1,721,296 research outputs found
SOLVOLYSIS OF BENZYLIC ALCOHOLS - MECHANISM AND STEREOCHEMISTRY OF THE ACID METHANOLYSIS OF DIASTEREOISOMERIC TRANS-1,2,3,4,4A,10A-HEXAHYDROPHENANTHREN-9-OL AND 4-TERT-BUTYL-1-PHENYLCYCLOHEXANOL
No full textThe solvolysis (MeOH) of representative benzocondensed and cyclohexanic diastereoisomeric benzylic alcohols (title compounds) has been studied. Both systems afford mixtures of products (methyl ethers) arising from inversion or retention of configuration on the benzylic reaction centre, with an increase in the retention product on addition of a salt (LiClO4). The results obtained do not appear to support the previous hypothesis of the intermediacy in these systems of fully developed benzylic carbenium ions, pseudoaxially attacked by the nucleophile. A rationalization based on the ion-dipole pair mechanism, implying the intermediacy of different benzylic carbocationic species, is alternatively proposed
Synthesis of the propionates of (2R,8R)- and (2RS,8R)-8-methyl-2-decanol, the attractants of the western corn rootworm
No full text(2R,8R)-8-Methyl-2-decanoyl propionate has been prepd. from enantiomerically pure (R)-HuO2CCH2CHMeCH2CO2Me, and (S)-glutamic acid, as chiral precursors. These have been stereospecifically converted into (R)-EtCHMeCH2Br, and (R)-1,4-pentanediol, resp. Biol. active (2RS)-8R)-EtCHMe(CH2)5CHuMeO2CL was prepd. from (R)-CH2CH2Br and racemic HOCHMe(CH2)3OH
Insar multitemporal data over persistent scatterers to detect floodwater in urban areas: A case study in beletweyne, Somalia
No full textA stack of Sentinel-1 InSAR data in an urban area where flood events recurrently occur, namely Beletweyne town in Somalia, has been analyzed. From this analysis, a novel method to deal with the problem of flood mapping in urban areas has been derived. The approach assumes the availability of a map of persistent scatterers (PSs) inside the urban settlement and is based on the analysis of the temporal trend of the InSAR coherence and the spatial average of the exponential of the InSAR phase in each PS. Both interferometric products are expected to have high and stable values in the PSs; therefore, anomalous decreases may indicate that floodwater is present in an urban area. The stack of Sentinel-1 data has been divided into two subsets. The first one has been used as a calibration set to identify the PSs and determine, for each PS, reference values of the coherence and the spatial average of the exponential of the interferometric phase under standard non-flooded conditions. The other subset has been used for validation purposes. Flood maps produced by UNOSAT, analyzing very-high-resolution optical images of the floods that occurred in Beletweyne in April–May 2018, October–November 2019, and April–May 2020, have been used as reference data. In particular, the map of the April–May 2018 flood has been used for training purposes together with the subset of Sentinel-1 calibration data, whilst the other two maps have been used to validate the products generated by applying the proposed method. The main product is a binary map of flooded PSs that complements the floodwater map of rural/suburban areas produced by applying a well-consolidated algorithm based on intensity data. In addition, a flood severity map that labels the different districts of Beletweyne, as not, partially, or totally flooded has been generated to consolidate the validation. The results have confirmed the effectiveness of the proposed method
SYNTHESIS AND REACTIVITY OF BENZYLIC EPOXIDES DERIVED FROM 1,2,3,9,10,10A-HEXAHYDROPHENANTHRENE - SEARCH FOR A UNIFIED MECHANISM FOR THE RING-OPENING OF 2-ARYLOXIRANES
No full textEFFECT OF THE 9-METHYL SUBSTITUENT ON THE CHEMICAL BEHAVIOR UNDER ACID CONDITIONS OF THE DIASTEREOISOMERIC 9,10-OXIDES DERIVED FROM TRANS-1,2,3,4,4A,10A-HEXAHYDROPHENANTHRENE
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EFFECT OF THE 7-METHYL SUBSTITUENT ON THE RING-OPENING PROCESS OF THE DIASTEREOISOMERIC BENZYLIC EPOXIDES DERIVED FROM 1,2,3,9,10,10A-HEXAHYDROPHENANTHRENE - DIFFERENCES AND SIMILARITIES BETWEEN DIFFERENT 2-ARYLOXIRANE MODELS
No full textThe introduction of an electron-donating substituent (7-Me group) on the 1,2,3,9,10,10a-hexahydrophenanthrene system, influences differently the diastereoselectivity of the acid hydrolysis of the diastereoisomeric couples of benzylic epoxides 3a and 4a and 3b and 4b. While in 3b-4b an increase of the syn diastereoselectivity is observed, in 3a-4a a complete anti diastereoselectivity is found. On the other hand, the trichloroacetolyses of both 4a and 4b yield rearrangement products only, contrary to the unsubstituted derivatives 3a and 3b where consistent amounts of addition products were observed. The results obtained underline that system 3 presents apparent chemical similarities with system 2 and differs from 1 to which it is more closely related
Addressing the Target Identification and Accelerating the Repositioning of Anti-Inflammatory/Anti-Cancer Organic Compounds by Computational Approaches
No full textThe use of computational chemistry techniques has led to notable advances in the structural and pharmacological investigation of organic compounds. The combination of quantum mechanical (QM) approaches with experimental methods (e. g., NMR spectroscopy) has contributed to the configurational and conformational structural assignment of the investigated items. Once this information has been obtained, in silico tools have been employed for assessing the pharmacological features of natural and synthetic molecules, especially those lacking precise information about their interacting macromolecules. With this aim, we have developed and implemented the Inverse Virtual Screening (IVS) computational methodology for addressing the target identification task. This minireview focuses on the key technical information and on successful examples about the convenient and fast use of such computational methods in the frame of the drug repositioning and the discovery of anti-inflammatory/anti-cancer agents
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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