Hans Reuter

The High‐Anti Conformation of 7‐Halogenated 8‐Aza‐7‐deaza‐2′‐deoxy‐guanosines: A Study of the Influence of Modified Bases on the Sugar Structure of Nucleosides

Introduction. – The conformational flexibility of nucleic acids can be more complexthan that of peptides because the sugar-phosphate backbone conformation is descibedby five single-bond rotations in addition to five sugar torsions [1a]. It is expected that inmany cases, the conformational changes among nucleoside or nucleotide structuresobey a certain conformational pathway. This means that the movement of one torsion islinearly coupled with another one [2][3]. In general, the molecular structures ofnucleosides and nucleotides have been regarded as conformationally ˝rigid˛ [4]probably due to the small variances of torsion angles. Besides gauche and anomericeffects [5], important determinants of the overall structure of a nucleoside are the stericand stereoelectronic effects of the nucleobases [6]. In a series of influential reports, atfirst Gassen and coworkers [7], and later Chattopadhyaya and coworkers [8] havedemonstrated the importance of such effects on both the structure of a nucleoside aswell as on the secondary structure of a DNA molecule. Recently, our interest wasfocussed on the stereoelectronic influence of modified nucleobases – and here inparticular of aza- and deazapurines – on the structure and stability of oligonucleotidescontaining such compounds [9–13]. We have observed that the incorporation of 8-aza-7-deazapurine 2’-deoxynucleotides into oligodeoxynucleotides exerts an extraordinaryinfluence on their duplex stability which is significantly enhanced over that of theparent unmodified oligomers [14–16]. This may be traced to an altered secondarystructure of the base-modified oligomers with probably enhanced stacking interactions

Chemistry of Monomeric and Dinuclear Non-Oxido Vanadium(IV) and Oxidovanadium(V) Aroylazine Complexes: Exploring Solution Behavior

A series of mononuclear non-oxido vanadium(IV) [V(IV)(L(1-4))2] (1-4), oxidoethoxido vanadium(V) [V(V)O(L(1-4))(OEt)] (5-8), and dinuclear μ-oxidodioxidodivanadium(V) [V(V)2O3(L(1))2] (9) complexes with tridentate aroylazine ligands are reported [H2L(1) = 2-furoylazine of 2-hydroxy-1-acetonaphthone, H2L(2) = 2-thiophenoylazine of 2-hydroxy-1-acetonaphthone, H2L(3) = 1-naphthoylazine of 2-hydroxy-1-acetonaphthone, H2L(4) = 3-hydroxy-2-naphthoylazine of 2-hydroxy-1-acetonaphthone]. The complexes are characterized by elemental analysis, by various spectroscopic techniques, and by single-crystal X-ray diffraction (for 2, 3, 5, 6, 8, and 9). The non-oxido V(IV) complexes (1-4) are quite stable in open air as well as in solution, and DFT calculations allow predicting EPR and UV-vis spectra and the electronic structure. The solution behavior of the [V(V)O(L(1-4))(OEt)] compounds (5-8) is studied confirming the formation of at least two different types of V(V) species in solution, monomeric corresponding to 5-8, and μ-oxidodioxidodivanadium [V(V)2O3(L(1-4))2] compounds. The μ-oxidodioxidodivanadium compound [V(V)2O3(L(1))2] (9), generated from the corresponding mononuclear complex [V(V)O(L(1))(OEt)] (5), is characterized in solution and in the solid state. The single-crystal X-ray diffraction analyses of the non-oxido vanadium(IV) compounds (2 and 3) show a N2O4 binding set and a trigonal prismatic geometry, and those of the V(V)O complexes 5, 6, and 8 and the μ-oxidodioxidodivanadium(V) (9) reveal that the metal center is in a distorted square pyramidal geometry with O4N binding sets. For the μ-oxidodioxidodivanadium species in equilibrium with 5-8 in CH2Cl2, no mixed-valence complexes are detected by chronocoulometric and EPR studies. However, upon progressive transfer of two electrons, two distinct monomeric V(IV)O species are detected and characterized by EPR spectroscopy and DFT calculations.

The DNA-stabilising nucleoside 7-iodo-2′-deoxytubercidin: its structure in the solid state and in solution

The crystal structure of 7-iodo-2′-deoxytubercidin 2 has been determined and was compared with those of 2′-deoxytubercidin 3 and 2′-deoxyadenosine 4. The bulky 7-iodo substituent lies 13.2 pm below and the nitrogen of the 6-amino group 5.5 pm above the 7-deazapurine plane. The puckering of compound 2 is 3′E while compound 3 shows a 2′T3′ sugar pucker. The conformation in aqueous solution, determined by 1H NMR spectroscopy, is only slightly different, showing a 2′E conformation. The glycosylic bond torsion angle is anti in all cases.

