Showing papers on "Xanthone published in 1976"
TL;DR: In the presence of hydrogen donors the xanthone triplet state is shown to react to give Xanthone ketyl radical the absorption spectrum of which has been measured in several solvents.
Abstract: A strong transient absorption with a peak near 600 nm has been observed following laser photolysis of xanthone in fluid solution: this absorption is due to the first excited triplet state of xanthone and an estimate of its extinction coefficient is given. Triplet decay in various solvents depends upon solvent dielectric and hydrogen atom donating ability; however, an unusually short lifetime of 92 ns is noted with benzene as solvent. The quenching constants of triplet xanthone by naphthalene, oxygen and 3-methylindole are 9.5, 5.6 and 8.4 × 109 dm3 mol–1 s–1 respectively. Oxygen quenching is greater than the expected limiting value of one ninth diffusion controlled.In the presence of hydrogen donors the xanthone triplet state is shown to react to give xanthone ketyl radical the absorption spectrum of which has been measured in several solvents. The decay of this radical in the presence and absence of oxygen has also been investigated.
59 citations
TL;DR: Carbon-13 and carbon-14 labelling experiments have shown that the fungal xanthone ravenelin is acetatederived and enrichment studies with [1,2–13C]acetate have demonstrated that an oxygenated benzophenone derivative is an intermediate in the biosynthesis pathway.
Abstract: Carbon-13 and carbon-14 labelling experiments have shown that the fungal xanthone ravenelin (1) is acetatederived. Enrichment studies with [1,2–13C]acetate have demonstrated that an oxygenated benzophenone derivative is an intermediate in the biosynthetic pathway.
43 citations
43 citations
TL;DR: In this paper, the authors investigated the phosphorescence of xanthone and 18O1 in ethanol-ether-isopentane (EPA) and 3-methylpentane (3-MP) and found that the longer-lived versions of the two ground state conformations have a characteristic triplet state.
Abstract: The phosphorescence of xanthone and xanthone-18O1 in ethanol-ether-isopentane (EPA) and in 3-methylpentane (3-MP) has been studied between 12 and 125 K. The dual phosphorescence in this ketone is attributed to the existence of two different ground-state conformations, each of which has a characteristic triplet state. The longer-lived phosphorescence is assigned to a more planar conformation than the short-lived species. Because a progression based on the carbonyl stretch frequency appears in both short and long-lived components, we assign some n, π* character to both forms. Thermally populated fluorescence from the lowest 1(n, π*) state of xanthone is also reported for the first time.
23 citations
TL;DR: The structure of 1-hydroxy-6-methyl-8-hydroxymethylxanthone, a new xanthone isolated from the culture broth of Cyathus intermedius, has been confirmed by synthesis.
Abstract: The structure of 1-hydroxy-6-methyl-8-hydroxymethylxanthone, a new xanthone isolated from the culture broth of Cyathus intermedius, has been confirmed by synthesis. Regioselective hydroxylation of ...
16 citations
TL;DR: In this article, a new acylated xanthone glycoside from Gentiana bavarica L. was identified and the attach position of the acetyl group was shown to be at 4 of the rhamnose moiety.
Abstract: Phytochemistry of genus Gentiana, XVIII: Structure of gentiabavarutinoside, a new acylated xanthone glycoside from Gentiana bavarica L.
In a previous work [1], we isolated from Gentiana bavaricaL. an acylated xanthone glycoside (1,8-dihydroxy-3-methoxy-xanthone-7-O-acetylrutinoside 1 or gentiabavarutinoside) without locating the acetyl group. By 13C-NMR. spectroscopy, the attach position of the acetyl is now shown to be at 4 of the rhamnose moiety. In addition, a new compound (2), the desacetyl derivative of 1, has also been isolated and identified.
13 citations
TL;DR: It has been shown that new substituents can be introduced in the xanthone portion of the molecule and that the antitumor activity is in some cases preserved.
Abstract: A series of derivatives of 5-methoxysterigmatocystin (3a,12c-dihydro-8-hydroxy-6,11-dimethoxy-7H-furol[3',2':4,5]furo[2,3-c]xanthen-7-one) has been prepared and evaluated for antitumor activity. The potency of the parent compound has been associated with the intact bisfurano ring system and with the double bond in the terminal furan ring. It has been shown that new substituents can be introduced in the xanthone portion of the molecule and that the antitumor activity is in some cases preserved.
11 citations
TL;DR: In this paper, a xanthone glucoside, dillanoside, was isolated from the ethyl acetate extract of a crude drug, Dill (Zira), the fruits of Anethum graveolens L. (Umbelliferae), and it was elucidated as 9, 11-dihydroxy-2-methoxybenzo [a] Xanthone 9 O-β-D-glucoside (I).
Abstract: A xanthone glucoside, dillanoside, was isolated from the ethyl acetate extract of a crude drug, dill (Zira), the fruits of Anethum graveolens L. (Umbelliferae), and it was elucidated as 9, 11-dihydroxy-2-methoxybenzo [a] xanthone 9-O-β-D-glucoside (I).
5 citations
3 citations
3 citations
TL;DR: In the presence of hydrogen donors the xanthone triplet state is shown to react to give Xanthone ketyl radical the absorption spectrum of which has been measured in several solvents.
Abstract: A strong transient absorption with a peak near 600 nm has been observed following laser photolysis of xanthone in fluid solution: this absorption is due to the first excited triplet state of xanthone and an estimate of its extinction coefficient is given. Triplet decay in various solvents depends upon solvent dielectric and hydrogen atom donating ability; however, an unusually short lifetime of 92 ns is noted with benzene as solvent. The quenching constants of triplet xanthone by naphthalene, oxygen and 3-methylindole are 9.5, 5.6 and 8.4 × 109 dm3 mol–1 s–1 respectively. Oxygen quenching is greater than the expected limiting value of one ninth diffusion controlled.In the presence of hydrogen donors the xanthone triplet state is shown to react to give xanthone ketyl radical the absorption spectrum of which has been measured in several solvents. The decay of this radical in the presence and absence of oxygen has also been investigated.