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 (later called fallacinal) and fallacin-B (fallacinol). The latter compound is also known as teloschistin due to its structural match with the substance isolated earlier.
In 1936, Japanese chemists Mitizo Asano and Sinobu Fuziwara reported on their chemical investigations into the colour pigments of the lichen Xanthoria fallax (now known as Oxneria fallax), found growing on the bark of mulberry trees. They isolated a pigment they named fallacin.[1] A few years later Asano and Yosio Arata further purified the crude material from this lichen, ultimately obtaining an orange-yellow compound with a molecular formula of C16H12O6. Using information from additional chemical tests, they proposed a tentative structural formula for fallacin.[2] In 1949,[3]T. R. Seshadri and S. Subramanian published their investigations into the chemistry of Teloschistes flavicans, a lichen from which they isolated an orange substance they named teloschistin, and which had a structural formula identical to that of fallacin proposed by Asano and Arata years earlier.[4]
In 1956, Takao Murakami reported reexamining the crude pigment obtainable from Xanthoria fallax using Asano's original 1936 procedure. He separated out fallacin from parietin, a co-occurring substance, using several rounds of column chromatography, and showed that Asano's original pigment was actually a combination of two pigments with different melting points, which he designated as fallacin-A and fallacin-B. After chemically determining the structure of fallacin-A, Murakami designated this substance as fallacinal. He named the biogenically related compound fallacin-B as fallacinol.[4] Because of Seshadri and Subramanian's work, this substance is also known as "teloschistin" in the literature.[5]
Extraction and isolation
In an early chemical examination of the lichen Teloschistes flavicans, Friedrich Wilhelm Zopf identified two substances: physcion (now known more commonly as parietin) with a melting point (m.p.) of 207°C (405°F) and an unidentified colourless compound with a m.p. of 240–245°C (464–473°F). Subsequent studies by Seshadri and Sankara Subramanian refined the extraction process, utilising a series of solvents—ether, acetone, and water—to isolate the constituents. The ether phase was found to contain all the crystalline compounds, while subsequent solvents did not yield additional extracts.[6]
Within the ether extract, a colourless compound, referred to as substance A, was separated based on its insolubility in alkali. The alkali-soluble fraction exhibited characteristics of parietin, though impurities complicated its purification. It was eventually purified to a parietin fraction with a melting point of 206–207°C (403–405°F) after multiple stages of fractional crystallization using an alcohol-chloroform mixture.[6]
The presence of another compound with a higher melting point posed a purification challenge, which was resolved by employing petroleum ether and chloroform for sequential extraction. The petroleum ether extract contained the colourless substance A and a majority of parietin, allowing for easier purification of the latter. The chloroform extract revealed the higher-melting compound, which the authors thought was a novel substance, and which they named "teloschistin".[6]
In 1951, Neelakantan and colleagues expanded on the initial identification of fallacinol, focusing on its chemical structure. They confirmed its molecular formula as C16H12O6 and identified it as a hydroxyl derivative of parietin, lacking specific hydroxy groupings that would typically cause fluorescence or colour changes in acidic conditions. To conclusively determine the position of its methoxyl group, fallacinol was chemically altered into a compound with a known methoxyl position, establishing it firmly in the 7-position. This process involved a series of reactions, including demethylation, reduction, and oxidation. Additionally, comparisons with similar anthraquinone derivatives through hydrolysis and other reactions further substantiated the structural findings.[7]
The research also noted the slower-than-expected reaction rates during oxidation, suggesting a distinctive reactivity pattern for fallacinol, possibly due to its additional hydroxyl group. Finally, the study described the anthranol form of fallacinol, providing a reference for its properties and transformative behaviour.[7]
Properties
