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Covalently Cross-Linked Watson-Crick Base Pair Models.

Structural characteristics of Watson-Crick hydrogen-bonded base pairs are displayed by methylene-bridged base pairs of type A. The shown superposition of the X-ray structure obtained for the base pair A (Rib1 =Et; Rib2 =Me) over that of a C-G base pair illustrates that A occupies an area similar to that occupied by a traditional Watson-Crick hydrogen-bonded base pair. Temperature-dependent 1 H NMR studies indicate that the energy barrier for rotation along its CH2 bridge is about 10 kcal mol-1 , and that it exists predominantly in one conformer at -70°C.