DNA duplexes stabilized by modified monomer residues: synthesis and stability
The synthesis of a series of 2′-deoxyuridine analogues modified at the 5-position and a series of 2′-deoxypurines modified at the 8-position is described. Ultraviolet melting studies have been used to assess the stability of DNA duplexes 12- and 8-residues in length that contain these modifications. Of those modified residues which have been incorporated into oligonucleotides, 5-(prop-1-ynyl)-2′-deoxyuridine is found to impart the greatest increase in stability on the DNA duplexes studied.
Thermodynamic analyses show that the reason for this increase in stability arises from a decrease in enthalpy which is related to the DNA base stacking process. We suggest that the degree of stabilisation imparted by the propyne moiety may be sequence dependent.