Preparation of psoralen-derivatized oligodeoxyribonucleoside methylphosphonates

This chapter describes the preparation of 4'-{[N-(aminoethyl)amino]methyl}-4,5',8-trimethylpsoralen [(ae)AMT]-derivatized oligodeoxyribonucleoside methylphosphonates and the general procedures for cross-linking the oligomers to complementary nucleic acids. Oligodeoxyribonucleoside methylphosphonates are nonionic nucleic acid analogs, which contain nuclease-resistant methylphosphonate linkages in place of the negatively charged phosphodiester internucleotide bonds found in naturally occurring nucleic acids. Oligonucleoside methylphosphonates form duplex hybrids with complementary nucleic acids via standard Watson–Crick base-pairing interactions. The formation of these hybrids is reversible, and their stability is dependent on the length and base composition of the oligomer. Duplex formation can be rendered irreversible by derivatizing oligonucleoside methylphosphonates with the photoreactive, cross-linking group, (ae)AMT. On irradiation with long-wavelength ultraviolet light, the psoralen functionality undergoes a 2+2 cycloaddition reaction with an appropriately placed pyrimidine residue in the target strand, thus cross-linking the oligomer to its target. Psoralen derivatized oligonucleoside methylphosphonates have been shown to cross-link in a sequence-specific manner to single-stranded DNA and to mRNA in vitro. These oligomers are taken up intact by mammalian cells and have been shown to have light dependent antiviral activity in cultured cells infected with herpes simplex virus type-1.