Synthesis of carbon-bridged pyrimidine cyclonucleosides.

6,5'-Cyclo-5'-deoxyuridine 2',3'-cyclic phosphate and its derivatives were prepared as the conformationally fixed substrates of pancreatic ribonuclease. 6,6'-Cyclouridine, 6,3'-methylene-cyclo-2', 3'-dideoxyuridine, and 6,2'-ethylene-cyclo-2'-dexoyuridine were prepared as the new types of C-cyclopyrimidine nucleosides fixed in the anti conformation. The relationship between the sign and magnitude of CD Cotton bands and glycosylic torsion angles is discussed.