Oligonucleotide formation catalyzed by divalent metal ions. The uniqueness of the ribosyl system.

Polymerization of various nucleoside-5'-phosphorimidazolides has been conducted in neutral aqueous solution using divalent metal ions as catalysts. Oligonucleotide formation took place from each of the ribonucleoside-5'-phosphorimidazolides, ImpC, ImpU, ImpA, ImpG, and ImpI. The yields and distributions of the resulting oligonucleotides varied depending on the difference of the nucleic acid base and the metal ions used. The catalytic effect of divalent metal ions on the formation of oligocytidylates occurred in the following order: Pb2+ greater than Zn2+ greater than Co2+, Mn2+ greater than Cd2+ greater than Cu2+ greater than Ni2+ greater than Ca2+, Mg2+, none greater than Hg2+. The order changes slightly for other types of oligoribonucleotide formation. Oligoribonucleotides up to hexamers were obtained in 35-55% overall yield, when Pb2+ ion was used as a catalyst. Zn2+ ions yielded oligoribonucleotides up to tetramers in 10-20% overall yield. The resulting oligonucleotides contained mainly 2'-5' internucleotide linkages. Little or no oligonucleotide was obtained from nucleoside-5'-phosphorimidazolides modified in the sugars, Imp(3'-dA), Imp(2'-dA), Imp(Ara), Imp-(Aris), and Imp(Nep). The results indicate that a ribosyl system is required for the metal ion-catalyzed synthesis of oligonucleotides.