Fallacinol is a member of the class of chemical compounds called anthraquinones. Its IUPAC name is 1,8-dihydroxy-3-hydroxymethyl-6-methoxyanthraquinone. The absorbance maxima (λmax) of fallacinol in the ultraviolet spectrum has five peaks of maximum absorption at 223, 251, 266, 287 nanometres; the visible spectrum has peaks at 434 and 455nm.[8] In the infrared spectrum, it has peaks at 1624, 1631, 1670, 3450, 3520cm-1. Fallacinol's molecular formula is C16H12O6; it has a molecular mass of 300.26grams per mole. In its purified crystalline form, it exists as orange needles, with a melting point of 244–246°C (471–475°F).[5]
It is soluble in cold dilute potassium hydroxide, forming red-violet crystals, and is insoluble in sodium bicarbonate and carbonate solutions. Similar to parietin, it produces a reddish-brown colour with alcoholic ferric chloride and yields a deep orange-red solution with concentrated sulfuric acid, which appears eosin-like in thin layers. To early researchers, these properties suggested that fallacinol was structurally similar to parietin but with an additional oxygen atom, inferred to be a hydroxyl group, based on its higher melting point and reduced solubility. The sparing solubility of its potassium salt and its insolubility in aqueous sodium carbonate suggested a methoxyl group placement consistent with other known compounds like parietin and erythroglaucin.[6]
A synthetic route to fallacinol has been developed using parietin as an intermediate, highlighting a biogenetic link between the two compounds found in the lichen. The process involves the conversion of parietin diacetate to an ω-bromo derivative via N-bromosuccinimide in the presence of benzoyl peroxide, a technique also applied to various anthraquinones and related compounds. The brominated intermediate is then converted to fallacinol triacetate using silver acetate and acetic anhydride, yielding the target compound. Final steps include hydrolysis with methanolic sulfuric acid to produce fallacinol and a methylation stage for complete conversion. The synthesis not only mirrors the natural biogenesis but also achieves a melting point of 244–246°C (471–475°F), consistent with the purified natural product.[12] An alternative synthesis was proposed in 1984, using a methodology employing Diels–Alder additions of napthoquinones to mixed trimethylsilyl vinylketene acetals as a route to synthetic hydroxyanthraquinones.[13]
Fallacinol occurs in many species of the Teloschistaceae, a large family of mostly lichen-forming fungi. Historically, the substance was most associated with Caloplaca, Teloschistes, and Xanthoria, but these genera have since been subdivided into many smaller, monophyletic genera.[14] The cultivated mycobiont of Xanthoria fallax, grown in isolation from its green algalphotobiont , does not produce fallacinol.[15]
Fallacinol is also a common secondary metabolite in the lichen genus Teloschistes, typically occurring in smaller amounts alongside parietin and other related compounds like fallacinal and emodin. In 1970, Johan Santesson proposed a possible biogenetic relationship between the anthraqunone compounds commonly found in Caloplaca. According to this scheme, emodin is methylated to give parietin, which then undergoes three successive oxidations, sequentially forming fallacinol, fallacinal, and then parietinic acid.[16] A chemosyndrome is set of lichen products produced by a species, which typically includes one or more major compounds and a set of biosynthetically related minor compounds. In 2002, Ulrik Søchting and Patrik Frödén identified chemosyndromeA, the most common chemosyndrome in the genus Teloschistes and in the entire family Teloschistaceae, which features parietin as the main substance with smaller proportions of fallacinol, fallacinal, parietinic acid, and emodin.[17]
Parietin is the predominant cortical pigment of lichens in the genus Caloplaca, a secondary product of the lichen Xanthoria parietina, and a pigment found in the roots of curled dock. It has an orange-yellow color and absorbs blue light.
The Teloschistaceae are a large family of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. The family has a cosmopolitan distribution, although its members occur predominantly in temperate regions. Most members are lichens that either live on rock or on bark, but about 40 species are lichenicolous – meaning they are non-lichenised fungi that live on other lichens. Many members of the Teloschistaceae are readily identifiable by their vibrant orange to yellow hue, a result of their frequent anthraquinone content. The presence of these anthraquinone pigments, which confer protection from ultraviolet light, enabled this group to expand from shaded forest habitats to harsher environmental conditions of sunny and arid ecosystems during the Late Cretaceous.