1-DEAZA-3'-O-METHYLADENOSINE : A NUCLEOSIDE WITH THE SYN-CONFORMATION IN THE SOLID STATE AND IN SOLUTION

Abstract The 2′-O-methyl (2) and the 3′-O-methyl (3) derivatives of 1-deazaadenosine (1) were prepared. Single crystal X-ray analysis as well as 1H and 13C NMR studies were performed on the 3′-O-methyl-1-deazaadenosine 3. In the solid state, the glycosyl torsion angle (χ = 64.7°) is in the syn-range which is caused by an intramolecular (5′)CH2OH…N(3) hydrogen bond. The ribofuranose moiety adopts a 2 E (C-3′-exo; S) conformation and the orientation of the exocyclic C(4′)-C(5′) bond is + sc (γ(+)g). The conformation in solution was found to be very similar to that in solid state. Whereas the 2′-O-methyl derivative of 1 is a strong inhibitor of adenosine deaminase the 3′-O-methyl derivative is neither inhibitor nor substrate.

[( i PrSn)12O14(OH)6][( i PrSn)3(OV)4O10(OH)3] · 4DMSO: Evidence for the Formation of Contact Ion Pairs Resulting from the Nucleophilic Attack on a Square Pyramidally Coordinated Tin Atom

Abstract The title compound has been prepared via self-assembly of an RSn and VO source. In the solid, the cation and anion form an intimate ion pair via a V˭O−Sn bond expanding the coordination sphere at tin from square-pyramidal to trigonal-prismatic. Supplemental materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT

The anomers of 8-aza-7-deaza-2'-deoxyadenosine

The structures of 4-amino-1-(2-deoxy-β-D-erythropentofuranosyl)-1H-pyrazolo[3,4-d]pyrimidine, (I), and 4-amino-1-(2-deoxy-α-D-erythro-pentofuranosyl)-1H-pyrazolo[3,4-d]pyrimidine, (II), both C 10 H 13 N 5 O 3 , have been determined. The sugar puckering of both compounds is C-2-endo-C-3exo ( 2 T 3 ) (S-type sugar). The N-glycosidic torsion angle X 1 is in the anti range [-106.3 (2)° for (I) and 111.5(3)° for (II)] and the crystal structure is stabilized by hydrogen bonds.

Synthesis, structure and cytotoxicity of a series of Dioxidomolybdenum(VI) complexes featuring Salan ligands

Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO2L1-7] (1-7) derived from various tetradentate diamino bis(phenolato) salan ligands, N,N-dimethyl-N,N-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminoethane {(X=Br, Y=Me, Z=H (H2L1); X=Me, YCl, Z=H (H2L2); X=iPr, Y=Cl, Z=Me (H2L3)} and N,N-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminopropane {(X=Y=tBu, Z=H (H2L4); X=Y=Me, Z=H (H2L5); X=iPr, YCl, Z=Me (H2L6); X=Y=Br, Z=H (H2L7)} containing O-N donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV-vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. X-ray crystallography showed the O2N2 donor set to define an octahedral geometry in each case. The complexes (1-7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell line. IC50 values of the complexes in HT-29 follow the order 6<7<<1<2<5<<3<4 while the order was 6<7<5<1<<3<4<2 in HeLa cells. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 (IC50 values of 6 are 2.62 and 10.74μM and that of 7 is 11.79 and 30.48μM in HT-29 and HeLa cells, respectively) may be dependent on the substituents in the salan ligand environment coordinated to the metal.

Methyl­phospho­nic acid, CH3PO(OH)2

The asymmetric unit of the title compound, CH5O3P, contains two independent molecules with nearly identical bond lengths and angles. In the crystal, each of the molecules acts as acceptor (P=O) and donor (P—OH) of four hydrogen bonds to three adjacent molecules, resulting in the formation of two different bilayers (one for each molecule) stacked perpendicular to the a axis in the crystal.

9-(2-Deoxy-α-d-ribofuranosyl)-7-iodo-7-deazaadenine

The structure of 4-amino-7-(2-deoxy-α-D-erythropentofuranosyl)-5-iodo-7H-pyrrolo[2,3-d]pyrimidine, C 11 H 13 IN 4 O 3 , has been determined. The N-glycosidic bond torsion angle X is in the anti range [128.7 (12)°]. Both, the bulky iodo substituent and the N atom of the 6-amino group lie out of the 7-deazapurine plane, with deviations of -0.013 (10) and -0.0632 (12) A, respectively.

Structural parameters of dimethyl sulfoxide, DMSO, at 100 K, based on a redetermination by use of high-quality single-crystal X-ray data

Accurate structural parameters (bond lengths and angles) of dimethyl sulfoxide, DMSO, have been obtained from the redetermination of its crystal structure by single-crystal X-ray diffraction at 100u2005K using CCD data in order to get a reference point for the deformation of the chemically bonded molecule. In addition, the new data show that molecule approximates C s symmetry in the solid state where all atoms occupy general positions.