- Acylation of 2,2-Dimathyl-2H-chromenes
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Orientation in acylation reactions of 2,2-dimethyl-2H-chromenes was studied.Five acetylchromenes were obtained with two methods and six formylchromenes were obtained with a third method.Demethylation of four acyl-methoxy-substituted chromenes gave the corresponding acylchromenols. 2,2-Dimethyl-2H-chromene-6-carboxylic acid (anofinic acid) was also obtained by oxidation of 6-formylchromene.
- Yamaguchi, Seiji,Yamamoto, Satoru,Abe, Shoichi,Kawase, Yoshiyuki
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- Isolation and synthesis of chalcones with different degrees of saturation
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Crotaoprostrin, a chalcone not yet known as a plant constituent, was isolated from the aerial parts of the Indian medicinal plant Crotalaria prostrata. The structures of the chalcone polyarvin and the partially hydrogenated naturally occurring derivatives
- Krohn, Karsten,Steingr?ver, Klaus,Srinivasa Rao
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- Natural product derived antiprotozoal agents: Synthesis, biological evaluation, and structure-activity relationships of novel chromene and chromane derivatives
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Various natural products with the chromane and chromene scaffold exhibit high antiprotozoal activity. The natural product encecalin (7) served as key intermediate for the synthesis of different ethers 9, amides 11, and amines 12. The chromane analogues 14 and the phenols 15 were obtained by reductive amination of ketones 13 and 6, respectively. Angelate 3, ethers 9, and amides 11 did not show considerable antiprotozoal activity. However, the chromene and chromane derived amines 12, 14, and 15 revealed promising antiprotozoal activity and represent novel lead compounds. Whereas benzylamine 12a and α-methylbenzylamine 12g were active against P. falciparum with IC 50 values in the range of chloroquine, the analogous phenols 15a and 15b were unexpectedly 10- to 25-fold more potent than chloroquine with selectivity indexes of 6760 and 1818, respectively. The phenylbutylamine 14d based on the chromane scaffold has promising activity against T. brucei rhodesiense and L. donovani.
- Harel, Dipak,Schepmann, Dirk,Prinz, Helge,Brun, Reto,Schmidt, Thomas J.,Wünsch, Bernhard
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p. 7442 - 7448
(2013/10/21)
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- Encecalol angelate, an unstable chromene from Ageratum conyzoides L.: Total synthesis and investigation of its antiprotozoal activity
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Ethnopharmacological relevance: In agreement with ethnomedicinal reports, the dichloromethane extract of Ageratum conyzoides L. (Asteraceae) was recently shown to be of considerable activity against Trypanosoma brucei rhodesiense, the etiologic agent of East African Human Trypanosomiasis (East African Sleeping Sickness). Isolated compounds, namely, methoxylated flavonoids as well as the chromene derivative encecalol methyl ether, were less active than the crude extract. The activity of the extract was found to decrease considerably while stored in solution. An unstable compound was detected in the fresh extract by HPLC, which was converted rapidly into the encecalol methyl ether while stored in methanolic solution. This compound, deemed to represent a constituent with antitrypanosomal activity, could not be isolated from the extract in intact form. Aim of the study: To elucidate the structure of this unstable compound and to investigate its potential role in the antitrypanosomal activity of the total extract. Materials and Methods: UHPLC/ESI-qQTOF MSMS and NMR data of the degraded product indicated its chemical identity as encecalol angelate (1) which was therefore prepared by total synthesis via a linear six steps synthesis, starting from resorcinol and 2-methylbut-3-en-2-ol. Results: Total synthesis, in an overall yield of 15%, led to pure 1, which was chromatographically and spectroscopically identical with the natural product. The compound degraded in methanol with a half-life of approximately 6 h to yield encecalol methyl ether (2). The antiprotozoal activity of synthetic encecalol angelate against T. brucei rhodesiense as well as T. cruzi, Leishmania donovani and Plasmodium falciparum was investigated and found to be quite low. Conclusions: The synthetic approach applied here for the first time also provides access to the related bioactive chromenes encecalin (7) and encecalol (8) with improved yields compared with reported methods. Encecalol angelate, however, is most likely not responsible for the high antitrypanosomal activity of the freshly prepared dichloromethane extract of A. conyzoides.
