REACTION OF NUCLEIC-ACID BASES WITH ALPHA-ACETYLENIC ESTERS .5. SYNTHESIS AND PROPERTIES OF ADENOSINE AND CYTIDINE DERIVATIVES

Alpha-Acetylenic esters are able to react under mild experimental conditions with the base moiety of adenosine and cytidine, while guanosine is unreactive. A double reaction of the triple bond and the ester group of the reagent with the NH2 group and the adjacent ring nitrogen of the base yields derivatives in which an additional pyrimidone ring is fused to the original base. These derivatives can exist in two isomeric forms. In alkaline solution, or by prolonged heating in water, the medium pyrimidine ring of adenosine derivatives opens by loss of carbon 5. If the derivatization is performed with chlorotetrolic (4-chloro-2-butynoic) acid esters, the modified nucleobases contain a chloromethyl side chain. Tests of the alkylating abilities of the latter in the two isomeric adenosine derivatives show that the chlorine can be easily substituted by a thiol in the presence of alkali; a partial Dimroth rearrangement of one of the reaction products is observed. The reaction with amines is accompanied by ring opening. Nucleic acids containing these alkylating base derivatives can be cross-linked to other macromolecules such as solid supports or contact proteins.