Browsing by Author "Valderrama, JA"

Now showing 1 - 13 of 13
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    Diels-Alder reactions of 1-dimethylamino-1-aza-1,3-dienes with benzo[b]thiophene-4,7-quinones
    (2003) Valderrama, JA; Cárdenas, L
    The cycloaddition reactions of 1-dimethylamino-1-azabuta-1,3-dienes with benzo[b]thiophene-4,7-quinones substituted at 2- and 2,3-positions have been investigated. The reactions afforded thienoquinolinequinones or mixture of regioisomeric thienoquinolinequinones depending upon the substituents of the partners. The regiochemistry of the cycloadditions are in accord with the HOMOdiene/LUMOdienophile interactions.
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    Epoxidation of quinones with urea hydrogen peroxide
    (PERGAMON-ELSEVIER SCIENCE LTD, 2003) Valderrama, JA; Gonzalez, MF; Torres, C
    Quinones reacted with urea-hydrogen peroxide complex in the presence of a base at room temperature, to give the corresponding quinone epoxides in 22-92% yields. The advantages of this new quinone epoxidation procedure are the requirement of organic solvent media, a easily handled solid reagent and a simple workup procedure.
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    Regioselectivity in the Diels-Alder reaction of 8,8-dimethylnaphthalene-1,4,5(8H)-trione with 2,4-hexadien-1-ol
    (1999) Araya-Maturana, R; Cassels, BK; Delgado-Castro, T; Valderrama, JA; Weiss-López, BE
    The Diels-Alder reactions of 8,8-dimethylnaphtalene-1,4,5(8H)-trione with 2,4-hexadien-1-ol and its O-acetyl derivative were investigated in different solvents. The regiochemistry of the cycloaddition of the hexadienol was determined through chemical correlation of one of the products. The solvent effect on the regioselectivity and endo/exo selectivity of this reaction is attributed to intermolecular hydrogen bonding between the hydroxyl group of the diene and the carbonyl oxygen atoms at C-4 and C-5 of the quinone in the transition state. The possible transition states have been modelled by AMI calculations in order to better interpret these experimental results. (C) 1998 Elsevier Science Ltd. All rights reserved.
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    Studies on quinones .30. Synthesis of benzo[b]thiophene-4,7-quinones
    (1997) Valderrama, JA; Valderrama, C
    The synthesis of a variety of benzo[b]thiophene-4,7-quinones (4a-f) by oxidative demethylation of the corresponding 4,7-dimethoxybenzo[b] thiophenes (3a-f) with cerium(IV) ammonium nitrate is reported. Heterocycles (3a,b) were prepared by cyclization of the corresponding 2,5-dimethoxy-6-nitrobenzaldehyde (1a) and 2,5-dimethoxy-6-nitroacetophenone (1b) with methyl thioglycolate.
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    Studies on quinones .31. Synthesis and cyclization of substituted 2-acetylamino-1,4-benzoquinones
    (1997) Valderrama, JA; Gonzalez, MF
    The synthesis of 4-acetylamino-5-hydroxybenzo[b]furans (7a), (7b), (13), and their oxidative furan ring opening to the corresponding substituted 2-acetylamino-1,4-benzoquinones (1a), (1b), and (2) are reported. The acid-induced cyclization of quinones (1a) and (2) to afford N-heterocyclic quinones (15) and (16) is also described.
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    Studies on quinones. Part 32. Regioselective synthesis of benz[b]phenantridines related to phenantroviridone
    (PERGAMON-ELSEVIER SCIENCE LTD, 1999) Valderrama, JA; Gonzalez, MF; Valderrama, C
    The Diels-Alder reaction of juglone (4) and bromojuglone 18 with 1-cyclohesenecarbosaldehyde dimethylhydrazone (3) is described. Through these cycloaddition reactions 8-hydroxy-1,2,3,4-tetrahydrobenz[b]phenantridin-7,12-dione (5) was obtained in 55 and 78% yield, respectively. Oxidation of 5 to 8-hydroxybenz[b]phenantridin-7,12-dione (6) and 8-hydroxy-1,2,3,4-tetrahydrobenz[b]phenantridin-1,7,12-trione (15) is also reported. (C) 1999 Elsevier Science Ltd. All rights reserved.
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    Studies on quinones. Part 33. Synthetic approach to podands containing quinone fragments
    (2000) Valderrama, JA; Leiva, H; Tapia, R
    The preparation and oxidative demethylation attempts of podands 3-5, and 9 containing the 2,5-dimethoxyphenyl substituent are described. The reaction of alizarine 13 with chloroethanol afforded compounds 14 and 15. The pathway formation of heterocycle 15 from 14 is proposed. The synthesis of podand 16 containing the cytotoxic 1-hydroxy-9,10-anthraquinone fragment as the terminal groups is reported.
