Confluentic acid

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Contents

Confluentic acid
Confluentic acid.svg
Names
IUPAC name
4-[2-Hydroxy-4-methoxy-6-(2-oxoheptyl)benzoyl]oxy-2-methoxy-6-pentylbenzoic acid
Other names
Confluentinic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
PubChem CID
  • InChI=1S/C28H36O8/c1-5-7-9-11-18-14-22(17-24(35-4)26(18)27(31)32)36-28(33)25-19(13-20(29)12-10-8-6-2)15-21(34-3)16-23(25)30/h14-17,30H,5-13H2,1-4H3,(H,31,32) Yes check.svgY
    Key: UANVCGQMNRTKGM-UHFFFAOYSA-N Yes check.svgY
  • CCCCCC1=C(C(=CC(=C1)OC(=O)C2=C(C=C(C=C2O)OC)CC(=O)CCCCC)OC)C(=O)O
Properties
C28H36O8
Molar mass 500.588 g·mol−1
Melting point 157 °C (315 °F; 430 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Confluentic acid is an organic compound belonging to the chemical class known as depsides. It serves as a secondary metabolite in certain lichens and plays a role in distinguishing closely related species within the genus Porpidia . In 1899, Friedrich Wilhelm Zopf isolated a compound from Lecidea confluens , which he initially named confluentin and noted for its melting point of 147–148 °C. This substance demonstrated the ability to turn litmus paper red and, when interacting with alkali, decomposed into carbon dioxide and phenol-like compounds. Zopf subsequently revised the chemical formula and melting point of the compound. Siegfried Huneck renamed it confluentinic acid in 1962, characterising it as optically inactive, with distinct colour reactions and solubility properties, and determined its molecular formula as C28H36O8.

Researchers typically identify the presence of confluentic acid using methods such as thin-layer chromatography and high-performance liquid chromatography. Additionally, an alternative visual detection method involves examining the lichen's thallus or apothecium (fruiting body) under a microscope on a slide treated with potassium hydroxide, which reveals oil droplets indicative of confluentic acid. Several structural analogues of confluentic acid have been isolated from a variety of lichen species.

History

In 1899, Friedrich Wilhelm Zopf reported isolating a substance from Lecidea confluens , which he named confluentin, characterised by a melting point of 147–148 °C (297–298 °F). [1] He also found that this substance turns litmus paper red, reacts with FeCl3 to produce a red-brown colour, and decomposes into carbon dioxide, a volatile substance, and a phenol-like compound with a melting point of 52°C upon interaction with alkali. Zopf initially proposed the formula C37H50O10 for this compound [1] before revising it to C26H36O7, noting the updated melting point as 154 °C (309 °F). [2]

In his 1962 report of his chemical investigations into the substance, German chemist Siegfried Huneck proposed naming it 'confluentinic acid' due to the presence of the carboxylic acid functional group, aligning with the naming conventions of other lichen products. [note 1] Huneck described the substance as optically inactive and noted its poor solubility in petroleum ether, ethyl acetate, and acetone, but found it readily soluble in ether, benzene, and methanol. He noted the following colour reactions: weak brownish with alcoholic FeCl3 solution, blue, green, and finally violet with potassium hydroxide and chloroform upon heating, orange to orange-red with tetrazotised benzidine, and gray-violet with p-phenylenediamine; no colouration was observed with barium hydroxide. Huneck used elemental analysis and molecular weight determination by titration to determine the molecular formula of confluentinic acid as C28H36O8. The Zeisel determination for methoxyl group analysis indicated two methoxyl groups per molecule. [2]

John Elix and Brian Ferguson's proposal for the total synthesis of confluentic acid in 1978 marked a significant advancement in understanding of this lichen substance, enabling scientists to better study and understand the compound's structure and biological activity without relying solely on natural extraction. The synthesis began with the direct condensation of suitably substituted aromatic carboxylic acids and phenols, using dicyclohexylcarbodiimide. Key precursors involved were specially prepared benzoic acids, with protective measures for reactive groups. The process included steps like bromination, alkylation, and the strategic use of protecting groups for the phenol and carboxyl functionalities. The synthesis culminated in the removal of protecting groups and hydrogenolysis over palladised carbon to yield the desired depsides including confluentic acid. [4] In 1993, G. Fegie and colleagues introduced a standardised high-performance liquid chromatographic method that enabled the separation and detection of hundreds of lichen products, confluentic acid included. [5]

