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organic compounds
1-(β-D-Erythrofuranosyl)cytidine, C8H11N3O4, (I), a derivative of β-cytidine, (II), lacks an exocyclic hydroxymethyl (–CH2OH) substituent at C4′ and crystallizes in a global conformation different from that observed for (II). In (I), the β-D-erythrofuranosyl ring assumes an E3 conformation (C3′-exo; S, i.e. south), and the N-glycoside bond conformation is syn. In contrast, (II) contains a β-D-ribofuranosyl ring in a 3T2 conformation (N, i.e. north) and an anti-N-glycoside linkage. These crystallographic properties mimic those found in aqueous solution by NMR with respect to furanose conformation. Removal of the –CH2OH group thus affects the global conformation of the aldofuranosyl ring. These results provide further support for S/syn–anti and N/anti correlations in pyrimidine nucleosides. The crystal structure of (I) was determined at 200 K.
organic compounds
The ![[beta]](/logos/entities/beta_rmgif.gif)
-pyranose form, (III), of 3-deoxy-D-ribo-hexose (3-deoxy-D-glucose), C6H12O5, crystallizes from water at 298 K in a slightly distorted 4C1 chair conformation. Structural analyses of (III), -D-glucopyranose, (IV), and 2-deoxy--D-arabino-hexopyranose (2-deoxy--D-glucopyranose), (V), show significantly different C-O bond torsions involving the anomeric carbon, with the H-C-O-H torsion angle approaching an eclipsed conformation in (III) (-10.9°) compared with 32.8 and 32.5° in (IV) and (V), respectively. Ring carbon deoxygenation significantly affects the endo- and exocyclic C-C and C-O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species (III) and (V) compared with (IV). These structural changes are attributed to differences in exocyclic C-O bond conformations and/or hydrogen-bonding patterns superimposed on the direct (intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in (III) (gt) differs from that observed in (IV) and (V) (gg).
-pyranose form, (III), of 3-deoxy-D-ribo-hexose (3-deoxy-D-glucose), C6H12O5, crystallizes from water at 298 K in a slightly distorted 4C1 chair conformation. Structural analyses of (III), -D-glucopyranose, (IV), and 2-deoxy--D-arabino-hexopyranose (2-deoxy--D-glucopyranose), (V), show significantly different C-O bond torsions involving the anomeric carbon, with the H-C-O-H torsion angle approaching an eclipsed conformation in (III) (-10.9°) compared with 32.8 and 32.5° in (IV) and (V), respectively. Ring carbon deoxygenation significantly affects the endo- and exocyclic C-C and C-O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species (III) and (V) compared with (IV). These structural changes are attributed to differences in exocyclic C-O bond conformations and/or hydrogen-bonding patterns superimposed on the direct (intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in (III) (gt) differs from that observed in (IV) and (V) (gg).
