https://www.repositorio.ufop.br/bitstream/123456789/805/6/ARTIGO_TrioxygenatedNaturallyOccurring.pdf

Tetraoxygenated naturally occurring xanthones

Many fungi, lichens, and bacteria produce xanthones (derivatives of 9H-xanthen-9-one, “xanthone” from the Greek “xanthos”, for “yellow”) as secondary metabolites. Xanthones are typically polysubstituted and occur as either fully aromatized, dihydro-, tetrahydro-, or, more rarely, hexahydro-derivatives. This family of compounds appeals to medicinal chemists because of their pronounced biological activity within a notably broad spectrum of disease states, a result of their interaction with a correspondingly diverse range of target biomolecules. This has led to the description of xanthones as “privileged structures”.(1) Historically, the total synthesis of the natural products has mostly been limited to fully aromatized targets. Syntheses of the more challenging partially saturated xanthones have less frequently been reported, although the development in recent times of novel and reliable methods for the construction of the (polysubstituted) unsaturated xanthone core holds promise for future endeavors. In particular, the fascinating structural and biological properties of xanthone dimers and heterodimers may excite the synthetic or natural product chemist.

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

The C-glycosylation of flavonoids in cereals.

Xanthones from fungi, lichens, and bacteria : the natural products and their synthesis

Lichen chemistry continues to be a flourishing branch of natural product chemistry. Since the last major review by Elix et al. in volume 35 of this series (274) many new and interesting lichen substances have been isolated and synthesized. This suggests that an update is desirable. As in the previous articles new methods for structure elucidation and synthesis, biosynthesis, chemotaxonomy and biological activities of lichen substances will be discussed. Some other relatively recent treatments of the subject need to be mentioned: A short chapter by Culberson and Elix (100) in Harborne’s Methods in Plant Biochemistry treated lichen constituents. Several minor reviews were published in 1984 (382), 1991 (385) and 1994 (386). Volume III of Galun’s Handbook of Lichenology (311) contains a chapter on chemical constituents of lichens including secondary metabolic products, storage products of lichens, carotenoids and phycobiliproteins.

New Results on the Chemistry of Lichen Substances

A new synthetic route to norlichexanthone (1,3,6-trihydroxy-8-methyl- 9H-xanthen-9-one) derivatives has been developed by using a Smiles rearrangement of an appropriately substituted depside in the key step. 2,4,7-Trichloronorlichexanthone (22) and 4,5,7- trichloronorlichexanthone (29) have been prepared by this method. The former xanthone (22) was shown to be a constituent of the lichens Lecanora sulphurata and L. flavo-pallescens and the latter (29) a constituent of Micarea austroternaria var. isabellina.

H. Jiang

Papers

A New Synthesis of Xanthones. 2,4,7-Trichloronorlichexanthone and 4,5,7-Trichloronorlichexanthone, Two New Lichen Xanthones

A New Synthesis of Xanthones. 2,4,7‐Trichloronorlichexanthone and 4,5, 7‐Trichloronorlichexanthone, Two New Lichen Xanthones.