Rusavskia elegans, commonly known as the elegant sunburst lichen, is a lichenized species of fungus in the genus Rusavskia, family Teloschistaceae. Recognized by its bright orange or red pigmentation, this species grows on rocks, often near bird or rodent perches. It has a circumpolar and alpine distribution. It was one of the first lichens to be used for the rock-face dating method known as lichenometry.
Caloplaca allanii is a species of saxicolous (rock-dwelling) and crustose lichen in the family Teloschistaceae. Found in New Zealand, it was formally described as a new species by Alexander Zahlbruckner. The type specimen was collected by Lucy Cranwell on Anawhata Beach in 1932; she sent a dried specimen to Zahlbruckner for identification. The specific epithet allanii honours New Zealand botanist Harry Allan.
Polycauliona comandorica is a species of fruticulose lichen in the family Teloschistaceae. It was formally described as a new species in 2021 by Dmitry Himelbrant, Irina Stepanchikova, and Ivan Frolov.
Golubkovia is a single-species fungal genus in the family Teloschistaceae. It contains the species Golubkovia trachyphylla, a rock-dwelling lichen that is found in Asia and North America. This crustose lichen has a yellow-orange thallus that is placodioid in form.
Parvoplaca nigroblastidiata is a species of corticolous (bark-dwelling), crustose lichen in the family Teloschistaceae. Found in Europe and Alaska, it was formally described as a new species in 2015 by Ulf Arup, Jan Vondrák, and Mehmet Halıcı. The type specimen was collected in the Nyhem Parish, Jämtland (Sweden), where it was growing on the bark of Populus tremula. In Turkey, it has been recorded at high altitudes on the bark of Juniperus excelsa and Abies cilicica, while in a single record from Alaska it is growing on Populus. In 2018 it was reported from the sacred groves of Epirus in Greece, and in 2020 from Norway.
Tomnashia is a genus of lichen-forming fungi in the family Teloschistaceae. It has four species of saxicolous (rock-dwelling), crustose lichens that occur in southwestern North America.
Martinjahnsia is a single-species fungal genus in the family Teloschistaceae. It contains the sole species Martinjahnsia resendei, a saxicolous (rock-dwelling) crustose lichen.
Pisutiella is a genus of lichen-forming fungi in the family Teloschistaceae. It contains five species of saxicolous (rock-dwelling), crustose lichens that are found in a variety of environments in the Northern Hemisphere.
Xanthaptychia is a genus of lichen-forming fungi in the family Teloschistaceae. The genus, circumscribed in 2017, has three corticolous (bark-dwelling) species.
Charcotiana is a single-species genus in the family Teloschistaceae. It contains the species Charcotiana antarctica, a crustose lichen found in Antarctica.
Polycauliona coralloides, the coral firedot lichen, is a species of small fruticose (bushy), saxicolous (rock-dwelling) lichen in the family Teloschistaceae. First formally described in 1866, it was later shuffled to a few different genera in its taxonomic history before ending up in Polycauliona, a genus resurrected from taxonomic obscurity in the molecular phylogenetics era. The lichen occurs on seaside rocks in the intertidal spray zone of California and northwestern Mexico. The species is readily recognized due to its distinctive coral-like form–its thallus grows as a tangle of orange, filamentous branches.
Kuettlingeria soralifera is a saxicolous (rock-dwelling), crustose lichen species in the family Teloschistaceae, first described in 2006. It is similar to Kuettlingeria xerica but distinguished by the presence of soredia on its thallus.
Gallowayella weberi is a species of corticolous and saxicolous, foliose lichen in the family Teloschistaceae. Found in the eastern United States, it is a small lichen with a smooth yellow to orange upper surface and a contrasting white lower surface.
Austroplaca soropelta is a species of saxicolous and muscicolous, crustose lichen in the family Teloschistaceae. It has a bipolar distribution, meaning it occurs in polar areas of both the Northern and Southern Hemispheres.
