Showing papers on "Xanthone published in 1974"
TL;DR: From the bark extractives of Calophyllum trapezifolium thw. calabaxanthone (I), taraxerol, β-simiarenol and β-sitosterol, and a new xanthone, trapezifiolixanthone(III) have been isolated.
Abstract: From the bark extractives of Calophyllum trapezifolium Thw. calabaxanthone (I), taraxerol, β-simiarenol, β-sitosterol, and a new xanthone, trapezifolixanthone (III) have been isolated. The latter has been shown to be 5,10-dihydroxy-2,2-dimethyl-12-(3-methylbut-2-enyl)pyrano[3,2-b]xanthen-6(2H)-one.
31 citations
TL;DR: The pharmacological profile of activities of these compounds indicated that the curative properties ascribed to the plant extracts, in the Indian system of medicine, are essentially due to the xanthone-O-glucosides.
28 citations
TL;DR: From the heartwood of Garcinia pedunculata, 2,4,6,3′,5′-pentahydroxybenzophenone and 1,3,5,7-tetrahydroxyxanthone have been isolated as mentioned in this paper.
26 citations
TL;DR: The 13C N.m.r. spectra of tajixanthone (I) and related compounds (VI, VII, and XV) have been completely assigned as mentioned in this paper, and they show patterns of enrichment consistent with a biosynthetic pathway in which the xanthone arises by ring scission of 1,8-dihydroxy-3-methyl-9-anthrone (chrysophanol anthrone).
Abstract: The 13C N.m.r. spectra of tajixanthone (I) and related compounds (VI)–(XV) have been completely assigned Spectra of tajixanthone derived by incorporation of [1-13C]- and [2-13C]-acetate show patterns of enrichment consistent with a biosynthetic pathway in which the xanthone arises by ring scission of 1,8-dihydroxy-3-methyl-9-anthrone (chrysophanol anthrone), derived on a β-ketide pathway, with introduction of C- and O-prenyl units from mevalonate.
25 citations
TL;DR: In this article, the bark and timber extractives of C. thwaitesii Planch and Triana and C. walkeri Wight have been studied and a new di-isoprenylated xanthone has been isolated from the former and shown to be 13.
Abstract: The bark and timber extractives of C. thwaitesii Planch and Triana and C. walkeri Wight have been studied. The former contained taraxerol and friedelin in the bark whilst the latter had taraxerol and β-simiarenol. In addition a new di-isoprenylated xanthone, named thwaitesixanthone, has been isolated from the former and shown to be 13-hydroxy-3,3,10,10-tetramethyl-3H,10H-dipyrano[3,2-a:2′,3′-i]xanthen-14-one (IV) while calabaxanthone, 5-hydroxy-8-methoxy-2,2-dimethyl-7-(3-methylbut-2-enyl)-2H-pyrano[3,2-b]xanthen-6-one (I) was isolated from the latter. The timber extractives of both species gave 1,5-dihydroxyxanthone, 1,7-dihydroxyxanthone, jacareubin (IIa), and β-sitosterol. The latter species also contained guanandin (VIII), 1,3,5-trihydroxy-2-(3-methylbut-2-enyl)xanthone (X), and the new metabolite 1,5-dihydroxy-2,3-dimethoxyxanthone (IX).
24 citations
TL;DR: In this paper, Salicylic acid and C-methylphloroglucinol gave the already known 1,3-dihydroxy-2-methylxanthone (1) along with two new compounds: 1, 3-dhedroxy-4-methyl xanthone(2) and a second one tentatively presented as being 1.3dhedioxymethyl-2.4-(2-hydroxybenzoyl)xanthones (3).
Abstract: Condensation of salicylic acid and C-methylphloroglucinol gave the already known 1,3-dihydroxy-2-methylxanthone (1) along with two new compounds: 1,3-dihydroxy-4-methylxanthone (2) and a second one tentatively presented as being 1,3-dihydroxy-2-methyl-4-(2-hydroxybenzoyl)xanthone (3). The UV., IR., NMR, and mass spectra for the two first compounds are reported and their structures discussed on the basis of δ-values for H(2), H(4), CH3(4) and CH3(2). The UV. and IR. spectra for the third compound are reported too.
12 citations
TL;DR: Methylenedioxyphenyl derivatives and the compounds structurally related to piperonyl butoxide, which has been found to be a potent protectant against ozone injury to plants, were tested for effectiveness against the same injury to tobacco leaves as discussed by the authors.
Abstract: Methylenedioxyphenyl derivatives and the compounds structurally related to piperonyl butoxide, which has been found to be a potent protectant against ozone injury to plants, were tested for effectiveness against the same injury to tobacco leaves. Five of 90 materials tested, namely 3,4-methylenedioxyphthaldehyde, benzimidazole, safroxane, xanthone and piperonal, showed high protective activity though the effectiveness was inferior to piperonyl butoxide. The protective mechanism was discussed.
