Recent advances in the synthesis of conformationally locked nucleosides and their success in probing the critical question of conformational preferences by their biological targets.

The present work describes some recent approaches to the syntheses of three classes of locked-North nucleosides: beta-D-ribo-, beta-D-deoxyribo-, and beta-D-dideoxyribonucleosides. The method developed for the latter class permitted access to a novel bicyclo[3.1.0]hexene-type nucleosides structurally similar to D4T and carbovir. A structural analysis and biological activities are discussed.