Lichexanthone

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Lichexanthone
Names
IUPAC name
1-Hydroxy-3,6-dimethoxy-8-methyl-9H-xanthen-9-one
Other names
Lichenxanthone,
1-hydroxy-3,6-dimethoxy-8-methylxanthen-9-one
Identifiers
3D model (
JSmol
)
ChEBI
ChEMBL
ChemSpider
  • InChI=1S/C16H14O5/c1-8-4-9(19-2)6-12-14(8)16(18)15-11(17)5-10(20-3)7-13(15)21-12/h4-7,17H,1-3H3 checkY
    Key: QDLAGTHXVHQKRE-UHFFFAOYSA-N checkY
  • CC1=CC(=CC2=C1C(=O)C3=C(C=C(C=C3O2)OC)O)OC
Properties
C16H14O5
Molar mass 286.283 g·mol−1
Appearance long yellow prismatic crystals
Density 1.323 g/cm3
Melting point 189–190 °C (372–374 °F; 462–463 K)
Boiling point 494 °C (921 °F)
Structure[1]
Monoclinic
P21/c (No. 14)
a = 11.6405 Å, b = 7.5444 Å, c = 15.2341 Å
1307.26 Å3
4
Hazards
Flash point 186.9 °C (368.4 °F)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Lichexanthone is an

fungi
that do not form lichens.

In lichens, the

larvicidal, and sperm motility-enhancing activities. Many lichexanthone derivatives are known, some produced naturally in lichens, and others created synthetically
; like lichexanthone, some of these derivatives are also biologically active.

History

Lichexanthone was first reported by Japanese chemists Yasuhiko Asahina and Hisasi Nogami in 1942. They isolated the lichen product from Parmelia formosana[2] (known today as Hypotrachyna osseoalba), a lichen that is widespread in Asia.[3] Another early publication described its isolation from Parmelia quercina (now Parmelina quercina[4]).[5] Lichexanthone was the first xanthone to be reported from lichens,[6] and it was given its name by Asahina and Nogami for this reason.[2]

Asahina and Nogami used a chemical method called potash fusion (

demethylated to yield lichexanthone.[2] A simpler synthesis, starting from everninic acid (2-hydroxy-4-methoxy-6-methylbenzoic acid) and phloroglucinol,[7] was proposed in 1956.[9] These early syntheses also helped to confirm the structure of lichexanthone before spectral methods of analysis were widely available.[6] In 1977, Harris and Hay proposed a biogenetically modelled synthesis of lichexanthone starting from the polycarbonyl compound 3,5,7,9,11,13-hexaoxotetradecanoic acid. In this synthesis, an aldol cyclization between positions 8 and 13 followed by a Claisen cyclization between positions 1 and 6 leads to the formation of a group of compounds that includes lichexanthone.[10]

Properties

apothecia of the crustose lichen Ochrolechia africana
; the yellowish colour results from the fluorescence of lichexanthone.

Lichexanthone is a member of the class of chemical compounds called

UV light, a property that is used as a tool in lichen species identification.[12]

The

X-ray diffraction.[1]

Biological activities

Various

cell lines.[23]

In laboratory tests, the presence of lichexanthone enhances the

vector of the Dengue virus.[20][24]

Biosynthesis

Chemical structures
Part of a proposed biosynthetic pathway for lichexanthone-type lichen xanthones, depicting an aldol cyclization step followed by a cyclodehydration, which would lead to norlichexanthone.

In lichens, biosynthesis of lichexanthone occurs through the acetate-malonate

malonate units with one orsellinic acid-type cyclisation. The two rings are joined by a ketonic carbon and by an ether-oxygen arising from cyclodehydration (i.e., a dehydration reaction leading to the formation of a cyclic compound).[16] The exact mechanism is not known, but this ring closure might proceed through a benzophenone intermediate that could dehydrate to yield the central pyrone core of lichexanthone.[6][20]

A standardized

nm.[27]

Occurrence

Brownish, leathery cup-like structures growing on a tree branch
Parmelina quercina is one of the first lichens from which lichexanthone was isolated.

Although first isolated from foliose (leafy) Parmelia species, lichexanthone has since been found in a wide variety of lichens. For example, in the foliose genus Hypotrachyna, it is found in about a dozen species; when present, it usually completely replaces other cortical substances common in that genus, like atranorin and usnic acid.[12] The presence or absence of lichexanthone is a character used in classifying species of the predominantly tropical genus Pyxine; of about 70 species in the genus, 20 contain lichexanthone. This represents the largest group of foliose lichens with the compound, as it is generally restricted to some groups of tropical crustose lichens, chiefly pyrenocarps and Graphidaceae.[28] The large genus Pertusaria relies heavily on thallus chemistry to distinguish and classify species, some of which differ only in the presence or absence of a single secondary chemical. Lichexanthone, norlichexanthone, and their chlorinated derivatives are common in this genus.[29]

Although normally considered a secondary metabolite of lichens, lichexanthone has also been isolated from several plants, listed here organized by family:

Feroniella lucida
are two tropical plants that contain lichexanthone.