10 citations
9 citations
TL;DR: In this article, the oxygenation pattern of the major pentaoxygenated xanthones of Canscora decussata is shown by synthesis and reassessment of spectrsocopic evidence, to be 1,3,5,6,7- and not 1, 3, 6,7,8- as previously reported.
Abstract: The oxygenation pattern of the major pentaoxygenated xanthones of Canscora decussata is shown by synthesis and reassessment of spectrsocopic evidence, to be 1,3,5,6,7- and not 1,3,6,7,8- as previously reported. The structures of three of these xanthones are revised to 1-hydroxy-3,5,6,7-tetramethoxy-1,7-dihydroxy-3,5,6-trimethoxy-, and 1,6,7-trihydroxy-3,5-dimethoxy-xanthone, and that of a new xanthone is shown to be 1,3,7-trihydroxy-5,6-dimethoxyxanthone. The presence of minor amounts of 1,3,6,7,8-oxygenated xanthones has also been established.
8 citations
TL;DR: In this paper, variable-β type molecular orbital calculations of the π-systems were performed, assignment of the absorption spectra being made, and a method for obtaining the equilibrium constant without knowing the absolute intensity is proposed.
Abstract: Ultraviolet absorption, fluorescence, and excitation spectra of xanthone and its hydroxyl and methoxyl derivatives were measured in sulfuric acid solutions of various acidities. The basicities (pKa’s) of these compounds were obtained from the spectral change. Variable-β type molecular orbital calculations of the π-systems were performed, assignment of the absorption spectra being made. It was confirmed that protonation occurs at the carbonyl oxygen atom. A method for obtaining the equilibrium constant without knowing the absolute intensity is proposed.
7 citations
TL;DR: In this article, the authors show that normal Claisen rearrangement occurs in both the available ortho-positions, viz. 2 and 4, and is followed by spontaneous cyclisation to give linearly and angularly condensed dihydrofuro-derivatives.
Abstract: Claisen rearrangements of 1-hydroxy-3-(3-methylbut-2-enyloxy)xanthone (6a) and its 7-methoxy-(6b) and 6-methoxy-(6c) derivatives at 200–210°in vacuo yield mixtures of the corresponding dealkenylated xanthones (7a–c), angularly condensed 4,4,5-trimethyl-4,5-dihydrofuro-derivatives (8a–c), and their linear isomers (9a–c). These results show that normal Claisen rearrangement occurs in both the available ortho-positions, viz. 2 and 4, and is followed by spontaneous cyclisation to give linearly and angularly condensed dihydrofuro-derivatives. However, 1-hydroxy-5-methoxy-(3-methylbut-2-enyloxy)xanthone (6d) afford, besides the dealkenylated xanthone (7d), only linearly condensed dihydrofuroxanthones (9d) and (14).
TL;DR: In this paper, it was shown that the photo-oxidation of aromatic molecules containing an active methylene group can be used to introduce isotopic oxygen, and a brief discussion of other systems to which this method may be extended is also given.
Abstract: It it shown that the photo-oxidation of aromatic molecules containing an active methylene group can be used to introduce isotopic oxygen. Photo-oxidation of xanthene results in the formation of xanthone with the oxygen label appearing in the product at the carbonyl group. In this way, 100% enrichment can be realized. A brief discussion of other systems to which this method may be extended is also given.
TL;DR: The metabolism of xanthone by the rat has been investigated and conjugates of 4-hydroxyxanthone and 2-hydroxanthone were detected in both urine and bile, with no evidence for the formation of ring fission products.
Abstract: 1. The metabolism of xanthone by the rat has been investigated.2. The major unconjugated urinary metabolite was 4-hydroxyxanthone (24%). Smaller amounts of free 2-hydroxyxanthone (13%) and 3-hydroxy-xanthone (6%) were also formed. Other fluorescent metabolites were detected in trace amounts.3. Conjugates of 4-hydroxyxanthone and 2-hydroxyxanthone were detected in both urine and bile.4. No evidence was obtained for the formation of ring fission products.
TL;DR: In this article, variable-β type molecular orbital calculations of the π-systems were performed, assignment of the absorption spectra being made, and a method for obtaining the equilibrium constant without knowing the absolute intensity is proposed.
Abstract: Ultraviolet absorption, fluorescence, and excitation spectra of xanthone and its hydroxyl and methoxyl derivatives were measured in sulfuric acid solutions of various acidities. The basicities (pKa’s) of these compounds were obtained from the spectral change. Variable-β type molecular orbital calculations of the π-systems were performed, assignment of the absorption spectra being made. It was confirmed that protonation occurs at the carbonyl oxygen atom. A method for obtaining the equilibrium constant without knowing the absolute intensity is proposed.