Properties

Confluentic acid is a member of the class of chemical compounds called depsides. Its IUPAC name is 4-[2-hydroxy-4-methoxy-6-(2-oxoheptyl)benzoyl]oxy-2-methoxy-6-pentylbenzoic acid. The ultraviolet absorbance maxima (λmax) has two peaks at 268 and 304  nm. In the infrared spectrum, significant peaks indicative of the carboxylic acid functional group occur at 1700 cm-1 (C=O stretching in carbonyl groups) and within the broad range of 2600 to 3100 cm-1 (O-H stretching). The broad band at 3100 is due to hydrogen bonding, while the peak at 3500 is the COOH stretching band. [2] Confluentic acid's molecular formula is C28H36O8; it has a molecular mass of 500.57  grams per mole. In its purified form, it exists as crystalline needles with a melting point of 157 °C (315 °F). [6]

Occurrence

Porpidia cinereoatra can be distinguished from lookalikes by the presence of confluentic acid Porpidia cinereoatra (Ach.) Hertel & Knoph 271656.jpg
Porpidia cinereoatra can be distinguished from lookalikes by the presence of confluentic acid

The mycobiont (fungal partner) of the lichen Lecidea tessellata has been shown to produce confluentic acid when cultured without its algal photobiont partner. [7] Confluentic acid has also been reported from mycobiont cultures of Parmelina carporrhizans . [8] Confluentic acid is produced by almost all species of the genus Immersaria , which is usually accompanied by 2'-O-methylmicrophyllinic acid. [9] The absence of confluentic acid distinguishes Inoderma nipponicum , from others in genus Inoderma , which typically contain this chemical. [10] The only character reliably distinguishing Porpidia contraponenda and the morphologically similar Porpidia cinereoatra is their secondary chemistry: the former contains 2'-O-methylmicrophyllinate and the latter has confluentic acid. [11] A chemosyndrome is a set of biosynthetically related compounds produced by a lichen. The confluentic acid chemosyndrome was identified in several lichens in the family Lecideaceae; it contains confluentic acid as the major metabolite, and minor amounts of 2'-O-methylperlatolic acid, olivetonide monomethyl ether, and 2'-O-methylmicrophyllinic acid. [12]

Not just limited to lichen-forming fungi, confluentic acid has also been reported from the Brazilian plant Himatanthus sucuuba , highlighting the compound's broader biological distribution. [13]

Confluentic acid is a major lichen product in the crustose lichen Cryptothecia rubrocincta. Christmas Lichen - Flickr - pellaea.jpg
Confluentic acid is a major lichen product in the crustose lichen Cryptothecia rubrocincta .

A study on Cryptothecia rubrocincta reveals distinct biochemical compositions in various parts of its thallus, suggesting specialised roles for the compounds present. Specifically, confluentic acid was found exclusively in localised brown flecks within the red and pink zones of the thallus, alongside calcium oxalate monohydrate. This distribution is in contrast to other thallus areas, such as the white zone containing only calcium oxalate dihydrate and the dark red zone with chiodectonic acid, chlorophyll, beta-carotene, and additional calcium oxalate dihydrate in the pink sub-zone. The presence of confluentic acid in specific areas without beta-carotene and chiodectonic acid—both known UV protectants—suggests that confluentic acid plays a different role in the lichen's survival strategy. While the exact function of confluentic acid in these localised brown flecks remains unclear, it is indicated that it is not required for radiation protection. The study also highlights a transition within the lichen from calcium oxalate dihydrate to the more stable monohydrate form, associated with the ageing process and possibly the metabolic activities involving confluentic acid. [14]

