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Molecules, Volume 6, Issue 5 (May 2001) – 8 articles , Pages 424-495

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77 KiB  
Article
Thermal Rearrangement of Allyl Substituted Unsymmetric 4H-1,2,4-Triazoles to the Corresponding 1H-1,2,4-triazoles
by Kåre B. Jørgensen, Ragnhild B. Olsen and Per H.J. Carlsen
Molecules 2001, 6(5), 481-495; https://doi.org/10.3390/60500481 - 30 Apr 2001
Cited by 6 | Viewed by 9071
Abstract
A series of neat 4-(2-alkenyl) substituted 5-methyl-3-phenyl-4H-1,2,4-triazoles were thermolyzed at 320 oC producing a rearrangement products, of which the regioisomeric 1- and 2-substituted triazoles were the main products. The group migrations were rationalized in terms of consecutive SN2-type [...] Read more.
A series of neat 4-(2-alkenyl) substituted 5-methyl-3-phenyl-4H-1,2,4-triazoles were thermolyzed at 320 oC producing a rearrangement products, of which the regioisomeric 1- and 2-substituted triazoles were the main products. The group migrations were rationalized in terms of consecutive SN2-type reactions. This mechanism was supported by a study of the alkylations of the triazoles which gave similar product mixtures. 4-(2-alkenyl) substituted 3-phenyl-4H-1,2,4-triazoles, on the other hand, gave predominantly elimination products. Full article
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90 KiB  
Article
Synthesis of 2,4,6-Tris(4-N-isopropylamidinophenyl)pyrimidine trihydrochloride
by Miroslav Bajić and David W. Boykin
Molecules 2001, 6(5), 477-480; https://doi.org/10.3390/60500477 - 30 Apr 2001
Viewed by 7544
Abstract
The synthesis of 2,4,6-tris(4-N-isopropylamidinophenyl)pyrimidine from 1,3-di(4-bromophenyl)propen-3-one and 4-bromobenzamidine is reported. Full article
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30 KiB  
Article
Generation and Cycloaddition of o-Quinodimethane in Aqueous Medium
by Lothar W. Bieber and Margarete F. Da Silva
Molecules 2001, 6(5), 472-476; https://doi.org/10.3390/60500472 - 30 Apr 2001
Cited by 11 | Viewed by 9615
Abstract
o-Quinodimethane can be generated from =α,α'-dihalo-o-xylenes using zinc in aqueous solution. In the presence of activated dienophiles cycloadducts can be obtained directly. Catalysis with tris-triphenylphosphine ruthenium(II) dichloride reduces side reactions such as reduction and polymerisation and improves the yield. This is the first [...] Read more.
o-Quinodimethane can be generated from =α,α'-dihalo-o-xylenes using zinc in aqueous solution. In the presence of activated dienophiles cycloadducts can be obtained directly. Catalysis with tris-triphenylphosphine ruthenium(II) dichloride reduces side reactions such as reduction and polymerisation and improves the yield. This is the first example of an organometallic cyclisation in aqueous medium using dihalo compounds. Full article
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24 KiB  
Article
Facile and efficient synthesis of 3β-hydroxy-eupholanost-8-en-24-one
by N. El Aouad, A. Benharref and R. Gree
Molecules 2001, 6(5), 468-471; https://doi.org/10.3390/60500468 - 30 Apr 2001
Viewed by 7161
Abstract
The epoxidation of the natural product α-euphol followed by cleavage of the obtained epoxide with BF3-etherate, provides 3β-hydroxy-eupholanost-8-en-24-one in satisfactory overall yield. Full article
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251 KiB  
Article
Characterisation of Neuropeptide Y Receptor Subtypes by Synthetic NPY Analogues and by Anti-receptor Antibodies
by Christophe P. Eckard, Chiara Cabrele, Heike A. Wieland and Annette G. Beck-Sickinger
Molecules 2001, 6(5), 448-467; https://doi.org/10.3390/60500448 - 30 Apr 2001
Cited by 16 | Viewed by 9939
Abstract
Neuropeptide Y (NPY), a 36-mer neuromodulator, binds to the receptors Y1, Y2, Y4 and Y5 with nanomolar affinity. They all belong to the rhodopsin-like G-protein coupled, seven transmembrane helix spanning receptors. In this study, Ala-substituted and centrally [...] Read more.
