Xanthone Ring Research Articles

An Aflatoxin Biosynthesis Cluster Gene Encodes a Novel Oxidase Required for Conversion of Versicolorin A to Sterigmatocystin

Disruption of the aflatoxin biosynthesis cluster gene aflY (hypA) gave Aspergillus parasiticus transformants that accumulated versicolorin A. This gene is predicted to encode the Baeyer-Villiger oxidase necessary for formation of the xanthone ring of the aflatoxin precursor demethylsterigmatocystin.

1,6,7-Trihydroxy-3-methoxy-2,8-bis(3-methyl-2-butenyl)-9H-xanthen-9-one chloroform solvate

The title compound, C24H26O6·CHCl3, which we named pruniflo­xanthone A, was isolated for the first time from the roots of Cratoxylum formosum ssp. pruniflorum and has never been isolated from any other natural resources as yet. The xanthone ring systems of the mol­ecules are stacked along the a axis, with significant π–π inter­actions. In addition, O—H⋯O hydrogen bonds link glide-related mol­ecules into a chain along [201].

2-(3,7-Dimethylocta-2,6-dienyl)-1,3,5,8-tetrahydroxyxanthone

The title compound, C23H24O6, a xanthone derivative, was isolated from Garcinia polyantha Oliver. The orientation of the 3,7-dimethyl­octa-2,6-dienyl substituent with respect to the xanthone ring system is (+)synclinal. The crystal packing is stabilized by O—H⋯O and C—H⋯O inter­molecular hydrogen bonds and π–π inter­actions.

5,9,10-Trihydroxy-2,2-dimethyl-12-(3-methylbut-2-enyl)-2H,6H-pyrano[3,2-b]xanthen-6-one methanol solvate

The title compound, C23H22O6·CH3OH, has an essentially planar xanthone nucleus fused to a chromene ring which adopts a sofa conformation. The 3-methyl­but-2-en­yl substituent is axially attached to the xanthone ring system, with a (+)-anticlinal conformation. The crystal structure is stabilized by O—H⋯O and C—H⋯O intra­molecular and inter­molecular inter­actions.

Evolutionary significance of xanthones in Gentianaceae: A reappraisal

Three evolutionary assumptions for xanthone substitution patterns were analysed in 12 genera of Gentianaceae, computing cladograms based on chemical and morphological characters. Two types of specialization trends seem to prevail: one biosynthetic with oxidative steps in xanthone ring A and with reduction in ring B and another one with decreasing diversity of xanthone compounds, caused by evolutionary loss. Therefore hexaoxygenation (1,3-dioxygenation of ring A and tetraoxygenation of ring B) as well as co-occurrence of tri-, tetra-, penta- and hexasubstituted compounds are probably primitive characters in the family. This explanation will result in three main evolutionary lines of analysed taxa: subtribe Erythraeinae having the most primitive, the Swertia-line an intermediate and the Gentiana-line an advanced position. These constallations are in congruence with the constructed morphological cladograms.

The structure of 1,6-dihydroxy-7,8-dimethoxyxanthone

C 15 H 12 O 6 , M r =288.3, monoclinic, A2/a, a=14.081(4), b=12.397(4), c=16.335(5)A, β=116.38(7)°, V=2554(1)A 3 , Z=8, D m =1.48(3), D x =1.50Mgm -3 , λ(CoKα)=1.7903A, μ=1.55mm -1 , F(000)=1200, T=298K, R=0.078, wR=0.076 for 1250 independent reflections. The xanthone ring is roughly planar with normal bond lengths and angles, and the molecules in the crystal are stabilized by O—H···O type hydrogen bonds. The planes of the xanthone rings are stacked alternately at distances of 3.50(3) and 5.80(3)A.

Biosynthesis of tajixanthone and shamixanthone by Aspergillus variecolor: incorporation of oxygen-18 gas

Mass spectral and 13C n.m.r. analyses of tajixanthone (1) and shamixanthone (2) formed during growth of Aspergillus variecolor under atmospheres containing [18O2] oxygen gas showed incorporation of four and three 18O labels per molecule of (1) and (2), respectively, and provided information about the mode of xanthone ring formation.

Computer supported structure elucidation of polymethoxy‐ and polyacetoxyxanthones. V—13C NMR spectroscopy of substituted xanthones

AbstractA procedure for developing 13C NMR chemical shift additivity rules for all 136 polymethoxyxanthones and all 136 polyacetoxyxanthones, based on multiple linear regression analysis, is reported. The influence of steric interactions between the substituents on the chemical shifts of the carbon atoms in the xanthone ring system is discussed and included in the calculations of the additivity rules for the polymethoxyxanthones. The derived chemical shift increments are implemented into the computer program SEOX 1. The extended program, SEOX 2, allows an automated structure elucidation of polyhydroxy‐, polymethoxy‐ and polyacet‐oxyxanthones. The increments are tested using the leave‐one‐out method in conjunction with SEOX 2, and have been found to be very suitable for this purpose.

Biosynthesis of aflatoxins. Incorporation of [1,2-13C2]acetate, [2H3]acetate, and [1-13C, 2H3]acetate into sterigmatocystin in Aspergillus versicolor

The complete 13C–13C coupling pattern in sterigmatocystin enriched from [13C2]acetate has been determined and confirms that no fandomisation of labelling in ring-A occurs; 2H-labelling studies indicate that 2H from [2H3]acetate is retained at C-6 of sterigmatocystin to rule out mechanisms for xanthone ring formation requiring introduction of the phenolic hydroxy-group on this carbon.

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

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.