1,721,002 research outputs found
Stereoselective Synthesis of 4,5-Epoxy-1,2-Oxazin-6-ones via Reaction of beta-Lithiated Oxazolinyloxiranes with Nitrones
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Regio- and Stereoselective Lithiation of 2,3- Diphenylaziridines: A Multinuclear NMR Investigation
No full textThe R-lithiation-trapping sequence of trans-N-alkyl-2,3-diphenylaziridines (s-BuLi or s-BuLi/TMEDA),
taking place with a stereochemistry which dramatically depends on the solvent coordinating ability (inversion of configuration in THF and retention in toluene), has been carefully investigated. 1H,13C, and 7Li multinuclear NMR investigations at low temperature suggest that two differently configured lithiated aziridines (monomeric is-1-Li in THF and dimeric trans-1-Li in toluene) are involved
Lithiation of Cinnamyl Chloride: Stereoselective Synthesis of Propargylic Oxiranes and Aziridines
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Lactic Acid Bacteria as New Whole-Cells Biocatalysts for the Stereoselective Synthesis of Chiral Enantiopure Building Blocks
No full textBiocatalytic processes represent one of the most heavily used green methodologies in preparative chemistry to perform highly chemo-, regio-, and stereoselective organic transformations, which are typically run under very mild reaction conditions (e.g., almost neutral pH buffer solutions, ambient temperature or mild heating, atmospheric pressure).1. Whole-cell microorganisms offer several positive features as biocatalysts with respect to isolated enzymes as they are more accessible, stable and easier to handle. Moreover, the presence of efficient internal cofactors regeneration systems (e.g., NADH or NADPH in reduction reactions) allows for cheap biocatalytic processes to be carried out often using glucose as the sole carbon source.2.
In this Communication, we discuss the asymmetric bioreduction of aromatic ketones to the corresponding chiral secondary alcohols using lactic acid bacteria (LAB) as new whole-cells biocatalysts. Several strains among lactic acid bacteria LAB (LAB) and spore-forming bacteria (Bacillus spp.) bacilli from the culture collection of the Institute of Sciences of Food Production (CNR-ISPA, Bari) have been screened. Interestingly, among LAB, Weissella strains were found to be the most effective ones for the regioselective bioreduction of aromatic ketones to the corresponding S-alcohols, with high yields and enantiomeric excesses (ees), despite to the known R-stereopreference exhibited by other LAB species as Lactobacilli (Figure).2a,3. Overall, this methodology holds potential to become a promising cheap and environmentally friendly approach for the preparation of chiral nonracemic secondary alcohols and Active Pharmaceutical Ingredients (APIs).3
References:
[1] (a) K. Faber, Biotransformations In Organic Chemistry: A Textbook, 6 ed., Springer-Verlag: Berlin/Heidelberg, Germany, 2011; (b) R. C. Simon, F. G. Mutti, W. Kroutil, Drug Discov. Today Technol. 2013, 10, e37–e44;
[2] (a) P. Vitale, F. M. Perna, G. Agrimi, A. Scilimati, A. Salomone, C. Cardellicchio, V. Capriati, V. Org. Biomol. Chem. 2016, 14, 11438; (b) P. Vitale, V. M. Abbinante, F. M. Perna, A. Salomone, C. Cardellicchio, V. Capriati, Adv. Synth. Catal. 2017, 359, 1049.
[3] P. Vitale, F. M. Perna, G. Agrimi, I. Pisano, F. Mirizzi, R. Capobianco, V. Capriati, Catalysts 2018, 8, 55
Regioselective Lithiation of Aziridines: Synthetic Applications and NMR Structural Investigation
No full textAbstract: The “Aziridinyl Anion Methodology” (AAM), based on the metalation-trapping sequence of an easily available parent aziridine, has become an attractive way for the synthesis of functionalized aziridines.1 In our studies concerning the lithiation of N-unactivated aziridines we disclosed recently that the regioselectivity of the deprotonation reaction depends on the nature of the substitution on the carbon and nitrogen atoms of the aziridine ring as well as on the polarity of the medium in which the reaction is performed.
In this communication it will be reported that a regioselective α-lithiation of trans N-alkyl-2,3-diphenylaziridines occurs with inversion of configuration in a polar solvent (i.e. THF) and retention in a non polar solvent (i.e. toluene) making these results useful for synthetic purposes. A deep multinuclear (1H, 13C, 7Li, 6Li) 1D and 2D NMR investigation of the lithiated intermediates in different solvents has been performed with the aim to demonstrate that probably two differently configured organolithium species could be involved. The role of the nitrogen configuration on the regioselectivity of the lithiation will also be discussed for several functionalized aziridines
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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