Polynucleotides. LXI. Synthesis and properties of dinucleoside monophosphates containing 8,2'-S-cycloadenosine and 8,2'-S-cycloinosine residues. Sequence dependency of the stability of the stacking conformation

Three dinucleoside monophosphates containing 8, 2'-anhydro-8-thio-9-β-D-arabinofuranosyladenine (As) and its hypoxanthine derivative (Is), AspIs, IspAs and IspIs, were synthesized. Examination of their properties by ultraviolet absorption, circular dichroism and 1H nuclear magnetic resonance measurements and comparison with the properties of AspAs, which has been shown to take a left-handed stacked conformation, showed that all these dimers take a left-handed stacked conformation, and the order of extent of stacking is AspAsaIspAs>AspIsaIspIs. This sequence dependency of stability of stacking can be explained in terms of the mode of base-base overlap in a left-handed stack. A similar explanation may be applicable to the corresponding sequence dependency of natural dimers with a right-handed stack.