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971.
Sylvain Valère T. Sob Pierre Tane Bonaventure T. Ngadjui Joseph D. Connolly 《Tetrahedron》2007,63(36):8993-8998
Two novel labdane type diterpenoids, 8β(17)-epoxy-14,15,16-trihydroxylabd-12(E)-ene (aulacocarpin C) and 15,16-epoxy-14ξ,16ξ-dimethoxylabda-8(17),12-(E)-diene (aulacocarpin D) together with the known aulacocarpin A and B; 14,15-epoxy-8(17),12(E)-labdadien-16-al, coronarin E, and 15,16-epoxy-12β-hydroxy-labda-8(17)-13(16),14-triene were isolated from the seeds of Aframomum aulacocarpos. To the best of our knowledge, the last compound was isolated from a natural source for the first time. Acid hydrolysis of aulacocarpin D led to another new labdane type diterpenoid, 15,16-epoxy-12β-methoxylabda-8(17)-13(16),14-triene. The structures of all compounds were established on the basis of their spectroscopic data. These new compounds exhibit moderate trypanocidal activity. 相似文献
972.
Franois L. Lpine Sylvain M. Milot Mark L. J. Reimer Orval A. Mamer 《Journal of mass spectrometry : JMS》1992,27(11):1311-1316
Four tetrachlorinated bipbenyls were chlorinated with 35Cl2 to yield seventeen polychlorinated biphenyls (PCBs) substituted once or twice with chlorine enriched in 35Cl. Gas chromatographic analysis of the mixtures allowed the identification of the labelled PCBs produced by comparison of their relative retention times with published values. This also permitted the assignment of the position of the labels in these molecules. Mass spectrometric determination of the 35Cl/35Cl ratio of the ions corresponding to successive dechlorination of these PCBs in positive-ion electron impact (EI) allowed quantification of the residual 35Cl label in these ions. Chlorines in the ortho position are lost preferentially to those in meta or para positions. The first dechlorination reaction was found to be totally regioselective for at least two PCB congeners. 相似文献
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977.
Charles Audet Pierre Hansen Alejandro Karam Chi To Ng Sylvain Perron 《Optimization Letters》2008,2(4):483-495
We consider the problem of separating two sets of points in an n-dimensional real space with a (hyper)plane that minimizes the sum of L
p
-norm distances to the plane of points lying on the wrong side of it. Despite recent progress, practical techniques for the
exact solution of cases other than the L
1 and L
∞-norm were unavailable. We propose and implement a new approach, based on non-convex quadratic programming, for the exact
solution of the L
2-norm case. We solve in reasonable computing times artificial problems of up to 20000 points (in 6 dimensions) and 13 dimensions
(with 2000 points). We also observe that, for difficult real-life instances from the UCI Repository, computation times are
substantially reduced by incorporating heuristic results in the exact solution process. Finally, we compare the classification
performance of the planes obtained for the L
1, L
2 and L
∞ formulations. It appears that, despite the fact that L
2 formulation is computationally more expensive, it does not give significantly better results than the L
1 and L
∞ formulations. 相似文献
978.
Luis Arturo García Sylvain Berns Cecilia Anaya de Parrodi 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(6):o319-o321
The title compound, C20H30O3, is a new functionalized perhydrotriphenylene derivative formed via a tandem Michael addition–aldol reaction. The structural study reveals that the system of fused rings approximates a C2 point symmetry, with trans–cis–cis ring junctions, while highly symmetric all‐trans perhydrotriphenylene, previously characterized, approximates a D3 symmetry. The perhydrotriphenylene nucleus of the title compound corresponds to the third stable stereoisomer isolated for this polycyclic system. Considering that the Cs isomer was obtained recently through a similar tandem reaction, a general strategy is proposed which may help to obtain other stable stereoisomers of perhydrotriphenylene. 相似文献
979.
Manuel Velasco Ulises Hernández Joel L. Terán Dino Gnecco María L. Orea David M. Aparicio Víctor Gómez-Calvario Sylvain Bernès Jorge R. Juárez 《Tetrahedron letters》2019,60(12):820-824
The stereoconvergent synthesis of N-Boc-(2R,3S)-3-hydroxy-2-phenylpiperidine from (R)-1-(2-((tert-butyldimethylsilyl)oxy)-1-phenylethyl)piperidin-2-one is described. The key steps involved are α-hydroxylation of quiral lactam with O2, stereoconvergent reduction of (R)- or (S)-3-(benzyloxy)-piperidin-2-one with Red-Al® which afforded in both cases the trans-bicyclic oxazolidine in high stereoselectivity after chromatographic purification and a stereospecific Grignard addition to chiral bicyclic oxazolidine. 相似文献
980.
Broussy S Bernardes-Génisson V Quémard A Meunier B Bernadou J 《The Journal of organic chemistry》2005,70(25):10502-10510
[reaction: see text] An isoniazid-NAD adduct has been recently proposed as the ultimate metabolite responsible for the antituberculous activity of isoniazid (INH). Its structure results from binding of the isonicotinoyl radical at C4 position of the nicotinamide ring of NAD with further possible and debated cyclization to form a cyclic hemiamidal derivative. Replacing the pyridine cycle of INH in INH-NAD adduct by a phenyl cycle (BH-NAD adduct) was shown previously to still retain the activity. On these bases, the core structure (4-benzoyl-1,4-dihydronicotinamide ribonucleoside) of the BH-NAD adduct and a series of analogues have been synthesized by using 3,4-pyridinedicarboximide as starting material. Depending on the nature of the substituent (pyridine or aryl) and on the oxidized or the reduced state of the nicotinamide nucleus, they were found either in a cyclized hemiamidal or an opened form or were shown to exist in equilibrium under cyclized or opened forms. Although none of these compounds could significantly inhibit activity of the InhA or MabA reductases (two possible targets of isoniazid), they represent attractive targets to develop potential second-generation inhibitors, including the total chemical synthesis of the bioactive BH-NAD adduct. 相似文献