Preparation of the 1-(2,5-anhydro-β-d-arabinofuranosyl) derivatives of cytosine and uracil and their cleavage with hydrogen bromide

Abstract

Anhydronucleoside Ia was prepared from chloroarabinofuranosylcytosine IIIc or from 2,2'-anhydro-1-(5-chloro-5-deoxy-β-D-arabinofuranosyl)cytosine by the action of a strongly basic ion exchanger. The anhydro derivative IIa was prepared from 2,2'-anhydro-1-(5-chloro-5-deoxy-β-D-arabinofuranosyl)uracil by treatment with aqueous solution of sodium hydroxide. The action of hydrogen bromide in dimethylformamide on 2',5'-anhydronucleosides Ia and IIa leads both to the cleavage of the anhydro bond under formation of the 5'-bromo derivatives IIIa and IVa and to the cleavage of nucleosidic bond. In case of the uracil derivative IIa, the α-arabinofuranosyl derivative V was also isolated after preceding acetylation. For unambiguous proof of the structure, an alternative synthesis of compound V was performed.