Isolation and Structure Determination of Demethylchodatin—a New Lichen Xanthone

Abstract

The structure of demethylchodatin, a xanthone from the lichen Lecanora pachysoma, has been established by X-ray analysis of the corresponding triacetate derivative. Crystals of demethylchodatin triacetate are monoclinic, P 21/a, a 10.120(3), b 11.278(3), c 19.173(4) Ǻ, β 94.68(3)°; Z 4. Refinement of 1411 data with I > 3σ(I) gave conventional R factors of 0.041 and 0.033.

Xanthones-A Structural Perspective

“…A series of chlorinated xanthones were already identified in a wide variety of lichens and the structure of three of these compounds, demethylchodatin (30), thiomelin diacetate (31), and hexachloroxanthone (33), was determined by X-ray diffraction [21][22][23]. It revealed a small twist along the longitudinal axis of the xanthone skeleton, probably due to steric factors associated with the chlorine substitution.…”

“…In these three compounds, the xanthone skeleton is almost flat, the planes of the benzenoid rings define angles lower than 8º and the extra ring assumes a half chair conformation. Two other natural compounds, garcinone B (19) and isojacareubin (22), having the extra ring angularly fused, had their structures elucidated. It was Less frequent than the OMe and OH substituents is the acetoxy group.…”

Xanthones from Fungi, Lichens, and Bacteria: The Natural Products and Their Synthesis

“…Knoph and Leuckert and L. dimelaenophila by Knoph in 1990. 106 The structure of the latter was resolved by Elix et al with X-ray crystallographic analysis of the triacetate derivative, which was isolated from Lecanora pachysoma, 107 but it appears that the structure (i.e., methylation position) of chodatin (C 16 H 11 Cl 3 O 6 ) itself remains presently unresolved (presumably it is methylated at the more commonly observed 3-or 6-position). These two species have also been found in Lecanora tropica Zahlbr., 108 L. immersa ssp.…”

DP4-Assisted Structure Elucidation of Isodemethylchodatin, a New Norlichexanthone Derivative Meager in H-Atoms, from the Lichen Parmotrema tsavoense

“…Collectively, these spectroscopic features defined compound 1 as a fully substituted trichlorinated xanthone. Up to now, only one such structure was reported, i.e., the isomeric demethylchodatin [23]. Unfortunately, this structure was elucidated by single-crystal X-ray crystallography analyses of its triacetate derivative and its 13 C-NMR spectroscopic data were not reported.…”