Molecular and crystal properties of ethyl 4,6-dimethyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate from experimental and theoretical electron densities.

The electron density and electronic energy densities in ethyl 4,6-dimethyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate have been studied from accurate X-ray diffraction measurements at 110 K and theoretical single-molecule and periodic crystal calculations. The Quantum Theory of Atoms in Molecules and Crystals (QTAMC) was applied to analyze the electron-density and electronic energy-density features to estimate their reproducibility in molecules and crystals. It was found that the local electron-density values at the bond critical points derived by different methods are in reasonable agreement, while the Laplacian of the electron density computed from wavefunctions, and electron densities derived from experimental or theoretical structure factors in terms of the Hansen-Coppens multipole model differ significantly. This disagreement results from insufficient flexibility of the multipole model to describe the longitudinal electron-density curvature in the case of shared atomic interactions. This deficiency runs through all the existing QTAMC bonding descriptors which contain the Laplacian term. The integrated atomic characteristics, however, suffer noticeably less from the aforementioned shortcoming. We conclude that the electron-density and electronic energy QTAMC characteristics derived from wavefunctions, especially the integrated quantities, are nowadays the most suitable candidates for analysis of the transferability of atoms and atomic groups in similar compounds.

New pyrimidine cyclonucleosides with hydrogenated aglycones: synthesis and X-ray structures.

Acid catalysed transformations of (6S)-6,5'-anhydro-6-hydroxy-1-(2',3'-O-isopropylidene-beta-D-ribofuranosyl)hexahydropyrimidine-2-thione are studied. (6R)-6,2'-anhydro-6-hydroxy-1-(alpha-D-ribofuranosyl)hexahydropyrimidine-2-thione was formed as a thermodynamically stable product. Two intermediates, (6S)-6,5'-anhydro-6-hydroxy-1-(beta-D-ribofuranosyl)hexahydropyrimidine-2-thione and 6-hydroxy-1-(D-ribosyl)hexahydropyrimidine-2-thione and products of cleavage of glycosidic bond were identified in the reaction mixtures. Results of X-ray structural determination of the synthesised nucleosides are presented.

Triribbed-functionalized clathrochelate iron(II) dioximates as a new and promising tool to obtain polynucleating and polynuclear compounds with improved properties.

Template condensation on iron(II) ion of dichloroglyoxime (H2C12Gm) with (C6H5O)3, n-C4H9B(O-n-C4H9)2, and BF3.O(C2H5)2 in CH3NO2 afforded reactive clathrochelate precursors Fe(C12Gm)3(BC6H5)2 (2), Fe(C12Gm)3(B-n-C4H9)2 (3), and Fe(C12Gm)3(BF)2 (4). A series of triribbed-functionalized clathrochelate dioximates have been synthesized. Reaction of 2 with C6H5SH/K2CO3 and CH3SH/t-C4H9OK in 1,4-dioxane and THF afforded Fe((C6H5S)2Gm)3(BC6H5)2 (5) and Fe((CH3S)2Gm)3(BC6H5)2 (6). Reaction of 3 with C6H5OK in THF afforded Fe((C6H5O)2Gm)3(B-n-C4H9)2 (7). Condensation of 3 with bis(2-(o-oxyphenoxy))diethyl ether in THF afforded di- and tricrown etheric Fe(CwGm)2(C12Gm)(Bn-C4H9)2 (8) and Fe(CwGm)3(B-n-C4H9)2 (9) clathrochelates. Condensation of 3 with 3,5-dithiaoctane-1,8-dithiol/Cs2CO3 in DMF afforded the thiocrown etheric Fe((12anS4)Gm)3(BC6H5)2 complex (10). Reaction of 2 with n-butylamine in DMF resulted in the tetrasubstituted Fe((n-C4H9NH)2Gm)2(C12Gm)(BC6H5)2 clathrochelate (11). The clathrochelates obtained have been characterized both on the basis of elemental analysis, FAB and PD mass spectrometry, IR, UV-vis, 57Fe Mössbauer, and NMR spectroscopies and crystallographically (compounds 3, 4, 6, 7, and 11). An encapsulated iron(II) ion in a distorted trigonal-prismatic environment of six nitrogen atoms of the macrobicyclic ligand was found to be in a low-spin state. The cyclic voltammograms for the complexes 2-11 show irreversible oxidation waves assignable to Fe3+/Fe2+ couples. The correlation of E1/2 for these couples with Hammet sigma para constants for substituents in dioximate fragments has been demonstrated.

[3'-(Tetrazol-2''-yl-3'-deoxythymidine and its 5''-substituted form: synthesis and conformation in the crystalline state. Substrate properties of 3'-(tetrazol-2''-yl)-3'-deoxythymidine-5'-triphosphate in relation to DNA polymerases]. / 3'-(Tetrazol-2''-il)-3'-dezoksitimidin i ego 5''-zameshchennye: sintez i konformatsiia v kristallicheskom sostoianii. Substratnye svoistva 3'-(tetrazol-2''-il)-3'-dezoksitimidin-5'-trifosfata po otnosheniiu k DNK-polimerazam.

5''-Derivatives of 3'-(tetrazole-2''-yl)-3'-deoxythymidines were synthesized by interaction of 5'-benzoyl-2',3'-anhydrothymidine with tetrazole or its 5-derivatives followed by debenzoylation. Structures of two of them, 3'-(tetrazole-2''-yl)-3'-deoxythymidine and 3'-(5''-methyltetrazole-2''-yl)-3'-deoxythymidine, elucidated by X-ray analysis, revealed anti conformation of thymine about the glycosidic bond and 2'-endo-3'-exo-conformation of the sugar residue with gauche+ orientation with respect to C4'-C5'-bond. 3'-(Tetrazole-2''-yl)-3'-deoxythymidine 5'-triphosphate demonstrated poor substrate properties for the avian myeloblastosis virus reverse transcriptase and none for several other DNA polymerases.