Reactions of nucleic acid bases with α‐acetylenic esters

Abstract

The reaction of chlorotetrolic (4-chloro-2-butynoic) esters with adenine and cytosine derivatives, in which a new heterocycle bearing an alkylating chloromethyl side chain is fused to the purine or pyrimidine ring, was extended to poly(A) and poly(C) used as models of nucleic acids. The derivatization proceeds under mild conditions and its extent can be controlled by the reaction time. The additional rings can exist in two isomeric forms and the nature of the isomer formed depends on steric factors in the vicinity of the reacting base. The reaction with chlorotetrolic esters discriminates between the single-stranded (reactive) and double-stranded (unreactive) forms, between the exposed an hidden adenine and cytosine bases and even between the exposed and sterically hindered fragments of the base moiety and thus allows structural investigations of these nucleic acids. The chloromethyl group of the derivatized nucleobases can be used to bind the modified polymers to other molecules.In preceding papers [l -31 we have shown that the nucleic acid bases in adenine and cytosine (but not guanine) nucleotides and/or nucleosides react easily with a-acetylenic esters. Thus, for example, treatment of adenosine with a chlorotetrolic (4-chloro-2-butynoic) acid ester in hydroalcoholic solution of apparent pH 4-5, at room temperature, leads to the %ox0 derivative in good yield, while at pH 7 the isomeric 7-0x0 compound is obtained (see Scheme). In the case of cytidine, whatever the pH of the reaction medium, only product 3 was isolated. Thus, the triple bond and the ester group of chlorotetrolic esters react with the nucleobases while the chloromethyl group remains as a substituent on the new heterocycle fused to the original purine or pyrimidine ring.This new derivatization of nucleobases was first studied on nucleosides and nucleotides and some basic information about this reaction was gained at this model level. An interesting feature of this derivatization is the mildness of the experimental conditions under which it occurs. It could therefore be anticipated that this reaction might be used not only for the synthesis of analogues of small molecules containing a nucleobase fragment but also for chemical modification of nucleic acids. The use of chlorotetrolic esters for a controlled derivatization of a certain number of residues in nucleic acids could offer some attractive prospects, among others the possibility of investigating the structure of these macromolecules or of cross-linking nucleic acids to proteins or to some other molecules. This paper describes the first attempt to extend the reaction to nucleic acids using poly(A) and poly(C) as models.

Anti-HIV Activities of Novel Nucleoside Analogues: Acyclic and Tricyclic Base Nucleosides

“…The main characteristic of tricyclic ribonucleoside derivatives (Figs2 and 3, Olomucki et aI., 1985;Roques et al, 1987;Roques, 1989) is the presence of an additional pyrimidine ring with an alkylating group on the purine nucleus.…”

Cross‐linking of nucleic acids to proteins

“…The degree of modification was measured in each case by two methods. Since the ultraviolet spectrum of the modified nucleotide has an additional absorbance maximum, the ab-sorbance increase at this wavelength may be used to calculate the amount of modified bases [12]. In addition, the poly(A) fraction was hydrolyzed to mononucleotides with the aid of T,-RNase, and the amount of modified nucleotides was determined via HPLC (see Materials and Methods).…”

“…The bases adenine or cytosine may be modified by methylchlorotetrolic ester (a reaction described by Olomucki et al [12,131). Here, we describe the use of the modification for cross-linking nucleic acids to proteins.…”