- Harel, Dipak,Khalid, Sami A.,Kaiser, Marcel,Brun, Reto,Wuensch, Bernhard,Schmidt, Thomas J.
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p. 620 - 625
(2012/06/01)
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- Anti-AIDS agents 83. Efficient microwave-assisted one-pot preparation of angular 2,2-dimethyl-2H-chromone containing compounds
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A novel and efficient microwave-assisted one-pot reaction was developed to synthesize angular 2,2-dimethyl-2H-chromone-containing compounds, which is the first and key step in the synthesis of potent DCK and DCP anti-HIV agents. The newly developed microwave synthesis conditions dramatically shortened the reaction time from 2 days to 4 h with improved yields.
- Zhou, Ting,Shi, Qian,Lee, Kuo Hsing
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experimental part
p. 4382 - 4386
(2010/09/12)
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- The first asymmetric total synthesis of several 3,4-dihydroxy-2,2-dimethyl- chroman derivatives
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The stereoisomers of 3,4-dihydroxy-6-methoxy-2,2-dimethyl-chroman 1a-c and 3,4,7-trihydroxy-6-acetyl-2,2-dimethyl-chroman 2a-c were conveniently prepared for the first time via a synthesis in which Sharpless asymmetric dihydroxylation and Jacobsen's catalytic asymmetric epoxidation are the key steps.
- Wang, Qiaoling,She, Xuegong,Ren, Xinfeng,Ma, Junying,Pan, Xinfu
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- Natural product-like combinatorial libraries based on privileged structures. 1. General principles and solid-phase synthesis of benzopyrans
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Herein we report a novel strategy for the design and construction of natural and natural product-like libraries based on the principle of privileged structures, a term originally introduced to describe structural motifs capable of interacting with a variety of unrelated molecular targets. The identification of such privileged structures in natural products is discussed, and subsequently the 2,2-dimethylbenzopyran moiety is selected as an inaugural template for the construction of natural product-like libraries via this strategy. Initially, a novel solid-phase synthesis of the benzopyran motif is developed employing a unique cycloloading strategy that relies on the use of a new, polystyrene-based selenenyl bromide resin. Once the loading, elaboration, and cleavage of these benzopyrans was established, this new solid-phase method was then thoroughly validated through the construction of six focused combinatorial libraries designed around natural and designed molecules of recent biological interest.
- Nicolaou,Pfefferkorn,Roecker,Cao,Barluenga,Mitchell
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p. 9939 - 9953
(2007/10/03)
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- A short synthetic route to benzofurans. syntheses of naturally occurring euparin and related compounds
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Euparin (4a) and related benzofurans (4b-e, g) were synthesized by conversion of the corresponding o-(3-hydroxy-3-methylbutynyl)phenyl tosylates (2) in the presence of base into the 2-(1-hydroxy-1-methylethyl)benzofurans (3), followed by dehydration in hi
- Sogawa, Akihiro,Tsukayama, Masao,Nozaki, Hiroshi,Nakayama, Mitsuru
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p. 101 - 111
(2007/10/02)
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- REGIOSELECTIVE PRENYLATION OF PHENOLS BY PALLADIUM CATALYST: SYNTHESES OF PRENYLPHENOLS AND CHROMANS
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The palladium-catalyzed coupling reaction of iodophenols (1) with 2-methyl-3-butyn-2-ol gave alkynylphenols (2).Catalytic hydrogenation of 2 over Raney nickel and the subsequent dehydration of the resultant alkylphenols (3) gave regioselectively the desired prenylphenols (4).Dehydration of alkylphenols (3f-h) gave chromans (7).
- Tsukayama, Masao,Kikuchi, Makoto,Kawamura, Yasuhiko
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p. 1487 - 1490
(2007/10/02)
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- HETEROCYCLES FROM DIACETYL PHENOLS: SYNTHESIS OF BENZODIPYRANS, ACETYLCHROMENES AND PYRANOBENZISOXAZOLES
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Novel and facile syntheses of benzodipyrans, acetylchromenes and pyranolbenzisoxazoles from 2,4- and 4,6-diacetylresorcinols have been described.Regioselective condensations and reductions have been used as the key steps.
