Selective intracomplex reaction of pendant groups in a purine-pyrimidines base pair

Evidence is presented suggesting that hydrogen-bonded base pairing and/or aryl stacking interactions between derivatives of guanine (9-[(4-aminobutyloxy)-methyl]guanine) and cytosine (1-([(2-benzyloxy)ethoxy]methyl)cytosine) lead to enhanced intracomplex chemical reaction between the corresponding amino and ester groups. On the basis of analysis of the kinetic data it is concluded that a chain length of four methylene groups (4-amino- butyloxy as compared to 2-aminoethoxy or 6-aminohexyloxy) on the guanine is necessary to achieve the appropriate geometry for intracomplex reaction. Support for the reaction scheme is provided by the absence of reaction between the guanine derivative and a corresponding ester derivative of thymine, not expected to associate.