title: Crystal and molecular structures of carbon-bridged pyrimidine cyclonucleosides. Substrate analogs of ribonuclease A.
abstract: The crystal and molecular structures of carbon-bridged 6,5'-cyclo-5'-deoxy-4-thiouridine (6,5'-Cs4U), 6,5'-cyclo-5'-deoxy-2',3'-O-isopropylideneuridine (6,5'-CiU) and 6,6'-cyclo-5',6'-dideoxy-allofuranosyluracil (6,6'-CU) have been determined by X-ray diffraction. The molecular conformations of 6,5'-Cs4U and 6,5'-CiU are very similar; the conformation about the glycosidic bond is anti (low region), the torsion angle O(4')-C(1')-N(1)-C(2) being -150.0 degrees for 6,5'-Cs4U and -145.5 degrees for 6,5'-CiU, and the sugar puckering being both O(4')-exo. On the other hand, 6,6'-CU takes the glycosidic torsion angle of -116.9(4) degrees (middle anti region) and the sugar conformation of C(4')-endo. The cyclization causes little alteration in the geometry of the base moiety. 6,5'-Cs4U and 6,5'-CiU exhibit the similar base-base interactions between adjacent molecules, although their molecular packings are quite different; the 4-thiouracil or uracil moiety interacts with adjacent base moieties through hydrogen bonding and stacking interactions. In 6,6'-CU, cyclonucleosides were connected by hydrogen bondings between the hydroxyl and sugar ring oxygen atoms and between the hydroxyl groups and the base nitrogen and oxygen atoms. As the 2',3'-cyclic phosphates of these carbon-bridged cyclonucleosides are hydrolyzed by ribonuclease A, it is suggested that the conformers found in these cyclonucleosides are recognized by the enzyme.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamagata
authors.forename: K
authors.initials: K
authors.lastname: Tomita
authors.forename: H
authors.initials: H
authors.lastname: Usui
authors.forename: T
authors.initials: T
authors.lastname: Sano
authors.forename: T
authors.initials: T
authors.lastname: Ueda
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D003460:Crystallization; D015394:Molecular Structure; D011741:Pyrimidine Nucleosides / Q000032:analysis / Q000138:chemical synthesis*; D012259:Ribonuclease, Pancreatic / Q000032:analysis*; D014961:X-Ray Diffraction
chemical_list: D011741:Pyrimidine Nucleosides; D012259:Ribonuclease, Pancreatic