Fallacinol (teloschistin) is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

in the structural class of chemicals known as

anthraquinone Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic organic compound with formula . Isomers include various quinone derivatives. The term anthraquinone however refers to the isomer, 9,10-anthraquinone (IUPAC: 9,10-dioxoan ...

s. It is found in some lichens, particularly in the family

Teloschistaceae The Teloschistaceae are a large family of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. The family, estimated to contain over 1800 species, was extensively revised in 2013, including the creation ...

, 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 The structural formula of a chemical compound is a graphic representation of the molecular structure (determined by structural chemistry methods), showing how the atoms are possibly arranged in the real three-dimensional space. The chemical bond ...

; by 1949, Indian chemists had isolated a substance from ''

Teloschistes flavicans ''Teloschistes flavicans'', also known as the golden hair-lichen is a lichenized species of fungus in the genus ''Teloschistes'', family Teloschistaceae. Recognized by its safron coloured pigmentation, this species grows on rocks and branches of ...

'' with an identical structural formula to fallacin. Later research further separated fallacin into two distinct pigments, fallacin-A (later called

fallacinal 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. History In 1936, Japanese chemists Mitizo Asano and Sinobu Fuziwara reported on ...

) and fallacin-B (fallacinol). The latter compound is also known as teloschistin due to its structural match with the substance isolated earlier.

History

In 1936, Japanese chemists Mitizo Asano and Sinobu Fuziwara reported on their chemical investigations into the colour

pigments A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...

of the lichen ''Xanthoria fallax'' (now known as '' Oxneria fallax''), found growing on the bark of mulberry trees. They isolated a

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic comp ...

they named fallacin. 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 In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

of C₁₆H₁₂O₆. Using information from additional chemical tests, they proposed a tentative

for fallacin. In 1949, T. R. Seshadri and S. Subramanian published their investigations into the chemistry of ''

'', 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. 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 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 (''Rumex crispus''). It has an orangy-yellow color a ...

, a co-occurring substance, using several rounds of

column chromatography Column chromatography in chemistry is a chromatography method used to isolate a single chemical compound from a mixture. Chromatography is able to separate substances based on differential adsorption of compounds to the adsorbent; compounds move t ...

, and showed that Asano's original pigment was actually a combination of two pigments with different

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...

s, which he designated as fallacin-A and fallacin-B. After chemically determining the structure of fallacin-A, Murakami designated this substance as

. He named the biogenically related compound fallacin-B as fallacinol. Because of Seshadri and Subramanian's work, this substance is also known as "teloschistin" in the

literature Literature is any collection of written work, but it is also used more narrowly for writings specifically considered to be an art form, especially prose fiction, drama, and poetry. In recent centuries, the definition has expanded to inclu ...

Extraction and isolation

In an early chemical examination of the lichen ''

'',

Friedrich Wilhelm Zopf Friedrich (or Friederich) Wilhelm Zopf (12 December 1846 – 24 June 1909) was a well-known German botanist and mycologist. He dedicated to his whole life with fungal biology, particularly in classification of fungi and dye production in fungi an ...

identified two substances: physcion (now known more commonly as parietin) with a melting point (m.p.) of and an unidentified colourless compound with a m.p. of . Subsequent studies by Seshadri and Sankara Subramanian refined the extraction process, utilising a series of

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

s—

ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again b ...

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscible wi ...

, 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. Within the ether extract, a colourless compound, referred to as substance A, was separated based on its insolubility in

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of ...

. The alkali-soluble

fraction A fraction (from la, fractus, "broken") represents a part of a whole or, more generally, any number of equal parts. When spoken in everyday English, a fraction describes how many parts of a certain size there are, for example, one-half, eight ...

exhibited characteristics of parietin, though impurities complicated its purification. It was eventually purified to a parietin fraction with a melting point of after multiple stages of

fractional crystallization Fractional crystallization may refer to: * Fractional crystallization (chemistry), a process to separate different solutes from a solution * Fractional crystallization (geology) Fractional crystallization, or crystal fractionation, is one of the ...

using an

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

chloroform Chloroform, or trichloromethane, is an organic compound with formula C H Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to PTFE. It is also a precursor to various re ...

mixture. The presence of another compound with a higher melting point posed a purification challenge, which was resolved by employing

petroleum ether Petroleum ether is the petroleum fraction consisting of aliphatic hydrocarbons and boiling in the range 35–60 °C, and commonly used as a laboratory solvent. Despite the name, petroleum ether is not classified as an ether; the term is used ...

