Deoxyadenosine and Thymidine Bases Held Proximal and Distal by Means of a Covalently-Linked Dimensional Analogue of dA·dT: Intramolecular vs Intermolecular Hydrogen Bonding1

Deoxyadenylic acid and deoxythymidilic acid have been attached to a covalently-linked cross section, dA dT, on the same side (proximal) and on opposite sides (distal) by synthetic sequences involving various combined protection/deprotection steps. The structures in aqueous solution buffered at pH 7.0 have been examined by 2D-NOESY NMR spectroscopy. The covalently-linked cross section provides a template that stabilizes dA·dT base pairing in the proximal isomer at 2 °C. In the distal isomer, it contributes to favorable conformations for intermolecular association.