-deoxy-isoguanosine as predominant `primary' product. The 2-hydroxy tautomer then transforms in 10~(-6)-10~(-5) s into the stable 2-oxo tautomer in an acid-base-catalysed reaction. A reaction mechanism is proposed and discussed in relation to previous UV low-intensity studies of these halogenodeoxyadenosines.