Enzymatic Synthesis of 18O(6)-Guanosine and Spectroscopic Characterization of Hoogsteen and Reverse Hoogsteen Hydrogen-Bonded Guanosine Structures

Abstract

Adenylic acid deaminase has been successfully used for the first time to convert Cl(6)-guanosine to 18O(6)-guanosine in the presence of H218O. Observations of infrared and Raman spectra of both guanosine and 18O(6)-guanosine permit assignment of the carbonyl vibrations in guanosine tetramer. In-plane normal mode wavenumbers have been calculated using a valence force field that incorporates an interaction force constant of νCO transition dipole coupling. This coupling alone between carbonyl groups of adjacent guanine residues provides the physical basis for understanding the observed CO splittings in guanosine tetramer and in hydrogen-bonded guanine bases adopting the Hoogsteen structure. This coupling is, however, absent in the dimer of 2‘-deoxy-3‘,5‘-bis(triisopropylsilyl)guanosine, which is known to adopt the reverse Hoogsteen structure. The νCO spectral profiles, then, permit the distinction between Hoogsteen and reverse Hoogsteen hydrogen-bonded guanine nucleobases in G*G·C triplets that may be presen...