- Banerji, Asoke,Kalena, Govind P.
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p. 711 - 718
(2007/10/02)
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- PHOTOCHEMISTRY OF 7-ACETOXYBENZOPYRAN DERIVATIVES. SYNTHESIS OF EUPATORIOCHROMENE AND ENCECALIN
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The photolysis of the 7-acetoxybenzopyran derivatives 1a-5a has been carried out.Chromen 1a was found to undergo extensive photopolymerization.Chromanone 2a underwent a rather inefficient photo-Fries rearrangement to the 6- and 8- acetyl derivatives 2b and 2c.Diacetoxychromene 3a gave the unsaturated ketone 8 as the main product, besides its deacetylation analogue 9 and chromanone 11.Diacetoxychroman 4a afforded a mixture of four C-acetyl products: 1b, 1c, 2b and 2c, together with chromene 1a and chromanone 2a.Finally, irradiation of chroman 5a gave rise to a mixture of the two possible photo-Fries products 5b (43percent) and 5c (52percent).The mechanistic implications of the above results are discussed, with special emphasis on the photoreactivity of the phenyl ester as compared with that of the pyran ring, the enol ester and the benzyl ester moieties.The synthetic applications of these transformations are illustrated with the preparation of eupatoriochromene 1b and encecalin 1e.
- Miranda, Miguel A.,Primo, Jaime,Tormos, Rosa
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p. 7593 - 7600
(2007/10/02)
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- A Study of Partial Demethylation of Isopentenylated Methoxyacetophenones with Trimethylsilyl Iodide
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Demethylation of 2,4-dimethoxy-5-C-(II) and 3-C-(V) prenylacetophenones and 6-acetyl-5-methoxy-(VIII) and 7-methoxy-(X)-2,2-dimethylchromenes according to the method of Morita et al affords the corresponding hydroxy compounds (II
- Jain, A. C.,Gupta, S. M.,Gupta, Atul
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p. 274 - 275
(2007/10/02)
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- AN ELEGANT SYNTHESIS OF SOME NATURALLY OCCURRING LINEAR ACETYLCHROMENES: EUPATORIOCHROMENE, METHYLEUPATORIOCHROMENE (ENCECALIN); EVODIONOL AND METHYLEVODIONOL
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An elegant synthesis of linear acetylchromenes, viz eupatoriochromene, methyleupatoriochromene (encecalin), evodionol and methylevodionol, has been achieved by blocking the reactive position C-3 of the appropriate ketones with an iodo group, prenylation with 3-chloro-3-methylbut-1-yne and subsequent cyclisation.Regiospecific introduction of C-prenyl group in the less reactive position C-5 has been achieved by the reaction of the appropriate 3-iodo ketones with 2-methylbut-3-en-2-ol.The 5-prenyl ketones are also essential intermediates for the synthesis of linear acetylchromenes.
- Ahluwalia, V. K.,Prakash, Chandra,Gupta, Ranjna
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p. 609 - 611
(2007/10/02)
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- NUCLEAR ISOPRENYLATION OF POLYHYDROXYACETHOPHENONES ACID CATALYSED CONDENSATION WITH ISOPRENE
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A novel method of nuclear isoprenylation leading to the exclusive formation of 2,2-dimethylchromans has been achieved by the direct condensation of polyhydroxyacetophenones with isoprene in presence of phosphoric acid.Acetylchromans, thus obtained, are dehydrogenated with DDQ to given corresponding 2,2-dimethylchromenes.Using this method, synthesis of number of naturally occuring chromenes, viz. ripariochromene A (6), eupatoriochromene (10), encecalin (11), isoevodionol (16), evodionol (17) and methylevodionol (18) has been affected.
- Ahluwalia, V. K.,Arora, K. K.
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p. 1437 - 1440
(2007/10/02)
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