Modification of cytosine nucleotides: preparation and metalation of a furyl derivative

O-Furfurylhydroxylamine (FHA) was synthesized and found to react with cytosine derivatives in the presence of sodium bisulfite. Conversion of cytidine to sodiumN⁴-furfuryloxy-5,6-dihydrocytidine-6-sulfonate by 1 M FHA in aqueous methanolic or ethanolic sodium bisulfite took place with a half-life of 11 min at pH 5 and room temperature. Adenine, guanine, thymine, and uracil derivatives did not react with FHA. The reaction of OsO₄/pyridine with a model compound.N⁶-furfuryadenine (kinetin), resulted in addition of the OsO₄ to the furyl group. Calf-thymus DNA and polycytidylic acid were treated with FHA and bisulfite under denaturing conditions. Perchloric acid hydrolysis of the DNA showed that 80% of the cytosines were modified after 1 day. Modification of the cytosine nucleotides in the nucleic acids was followed by treatment with mercuric acetate or osmium tetroxide. The resulting polymers contained three mercury atoms or two osmium atoms per cytosine nucleotide. The potential usefulness of these reactions for electron microscopic studies of nucleic acids is discussed.