255 research outputs found

    Complexes of Rhenium(V) with Aminoacetopehenones and their Reactions with some Bidentate Ligands

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    Complexes of rhenium(V) with 2-, 3- and 4-aminoacetophenone (H2aap) have been synthesized. The reaction of trans-ReOCl3(PPh3)2 with 2-H2aap in benzene yielded the imido complex [Re(2-aap)Cl3(PPh3)], in which the oxo oxygen and one of the PPh3 groups were substituted by the dianionic imido nitrogen and the neutral ketonic oxygen, respectively. With 3- and 4-H2aap the imido complexes trans-[Re(aap)Cl3(PPh3)2] were isolated. The monodentate coordination mode of these latter two ligands was authenticated by the X-ray crystal structure of trans-[Re(3-aap)Cl3(PPh3)2]; crystals are triclinic, P1, with a = 10.567(5), b = 11.989(6), c = 18.739(8) Ã…, α= 74.82(4)º, β= 75.27(4)º, γ= 73.15(4)º, U = 2152(2) Ã…3, Z = 2, R = 0.0469. The further reaction of [Re(3-aap)Cl3(PPh3)2] with the bidentate ligands 2-aminophenol and 8-hydroxyquinoline (HL) led to the isolation of complexes of the type [Re(3-aap)Cl2(PPh3)(L)]. However, with 1,2-diaminobenzene (H2dab), the 3-aap imido moiety was displaced by the imido group {N(C6H4)NH2}, to give the complex trans-[Re(dab)Cl3(PPh3)2]. (Bulletin of The Chemical Society of Ethiopia: 2002 16 (2): 149-156

    Effect of chirality on the compression of 2-(2-Oxo-1-pyrrolidinyl)butyramide : a tale of two crystals

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    Understanding polymorphism in chiral systems for drug manufacturing is essential to avoid undesired therapeutic effects. Generally, polymorphism is studied through changes in temperature and solution concentration. A less common approach is the application of pressure. The goal of this work is to investigate the effect of pressure on levetiracetam (pure enantiomer) and etiracetam (racemic compound). Anisotropic compressions of levetiracetam and etiracetam are observed to 5.26 and 6.29 GPa, respectively. The most compressible direction for both was identified to be perpendicular to the layers of the structure. Raman spectroscopy and an analysis of intermolecular interactions suggest subtle phase transitions in levetiracetam (∼2 GPa) and etiracetam (∼1.5 GPa). The stability of etiracetam increases with respect to levetiracetam on compression; hence, the chiral resolution of this system is unfavorable using pressure. This work contributes to the ongoing efforts in understanding the stability of chiral systems

    Active Site Design in a Chemzyme: Development of a Highly Asymmetric and Remarkably Temperature-Independent Catalyst for the Imino Aldol Reaction**

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    The asymmetric aldol reaction of an enolate or enolate equivalent with an imine is a reaction of established synthetic importance for the synthesis of chiral amines in general and bamino esters in particular. [1] The development of chiral catalysts for this reaction has proven to be a difficult task and had eluded all attempts until recently when Kobayashi and co-workers examined imines derived from o-aminophenol. [2±4] Their method involves the catalysis of the reactions of these imines and ketene acetals with a catalyst generated from zirconium(iv) tert-butoxide and two equivalents of (R)-6,6'-dibromoBINOL (BINOL 1,1'-binaphth-2-ol). Our interest in the synthesis of chiral amines led us to investigate the use of VAPOL-derived catalysts A comparison of catalysts prepared from BINOL, 6,6'-dibromoBINOL and VAPOL ligands on the asymmetric induction in the reaction of the phenyl-substituted imine 1 and acetal 2 is summarized in [2] The VAPOL catalyst could be prepared in either methylene chloride or toluene, but for solubility reasons, the BINOL catalysts were prepared in methylene chloride. The VAPOL and Br 2 BINOL catalysts were superior to the BINOL catalyst at À 45 8C. The asymmetric induction dropped for the Br 2 BINOL catalyst when the temperature was raised from À 45 8C to room temperature, but curiously, the asymmetric induction for the VAPOL catalyst was essentially unchanged over this same temperature range. Only a small drop-off is noted (85 % ee) when the temperature is raised to 41 8C and the substrate-to-catalyst ratio is raised to 200:1 (entry 5). Both the R enantiomers of BINOL and Br 2 BINOL ligands give the R enantiomer of the product 3, whereas with the VAPOL ligand, it is the S enantiomer that gives the R product. This reversal is not unexpected given the structures of the ligands where the zirconium is in the minor groove of the BINOL ligands and in the major groove of the VAPOL ligand. [2g] It is clear from the examination of space-filling CPK models that it is possible to bind two VAPOL ligands to one zirconium atom but only with a facial arrangement of the four oxygen atoms as is illustratred by structure 6 in Scheme 1. This is supported by 1 H NMR experiments on a catalyst generated from zirconium tetraisopropoxide and VAPOL in the presence of two equivalents of N-methyl imidiazole. A clean spectrum is only observed with two equivalents of VAPOL relative to zirconium and the spectrum is consistent with a single C 2 -symmetrical species were performed by using the TEXSAN [13] crystallographic software package. Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-153832. Copies of the data can be obtained free of charge on application to CCDC

    A systematic review of maternal antidepressant use in pregnancy and short- and long-term offspring's outcomes

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    The relative safety of antidepressants during pregnancy has received substantial attention, but most syntheses fail to account for mental illness effects. We aimed to evaluate the literature comparing low birth weight (LBW) and neurodevelopmental and neurobehavioural outcomes for children whose mothers took antidepressants in pregnancy compared to those whose mothers had common mental disorders, or symptoms, but who did not take antidepressants during pregnancy. A systematic review was conducted searching PubMed, MEDLINE, PsycINFO and Embase in January 2015. A modified version of the Newcastle Ottawa Scale was used to assess study quality. Eleven cohort studies were included: four reporting a LBW outcome (all with higher risk of bias) and seven reporting a neurodevelopmental outcome (five with higher risk of bias). We found only limited evidence of gestational age-adjusted LBW in exposed children in two studies which had a higher risk of bias and did not control for depressive symptom severity. Only five (7.5%) neurodevelopmental outcomes and one (12.5%) neurobehavioural outcome showed evidence of a statistically significant effect, three out of four were from studies with a higher risk of bias. There is little robust evidence indicating a detrimental effect of antidepressant use during pregnancy on LBW and neurodevelopmental and neurobehavioural outcomes. More rigorous study designs are needed

    Crystal structure of C11H18N2O2�HBr: Corrigendum

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