Polynucleotides. XXXIV. Ultraviolet Absorption and Circular Dichroism of ApUpG Analogs containing Modified Adenosine Residues

Abstract

Ultraviolet absorption and circular dichroism properties of ApUpG and its analogs in which the adenosine is modified are reported. The adenosine analogs include formycin (F), 8, 5'-S-cycloadenosine (^sA), 8, 2'-S-cycloadenosine (A^s), 8, 5'-O-cycloadenosine (^oA), 8, 2'-O-cycloadenosine (A^o), 8-bromoadenosine (Br-A) and 8-oxyadenosine (HO-A). S-and-O-Cyclonucleosides and F take torsion angles of anti type, while Br-A and HO-A assumed to take syn conformation in these analog trinucleotides. All analogs have very weak stacking interaction and show a tendency to form an aggregate at low temperature.