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

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Research

Open AccessArticle On the Additions of Lithium Methyl p-Tolyl Sulfoxide to N-(PMP)Arylaldimines
Molecules 2001, 6(5), 424-432; doi:10.3390/60500424
Received: 8 March 2001 / Revised: 3 April 2001 / Accepted: 4 April 2001 / Published: 30 April 2001
Cited by 2 | PDF Full-text (93 KB) | HTML Full-text | XML Full-text
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
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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
Open AccessArticle Molecular and Crystal Structures of Three Berberine Derivatives
Molecules 2001, 6(5), 433-441; doi:10.3390/60500433
Received: 23 February 2001 / Revised: 9 April 2001 / Accepted: 10 April 2001 / Published: 30 April 2001
Cited by 10 | PDF Full-text (177 KB) | HTML Full-text | XML Full-text
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
Open AccessArticle Facile and Fast Pinacol Rearrangement by AlCl3 in the Solid State
Molecules 2001, 6(5), 442-447; doi:10.3390/60500442
Received: 12 February 2001 / Revised: 9 April 2001 / Accepted: 10 April 2001 / Published: 30 April 2001
Cited by 3 | PDF Full-text (69 KB) | HTML Full-text | XML Full-text
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
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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
Open AccessArticle Characterisation of Neuropeptide Y Receptor Subtypes by Synthetic NPY Analogues and by Anti-receptor Antibodies
Molecules 2001, 6(5), 448-467; doi:10.3390/60500448
Received: 1 November 2000 / Accepted: 6 November 2000 / Published: 30 April 2001
Cited by 4 | PDF Full-text (251 KB) | HTML Full-text | XML Full-text
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
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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
Open AccessArticle Facile and efficient synthesis of 3β-hydroxy-eupholanost-8-en-24-one
Molecules 2001, 6(5), 468-471; doi:10.3390/60500468
Received: 24 November 2000 / Revised: 20 December 2000 / Accepted: 20 December 2000 / Published: 30 April 2001
PDF Full-text (24 KB) | HTML Full-text | XML Full-text
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
Open AccessArticle Generation and Cycloaddition of o-Quinodimethane in Aqueous Medium
Molecules 2001, 6(5), 472-476; doi:10.3390/60500472
Received: 9 March 2001 / Revised: 24 April 2001 / Accepted: 24 March 2001 / Published: 30 April 2001
Cited by 5 | PDF Full-text (30 KB) | HTML Full-text | XML Full-text
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
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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
Open AccessArticle Synthesis of 2,4,6-Tris(4-N-isopropylamidinophenyl)pyrimidine trihydrochloride
Molecules 2001, 6(5), 477-480; doi:10.3390/60500477
Received: 20 January 2001 / Accepted: 17 March 2001 / Published: 30 April 2001
PDF Full-text (90 KB) | HTML Full-text | XML Full-text
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
Open AccessArticle Thermal Rearrangement of Allyl Substituted Unsymmetric 4H-1,2,4-Triazoles to the Corresponding 1H-1,2,4-triazoles
Molecules 2001, 6(5), 481-495; doi:10.3390/60500481
Received: 14 March 2001 / Revised: 26 April 2001 / Accepted: 26 April 2001 / Published: 30 April 2001
Cited by 3 | PDF Full-text (77 KB) | HTML Full-text | XML Full-text
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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