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". In 1951, Neelakantan and colleagues expanded on the initial identification of fallacinol, focusing on its chemical structure. They confirmed its

as C₁₆H₁₂O₆ and identified it as a

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...

derivative of parietin, lacking specific hydroxy groupings that would typically cause

fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, ...

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 Demethylation is the chemical process resulting in the removal of a methyl group (CH3) from a molecule. A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen ato ...

, reduction, and oxidation. Additionally, comparisons with similar anthraquinone derivatives through

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

and other reactions further substantiated the structural findings. 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.

Properties

Fallacinol is a member of the class of chemical compounds called

s. Its

IUPAC name In chemical nomenclature, a preferred IUPAC name (PIN) is a unique name, assigned to a chemical substance and preferred among the possible names generated by IUPAC nomenclature. The "preferred IUPAC nomenclature" provides a set of rules for cho ...

is 1,8-dihydroxy-3-hydroxymethyl-6-methoxyanthraquinone. The absorbance maxima (λ_max) of fallacinol in the

ultraviolet spectrum Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

has five peaks of maximum absorption at 223, 251, 266, 287

nanometre 330px, Different lengths as in respect to the Molecule">molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer ( American spelling) is a unit of length ...

s; the

visible spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye will respond to wav ...

has peaks at 434 and 455 nm. In the

infrared spectrum Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

, it has peaks at 1624, 1631, 1670, 3450, 3520 cm^-1. Fallacinol's

is C₁₆H₁₂O₆; it has a

molecular mass The molecular mass (''m'') is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quant ...

of 300.26

grams per mole In chemistry, the molar mass of a chemical compound is defined as the mass of a sample of that compound divided by the amount of substance which is the number of moles in that sample, measured in moles. The molar mass is a bulk, not molecular, p ...

. In its purified crystalline form, it exists as orange needles, with a melting point of . It is

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

in cold dilute

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which expl ...

, forming red-violet crystals, and is insoluble in sodium bicarbonate and

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonat ...

solutions. Similar to parietin, it produces a reddish-brown colour with alcoholic

ferric chloride Iron(III) chloride is the inorganic compound with the formula . Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The colo ...

and yields a deep orange-red solution with concentrated

sulphuric acid Sulfuric acid ( American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...

, which appears

eosin Eosin is the name of several fluorescent acidic compounds which bind to and form salts with basic, or eosinophilic, compounds like proteins containing amino acid residues such as arginine and lysine, and stains them dark red or pink as a resu ...

-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 In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

, 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. Fallacinol was shown to have

antifungal An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as cry ...

activity and

antibacterial An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...

activity in laboratory tests; it was particularly active against the fungus species ''

Trichoderma harzianum ''Trichoderma harzianum'' is a fungus that is also used as a fungicide. It is used for foliar application, seed treatment and soil treatment for suppression of fungal pathogens causing various fungal plant diseases. Commercial biotechnological ...

'', ''

Aspergillus niger ''Aspergillus niger'' is a mold classified within the ''Nigri'' section of the ''Aspergillus'' genus. The ''Aspergillus'' genus consists of common molds found throughout the environment within soil and water, on vegetation, in fecal matter, on de ...

'', and ''

Penicillium verrucosum ''Penicillium verrucosum'' is a psychrophilic fungus which was discovered in Belgium and introduced by Dierckx in 1901. Six varieties of this species have been recognized based primarily on differences in colony colour: ''P. verrucosum var. album ...

''. In a study exploring lichen compounds for COVID-19 therapeutics, fallacinol demonstrated the highest

binding energy In physics and chemistry, binding energy is the smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts. In the former meaning the term is predominantly us ...

against SARS-CoV-2's

spike protein In virology, a spike protein or peplomer protein is a protein that forms a large structure known as a spike or peplomer projecting from the surface of an enveloped virus. as cited in The proteins are usually glycoproteins that form dimers o ...

