SYNTHESIS OF A THYMIDYL PENTAMER OF DEOXYRIBONUCLEIC GUANIDINE AND BINDING-STUDIES WITH DNA HOMOPOLYNUCLEOTIDES

Replacement of the phosphodiester linkages of the polyanion DNA with guanidine linker's provides the polycation deoxynucleic guanidine (DNG). The synthesis of pentameric thymidyl DNG is provided. This polycationic DNG species binds with unprecedented affinity and with base-pair specificity to negatively charged poly(dA) to provide both double and triple helices. The dramatic stability of these hybrid structures is shown by their denaturation temperatures (T-m). For example, the double helix of the pentameric thymidyl DNG and poly(dA) does not dissociate in boiling water (ionic strength = 0.12), whereas the T-m for pentameric thymidyl DNA associated with poly(dA) is approximate to 13 degrees C (ionic strength = 0.12). The effect of ionic strength on T-m for DNG complexes with DNA shows an opposite correlation compared with double-stranded DNA and is much more dramatic than for double-stranded DNA.