Detection

Alan Fryday (1991) outlined a technique for the detection of confluentic acid in lichen samples. This method involves placing a section of the lichen's thallus or apothecium (fruiting body) on a microscope slide, which is then saturated with a 10% potassium hydroxide (KOH) solution. When examined under a compound microscope at 40x magnification, a distinctive 'halo' of small oil droplets or bubbles emanating from the tissue section indicates the presence of confluentic acid. [15] The oil droplets generated during this detection process consist of 4-O-methylolivetonide, a compound that is insoluble in potassium hydroxide solution. This substance forms as a result of confluentic acid undergoing hydrolysis in the presence of potassium hydroxide. [16] This test is particularly useful in distinguishing between morphologically similar yet chemically distinct species within the genus Porpidia , aiding accurate identification and study. [17]

The chemical diversity within lichens includes a variety of compounds related to confluentic acid, reflecting the complex biosynthetic capabilities of these symbiotic organisms and their significance in lichen taxonomy and ecology. In 1987, Chicita Culberson and colleagues reported the use of high-performance liquid chromatography to isolate and identify additional higher-carbon analogue substances in the "confluentic series", including hyperconfluentic acid, superconfluentic acid, and subconfluentic acid. These substances were isolated from the lichen Pseudobaeomyces pachycarpa . [18] The structure of subconfluentic acid (4-[2'-hydroxy-4'-methoxy-6'-(2"-oxopentyl)benzoyloxy]-2-methoxy-6-pentylbenzoic acid) was later established by synthesis. [19] The compound 4-O-demethylsuperconfluentic acid, structurally similar to confluentic acid, was isolated from Stirtonia ramosa . Another analogue, 2-O-methylconfluentic acid, was identified from Lecidea fuscoatra . [6]

Gowan (1989) suggested a close chemical and biosynthetic relationship between methyl 2'-O-methylmicrophyllinate and confluentic acid, noting that the biosynthetic pathways leading to these compounds primarily differ in the length of the acetyl-polymalonyl segment. This means that the two compounds are synthesised through similar processes, differing mainly in the size of a specific chain within the molecule. Additionally, there is only a minor variation in their methylation patterns. Gowan further suggested that methyl 2'-O-methylmicrophyllinate likely originated from an ancestor that already produced confluentic acid. [12]

Notes

  1. ↑ The name "confluentin" was later used in 2003 for a natural prenylphenol isolated from specimens of the mushroom-forming fungus Albatrellus confluens . [3]

Related Research Articles

<i>Psora</i> Genus of lichens

Psora is a genus of lichen-forming fungi in the family Psoraceae. Members of the genus are commonly called fishscale lichens. Lichens in the genus Psora generally have a squamulose thallus and anthraquinones in the hymenium. Photobiont partners of Psora lichens include members of the green algal genera Asterochloris, Chloroidium, Myrmecia, and Trebouxia.

<span class="mw-page-title-main">Lecideaceae</span> Family of lichen-forming fungi

The Lecideaceae are a family of lichen-forming fungi in the order Lecideales. It contains about 30 genera and roughly 250 species. A major distinguishing characteristic of the family is the lecanoroid form of the fruiting bodies: typically circular, dark, and without a thalline margin. Most species in the family are lichenised with green algae, although a few species, scattered amongst several genera, are lichenicolous—they live on other lichens. Lecideaceae lichens tend to grow on rocks, wood, and soil. Several Lecideaceae species accelerate the weathering of rock surfaces, a process known as pedogenesis, by extending their hyphae into cracks and expelling rock flakes. This contributes to significantly faster weathering rates in certain environments, impacts various materials from natural rocks to man-made Sekishu roof tiles, and involves key biomolecules identified for survival and biodeterioration, including compounds to withstand intense ultraviolet radiation.

<i>Cryptothecia rubrocincta</i> Species of fungus

Cryptothecia rubrocincta is a species of lichen in the fungal family Arthoniaceae. The species is distributed in subtropical and tropical locations throughout the southeastern United States, as well as Central and South America, and has been collected infrequently in a few locales in Africa. The body of the lichen forms continuous, circular crust-like patches on dead wood, readily recognizable by the prominent red pigment. The older, central region is covered with red, spherical to cylindrical granules. Moving outwards from the center, zones of color may be distinguished, the first gray-green, the second white, and finally a bright red cottony rim. The red and green colors of this unmistakable woodland lichen give the appearance of a Christmas wreath, suggestive of its common North American name, the Christmas (wreath) lichen. The red pigment, called chiodectonic acid, is one of several chemicals the lichen produces to help tolerate inhospitable growing conditions.

