Oligonucleotide Analogues with Integrated Bases and Backbone

The thiomethylene‐linked U*s]U⁽*⁾ dimers 9 – 14 were synthesized by substitution of the 6‐(mesyloxy)methyl]uridine 6 by the thiolate derived from the uridine‐5′‐thioacetates 7 and 8 followed by O‐deprotection. Similarly, the thiomethylene‐linked A*s]A⁽*⁾ dimers 9 – 14 were obtained from the 8‐(bromomethyl)adenosine 15 and the adenosine‐5′‐thioacetates 16 and 17 . The concentration dependence of both H? N(3) of the U*s]U⁽*⁾ dimers 9 – 14 evidences the formation of linear and cyclic duplexes, and of linear higher associates, C(8 or 6)CH₂OH and/or C(5′/II)OH groups favouring the formation of cyclic duplexes. The concentration dependence of the chemical shift for both H₂N? C(6) of the A*s]A⁽*⁾ dimers 18 – 23 evidences the formation of mainly linear associates. The heteroassociation of U*s]U⁽*⁾ to A*s]A⁽*⁾ dimers is stronger than the homoassociation of U*s]U⁽*⁾ dimers, as evidenced by diluting equimolar mixtures of 11 / 20 and 13 / 22 . A 1 : 1 stoichiometry of the heteroassociation is evidenced by a Job's plot for 11 / 20 , and by mole ratio plots for 9 / 18, 10 / 19, 12 / 21, 13 / 22 , and 14 / 23 .