Showing papers on "Xanthone published in 1977"

A New Xanthone Diglucoside from Swertia perennisL.

Abstract: A new xanthone diglucoside (1) has been isolated from the aerial parts of Swertia perennisL. (Gentianaceae) by means of column chromatography on polyamide, followed by preparative TLC. on silica gel. From UV. and NMR. data, its structure has been established as 1,3-di-β-D-glucopyranosyl-7,8-dihydroxyxanthone or norswertianine-1,3-diglucoside.

Chemical constituents of gentianaceae. Part 22. Structures of new 1,3,5-tri- and 1,3,5,6,7-penta-oxygenated xanthones of Canscora decussata Schult

Abstract: Two new xanthone glucosides and two free xanthones, isolated from Canscora decussata, have been identified as 1-glucosyloxy-3-hydroxy-5-methoxy-(1), 7-glucosyloxy-1,6-dihydroxy-3,5-dimethoxy-(2), 1.5.6-trihydroxy-3,7-dimethoxy-(4), and 1.5.7-tryhydroxy-3,6-dimethoxy-xanthone (7) on the basis of chemical transformations and spectral evidence. On the basis of reassessment of the spectroscopic data and additional chemical evidence, it has been shown that the pentaoxygenated xanthones previously reported to be 1,3,7-trihydroxy-5,6-dimethoxy-xanthone (‘Xanthone IV’) and 1,7-dihydroxy-3,5,6-trimethoxyxanthone (‘Xanthone XII’) are in fact 1,3,5-trihydroxy-6,7-dimethoxy-(9) and 1,5-dihydroxy-3,6,7-trimethoxy-xanthone (10), respectively. The stucture of 1,6,7-trihydroxy-3,5-dimethoxyxanthone (‘Xanthone XIII’) has been confirmed.

Polarized Absorption Spectra and Configuration Analyses of Xanthene and Xanthone

Abstract: The polarized absorption sepctra of xanthene and xanthone were measured in stretched poly (vinyl alcohol) films, and the polarization direction of each electronic transition was determined. It was confirmed that xanthone has the short molecular-axis polarized bands (1A1←1A1) at 343, 260, and 226 nm, and the long molecular-axis polarized ones (1BA2←1A1) at 290, 266, and 242 nm. The electronic transitions of xanthone are discussed in connection with those of xanthene by use of the configuration analysis. For the 266 and 260 nm bands, the contributions of the intramolecular charge transfer character from the xanthene skeleton to the carbonyl group are considerable.

Extractives from Guttiferae. Part 33. Synthesis of the ozonolysis product from dimethylmangostin, 1-hydroxy-3,6,7-trimethoxy-2,8-bis-(2-oxoethyl)xanthone; some 13C nuclear magnetic resonance spectra of xanthones

Abstract: The synthesis of the dialdehyde 1-hydroxy-3,6,7-trimethoxy-2,8-bis-(2-oxoethyl)xanthone, first obtained from ozonolysis of dimethylmangostin, is described. Xanthone formation by cyclisation of a benzophenone intermediate is followed by selective demethylations, allylation, and Claisen rearrangement. Oxidative cleavage of the allyl side chains in 2,8-diallyl-1,3,6,7-tetramethoxyxanthone, followed by demethylation with boron trichloride, gave the required dialdehyde (5). Some 13C n.m.r. spectra of xanthones are discussed.

Xanthone C-glycosides of Hedysarum denticulatum

Abstract: The leaves of Hedysarum denticulatum (140 g) were extracted three times with a c e t o n e w a t e r (1 : 1), the combined extracts were evaporated to half bulk, and the xanthone glycosides were repeatedly extracted with butanol. The butanolic extracts were evaporated to dryness , and the residue was dissolved in d i o x a n e w a t e r (1 : 1). On standing, the solution deposited substance (I). The mother l iquor of the separat ion of substance (1) was t r ans f e r r ed to a column containing cellulose. Elution was per formed with 5c~ acetic acid. The f irs t f r ac tions contained substance (I), and f rom the subsequent fract ions substance (ID was isolated.

General Kinetics of Reversible Reactions in the Excited State. Application to Excited Singlet pK Determination of Acridone, Xanthone and Thioxanthone*

Abstract: From steady state kinetics of a general excited state reversible reaction scheme, a linear relation between the total luminescence and the concentration of one reactant is derived, showing that the equilibrium constant of certain excited state reactions can be determined from the total fluorescence spectra without the separation of the components and irrespective of the ground state equilibrium. The relation is checked by comparison with published results, and it is applied to the determination of excited state acidity constants of acridone, xanthone and thioxanthone in ethanol-water (1:1).

Zur Bildung von 2-(2-Hydroxy-benzoyl)-xanthon†

Abstract: Die Bildung des 2-[2-Hydroxy-benzoyl]-xanthon (3) durch Umsetzung von Ω-Acetyl-2-hydroxy-acetophenon (1) mit N,N-Dimethylformamid-dimethylacetal wird beschrieben und der Reaktionsmechanismus diskutiert. Die Struktur von 3 wird durch Umlagerung des Xanthon-2-carbonsaure-phenylesters (5) bewiesen. Formation of 2-(2-Hydroxybenzoyl)xanthone (3) The formation of 2-(2-hydroxybenzoyl)xanthone (3), starting from Ω-acetyl-2-hydroxy-acetophenone (1) and N,N-dimethylformamide dimethylacetal is described and the mechanism is discussed. The structure of 3 is elucidated by rearrangement of 5.

Preparation and antitumor activities of some derivatives of 5-methoxysterigmatocystin

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.