Neuropeptide Y (NPY), a 36-mer neuromodulator, binds to the receptors Y1, Y2, Y4 and Y5 with nanomolar affinity. They all belong to the rhodopsin-like G-protein coupled, seven transmembrane helix spanning receptors. In this study, Ala-substituted and centrally truncated NPY analogues were compared with respect to affinity to the Yreceptors. Furthermore, antibodies against the second (E2) and the third (E3) extracellular loop of NPY Y1-, Y2- and Y5-receptor subtypes were raised and affinity to intact cells was tested by immunofluorescence assays. Both methods were applied in order to receive subtype selective tools and to characterise ligand binding. The analogues [A13]-pNPY and [A27]-pNPY showed subtype selectivity for the Y2-receptor. Sera against the E2 loop of the Y1-receptor and against the E2 loop of the Y2-receptor were subtype selective. Two antibodies against the Y5 E2 and E3 loop recognised the Y5- and Y2-receptor subtypes. In combination, these sera are able to distinguish between the Y1-, Y2-, and Y5-receptor subtypes. The analogues and antibodies represent valuable tools to distinguish NPY receptors on membranes and intact cells. Full article
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69 KiB  
Article
Facile and Fast Pinacol Rearrangement by AlCl3 in the Solid State
by Parviz Rashidi-Ranjbar and Ebrahim Kianmehr
Molecules 2001, 6(5), 442-447; https://doi.org/10.3390/60500442 - 30 Apr 2001
Cited by 11 | Viewed by 10293
Abstract
A facile and efficient synthetic procedure for effecting the pinacol rearrangement catalyzed by AlCl3 in the absence of solvent is developed. The rearrangement product is obtained at room temperature in a few minutes and in almost quantitative yield. Benzylic pinacols rearrange under [...] Read more.
A facile and efficient synthetic procedure for effecting the pinacol rearrangement catalyzed by AlCl3 in the absence of solvent is developed. The rearrangement product is obtained at room temperature in a few minutes and in almost quantitative yield. Benzylic pinacols rearrange under these conditions, while aliphatic pinacols do not react. Full article
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177 KiB  
Article
Molecular and Crystal Structures of Three Berberine Derivatives
by Stanislav Man, Milan Potáček, Marek Nečas, Zdirad Žák and Jiří Dostál
Molecules 2001, 6(5), 433-441; https://doi.org/10.3390/60500433 - 30 Apr 2001
Cited by 20 | Viewed by 8879
Abstract
Berberine azide, berberine thiocyanate, and 8-cyano-8H-berberine were prepared from berberine chloride, a quaternary protoberberine alkaloid. The molecular and crystal structures of all compounds are reported and discussed. Full article
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93 KiB  
Article
On the Additions of Lithium Methyl p-Tolyl Sulfoxide to N-(PMP)Arylaldimines
by Cristina Zucca, Pierfrancesco Bravo, Eleonora Corradi, Stefano V. Meille, Alessandro Volonterio and Matteo Zanda
Molecules 2001, 6(5), 424-432; https://doi.org/10.3390/60500424 - 30 Apr 2001
Cited by 4 | Viewed by 9230
Abstract
The results presented in this paper confirm that the stereochemical outcome of the reversible additions of lithium (R)-methyl p-tolyl sulfoxide to N-arylidene-p-anisidines (NPMP imines) depends on: (a) the reaction conditions used and (b) the electronic properties of the arylidene moiety on the starting [...] Read more.
The results presented in this paper confirm that the stereochemical outcome of the reversible additions of lithium (R)-methyl p-tolyl sulfoxide to N-arylidene-p-anisidines (NPMP imines) depends on: (a) the reaction conditions used and (b) the electronic properties of the arylidene moiety on the starting imine. In particular, we show that under kinetic control (-70 °C) the additions involving electron-rich N-arylidene groups occur with very high stereocontrol in favor of the (2S,RS)-diastereomers, whereas an electron-deficient group favors the opposite stereochemical outcome. Based on the observations above, a mechanistic hypothesis is proposed. Full article
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