A spot test in lichenology is a spot analysis used to help identify lichens. It is performed by placing a drop of a chemical reagent on different parts of the lichen and noting the colour change associated with application of the chemical. The tests are routinely encountered in dichotomous keys for lichen species, and they take advantage of the wide array of lichen products produced by lichens and their uniqueness among taxa. As such, spot tests reveal the presence or absence of chemicals in various parts of a lichen. They were first proposed as a method to help identify species by the Finnish lichenologist William Nylander in 1866.

Punctelia subalbicans is a species of foliose lichen in the family Parmeliaceae. It is found in Australia and New Zealand, where it grows on the bark of various tree species.

Porpidia seakensis is a species of crustose lichen in the family Lecideaceae. It is an endolithic species, meaning it grows inside the rocks, between the grains. Found only in Alaska, it was formally described as a new species in 2020 by British lichenologist Alan Fryday. The type specimen was collected in the Hoonah-Angoon Census Area, in Glacier Bay National Park. Here it was discovered growing on granitic rock in a woodland. The lichen is only known from this area, although it is locally common. Its preferred habitat is siliceous rocks and boulders in wooded areas that are open and well lit. The specific epithet seakensis uses the letters "seak" to refer to a standard abbreviation for southeast Alaska.

<span class="mw-page-title-main">Salazinic acid</span> Chemical compound found in some lichens

Salazinic acid is a depsidone with a lactone ring. It is found in some lichens, and is especially prevalent in Parmotrema and Bulbothrix, where its presence or absence is often used to help classify species in those genera.

<span class="mw-page-title-main">Lichexanthone</span> Chemical compound found in some lichens

Lichexanthone is an organic compound in the structural class of chemicals known as xanthones. Lichexanthone was first isolated and identified by Japanese chemists from a species of leafy lichen in the 1940s. The compound is known to occur in many lichens, and it is important in the taxonomy of species in several genera, such as Pertusaria and Pyxine. More than a dozen lichen species have a variation of the word lichexanthone incorporated as part of their binomial name. The presence of lichexanthone in lichens causes them to fluoresce a greenish-yellow colour under long-wavelength UV light; this feature is used to help identify some species. Lichexanthone is also found in several plants, and some species of fungi that do not form lichens.

Lichen products, also known as lichen substances, are organic compounds produced by a lichen. Specifically, they are secondary metabolites. Lichen products are represented in several different chemical classes, including terpenoids, orcinol derivatives, chromones, xanthones, depsides, and depsidones. Over 800 lichen products of known chemical structure have been reported in the scientific literature, and most of these compounds are exclusively found in lichens. Examples of lichen products include usnic acid, atranorin, lichexanthone, salazinic acid, and isolichenan, an α-glucan. Many lichen products have biological activity, and research into these effects is ongoing.

<span class="mw-page-title-main">Sekikaic acid</span> Chemical compound found in some lichens

Sekikaic acid is an organic compound in the structural class of chemicals known as depsides. It is found in some lichens. First isolated from Ramalina sekika, it is a fairly common lichen product in Ramalina and Cladonia, both genera of lichen-forming fungi. The species epithet of the powdery lichen Lepraria sekikaica refers to the presence of this substance—a rarity in genus Lepraria.

<span class="mw-page-title-main">Barbatic acid</span> Chemical compound found in some lichens

Barbatic acid is an organic compound that is made by some lichens. It is in the structural class known as depsides. It is particularly common in the genera Usnea and Cladonia.

Inoderma sorediatum is a species of crustose lichen in the family Arthoniaceae. It is only known to occur on the bark of trees in Poland's Białowieża National Park. It is differentiated from other species in genus Inoderma by the form of its thallus, which is entirely made of powdery, granular soredia, as well as by the presence of a unique combination of lichen products.

<span class="mw-page-title-main">Solorinic acid</span> Chemical compound found in some lichens

Solorinic acid is an anthraquinone pigment found in the leafy lichen Solorina crocea. It is responsible for the strong orange colour of the medulla and the underside of the thallus in that species. In its purified crystalline form, it exists as orange-red crystals with a melting point of 201 °C (394 °F).

