Highly efficient cleavage of the single-stranded oligonucleotide 5'-d(CTGGCTCACAAATACCACTGAGATCTTTTTC)-3' (O1) at nucleotides G20, A21, and G22 was achieved by an iron-bipyridine complex linked to a targeting oligonucleotide 5'-d(AAA AAG ATC T*CA)-3' (O2) through -SCH2CH2NHC(O)- at C5 of a 2'-deoxyuridine (T*). Copyright (C) 1996 Elsevier Science Ltd