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Cyclohexane Ring (cyclohexane + ring)
Selected AbstractsScreening the Structural Space of Bicyclo-DNA: Synthesis and Thermal Melting Properties of bc4,3 -DNAEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2009Andrea Stauffiger Abstract In attempts to screen the structural and functional properties of bicyclo-DNA, in which the ribose C(3,) and C(5,) centers are integrated into an additional five-membered carbocyclic ring ([3.3.0]-series) we have now synthesized and investigated a ring enlarged analogue in which C(5,) and C(3,) are spanned by a six-membered carbocyclic ring ([4.3.0]-series). The synthesis of the corresponding bc4,3 -T nucleoside 13 was performed in 12 steps by starting from known allyl furanose 1. X-ray analysis of its benzyl protected precursor 12 showed the cyclohexane ring to adopt a chair conformation with the O(5,) substituent in an axial position. The furanose part shows clearly S-type sugar pucker. This nucleoside was converted into the corresponding phosphoramidite building block 15 and incorporated into oligodeoxynucleotides by standard phosphoramidite chemistry. The thermal stabilities of oligonucleotides with single or double incorporations of bc4,3 -T residues, paired to complementary DNA or RNA, were found to be similar to those of unmodified oligonucleotides (,2.3 to +0.7 °C per modification) and to those with the known bc-T modifications. We also found that mismatch discrimination in the bc4,3 -T series was similar to that of the natural series but less discriminative in comparison to the known bc-T series.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Synthesis and Crystal Structures of O -2,,3,-Cyclic Cyclopentanone and Cyclohexanone Ketals of the Cytostatic 5-FluorouridineHELVETICA CHIMICA ACTA, Issue 10 2009Edith Malecki Abstract The synthesis of two O- 2,,3,-cyclic ketals, i.e., 5 and 6, of the cytostatic 5-fluorouridine (2), carrying a cyclopentane and/or a cyclohexane ring, respectively, is described. The novel compounds were characterized by 1H-, 19F-, and 13C-NMR, and UV spectroscopy, as well as by elemental analyses. Their crystal structures were determined by X-ray analysis. Both compounds 5 and 6 show an anti -conformation at the N -glycosidic bond which is biased from +ac to +ap compared to the parent nucleoside 2. The sugar puckering is changed from 2,E to 3,E going along with a reduction of the puckering amplitude ,m by ca. 10,13° due to the ketalization. The conformation about the sugar exocyclic bond C(4,)C(5,) of 5 and 6 remains unchanged, i.e., g+, compared with compound 2. [source] Chemoenzymatic Route to Both Enantiomers of a 1-Isopropyl-3a-methyloctahydroinden-4-one Derivative: A Synthetic Intermediate for Sesqui- and DiterpenoidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2005Shigeo Fujieda Abstract On the way to a chemoenzymatic synthesis of a key intermediate for sesquiterpenoids and diterpenoids, 2-methyl-2-(4-methyl-3-oxopentyl)-1,3-cyclohexanedione was reduced with the whole cells of yeast biocatalysts. Torulaspora delbrueckii NBRC10921 reduced a cyclic ketone of three carbonyl groups in an enantiofacially selective manner (re -face attack), but there was poor enantiotopic group selectivity between two carbonyl groups on the cyclohexane ring to yield a mixture of diastereomeric products. Candida floricola IAM13115 reduced mainly the pro -(R) carbonyl group. In contrast, the reduction proceeded in an enantiofacially poorly selective manner to give another set of diastereomeric products. In both cases, another carbonyl group on the side chain worked as a ,trapping arm' of the resulting secondary alcohol. The diastereomeric products were effectively separated as the ,syn' or ,cis' isomer exclusively exist in the intramolecular hemiacetal structure, while ,anti' or ,trans' isomer being an equilibrated mixture of cyclic hemiacetal and open-chain hydroxyketone (ca. 0.7,:,1). Starting separately from the enantiomerically enriched products as above, both enantiomers of the target compound, a key intermediate for terpenoids, were efficiently prepared via stereoselective ring closure under pinacol coupling reaction conditions. Furthermore, a daucane sesquiterpene intermediate, a hydroazulene derivative, was provided after one-carbon homologation of the six-membered ring. [source] Spatial substituent effects of various fluorinated groups on the 13C chemical shifts in cyclohexanesMAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2007Yvan Carcenac Abstract The effect of introduction of fluorinated groups (CH2F, CHF2, CF3, C2F5, OCF3, SCF3) on the 13C NMR chemical shifts in cyclohexanes is examined. The two main effects are caused by location at the , and , carbon positions. Comparison of the various data allowed the calculation of increments corresponding to the introduction of fluorinated groups at axial or equatorial positions on the cyclohexane ring. The introduction of fluorine atoms in methoxy and thiomethoxy groups has only a slight effect through the heteroatom on the 13C chemical shifts. Copyright © 2007 John Wiley & Sons, Ltd. [source] Poly[(,6 - rac - cis -cyclohexane-1,2-dicarboxylato)strontium]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Karen A. Robertson In the title layered coordination polymer, [Sr(C8H10O4)]n, the strontium ion adopts a distorted square-antiprismatic SrO8 geometry, arising from its coordination by six different cis -cyclohexane-1,2-dicarboxylate dianions (two bidentate and four monodentate). Within the dianion, the cyclohexane ring adopts a chair conformation and the dihedral angle between the planes of the ,CO2, groups is 80.4,(6)°. The polyhedral linkage pattern leads to (100) sheets in the crystal in which the SrO8 groups share triangular faces and edges in which the Sr...Sr topological connectivity is a 63 net. The crystal studied was a nonmerohedral twin, with the components related by a 180° rotation about [100]. [source] Structure and conformational analysis of a bidentate pro-ligand, C21H34N2S2, from powder synchrotron diffraction data and solid-state DFTB calculationsACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2009Edward E. Ávila The molecular and crystalline structure of ethyl 1,,2,,3,,4,,4a,,5,,6,,7,-octahydrodispiro[cyclohexane-1,2,-quinazoline-4,,1,,-cyclohexane]-8,-carbodithioate (I) was solved and refined from powder synchrotron X-ray diffraction data. The initial model for the structural solution in direct space using the simulated annealing algorithm implemented in DASH [David et al. (2006). J. Appl. Cryst.39, 910,915] was obtained performing a conformational study on the fused six-membered rings of the octahydroquinazoline system and the two spiran cyclohexane rings of (I). The best model was chosen using experimental evidence from 1H and 13C NMR [Contreras et al. (2001). J. Heterocycl. Chem.38, 1223,1225] in combination with semi-empirical AM1 calculations. In the refined structure the two spiran rings have the chair conformation, while both of the fused rings in the octahydroquinazoline system have half-chair conformations compared with in-vacuum density-functional theory (DFT) B3LYP/6-311G*, DFTB (density-functional tight-binding) theoretical calculations in the solid state and other related structures from X-ray diffraction data. Compound (I) presents weak intramolecular hydrogen bonds of the type N,H...S and C,H...S, which produce delocalization of the electron density in the generated rings described by graph symbols S(6) and S(5). Packing of the molecules is dominated by van der Waals interactions. [source] | |||||||||||||||||||