Parietinic acid is an organic compound in the structural class of chemicals known as anthraquinones. It is found in many species of the lichen family Teloschistaceae. The substance was first reported in the literature by the German chemist Walter Eschrich in 1958.
Gallowayella borealis is a species of saxicolous and muscicolous, lichen in the family Teloschistaceae. The lichen is characterized by a foliose (leafy) thallus that forms small, cushion-like clusters, with lobes that are often convex and have a distinctive orange colour with a reddish tint, occasionally covered in pruina. It reproduces vegetatively through abundant soralia producing rounded, granule-like soredia. Chemically, it contains high levels of parietin among other lichen products. Gallowayella borealis thrives on both horizontal and vertical rock surfaces, often enriched by guano, and is particularly abundant in continental Antarctica, co-existing with Polycauliona candelaria near penguin rookeries. It has a bipolar distribution, found in the Arctic and boreal forests of the Northern Hemisphere as well as in ice-free zones of continental Antarctica.
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.
Teloschistes exilis is a species of corticolous (bark-dwelling), fruticose lichen in the family Teloschistaceae. It was first formally described in 1803 by French botanist André Michaux, as Physcia exilis. Finnish lichenologist Edvard Vainio transferred the taxon to the genus Teloschistes in 1890. The lichen is found in the Americas. Secondary metabolites that have been identified from the lichen include parietin and teloschistin.
1 2 Neelakantan, S.; Rangaswami, S.; Seshadri, T. R.; Subramanian, S. Sankara (1951). "Chemical investigation of Indian lichens". Proceedings of the Indian Academy of Sciences - Section A. 33 (3): 142–147. doi:10.1007/bf03172197.
↑ Manojlovic, Nedeljko T.; Solujic, Slavica; Sukdolak, Slobodan (2002). "Antimicrobial activity of an extract and anthraquinones from Caloplaca schaereri". The Lichenologist. 34 (1): 83–85. doi:10.1006/lich.2001.0365.
↑ Łaska, G.; Kiercul, S.; Piotrowska-Niczyporuk, A.; Jacob, M.; Pasco, D. (2016). "Secondary metabolites isolated from Xanthoria parietina (L.) Th. Fr. lichen and their biological activity". Planta Medica. 81 (S 01): S1–S381. doi:10.1055/s-0036-1596402.
↑ Neelakantan, S.; Seshadri, T.R.; Subramanian, Sankara (1956). "Chemical investigation of indian lichens". Proceedings of the Indian Academy of Sciences – Section A. 44 (1): 42–45. doi:10.1007/bf03051864.
↑ Benfaremo, Nicholas; Cava, Michael P. (1984). "Studies in anthracycline synthesis: simple Diels–Alder routes to pachybasin, ω-hydroxypachybasin, aloe-emodin, and fallacinol". Journal of Organic Chemistry. 50 (1): 139–141. doi:10.1021/jo00201a033.
↑ Arup, Ulf; Søchting, Ulrik; Frödén, Patrik (2013). "A new taxonomy of the family Teloschistaceae". Nordic Journal of Botany. 31 (1): 16–83. doi:10.1111/j.1756-1051.2013.00062.x.
↑ Yoshimura, Isao; Kurokawa, Teiko; Kinoshita, Yasuhiro; Yamamoto, Yoshikazu; Miyawaki, Hiromi (1994), "Lichen substances in cultured lichens", The Journal of the Hattori Botanical Laboratory, 76: 249–261, doi:10.18968/jhbl.76.0_249
↑ Alemayehu, Gizachew; Abegaz, Berhanu; Snatzke, G; Duddeck, H. (1989). "Quinones of Senna didmobotrya". Bulletin of the Chemical Society of Ethiopia. 3 (1): 37–40.
↑ Shen, Lu-Lu (2013). "Anti-complementary anthraquinones from Polygonum cuspidatum and their action targets". Chinese Traditional and Herbal Drugs. 24: 2502–2507.
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