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

Summary 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⁺>Zn²⁺>Co²⁺, Mn²⁺>Cd²⁺>Cu²⁺>Ni²⁺>Ca²⁺, Mg²⁺, none >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.Abbreviations. EDTA, ethylenediaminetetraacetic acid; Versenol,N-hydroxyethylethylenediaminetriacetic acid; Tris, tris-(hydroxymethyl)aminomethane; pN (N is A, C, G, U, I, 3-dA, 2-dA, AraA, Aris, or Nep), nucleoside-5-phosphate; Np, nucleoside-2(3)-phosphate; I, inosine; 3-dA, 3-deoxyadenosine; 2-dA, 2-deoxyadenosine; AraA, arabinosyladenine; Aris, aristeromycin; Nep, neplanocin A; ImpN, nucleoside-5-phosphorimidazolide; NppN, P₁,P₂-dinucleoside-5,5-pyrophosphate; (pN)_n (n=2, 3, ...), oligomers of pN, numbers given between a nucleoside and a phosphate indicate the type of internucleotide linkage, e.g., pC₂ p₅C is 5-phosphorylcytidyl-(2–5)-cytidine;, cyclic dimers of pN; BAP, bacterial alkaline phosphatase; N.Pl, nuclease Pl; VPDase, venom phosphodiesterase; HPLC, high pressure liquid chromatography