Showing papers on "Xanthone published in 1981"

6-Geranyloxy-3-methyl-1,8-dihydroxyanthrone, a novel antileukemic agent from Psorospermum febrifugum Sprach var. ferrugineum (Hook. fil).

Abstract: A systematic fractionation of the root extract ofPsorospermum febrifugum was carried out in an attempt to reisolate the antitumor xanthone psorospermin and related compounds for further structural work and testing. This activitydirected fractionation led to the isolation of 6-geranyloxy-3-methyl-1,8-dihydroxyanthrone (1). Compound (1) was characterized based on spectroscopic and chemical evidence and showed borderline but reproducible activity in the P-388 mouse leukemia system.

Iminodimagnesium Reagents. Condensation Reaction with Ketones. Direct Preparation of Anils and a Hydrazone of Xanthone

Abstract: The condensation reaction of ketones with iminodimagnesium reagents (RN(MgBr)2) derived from various primary amines as well as 1,1-disubstituted hydrazines was investigated. N-Arylimines and 1-methyl-1-phenylhydrazones of diaryl ketones were prepared, their yields being affected by the electronic and positional effects of substituents of reagent and substrate. Direct preparation of some anils of xanthone and its 1-methyl-1-phenylhydrazone was achieved by use of the corresponding iminodimagnesium reagents.

Temperature dependence of the dual phosphorescence from xanthone in n-hexane matrices

Abstract: The phosphoresence spectrum and lifetime of xanthone embedded in an n-hexane matrix has been investigated as a function of temperature (1·6-100 K). Vibrational analyses of the spectra reveal that emission occurs from three sites, two of which are dominant. Emission from one site (B) occurs from the 3 nπ* state of a planar xanthone molecule and is characterized by strong totally symmetric carbonyl stretching vibrations and a short lifetime (2·4 ms). Emission from the other site (C) is shown to arise from the 3ππ* state of an out-of-plane distorted xanthone molecule. It displays a vibrational structure rich in modes of a 1, b 1, and b 2 (C 2v notation) symmetry and a long lifetime (115 ms). Both direct spin orbit coupling via configurational mixing of the nπ* and ππ* states due to the non-planarity of the molecule in its 3ππ* state and spin-orbit vibronic interaction involving 3 A 1(ππ*)-1 A 2(nπ*) spin-orbit and 1 A 2(nπ*)-1 B 2(ππ*) vibronic interaction via out-of-plane b 1 vibrations are shown to be resp...

Oxidative coupling. Part 11. Approaches to the synthesis of bikaverin

Abstract: The synthesis of orcinoylhydroquinones has been achieved by photochemical Fries rearrangement of their esters. A study of their oxidation (DDQ) shows that oxidative coupling occurs to produce a spirocyclohexenedione which can be thermally isomerised to the xanthone. The synthesis of a tetracyclic xanthone (related to bikaverin) is described.

Biosynthesis of tajixanthone in Aspergillus variecolor; incorporation of [2H3]acetate and [1,2-13C2]acetate

Abstract: The results of 13C and 2H n.m.r. analyses of [2H33]- and [1,2-13C22]-acetate-enriched tajixanthone are reported, which indicate, inter alia, that ring cleavage of an anthraquinone, and not anthrone, precursor must precede C-prenylation, and that dihydropyran ring formation precedes xanthone ring formation during biosynthesis of tajixanthone.

Coumarins of the roots ofPhlojodicarpus sibiricus

Abstract: Compound (II), according to its NMR spectrum (CD3OD, 0 -TMS; 6.18, d, 9.5 Hz, 1 H, 3-H; 7.80, d, 9.5 Hz, 1 H, 4-H; 6.75, s, 1 H, 8-H; 7.07, s, 1 H, 5-H; 3.91, s, 3 H, Ar-OCH3), is a coumarin having two substituents, in positions 6 and 7. One of the substituents is a methoxy group and the other a hydroxy group. In order to establish their mutual positions, we obtained the UV spectra of compound (II) in ethanol and in ethanol with the addition of sodium methanolate. On passing from the spectrum in ethanol to the spectrum of the substance with the addition of sodium ethanolate a bathochromic shift of the long-wave band accompanied by an increase in its intensity was observed, which indicates the presence of a hydroxy group in position 7 of the coumarin nucleus [3].

Iminodimagnesium reagents. condensation reaction with ketones. direct preparation of anils and a hydrazone of xanthone

Abstract: The condensation reaction of ketones with iminodimagnesium reagents (RN(MgBr)2) derived from various primary amines as well as 1,1-disubstituted hydrazines was investigated. N-Arylimines and 1-methyl-1-phenylhydrazones of diaryl ketones were prepared, their yields being affected by the electronic and positional effects of substituents of reagent and substrate. Direct preparation of some anils of xanthone and its 1-methyl-1-phenylhydrazone was achieved by use of the corresponding iminodimagnesium reagents.