Structure and conformation of the hydrochloride of pseudoisocytidine, an antileukemic C-nucleoside

Abstract

. FOX. Can. J . Chem. 58, 1633 (1980). The three-dimensional structure of pseudoisocytidine hydrochloride was determined by X-ray crystallography. The crystals belong to the triclinic space group P I and the cell dimensions are a = 6.623(2), b = 8.053(2), c = 6.201(2) A, a = 108.35(2), = 101.36(2), y = 93.54(2)". Intensity data were measured with a diffractometer and the structure was solved by a combination of heavy-atom and direct methods. Least-squares refinement, which included hydrogen atoms, converged at R = 0.040. The conformation about the glycosyl bond is trrltr (xc( = 21.6"). the pucker of the furanose ring is C(l')eso, and the conformation of the -CH,OH side chain is gauche-trans (t). An examination of bond lengths indicates that of the three main resonance forms of the isocytosine cation the fully conjugated one contributes more to the structure than the cross-conjugated one. Bond angles in the sugar ring reflect its rare conformation. .6"), le plissement du cycle furannose est C(1')exo et la conformation de la chaine laterale CH,OH est gcrrlcl~e-trnns (t). Un examen des longueurs de liaison indique que parmi les trois formes principales de resonance du cation isocytosine, la forme completement conjuguee contribue plus a la structure que la forme ou la conjugaison est opposee. Les angles de liaison dans le cycle furannose refletent sa conformation rare.[Traduit par le journal]

Biochemical Detection of Cytidine Protonation within RNA

“…The third nucleotide used in this study, ΨiC, is a C-linked nucleoside that exists as an equilibrium mixture of two tautomeric forms in aqueous solution (Figure ) . NMR experiments and theoretical calculations have shown that the N3−H tautomer is favored over the N1−H form by about 2−9 kcal mol -1 , depending on the solvent polarity .…”

“…The third nucleotide used in this study, ΨiC, is a C-linked nucleoside that exists as an equilibrium mixture of two tautomeric forms in aqueous solution (Figure 4). 28 NMR experiments and theoretical calculations have shown that the N3-H tautomer is favored over the N1-H form by about 2-9 kcal mol -1 , depending on the solvent polarity. 29 The N3-H tautomer creates an "unnatural" donor-donor-acceptor hydrogen bonding face for base pairing, which might have a deleterious effect on the ability of this analogue to be recognized by the polymerase during transcription.…”

Theoretical ab initio study of the protomeric tautomerism of 2-hydroxypyrimidine, 4-hydroxypyrimidine, and their derivatives

“…(83) Handy, N. C. In Supercomputer Algorithms for Reactivity, Dynamics and Kinetics of Small Molecules; Ladana, A., Ed. ; Kluwer Academic Publishers: Dordrecht, 1989; pp [23][24][25][26][27][28][29][30][31][32][33][34][35][36]. "The hydration effect (he.)…”

“…28 The isocytosine moiety appears in the oxo-amino tautomeric forms, and no other forms (hydroxy, imino) were detected. 29 Another interesting feature of isocytosine is found from studies of its crystal structure. Two forms, oxoamino N(3)H and N(1)H, coexist in a 1:1 ratio in the crystalline state.…”

Solid-state transformation of 4,2′-anhydro-5-(β-D-arabinofuranosyl)uracil dihydrate to 4,2′-anhydro-5-(β-D-arabinofuranosyl)uracil monohydrate

“…A shortening of the C1 H ÐO4 H bond due to anomeric effects is generally observed in N-nucleosides. In C-nucleosides, however, such a bond shortening does not occur (Hempel et al, 1997;Birnbaum et al, 1980). Both crystal structures contain three-dimensional networks of hydrogen bonds (Tables 1 and 2).…”