<i>Lecidea tessellata</i> Species of lichen

Lecidea tessellata is a species of saxicolous (rock-dwelling), crustose lichen in the family Lecideaceae. It was formally described as a species in 1819 by German botanist Heinrich Flörke. In northern North America, it is common and widely distributed, growing on non-calcareous rocks. It also occurs in Afghanistan, China, Nepal, Europe, and Russian Asia. In India, it has been recorded only from the alpine Western Himalayas at an altitude of 3,450 m (11,320 ft). Its southern distribution extends to James Ross Island, where it is locally common.

Podotara is a fungal genus in the family Pilocarpaceae. It is a monotypic genus, containing the single species Podotara pilophoriformis, an uncommon foliicolous (leaf-dwelling), crustose lichen that grows on Podocarpus totara, a species of podocarp tree endemic to New Zealand. Both the genus and the species were proposed in 1996.

Sporodophoron primorskiense is a little-known species of corticolous (bark-dwelling) lichen in the family Arthoniaceae. It is notable for its distinctive white, thin growth patterns and small sporodochia, or spore-producing structures. The species is named after the Primorsky Krai region in the Russian Far East, where it was first discovered. It has since been recorded in Japan.

<span class="mw-page-title-main">Fallacinal</span> Chemical compound found in some lichens

Fallacinal is an organic compound in the structural class of chemicals known as anthraquinones. It is found in many species of the lichen family Teloschistaceae.

<span class="mw-page-title-main">Fallacinol</span> Chemical compound found in some lichens

Fallacinol (teloschistin) is an organic compound in the structural class of chemicals known as anthraquinones. It is found in some lichens, particularly in the family Teloschistaceae, as well as a couple of plants and non lichen-forming fungi. In 1936, Japanese chemists isolated a pigment named fallacin from the lichen Oxneria fallax, which was later refined and assigned a tentative structural formula; by 1949, Indian chemists had isolated a substance from Teloschistes flavicans with an identical structural formula to fallacin. Later research further separated fallacin into two distinct pigments, fallacin-A and fallacin-B (fallacinol). The latter compound is also known as teloschistin due to its structural match with the substance isolated earlier.

<span class="mw-page-title-main">Connorstictic acid</span> Chemical compound found in some lichens

Connorstictic acid is an organic compound in the structural class of chemicals known as depsidones. It occurs as a secondary metabolite in many lichen species in several genera.

Porpidia nadvornikiana is a rare species of saxicolous (rock-dwelling), crustose lichen in the family Lecideaceae. It is known to occur only in two localities, in the Czech Republic and in Spain, where it grows on serpentinite, an ultramafic rock.