, suggesting its potential as an inhibitor of virus growth.

Chemical synthesis

synthetic Synthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to: Science * Synthetic chemical or compound, produced by the process of chemical synthesis * Synthetic o ...

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 ''N''-Bromosuccinimide or NBS is a chemical reagent used in radical substitution, electrophilic addition, and electrophilic substitution reactions in organic chemistry. NBS can be a convenient source of Br•, the bromine radical. Preparatio ...

in the presence of

benzoyl peroxide Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide () ...

, a technique also applied to various anthraquinones and related compounds. The brominated intermediate is then converted to fallacinol triacetate using

silver acetate Silver acetate is an coordination compound with the empirical formula CH3CO2Ag (or AgC2H3O2). A photosensitive, white, crystalline solid, it is a useful reagent in the laboratory as a source of silver ions lacking an oxidizing anion. Synthesis a ...

and

acetic anhydride Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a c ...

, yielding the target compound. Final steps include

with methanolic sulphuric acid to produce fallacinol and a

methylation In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These t ...

stage for complete conversion. The synthesis not only mirrors the natural biogenesis but also achieves a

of , consistent with the purified natural product. 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.

Occurrence

Fallacinol occurs in many species of the

, a large

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of mostly lichen-forming

fungi A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...

. Historically, the substance was most associated with ''

Caloplaca ''Caloplaca'' is a lichen genus comprising a number of distinct species. Members of the genus are commonly called firedot lichen, jewel lichen.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, gold lichens, "or ...

'', ''Teloschistes'', and ''

Xanthoria ''Xanthoria'' is a genus of lichenized fungi in the family Teloschistaceae. Common names include orange lichen,monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic ...

genera. The cultivated mycobiont of ''Xanthoria fallax'', grown in isolation from its

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( Embryophytes) have emerged deep in the Charophyte alg ...

l , does not produce fallacinol. Fallacinol is also a common secondary metabolite in the lichen genus ''Teloschistes'', typically occurring in smaller amounts alongside parietin and other related compounds like

and emodin. In 1970, Johan Santesson proposed a possible

biogenetic A biogenic substance is a product made by or of life forms. While the term originally was specific to metabolite compounds that had toxic effects on other organisms, it has developed to encompass any constituents, secretions, and metabolites of p ...

relationship between the anthraqunone compounds commonly found in ''

''. According to this scheme, emodin is

methylated In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These te ...

to give

, which then undergoes three successive

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

s, sequentially forming fallacinol, fallacinal, and then parietinic acid. A chemosyndrome is set of

lichen product 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 de ...

s 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 chemosyndrome A, 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. Fallacinol has additionally been reported from the bushy shrub plant ''

Senna didymobotrya ''Senna didymobotrya'' is a species of flowering plant in the legume family known by the common names African senna, popcorn senna, candelabra tree, and peanut butter cassia. It is native to Africa, where it can be found across the continent in s ...

'', widespread in eastern and central Africa, as well as from ''

Reynoutria japonica ''Reynoutria japonica'', synonyms ''Fallopia japonica'' and ''Polygonum cuspidatum'', is a species of herbaceous perennial plant in the knotweed and buckwheat family Polygonaceae. Common names include Japanese knotweed and Asian knotweed. It is ...

'', a plant in the knotweed family. The substance has also been isolated from a culture of the

marine sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through ...

-associated fungus '' Talaromyces stipitatus''. It has also been isolated from ''

Dermocybe The fungi of the ''Dermocybe'' group, commonly known as skin-heads, form a group within the huge genus ''Cortinarius''. They are generally considered to be a subgenus though some authorities consider them to form a genus in their own right. The ...

'' mushrooms, and detected chromatographically in extracts from several ''

Cortinarius ''Cortinarius'' is a globally distributed genus of mushrooms in the family Cortinariaceae. It is suspected to be the largest genus of agarics, containing over 2,000 widespread species. A common feature among all species in the genus ''Cortinari ...

'' species.

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