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    Studies on quinones. Part 38: Synthesis and leishmanicidal activity of sesquiterpene 1,4-quinones
    (PERGAMON-ELSEVIER SCIENCE LTD, 2003) Valderrama, JA; Benites, J; Cortes, M; Pessoa Mahana, H; Prina, E; Fournet, A
    The reaction of (+)-euryfuran 1 with several benzo-, naphtho- and benzo[b]thiophene-1,4-quinones in acetic acid yields the corresponding euryfuryl-1.4-quinones 3, 5, 7, 8, 10, 12, and 14. The structure of compounds 7, 8, 12, and 14 was assigned through 2D NMR H-1-C-13 HMBC experiments. The influence of the acidity of the solvent upon the reactivity and regioselectivity of the quinones to the oxidative coupling reaction, is discussed. The in vitro activity of the euryfurylquinones and their corresponding precursors against Leishmania amazonensis is described. (C) 2003 Elsevier Ltd. All rights reserved.
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    Studies on quinones. Part 39: Synthesis and leishmanicidal activity of acylchloroquinones and hydroquinones
    (PERGAMON-ELSEVIER SCIENCE LTD, 2005) Valderrama, JA; Zamorano, C; Gonzalez, MF; Prina, E; Fournet, A
    Acylhydroquinone-based compounds are attractive targets for the design of new leishmanicidal drugs. We have previously described sesquiterpene quinones and hydroquinones series, which exhibit different degree of potency against Leishmania amazonensis. The present study details the preparation of acylchloroquinones and hydroquinones possessing lipophilic substituents and examines their in vitro activity against intracellular L. amazonensis amastigotes. The quinone or hydroquinone nucleus is essential for the activity of the members of the series. The lipophilicity of the cycloaliphatic systems in these members seems to attenuate the cytotoxical effect and increases the selectivity of those compounds containing the norbornene system. (c) 2005 Elsevier Ltd. All rights reserved.
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    Synthesis of 1-benzazepines as precursors of 1-benzazepinediones
    (MARCEL DEKKER INC, 2000) Pessoa Mahana, H; Valderrama, JA
    The synthesis of 6-hydroxy-7-nitro-1-benzazepine-2-one 7 from 5-hydroxy-1 -tetralone 1 and 6-hydroxy-1 -benzazepine-2-one 2 is described. Bromination of 6-hydroxy- 1-benzazepine-2-one 2 with NBS in ethyl acetate afforded 7-bromo-6-hydroxy-1 -benzazepine-2-one 13 and 7,9-dibromo-6-hydroxy-1-benzazepine-2-one 14. Oxidation of benzazepinone 13 with (diacetoxyiodo)benzene provided 7-bromo-1-benzazepine-2,6,9-trione 5.
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    Synthesis of 2H-naphtho[2,3-b]thiopyranoquinones and density functional study for the Diels-Alder reaction of a benzothiopyranoquinone
    (PERGAMON-ELSEVIER SCIENCE LTD, 2000) Tapia, RA; Garate, MC; Valderrama, JA; Zuloaga, F; Jenkins, PR; Fawcett, J; Russell, DR
    The synthesis of benzothiopyranoquinone (6) in three step from benzothiopyran (3) is described. Diels-Alder reaction of quinone (6) with 1,3-pentadiene (7), cyclopentadiene, 1-methoxy-1,3-cyclohexadiene (11) and 1-dimethylamino-1-aza-1,3-pentadiene (14) was studied. The Density Functional Theory was applied to explain the orientation of the cycloaddition reaction of quinone (6) with dienes (7), (11) and (14).
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    Synthesis of furanonaphthazarin derivatives
    (PERGAMON-ELSEVIER SCIENCE LTD, 1998) Tapia, RA; Garate, MC; Valderrama, JA; Jenkins, PR
    A three-step synthesis of the 58-dihydroxy-2-(1-methylethyl)naphtho[2,3-b]furan-4,9-dione (9) starting from 2-hydroxy-5,8-dimethoxy-1,4-naphthoquinone (4), is described. Further treatment of (9) with selenium dioxide in the presence of pyridine N-oxide as co-oxidant gave 2-(1-hydroxy-1-methylethyl)naphtho[2,3-b]furan-4,9-dione (10).
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    The Diels-Alder reaction of 1-cyclohexenecarbaldehyde N,N-dimethylhydrazone with juglone
    (1997) Valderrama, JA; Spate, M; Gonzalez, MF
    The synthesis of 1-cyclohexenecarbaldehyde N,N-dimethylhydrazone 7 from cyclohexanecarbaldehyde by using a three step sequence is reported. The Diels-Alder reaction of juglone 5 with azadiene 7 provides hexahydrobenzo[b]phenantridine 14a in 55% tetrahydrobenzo[b]phenantridines 15a and 15b. Angular tetracyclic quinone 15a was formed in 47% yield by caning out the cycloaddition of 5 and 7 in the presence of oxygen. Under this oxidant condition compound 15a undergoes partial oxidation to tetracyclic quinone 17.