References

  1. 1 2 Zopf, Wilhelm (1899). "Zur Kenntniss der Flechtenstoffe" [On the knowledge of lichen substances]. Justus Liebigs Annalen der Chemie (in German). 306 (3): 282–321. doi:10.1002/jlac.18993060304.
  2. 1 2 3 Huneck, Siegfried (1962). "Über Flechteninhaltsstoffe, I. Konstitution der Confluentinsäure" [About Lichen Constituents, I. Constitution of Confluentinic Acid]. Chemische Berichte (in German). 95 (2): 328–332. doi:10.1002/cber.19620950206.
  3. ↑ Hellwig, Veronika; Nopper, Reilinde; Mauler, Frank; Freitag, Joachim; Ji-Kai, Liu; Zhi-Hui, Ding; Stadler, Marc (2003). "Activities of prenylphenol derivatives from fruitbodies of Albatrellus spp. on the human and rat vanilloid receptor 1 (VR1) and characterisation of the novel natural product, confluentin". Archiv der Pharmazie. 336 (2): 119–126. doi:10.1002/ardp.200390008. PMID   12761765.
  4. ↑ Elix, John; Ferguson, B.A. (1978). "Synthesis of the lichen depsides, olivetoric acid, confluentic acid and 4-O-methylolivetoric acid". Australian Journal of Chemistry. 31 (5): 1041–1051. doi:10.1071/CH9781041.
  5. ↑ Feige, G.B.; Lumbsch, H.T.; Huneck, S.; Elix, J.A. (1993). "Identification of lichen substances by a standardized high-performance liquid chromatographic method". Journal of Chromatography A. 646 (2): 417–427. doi:10.1016/0021-9673(93)83356-W.
  6. 1 2 Huneck, Siegfried (1996). Identification of Lichen Substances. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 244–245. ISBN   978-3-642-85245-9. OCLC   851387266.
  7. ↑ Namada, N.; Tanahashi, T.; Goldsmith, S.; Nash III, T.H. (1997). "Induction of secondary products in isolated mycobionts from North American Lichens". Symbiosis. 23: 219–224.
  8. ↑ Alors, David; Divakar, Pradeep Kumar; Calchera, Anjuli; Schmitt, Imke; Crespo, Ana; Molina, María Carmen (2023). "The temporal variation of secondary metabolites in the mycobiont culture and thallus of Parmelina carporrhizans and Parmelina quercina analyzed using high-performance liquid chromatography". Separations. 10 (7): e399. doi: 10.3390/separations10070399 .
  9. ↑ Xie, Cong-Miao; Wang, Li-Song; Zhao, Zun-Tian; Zhang, Yan-Yun; Wang, Xin-Yu; Zhang, Lu-Lu (2022). "Revision of Immersaria and a new lecanorine genus in Lecideaceae (lichenised Ascomycota, Lecanoromycetes)". MycoKeys. 87: 99–132. doi: 10.3897/mycokeys.87.72614 . PMC   8863769 . PMID   35210924.
  10. ↑ Frisch, Andreas; Ohmura, Yoshihito; Ertz, Damien; Thor, Göran (2015). "Inoderma and related genera in Arthoniaceae with elevated white pruinose pycnidia or sporodochia". The Lichenologist. 47 (4): 233–256. doi:10.1017/S0024282915000201.
  11. ↑ Fryday, Alan M. (2005). "The genus Porpidia in northern and western Europe, with special emphasis on collections from the British Isles". The Lichenologist. 37 (1): 1–35. doi:10.1017/S0024282904014628.
  12. 1 2 Gowan, Sharon P. (1989). "A character analysis of the secondary products of the Porpidiaceae (lichenized Ascomycotina)". Systematic Botany. 14 (1): 77–90. doi:10.2307/2419052. JSTOR   2419052.
  13. ↑ Endo, Yuichi; Hayashi, Hiroko; Sato, Toshitsugu; Maruno (M.Chin), Masao; Ohta, Tomihisa; Nozoe, Shigeo (1994). "Confluentic acid and 2'-O-methylperlatolic acid, monoamine oxidase B inhibitors in a Brazilian plant, Himatanthus sucuuba". Chemical and Pharmaceutical Bulletin. 42 (6): 1198–1201. doi: 10.1248/cpb.42.1198 . PMID   8069971.
  14. 1 2 Edwards, Howell G.M.; de Oliveira, Luiz F.C.; Seaward, Mark R.D. (2005). "FT-Raman spectroscopy of the Christmas wreath lichen, Cryptothecia rubrocincta (Ehrenb.:Fr.) Thor". The Lichenologist. 37 (2): 181–189. doi:10.1017/S0024282905014611.
  15. ↑ Fryday, Alan (1991). "A microscopic test for confluentic acid" (PDF). British Lichen Society Bulletin. 70: 31.
  16. ↑ Fryday, Alan (1992). "The chemistry of the new confluentic acid test" (PDF). British Lichen Society Bulletin. 71: 41.
  17. ↑ Orange, A.; James, P.W.; White, F.J. (2001). Microchemical Methods for the Identification of Lichens. British Lichen Society. p. 13. ISBN   978-0-9540418-0-9.
  18. ↑ Culberson, Chicita F.; Culberson, William Louis; Gowan, Sharon; Johnson, Anita (1987). "New depsides from lichens: microchemical methodologies applied to the study of new natural products discovered in herbarium specimens". American Journal of Botany. 74 (3): 403–414. doi:10.1002/j.1537-2197.1987.tb08622.x.
  19. ↑ Elix, J.A.; Wardlaw, J.H.; David, F. (1996). "The structure of subconfluentic acid, a depside from the lichen Lecidella cf. cyanosarca". Australian Journal of Chemistry. 49 (1): 159–161. doi:10.1071/CH9960159.
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