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61.
Johannes J. Voegel Michael M. Altorfer Steven A. Benner 《Helvetica chimica acta》1993,76(5):2061-2069
A new synthesis is reported for 4-aminoimidazo[1,2-a]-1,3,5-triazin-2(1H)-one ( =5-aza-7-deaza-isoguanosine; 8 ), a purine analog that, when incorporated into an oligonucleotide chain, presents a H-bond donor-acceptor-acceptor pattern to a complementary pyrimidine analog. A protected ribose derivative was coupled to 8 to yield 4-amino-8-(β-D -ribofuranosyl)imidazo[1,2-a]-1,3,5-triazin-2(8H)-one ( =5-aza-7-deaza-isoguanosine; 11 ) after deprotection, Alternatively, direct synthesis of both the ribo derivative 11 and the corresponding deoxyribo derivative 17 as the β-D -anomers was achieved using the enzyme purine nucleoside phosphorylase in a one-pot reaction. This adapts a known synthetic approach to yield a new strategy for obtaining diastereoisomerically pure deoxyribonucleoside analogs on 1-gram scales. 相似文献
62.
The synthesis of a chemical compound library using diversity-oriented synthesis (DOS) is discussed. The library is structurally inspired by the Amaryllidaceae alkaloids, a family of natural products which has been known to demonstrate potent antiviral and antineoplastic activity. Highlights of this work include the rapid, high-yielding construction of the octahydroindolinone core and the solid-phase diversification of the lactam using a neutral phosphazene base. 相似文献
63.
Johannes André 《Journal of Geometry》1992,43(1-2):22-29
Configurational conditions (Schließungsaussagen) of a noncommutative space will be developped from pairs (,
) of digraphs where is a partial digraph of
. In this way we obtain an extensive generalization of Pfalzgraf 's q-simplex-conditions Simq.In Memoriam Hans Zassenhaus 相似文献
64.
65.
Chinnasamy Thangavel Vijayakumar Johannes Karl Fink 《Journal of polymer science. Part A, Polymer chemistry》1983,21(6):1617-1625
HET acid was condensed with either ethylene glycol or 1,4-butanediol to yield the respective oligoesters. These oligoesters were characterized by molecular weight, measured by vapor-pressure osmometry. The degradation mechanism of oligoesters of HET acid with either ethylene glycol or 1,4-butanediol was elucidated. The thermal properties of these polyesters were studied using differential thermal analysis and thermal volatilization analysis. The mechanism of degradation was proposed on the basis of pyrolysis–gas chromatography studies, the degradation products being subsequently identified by mass spectrometry. It turned out that in the course of decomposition, hexachlorocyclopentadiene was formed, which is believed to be the active substance for flame retardance in these systems. The aspect of tailoring flame retardancy by changing the chemical environment, i.e., by using different diols, is discussed. 相似文献
66.
Johannes Reisch Anura Wickramasinghe 《Monatshefte für Chemie / Chemical Monthly》1990,121(8-9):709-712
Summary Epoxidation of the acridone alkaloid acronycine (1) resulted in hydroxylation at the aromatic ring giving 5-hydroxyacronycine (3). The same reaction on 1,3-dimethoxy-10-methyl-9(10H)-acridinone (5) gave 1,3-dimethoxy-2-hydroxy-10-methyl-9(10H)-acridinone (6), 1,3-dimethoxy-2-hydroxy-4-peroxy-10-methyl-9(10H)-acridinone (8), and 1,3-dimethoxy-2,4-diperoxy-10-methyl-9(10H)-acridinone (9).
Naturstoffchemie, 137. Mitt.: Oxidierung von Acridonalkaloiden: Synthese des 5-Methoxyacronycins (Kurze Mitt.)
Zusammenfassung Die Epoxidierung des Acridonalkaloids Acronycin führte zu einer Hydroxylierung des aromatischen Rings, wobei 5-Hydroxyacronycin (3) entstand. Die gleiche Reaktion mit 1,3-Dimethoxy-10-methyl-9(10H)acridinon (5) ergab 1,3-Dimethoxy-2-hydroxy-10-methyl-9(10H)acridinon (6), 1,3-Dimethoxy-2-hydroxy-4-peroxy-10-methyl-9(10H)acridinon (8) und 1,3-Dimethoxy-2,4-diperoxy-10-methyl-9(10H)acridinon (9).相似文献
67.
68.
René Csuk Johannes Haas Helmut Hönig Hans Weidmann 《Monatshefte für Chemie / Chemical Monthly》1981,112(6-7):879-882
A synthesis of new boron containingMannich bases of salicylamide by reaction of salicylamide, formaldehyde and boron-heterocycles is reported.
VIII. Mitteilung:Stump, R. K., Zimmerman jr., H. K., Schleppnik, A. A., Gutsche, C. D., Liebigs Ann. Chem.667, 18 (1963). 相似文献
69.
Stereochemical effects in supramolecular self-assembly at surfaces: 1-D versus 2-D enantiomorphic ordering for PVBA and PEBA on Ag(111) 总被引:2,自引:0,他引:2
Barth JV Weckesser J Trimarchi G Vladimirova M De Vita A Cai C Brune H Günter P Kern K 《Journal of the American Chemical Society》2002,124(27):7991-8000
We present investigations on noncovalent bonding and supramolecular self-assembly of two related molecular building blocks at a noble metal surface: 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA) and 4-[(pyrid-4-yl-ethynyl)]benzoic acid (PEBA). These rigid, rodlike molecules comprising the same complementary moieties for hydrogen bond formation are comparable in shape and size. For PVBA, the ethenylene moiety accounts for two-dimensional (2-D) chirality upon confinement to a surface; PEBA is linear and thus 2-D achiral. Molecular films were deposited on a Ag(111) surface by organic molecular beam epitaxy and characterized by scanning tunneling microscopy. At low temperatures (around 150 K), both species form irregular networks of flat lying molecules linked via their endgroups in a diffusion-limited aggregation process. In the absence of kinetic limitations (adsorption or annealing at room temperature), hydrogen-bonded supramolecular assemblies form which are markedly different. With PVBA, enantiomorphic twin chains in two mirror-symmetric species running along a high-symmetry direction of the substrate lattice form by diastereoselective self-assembly of one enantiomer. The chirality signature is strictly correlated between neighboring twin chains. Enantiopure one-dimensional (1-D) supramolecular nanogratings with tunable periodicity evolve at intermediate coverages, reflecting chiral resolution in micrometer domains. In contrast, PEBA assembles in 2-D hydrogen-bonded islands, which are enantiomorphic because of the orientation of the supramolecular arrangements along low-symmetry directions of the substrate. Thus, for PVBA, chiral molecules form 1-D enantiomorphic supramolecular structures because of mesoscopic resolution of a 2-D chiral species, whereas with PEBA, the packing of an achiral species causes 2-D enantiomorphic arrangements. Model simulations of supramolecular ordering provide a deeper understanding of the stability of these systems. 相似文献
70.
A technique for imaging of charge inhomogeneities in dielectric layers with the aid of the mirror electron microscope is described. The experimental results given being interpreted in a semiquantitative way, are first of all related to silicon oxide evaporation layers. 相似文献