Lichexanthone has also been reported to occur in the bark of

Penicillium vulpinum,[48]
can synthesize lichexanthone.

Xanthones are known to have strong UV-absorbing properties.

solar radiation.[49] The presence of the photoprotective chemical in the cortex may allow them to survive in otherwise inhospitable habitats, like on exposed trees in tropical areas or high mountains.[50] It has been pointed out, however, that lichexanthone is also found in lichens living in less stressed environments, and from species that are in families where cortical substances are rare. In some instances, similar or related species exist that lack cortical substances entirely, suggesting that the actual ecological function of lichexanthone is not fully understood.[51]

Related compounds

Numbering scheme for lichexanthone;
Me = methyl (–CH3)

Norlichexanthone (1,3,6-trihydroxy-8-methylxanthone) differs from lichexanthone in having hydroxy rather than methoxy groups at positions 3 and 6.[11] In griseoxanthone C (1,6-dihydroxy-3-methoxy-8-methylxanthen-9-one), the methoxy at position 6 of lichexanthone is replaced with a hydroxy.[20] Dozens of chlorinated lichexanthone derivatives have been reported, some isolated from a variety of lichen species, and some produced synthetically. These derivatives are variously mono-, bi-, or trichlorinated with the chlorines at positions 2, 4, 5, and 7.[6] As of 2016, 62 molecules with the lichexanthone scaffold had been described, and another eight additional lichexanthone derivatives were considered "putative"–thought to exist in nature, but not yet discovered in lichens.[20]

The effects of chlorine

binding energies of complexes formed between lichexanthone, magnesium ion (Mg+2) and NH3.[52] A series of lichexanthone derivatives were synthesized and assessed for antimycobacterial activity against Mycobacterium tuberculosis. These derivatives consisted of ω-bromo and ω-aminoalkoxylxanthones; lichexanthone and several derivatives were found to have weak antimycobacterial activity. According to the authors, this chemometrics approach was useful to correlate structural and chemical features with in vitro antimycobacterial activity among the group of ω-aminoalkoxylxanthones.[19]

Eponyms

Some authors have explicitly named lichexanthone in the specific epithets of their published lichen species, thereby acknowledging the presence of this compound as an important taxonomic characteristic. These eponyms are listed here, followed by their author citation and year of publication. All of these species occur in Brazil:

In the case of

genera
that contain lichexanthone.

References

  1. ^ a b c d Buitrago Díaz, Alexis; Rojas Vera, Janne; Cote, Valentina; Bruno-Colmenárez, Julia; Díaz de Delgado, Graciela (2010). "NMR elucidation and crystal structure analysis of 1-hydroxy-3,6-dimethoxy-8-methyl-9h-xanthen-9-one (lichexanthone) isolated from Vismia baccifera (Guttiferae)" (PDF). Boletín Latinoamericano y del Caribe de Plantas Medicinales y Aromáticas. 9 (6): 470–474.
  2. ^
    doi:10.1246/bcsj.17.202
    . "Da dasselbe ein in der Flechte zum ersten mal entdeckte Xanthone-Derivat ist, so nennen wir es 'Lichexanthone'." [Since it is a xanthone derivative first discovered in lichen, we call it lichexanthone.]
  3. JSTOR 1220900
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  4. ^ "Record Details: Parmelia quercina (Willd.) Vain., Term. Füz. 22: 279 (1899)". Index Fungorum. Retrieved 4 February 2022.
  5. ^ Aghoramurthy, K.; Seshadri, T.R. (1953). "An improved synthesis of lichexanthone". Journal of Scientific and Industrial Research (India). 12B: 350–352.
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  9. ^ Grover, P.K.; Shah, G.D.; Shah, R.C. (1956). "Xanthones: part V. A new synthesis of lichexanthone". Journal of Scientific and Industrial Research (India). 15B: 629–630.
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    .
  15. ^ Manojlovic, Nedeljko T.; Vasiljevic, Perica J.; Marković, Zoran S. (2010). "Antimicrobial activity of extracts and various fractions of chloroform extract from the lichen Laurera benguelensis". Journal of Biological Research-Thessaloniki. 13: 27–34.
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