New, ionic side-products in oligonucleotide synthesis: formation and reactivity of fluorescent N-/purin-6-yl/pyridinium salts¹

Abstract

Fluorescent N-/purin-6-yl/pyridinium salts are formed in pyridine assisted phosphorylations and arenesulphonations of the hypoxanthine lactam system under various conditions including those used in oligonucleotide synthesis. The N1-methyl-N3-/purin-6-yl/imidazolium salt is generated in phosphorylation with TPSCl/1-methylimidazole as a coupling system. Both salts are representatives of a new family of ionic side-products in oligonucleotide synthesis involving hypoxanthine residues. Their isolation procedure has been developed. High reactivity of N-/purin-6-yl/pyridinium salts towards some reagents used in oligonucleotide chemistry, e.g. pyridinium mediated conversion of hypoxanthine into 6-aminopurine, can result in point mutations in synthesized oligomer.